Publications by authors named "Peter W Barlow"

39 Publications

FAL Clowes, 1921-2016: a Memoir.

Authors:
Peter W Barlow

Plant Signal Behav 2018 03 12;13(3):e1274484. Epub 2018 Mar 12.

a School of Biological Sciences , University of Bristol, Bristol Life Sciences Building , Bristol , UK.

With the death of Frederick Albert Lionel Clowes on 21 September 2016, plant sciences lost a member of that lineage of experimental morphologists which reaches back to Johann Wolfgang von Goethe. In 1949, he discovered a group of cells at the tip of the beech root apex which were metabolically inert. In 1954, he confirmed generality of this root apex feature and coined the term 'quiescent center'. He continued to study these unique cells throughout next decades up to his last papers published in 1980s. Concept of the quiescent centre of plant roots is one of the milestones in plant cell biology and plant physiology.
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http://dx.doi.org/10.1080/15592324.2016.1274484DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5927677PMC
March 2018

Distribution of some pectic and arabinogalactan protein epitopes during Solanum lycopersicum (L.) adventitious root development.

BMC Plant Biol 2017 01 25;17(1):25. Epub 2017 Jan 25.

Department of Cell Biology, Faculty of Biology and Environmental Protection, University of Silesia, 28 Jagiellońska St, 40-032, Katowice, Poland.

Background: The adventitious roots (AR) of plants share the same function as primary and lateral roots (LR), although their development is mainly an adaptive reaction to stress conditions. Regeneration of grafted plants is often accompanied by AR formation thus making the grafting technique a good model for studying AR initiation and development and their means of emergence. Pectins and arabinogalactan proteins (AGP) are helpful markers of particular cellular events, such as programmed cell death (PCD), elongation, proliferation or other differentiation events that accompany AR development. However, little is known about the distribution of pectins and AGPs during AR ontogeny, either in the primordium or stem tissues from which AR arise or their correspondence with these events during LR formation.

Results: AR were developed from different stem tissues such as parenchyma, xylem rays and the cambium, depending on the stem age and treatment (grafting versus cutting) of the parental tissue. Immunochemical analysis of the presence of pectic (LM8, LM19, LM20) and AGP (JIM8, JIM13, JIM16) epitopes in AR and AR-associated tissues showed differential, tissue-specific distributions of these epitopes. Two pectic epitopes (LM19, LM20) were developmentally regulated and the occurrence of the LM8 xylogalacturonan epitope in the root cap of the AR differed from other species described so far. AGP epitopes were abundantly present in the cytoplasmic compartments (mainly the tonoplast) and were correlated with the degree of cell vacuolisation. JIM8 and JIM13 epitopes were detected in the more advanced stages of primordium development, whereas the JIM16 epitope was present from the earliest division events of the initial AR cells. The comparison between AR and LR showed quantitative (AGP,) and qualitative (pectins) differences.

Conclusion: The chemical compositions of adventitious and lateral root cells show differences that correlate with the different origins of these cells. In AR, developmental changes in the distribution of pectins and AGP suggest the turnover of wall compounds. Our data extend the knowledge about the distribution of pectin and AGP during non-embryogenic root development in a species that is important from an agronomic point of view.
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http://dx.doi.org/10.1186/s12870-016-0949-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5267361PMC
January 2017

Why so many sperm cells? Not only a possible means of mitigating the hazards inherent to human reproduction but also an indicator of an exaptation.

Authors:
Peter W Barlow

Commun Integr Biol 2016 Jul-Aug;9(4):e1204499. Epub 2016 Jul 15.

School of Biological Sciences, University of Bristol , Bristol, UK.

Redundancy-the excess of supply over necessity-has recently been proposed for human sperm cells. However, the apparent superfluity of cell numbers may be necessary in order to circumvent the hazards, many of which can be quantified, that can occur during the transition from gametogenesis within the testes to zygosis within the female reproductive tract. Sperm cell numbers are directly related to testicular volume, and it is owing to a redundancy, and the possible exaptation, of this latter parameter that a putative excess of sperm cells is perceived.
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http://dx.doi.org/10.1080/19420889.2016.1204499DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4988455PMC
August 2016

Simultaneous and intercontinental tests show synchronism between the local gravimetric tide and the ultra-weak photon emission in seedlings of different plant species.

Protoplasma 2017 Jan 28;254(1):315-325. Epub 2016 Jan 28.

Sino-Dutch Centre for Preventive and Personalized Medicine/Centre for Photonics of Living Systems, Leiden University, Leiden, The Netherlands.

In order to corroborate the hypothesis that variations in the rate of spontaneous ultra-weak photon emission (UPE) from germinating seedlings are related to local variations of the lunisolar tidal force, a series of simultaneous tests was performed using the time courses of UPE collected from three plant species-corn, wheat and sunflower-and also from wheat samples whose grains were transported between continents, from Brazil to The Netherlands and vice versa. All tests which were run in parallel showed coincident inflections within the UPE time courses not only between seedlings of the same species but also between the different species. In most cases, the UPE inflections were synchronised with the turning points in the local gravimetric tidal variation. Statistical tests using the local Pearson correlation verified these coincidences in the two time series. The results therefore support the hypothesis of a relationship between UPE emissions and, in the oscillations, the local gravimetric tide. This applies to both the emissions from seedlings of different species and to the seedlings raised from transported grain samples of the same species.
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http://dx.doi.org/10.1007/s00709-016-0947-1DOI Listing
January 2017

The natural history of consciousness, and the question of whether plants are conscious, in relation to the Hameroff-Penrose quantum-physical 'Orch OR' theory of universal consciousness.

Authors:
Peter W Barlow

Commun Integr Biol 2015 Jul-Aug;8(4):e1041696. Epub 2015 Jul 9.

School of Biological Sciences; University of Bristol ; Bristol Life Sciences Building ; Bristol, UK.

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http://dx.doi.org/10.1080/19420889.2015.1041696DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4594572PMC
October 2015

Origin of the concept of the quiescent centre of plant roots.

Authors:
Peter W Barlow

Protoplasma 2016 Sep 10;253(5):1283-97. Epub 2015 Oct 10.

School of Biological Sciences, Bristol Life Sciences Building, University of Bristol, 24 Tyndall Avenue, Bristol, BS8 1TQ, UK.

Concepts in biology feed into general theories of growth, development and evolution of organisms and how they interact with the living and non-living components of their environment. A well-founded concept clarifies unsolved problems and serves as a focus for further research. One such example of a constructive concept in the plant sciences is that of the quiescent centre (QC). In anatomical terms, the QC is an inert group of cells maintained within the apex of plant roots. However, the evidence that established the presence of a QC accumulated only gradually, making use of strands of different types of observations, notably from geometrical-analytical anatomy, radioisotope labelling and autoradiography. In their turn, these strands contributed to other concepts: those of the mitotic cell cycle and of tissue-related cell kinetics. Another important concept to which the QC contributed was that of tissue homeostasis. The general principle of this last-mentioned concept is expressed by the QC in relation to the recovery of root growth following a disturbance to cell proliferation; the resulting activation of the QC provides new cells which not only repair the root meristem but also re-establish a new QC.
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http://dx.doi.org/10.1007/s00709-015-0886-2DOI Listing
September 2016

Leaf movements and their relationship with the lunisolar gravitational force.

Authors:
Peter W Barlow

Ann Bot 2015 Aug;116(2):149-87

School of Biological Sciences, University of Bristol, Bristol Life Sciences Building, 24 Tyndalls Avenue, Bristol BS8 1TQ, UK

Background: Observation of the diurnal ascent and descent of leaves of beans and other species, as well as experimental interventions into these movements, such as exposures to light at different times during the movement cycle, led to the concept of an endogenous 'clock' as a regulator of these oscillations. The physiological basis of leaf movement can be traced to processes that modulate cell volume in target tissues of the pulvinus and petiole. However, these elements of the leaf-movement process do not completely account for the rhythms that are generated following germination in constant light or dark conditions, or when plants are transferred to similar free-running conditions.

Scope: To develop a new perspective on the regulation of leaf-movement rhythms, many of the published time courses of leaf movements that provided evidence for the concept of the endogenous clock were analysed in conjunction with the contemporaneous time courses of the lunisolar tidal acceleration at the relevant experimental locations. This was made possible by application of the Etide program, which estimates, with high temporal resolution, local gravitational changes as a consequence of the diurnal variations of the lunisolar gravitational force due to the orbits and relative positions of Earth, Moon and Sun. In all cases, it was evident that a synchronism exists between the times of the turning points of both the lunisolar tide and of the leaftide when the direction of leaf movement changes. This finding of synchrony leads to the hypothesis that the lunisolar tide is a regulator of the leaftide, and that the rhythm of leaf movement is not necessarily of endogenous origin but is an expression of an exogenous lunisolar 'clock' impressed upon the leaf-movement apparatus.

Conclusions: Correlation between leaftide and Etide time courses holds for leaf movement rhythms in natural conditions of the greenhouse, in conditions of constant light or dark, under microgravity conditions of the International Space Station, and also holds for rhythms that are atypical, such as pendulum and relaxation rhythms whose periods are longer or shorter than usual. Even the apparently spontaneous short-period, small-amplitude rhythms recorded from leaves under unusual growth conditions are consistent with the hypothesis of a lunisolar zeitgeber. Two hypotheses that could account for the synchronism between leaftide and Etide, and which are based on either quantum considerations or on classical Newtonian physics, are presented and discussed.
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http://dx.doi.org/10.1093/aob/mcv096DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4512198PMC
August 2015

Fluorescence decay of dyed protozoa: differences between stressed and non-stressed cysts.

Luminescence 2015 Nov 18;30(7):1139-47. Epub 2015 Feb 18.

School of Technology, University of Campinas/Limeira, SP, Brazil.

Several series of tests have shown that fresh, intact samples of Giardia duodenalis and Cryptosporidium parvum (oo)cysts are not marked by fluorescent probes such as carboxyfluorcein-succinimidyl-diacetate-ester (CFDA-SE), C12-resazurin and SYTOX® Green, probably because of their robust cell walls. These dyes fail to indicate the viability of such protozoa and allow negative responses to be recorded from living and infectious samples. Cryptosporidium parvum showed stronger isolation from chemicals, with living oocysts remaining unstained by the probe for up to 90 days after extraction. However, in further fluorescence decay (FD) experiments run with G. duodenalis samples stained using CFDA-SE (comprising living, non-stressed but aged cysts, heat-killed samples and UV-C-stressed samples) each showed a different FD decay profile, here studied in seven series of tests of five replicates each. The FD profiles were fitted by double-exponential decay kinetics, with the decay constant k2 being five times higher than k1. This FD procedure is fast and can be easily reproduced in 10 steps, taking ~ 1 h of laboratory work for already purified samples.
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http://dx.doi.org/10.1002/bio.2872DOI Listing
November 2015

The origins of the quiescent centre concept.

New Phytol 2015 Apr 30;206(2):493-6. Epub 2015 Jan 30.

Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Apartado Postal 510-3, Cuernavaca, 62250, Mexico; Department of Plant Sciences, Oxford University, South Parks Road, Oxford, OX1 3RB, UK.

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http://dx.doi.org/10.1111/nph.13307DOI Listing
April 2015

Lunisolar tidal synchronism with biophoton emission during intercontinental wheat-seedling germination tests.

Plant Signal Behav 2014 8;9(3):e28671. Epub 2014 Apr 8.

School of Biological Sciences; University of Bristol; Bristol, United Kingdom.

Synchronic measurements of spontaneous ultra-weak light emission from germinating wheat seedlings both in Brazil and after transportation to Japan, and with a simultaneous series of germinations with local seedlings in the Czech Republic, are presented. A series of tests was also performed with samples returned from Japan to Brazil and results compared with those from undisturbed Brazilian seedlings. Native seedlings presented semi-circadian rhythms of emission which correlated with the gravimetric tidal acceleration at their locality, as did seeds which had been transported from Brazil to Japan, and then returned to Brazil. Here, however, there were very small disturbances within the periodicity of emissions, perhaps as a result of similar tidal profiles at locations whose longitudes are 180° apart, as in this case, different from previous results obtained in Brazil-Germany tests with other longitude shift. This feature of the Brazil and Japan locations may have minimized the requirement for the acclimatization of the transported seed to their new location.
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http://dx.doi.org/10.4161/psb.28671DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4091565PMC
April 2015

Swarms, swarming and entanglements of fungal hyphae and of plant roots.

Commun Integr Biol 2013 Sep 21;6(5):e25299. Epub 2013 Jun 21.

School of Biological Sciences; University of Bristol; Bristol, United Kingdom.

There has been recent interest in the possibility that plant roots can show oriented collective motion, or swarming behavior. We examine the evidence supportive of root swarming and we also present new observations on this topic. Seven criteria are proposed for the definition of a swarm, whose application can help identify putative swarming behavior in plants. Examples where these criteria are fulfilled, at many levels of organization, are presented in relation to plant roots and root systems, as well as to the root-like mycelial cords (rhizomorphs) of fungi. The ideas of both an "active" swarming, directed by a signal which imposes a common vector on swarm element aggregation, and a "passive" swarming, where aggregation results from external constraint, are introduced. Active swarming is a pattern of cooperative behavior peculiar to the sporophyte generation of vascular plants and is the antithesis of the competitive behavior shown by the gametophyte generation of such plants, where passive swarming may be found. Fungal mycelial cords could serve as a model example of swarming in a multi-cellular, non-animal system.
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http://dx.doi.org/10.4161/cib.25299DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3829901PMC
September 2013

Arabidopsis thaliana root elongation growth is sensitive to lunisolar tidal acceleration and may also be weakly correlated with geomagnetic variations.

Ann Bot 2013 May 26;111(5):859-72. Epub 2013 Mar 26.

School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK.

Background: Correlative evidence suggests a relationship between the lunisolar tidal acceleration and the elongation rate of arabidopsis roots grown under free-running conditions of constant low light.

Methods: Seedlings of Arabidopsis thaliana were grown in a controlled-climate chamber maintained at a constant temperature and subjected to continuous low-level illumination from fluorescent tubes, conditions that approximate to a 'free-running' state in which most of the abiotic factors that entrain root growth rates are excluded. Elongation of evenly spaced, vertical primary roots was recorded continuously over periods of up to 14 d using high temporal- and spatial-resolution video imaging and were analysed in conjunction with geophysical variables.

Key Results And Conclusions: The results confirm the lunisolar tidal/root elongation relationship. Also presented are relationships between the hourly elongation rates and the contemporaneous variations in geomagnetic activity, as evaluated from the disturbance storm time and ap indices. On the basis of time series of root elongation rates that extend over ≥4 d and recorded at different seasons of the year, a provisional conclusion is that root elongation responds to variation in the lunisolar force and also appears to adjust in accordance with variations in the geomagnetic field. Thus, both lunisolar tidal acceleration and the geomagnetic field should be considered as modulators of root growth rate, alongside other, stronger and more well-known abiotic environmental regulators, and perhaps unexplored factors such as air ions. Major changes in atmospheric pressure are not considered to be a factor contributing to oscillations of root elongation rate.
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http://dx.doi.org/10.1093/aob/mct052DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3631336PMC
May 2013

The primal integrated realm and the derived interactive realm in relation to biosemiosis, and their link with the ideas of J.W. von Goethe.

Authors:
Peter W Barlow

Commun Integr Biol 2012 Sep;5(5):434-9

School of Biological Sciences; University of Bristol; Bristol, UK.

Certain phenomena in Nature which might logically be regarded as indicating biosemiotic communication, with signal, receptor and interpretant, may, in fact, indicate no such thing. Instead, the respective phenomenological observations may point to an underlying system that JW von Goethe termed an "Urphänomen". From such Primal Phenomena emerge derived phenomena, or "Types", which are made substantial by processes that uniquely define Life and Living. Biosemiosis arises and takes place within the derived Types. Examples of Primal Phenomena and their derivatives are taken from recent observations on the putative influence of the lunisolar gravitational force upon animal and plant behavior, and from some aspects of plant development that show connection with Goethe's idea of the 'Urpflanze'.
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http://dx.doi.org/10.4161/cib.21253DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3502203PMC
September 2012

Coincidence of biophoton emission by wheat seedlings during simultaneous, transcontinental germination tests.

Protoplasma 2013 Jun 26;250(3):793-6. Epub 2012 Sep 26.

School of Technology, University of Campinas, Limeira, SP, Brazil.

Measurements of spontaneous ultra-weak light (biophoton) emission from native Brazilian and German wheat seedlings in three simultaneous series of germination tests are presented, two run in Germany and one in Brazil. Seedlings in both countries presented semi-circadian rhythms of emission that were in accordance with the local lunisolar gravimetric tidal acceleration, as did seeds which had been transported from Brazil to Germany. The simultaneity of the photon emission patterns in all tests argues for the lunisolar tide and its rhythmic variations as regulators of the natural rhythm of photon emission. However, seedlings from seed samples transported from Brazil to Germany showed, in addition, a temporary disturbance within the emission periodicity which may indicate a possible short-term acclimatization to the new location.
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http://dx.doi.org/10.1007/s00709-012-0447-xDOI Listing
June 2013

Spontaneous ultra-weak light emissions from wheat seedlings are rhythmic and synchronized with the time profile of the local gravimetric tide.

Naturwissenschaften 2012 Jun 26;99(6):465-72. Epub 2012 May 26.

School of Technology, University of Campinas, Rua Paschoal Marmo 1888, 13484-332, Limeira, SP, Brazil.

Semi-circadian rhythms of spontaneous photon emission from wheat seedlings germinated and grown in a constant environment (darkened chamber) were found to be synchronized with the rhythm of the local gravimetric (lunisolar) tidal acceleration. Time courses of the photon-count curves were also found to match the growth velocity profile of the seedlings. Pair-wise analyses of the data--growth, photon count, and tidal--by local tracking correlation always revealed significant coefficients (P > 0.7) for more than 80% of any of the time periods considered. Using fast Fourier transform, the photon-count data revealed periodic components similar to those of the gravimetric tide. Time courses of biophoton emissions would appear to be an additional, useful, and innovative tool in both chronobiological and biophysical studies.
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http://dx.doi.org/10.1007/s00114-012-0921-5DOI Listing
June 2012

A new theoretical approach to the functional meaning of sleep and dreaming in humans based on the maintenance of 'predictive psychic homeostasis'.

Commun Integr Biol 2011 Nov;4(6):640-54

Different theories have been put forward during the last decade to explain the functional meaning of sleep and dreaming in humans. In the present paper, a new theory is presented which, while taking advantage of these earlier theories, introduces the following new and original aspects:   • Circadian rhythms relevant to various organs of the body affect the reciprocal interactions which operate to maintain constancy of the internal milieu and thereby also affect the sleep/wakefulness cycle. Particular attention is given to the constancy of natraemia and osmolarity and to the permissive role that the evolution of renal function has had for the evolution of the central nervous system and its integrative actions. • The resetting of neuro-endocrine controls at the onset of wakefulness leads to the acquisition of new information and its integration within previously stored memories. This point is dealt with in relation to Moore-Ede's proposal for the existence of a 'predictive homeostasis'. • The concept of 'psychic homeostasis' is introduced and is considered as one of the most important states since it is aimed at the well-being, or eudemonia, of the human psyche. Sleep and dreaming in humans are discussed as important functions for the maintenance of a newly proposed composite state: that of 'predictive psychic homeostasis'. On the basis of these assumptions, and in accordance with the available neurobiological data, the present paper puts forward the novel hypothesis that sleep and dreaming play important functions in humans by compensating for psychic allostatic overloads. Hence, both consolatory dreams and disturbing nightmares can be part of the vis medicatrix naturae, the natural healing power, in this case, the state of eudemonia.
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http://dx.doi.org/10.4161/cib.17602DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3306324PMC
November 2011

Lunisolar tidal force and the growth of plant roots, and some other of its effects on plant movements.

Ann Bot 2012 Jul 20;110(2):301-18. Epub 2012 Mar 20.

School of Biological Sciences, University of Bristol, Bristol, UK.

Background: Correlative evidence has often suggested that the lunisolar tidal force, to which the Sun contributes 30 % and the Moon 60 % of the combined gravitational acceleration, regulates a number of features of plant growth upon Earth. The time scales of the effects studied have ranged from the lunar day, with a period of approx. 24.8 h, to longer, monthly or seasonal variations.

Scope: We review evidence for a lunar involvement with plant growth. In particular, we describe experimental observations which indicate a putative lunar-based relationship with the rate of elongation of roots of Arabidopsis thaliana maintained in constant light. The evidence suggests that there may be continuous modulation of root elongation growth by the lunisolar tidal force. In order to provide further supportive evidence for a more general hypothesis of a lunisolar regulation of growth, we highlight similarly suggestive evidence from the time courses of (a) bean leaf movements obtained from kymographic observations; (b) dilatation cycles of tree stems obtained from dendrograms; and (c) the diurnal changes of wood-water relationships in a living tree obtained by reflectometry.

Conclusions: At present, the evidence for a lunar or a lunisolar influence on root growth or, indeed, on any other plant system, is correlative, and therefore circumstantial. Although it is not possible to alter the lunisolar gravitational force experienced by living organisms on Earth, it is possible to predict how this putative lunisolar influence will vary at times in the near future. This may offer ways of testing predictions about possible Moon-plant relationships. As for a hypothesis about how the three-body system of Earth-Sun-Moon could interact with biological systems to produce a specific growth response, this remains a challenge for the future. Plant growth responses are mainly brought about by differential movement of water across protoplasmic membranes in conjunction with water movement in the super-symplasm. It may be in this realm of water movements, or even in the physical forms which water adopts within cells, that the lunisolar tidal force has an impact upon living growth systems.
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http://dx.doi.org/10.1093/aob/mcs038DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3394636PMC
July 2012

Histology and symplasmic tracer distribution during development of barley androgenic embryos.

Planta 2011 May 12;233(5):873-81. Epub 2011 Jan 12.

Laboratory of Cell Biology, University of Silesia, ul. Jagiellońska 28, 40-032 Katowice, Poland.

The present study concerns three aspects of barley androgenesis: (1) the morphology and histology of the embryos during their development, (2) the time course of fluorescent symplasmic tracers' distribution, and (3) the correlation between symplasmic communication and cell differentiation. The results indicate that barley embryos, which are developing via an androgenic pathway, resemble their zygotic counterparts with respect to their developmental stages, morphology and histology. Analysis of the distribution of the symplasmic tracers, HPTS, and uncaged fluorescein indicates the symplasmic isolation of (1) the protodermis from the underlying cells of the late globular stage onwards, and (2) the embryonic organs at the mature stage of development.
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http://dx.doi.org/10.1007/s00425-010-1345-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3074072PMC
May 2011

Root apex transition zone: a signalling-response nexus in the root.

Trends Plant Sci 2010 Jul 2;15(7):402-8. Epub 2010 Jun 2.

IZMB, University of Bonn, Kirschellee 1, 53115 Bonn, Germany.

Longitudinal zonation, as well as a simple and regular anatomy, are hallmarks of the root apex. Here we focus on one particular root-apex zone, the transition zone, which is located between the apical meristem and basal elongation region. This zone has a unique role as the determiner of cell fate and root growth; this is accomplished by means of the complex system of a polar auxin transport circuit. The transition zone also integrates diverse inputs from endogenous (hormonal) and exogenous (sensorial) stimuli and translates them into signalling and motoric outputs as adaptive differential growth responses. These underlie the root-apex tropisms and other aspects of adaptive root behaviour.
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http://dx.doi.org/10.1016/j.tplants.2010.04.007DOI Listing
July 2010

The 'root-brain' hypothesis of Charles and Francis Darwin: Revival after more than 125 years.

Plant Signal Behav 2009 Dec;4(12):1121-7

IZMB, University of Bonn, Bonn, Germany.

This year celebrates the 200(th) aniversary of the birth of Charles Darwin, best known for his theory of evolution summarized in On the Origin of Species. Less well known is that, in the second half of his life, Darwin's major scientific focus turned towards plants. He wrote several books on plants, the next-to-last of which, The Power of Movement of Plants, published together with his son Francis, opened plants to a new view. Here we amplify the final sentence of this book in which the Darwins proposed that: "It is hardly an exaggeration to say that the tip of the radicle thus endowed [with sensitivity] and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements." This sentence conveys two important messages: first, that the root apex may be considered to be a 'brain-like' organ endowed with a sensitivity which controls its navigation through soil; second, that the root apex represents the anterior end of the plant body. In this article, we discuss both these statements.
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http://dx.doi.org/10.4161/psb.4.12.10574DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2819436PMC
December 2009

Tree-stem diameter fluctuates with the lunar tides and perhaps with geomagnetic activity.

Protoplasma 2010 Nov;247(1-2):25-43

School of Biological Sciences, University of Bristol, Woodland Road, Bristol, UK.

Our initial objective has been to examine the suggestion of Zürcher et al. (Nature 392:665–666, 1998) that the naturally occurring variations in stem diameter of two experimental trees of Picea alba were related to near simultaneous variations in the lunisolar tidal acceleration. The relationship was positive: Lunar peaks were roughly synchronous with stem diameter peaks. To extend the investigation of this putative relationship, additional data on stem diameter variations from six other tree species were gathered from published literature. Sixteen sets of data were analysed retrospectively using graphical representations as well as cosinor analysis, statistical cross-correlation and cross-spectral analysis, together with estimated values of the lunisolar tidal acceleration corresponding to the sites, dates and times of collection of the biological data. Positive relationships were revealed between the daily variations of stem diameter and the variations of the lunisolar tidal acceleration. Although this relationship could be mediated by a 24.8-h lunar rhythm, the presence of a solar rhythm of 24.0 h could not be ruled out. Studies of transpiration in two of the observed trees indicated that although this variable was not linked to stem diameter variation, it might also be subject to lunisolar gravitational regulation. In three cases, the geomagnetic Thule index showed a weak but reciprocal relationship with stem diameter variation, as well as a positive relationship with the lunisolar tidal force. In conclusion, it seems that lunar gravity alone could influence stem diameter variation and that, under certain circumstances, additional regulation may come from the geomagnetic flux.
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http://dx.doi.org/10.1007/s00709-010-0136-6DOI Listing
November 2010

Mosaic, self-similarity logic, and biological attraction principles: three explanatory instruments in biology.

Commun Integr Biol 2009 Nov;2(6):552-63

Department of BioMedical Sciences, University of Modena and IRCCS Lido, Venezia, Italy.

From a structural standpoint, living organisms are organized like a nest of Russian matryoshka dolls, in which structures are buried within one another. From a temporal point of view, this type of organization is the result of a history comprised of a set of time backcloths which have accompanied the passage of living matter from its origins up to the present day. The aim of the present paper is to indicate a possible course of this 'passage through time, and suggest how today's complexity has been reached by living organisms. This investigation will employ three conceptual tools, namely the Mosaic, Self-Similarity Logic, and the Biological Attraction principles. Self-Similarity Logic indicates the self-consistency by which elements of a living system interact, irrespective of the spatiotemporal level under consideration. The term Mosaic indicates how, from the same set of elements assembled according to different patterns, it is possible to arrive at completely different constructions: hence, each system becomes endowed with different emergent properties. The Biological Attraction principle states that there is an inherent drive for association and merging of compatible elements at all levels of biological complexity. By analogy with the gravitation law in physics, biological attraction is based on the evidence that each living organism creates an attractive field around itself. This field acts as a sphere of influence that actively attracts similar fields of other biological systems, thereby modifying salient features of the interacting organisms. Three specific organizational levels of living matter, namely the molecular, cellular, and supracellular levels, have been considered in order to analyse and illustrate the interpretative as well as the predictive roles of each of these three explanatory principles.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2829830PMC
http://dx.doi.org/10.4161/cib.2.6.9644DOI Listing
November 2009

Are maternal mitochondria the selfish entities that are masters of the cells of eukaryotic multicellular organisms?

Commun Integr Biol 2009 ;2(2):194-200

Department of BioMedical Sciences; University of Modena and IRRCS Lido VE; Modena, Italy.

The Energide concept, as well as the endosymbiotic theory of eukaryotic cell organization and evolution, proposes that present-day cells of eukaryotic organisms are mosaics of specialized and cooperating units, or organelles. Some of these units were originally free-living prokaryotes, which were engulfed during evolutionary time. Mitochondria represent one of these types of previously independent organisms, the Energide, is another type. This new perspective on the organization of the cell has been further expanded to reveal the concept of a public milieu, the cytosol, in which Energides and mitochondria live, each with their own private internal milieu. The present paper discusses how the endosymbiotic theory implicates a new hypothesis about the hierarchical and communicational organization of the integrated prokaryotic components of the eukaryotic cell and provides a new angle from which to consider the theory of evolution and its bearing upon cellular complexity. Thus, it is proposed that the "selfish gene" hypothesis of Dawkins1 is not the only possible perspective for comprehending genomic and cellular evolution. Our proposal is that maternal mitochondria are the selfish "master" entities of the eukaryotic cell with respect not only to their propagation from cell-to-cell and from generation-to-generation but also to their regulation of all other cellular functions. However, it should be recognized that the concept of "master" and "servant" cell components is a metaphor; in present-day living organisms their organellar components are considered to be interdependent and inseparable.
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http://dx.doi.org/10.4161/cib.8320DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2686380PMC
July 2011

A strong nucleotypic effect on the cell cycle regardless of ploidy level.

Ann Bot 2008 Apr 13;101(6):747-57. Epub 2008 Mar 13.

School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK.

Background And Aims: In published studies, positive relationships between nucleotype and the duration of the mitotic cell cycle in angiosperms have been reported but the highest number of species analyzed was approx. 60. Here an analysis is presented of DNA C-values and cell cycle times in root apical meristems of angiosperms comprising 110 measurements, including monocots and eudicots within a set temperature range, and encompassing an approx. 290-fold variation in DNA C-values.

Methods: Data for 110 published cell cycle times of seedlings grown at temperatures between 20-25 degrees C were compared with DNA C-values (58 values for monocots and 52 for eudicots). Regression analyses were undertaken for all species, and separately for monocots and eudicots, diploids and polyploids, and annuals and perennials. Cell cycle times were plotted against the nuclear DNA C-values.

Key Results: A positive relationship was observed between DNA C-value and cell cycle time for all species and for eudicots and monocots separately, regardless of the presence or absence of polyploid values. In this sample, among 52 eudicots the maximum cell cycle length was 18 h, whereas the 58 monocot values ranged from 8-120 h. There was a striking additional increase in cell cycle duration in perennial monocots with C-values greater than 25 pg. Indeed, the most powerful relationship between DNA C-value and cell cycle time and the widest range of cell cycle times was in perennials regardless of ploidy level.

Conclusions: DNA replication is identified as a rate limiting step in the cell cycle, the flexibility of DNA replication is explored, and we speculate on how the licensing of initiation points of DNA replication may be a responsive component of the positive nucleotypic effect of C-value on the duration of the mitotic cell cycle.
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http://dx.doi.org/10.1093/aob/mcn038DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2710215PMC
April 2008

Reflections on 'plant neurobiology'.

Authors:
Peter W Barlow

Biosystems 2008 May 2;92(2):132-47. Epub 2008 Feb 2.

School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK.

Plant neurobiology, a new and developing area in the plant sciences, is a meeting place for scientists concerned with exploring how plants perceive signs within their environment and convert them into internal electro-chemical ('plant neurobiological') signals. These signals, in turn, permit rapid modifications of physiology and development that help plants adjust to changes in their environment. The use of the epithet 'neurobiology' in the context of plant life has, however, led to misunderstanding about the aims, content, and scope of this topic. This difficulty is possibly due to the terminology used, since this is often unfamiliar in the context of plants. In the present article, the scope of plant neurobiology is explored and some of analogical and metaphorical aspects of the subject are discussed. One approach to reconciling possible problems of using the term 'plant neurobiology' and, at the same time, of analysing information transfer in plants and the developmental processes which are regulated thereby, is through Living Systems Theory (LST). This theory specifically directs attention to the means by which information is gathered and processed, and then dispersed throughout the hierarchy of organisational levels of the plant body. Attempts to identify the plant 'neural' structures point to the involvement of the vascular tissue - xylem and phloem - in conveying electrical impulses generated in zones of special sensitivity to receptive locations throughout the plant in response to mild stress. Vascular tissue therefore corresponds, at the level of organismic organisation, with the informational 'channel and net' subsystem of LST.
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http://dx.doi.org/10.1016/j.biosystems.2008.01.004DOI Listing
May 2008

The anatomy of the chi-chi of Ginkgo biloba suggests a mode of elongation growth that is an alternative to growth driven by an apical meristem.

J Plant Res 2007 Mar 14;120(2):269-80. Epub 2006 Dec 14.

School of Biological Sciences, University of Bristol, Woodland Road, Bristol, UK.

The chi-chi of Ginkgo biloba L. are cylindrical woody structures that grow downwards from the branches and trunks of old trees, eventually entering the soil where they give rise to adventitious shoots and roots. Examination of segments of young chi-chi taken from a mature ginkgo tree revealed an internal woody portion with irregular growth rings of tracheid-containing secondary xylem covered by a vascular cambium and bark. The cambium was composed of both fusiform cells and parenchymatous ray cells. Near the tip of the chi-chi, these two types of cambial cells had orientations ranging between axial, radial and circumferential with respect to the cylindrical form of the chi-chi. The xylem rays and tracheids that derived from the cambium showed correspondingly variable orientations. Towards the base of the chi-chi, the fusiform cells and young tracheids were aligned parallel to the axis, indicating that the orientation of the cambial cells in basal regions of the chi-chi gradually became normalised as the tip of the chi-chi extended forwards. Nevertheless, in such basal sites, tracheids near the centre of the chi-chi showed variable orientations in accordance with their mode of formation during the early stages of chi-chi development. The initiation of a chi-chi is proposed to derive from a localised hyperactivity of vascular cambial-cell production in the supporting stem. The chi-chi elongates by tip growth, but it does so in a manner different from organ growth driven by an apical meristem. It is suggested that the chi-chi of Ginkgo is an "evolutionary experiment" that makes use of the vascular cambium, not only for its widening growth but also for its elongation.
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http://dx.doi.org/10.1007/s10265-006-0050-3DOI Listing
March 2007

Patterned cell development in the secondary phloem of dicotyledonous trees: a review and a hypothesis.

J Plant Res 2006 Jul 25;119(4):271-91. Epub 2006 May 25.

School of Biological Sciences, University of Bristol, Woodland Road, Bristol, BS8 1UG, UK.

The secondary phloem of dicotyledonous trees and shrubs is constructed of sieve tube cells (S) and their companion cells, as well as parenchyma (P) and fibre (F) cells. Different species have characteristic sequences of these S, P and F cells within the radial files of their phloem. The sequences are recurrent, and are evidence of rhythmic cell determination and differentiation. A model was devised to account for the sequences found in various dicot tree species. It is based on the pattern of radial displacement of cells through a gradient of morphogen which supports secondary phloem development. According to this model, each tree species shows a particular pattern of post-mitotic cellular displacement along each radial file as a result of a corresponding sequence of periclinal division in the cambial initial and its descendents. The divisions and displacements ensure that at each timestep (equivalent to an interdivisional interval) each cell resides in a specific location within the morphogenic gradient. Cells then emerge from the post-mitotic zone of cell determination, having acquired different final positional values. These values lie above a series of thresholds that permit the respective determination and subsequent differentiation of one or other of the three cell types S, P and F. The recurrent nature of the sequences of the three cell types within each radial cell file, as well as their tangential banding, are a consequence of a shared rhythmic spatio-temporal pattern of periclinal cambial divisions. With a single set of morphogen parameters required for cell determination, and using three positions for cambial cell divisions, all the cellular sequences of secondary phloem illustrated in the literature can be accounted for.
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http://dx.doi.org/10.1007/s10265-006-0280-4DOI Listing
July 2006

Cytokinesis in plant and animal cells: endosomes 'shut the door'.

Dev Biol 2006 Jun 3;294(1):1-10. Epub 2006 Apr 3.

Institute of Cellular and Molecular Botany, Rheinische Friedrich-Wilhelms-University of Bonn, Kirschallee 1, 53115 Bonn, Germany.

For many years, cytokinesis in eukaryotic cells was considered to be a process that took a variety of forms. This is rather surprising in the face of an apparently conservative mitosis. Animal cytokinesis was described as a process based on an actomyosin-based contractile ring, assembling, and acting at the cell periphery. In contrast, cytokinesis of plant cells was viewed as the centrifugal generation of a new cell wall by fusion of Golgi apparatus-derived vesicles. However, recent advances in animal and plant cell biology have revealed that many features formerly considered as plant-specific are, in fact, valid also for cytokinetic animal cells. For example, vesicular trafficking has turned out to be important not only for plant but also for animal cytokinesis. Moreover, the terminal phase of animal cytokinesis based on midbody microtubule activity resembles plant cytokinesis in that interdigitating microtubules play a decisive role in the recruitment of cytokinetic vesicles and directing them towards the cytokinetic spaces which need to be plugged by fusing endosomes. Presently, we are approaching another turning point which brings cytokinesis in plant and animal cells even closer. As an unexpected twist, new studies reveal that both plant and animal cytokinesis is driven not so much by Golgi-derived vesicles but rather by homotypically and heterotypically fusing endosomes. These are generated from cytokinetic cortical sites defined by preprophase microtubules and contractile actomyosin ring, which induce local endocytosis of both the plasma membrane and cell wall material. Finally, plant and animal cytokinesis meet together at the physical separation of daughter cells despite obvious differences in their preparatory events.
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http://dx.doi.org/10.1016/j.ydbio.2006.02.047DOI Listing
June 2006

Actin turnover-mediated gravity response in maize root apices: gravitropism of decapped roots implicates gravisensing outside of the root cap.

Plant Signal Behav 2006 Mar;1(2):52-8

Electrophysiology Laboratory; Department of Horticulture; University of Florence; Sesto Fiorentino, Italy.

The dynamic actin cytoskeleton has been proposed to be linked to gravity sensing in plants but the mechanistic understanding of these processes remains unknown. We have performed detailed pharmacological analyses of the role of the dynamic actin cytoskeleton in gravibending of maize (Zea mays) root apices. Depolymerization of actin filaments with two drugs having different mode of their actions, cytochalasin D and latrunculin B, stimulated root gravibending. By contrast, drug-induced stimulation of actin polymerization and inhibition of actin turnover, using two different agents phalloidin and jasplakinolide, compromised the root gravibending. Importantly, all these actin drugs inhibited root growth to similar extents suggesting that high actin turnover is essential for the gravity-related growth responses rather than for the general growth process. Both latrunculin B and cytochalasin D treatments inhibited root growth but restored gravibending of the decapped root apices, indicating that there is a strong potential for effective actin-mediated gravity sensing outside the cap. This elusive gravity sensing outside the root cap is dependent not only on the high rate of actin turnover but also on weakening of myosin activities, as general inhibition of myosin ATPases induced stimulation of gravibending of the decapped root apices. Collectively, these data provide evidence for the actin turnover-mediated gravity sensing outside the root cap.
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http://dx.doi.org/10.4161/psb.1.2.2432DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2633879PMC
March 2006
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