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Summary • To assess the influence of mechanical impedance on cell fluxes in the root cap, maize (Zea mays) seedlings were grown in either loose or compacted sand with penetration resistances of 0.2 MPa and 3.8 MPa, respectively. Numbers of cap cells were estimated using image analysis, and cell doubling times using the colchicine technique. • There were 5930 cells in the caps in the compact and 6900 cells in the loose control after 24 h growth in sand. Cell production rates were 2010 cells d−1 in compact and 1570 cells d−1 in loose sand. • These numbers represent accumulations of 4960 and 3540 detached cells d−1 around the cap periphery following the two types of treatment. The total number of detached cells was estimated as sufficient to completely cover the whole root cap in the compact sand, but only 11% of the root cap in the loose sand. • In conclusion, mechanical impedance slightly enhanced meristematic activities in the lateral region of the root cap. The release of extra border cells would aid root penetration into the compact sand.

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.

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.

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.

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. Copyright © 2015 John Wiley & Sons, Ltd.

The ultrastructure and fate of surface cells covering mature somatic embryos of Daucus carota grown in suspension culture were analyzed and new information obtained concerning somatic embryogenesis in these conditions. Our studies showed that during some developmental stages, these embryos were covered irregularly and discontinuously by cells with a typical protodermal phenotype characterized by a cuticle on the outer cell wall. We observed that cells with cuticles were peeled off from the surface of mature embryos. Before peeling off, these cells underwent programmed cell death, which was confirmed by the TdT-mediated dUTP nick end labeling method. Transmission electron microscopy revealed advanced processes of autophagy in these cells.

Within the tip of roots meristems of angiosperms and gymnosperms there is a small group of cells known as the quiescent centre (QC). The concept of the QC was developed 60 years ago by FAL Clowes, working in the Botany School, Oxford University, UK. To celebrate the Jubilee of the QC, a brief outline of the work that led to its demonstration by autoradiography was presented by Dubrovsky and Barlow (2015). The present article traces Clowes's subsequent experimental studies of the QC, especially with regard to how X-irradiation became an important tool for elucidating the properties and significance of the QC for root development. Also reviewed are some of the consequences that subsequently arose from this work with radiation, in particular the concerns over the use of radioisotopes in attempts to describe the kinetics of cell proliferation in the root meristem.

Background and aims Roots of Arabidopsis thaliana exhibit a 24.8 h oscillation of elongation rate when grown under free-running conditions. This growth rhythm is synchronized with the time course of the local lunisolar tidal acceleration. The present study aims at a physiological/physical model to describe the interaction of weak gravitational fields with cellular water dynamics that mediate rhythmic root growth profiles. Methods Fundamental physical laws are applied to model the water dynamics within single plant cells in an attempt to mimic the 24.8 h oscillations in root elongation growth. In particular, a quantum gravitational description of the time course in root elongation is presented, central to which is the formation of coherent assemblies of mass due to the lunisolar gravitational field. Mathematical equations that characterize lunisolar gravity-induced coherent assemblies of water molecules are derived and related to the mass of cellular water within roots of A. thaliana. Key results The derived physical model of gravitationally modulated water assemblies is capable of accounting for the experimentally observed arabidopsis root growth kinetics under free-running conditions. The close analogy between the derived time-dependent lunisolar effect upon coherent molecular states of water within single cells and the coherent assemblies of electrons that characterize the quantum Hall effect is emphasized. Conclusions The dynamics of the lunisolar-induced variation in coherent water assemblies provide a possible mechanism to describe the observed 24.8 h oscillation of root growth rate of A. thaliana. Therefore, this mechanism could function as an independent timekeeper to control cell elongation.

Orbital movement of the Moon generates a system of gravitational fields that periodically alter the gravitational force on Earth. This lunar tidal acceleration (Etide) is known to act as an external environmental factor affecting many growth and developmental phenomena in plants. Our study focused on the lunar tidal influence on stem elongation growth, nutations and leaf movements of peppermint. Plants were continuously recorded with time-lapse photography under constant illumination as well in constant illumination following 5 days of alternating dark–light cycles. Time courses of shoot movements were correlated with contemporaneous time courses of the Etide estimates. Optical microscopy and SEM were used in anatomical studies. All plant shoot movements were synchronised with changes in the lunisolar acceleration. Using a periodogram, wavelet analysis and local correlation index, a convergence was found between the rhythms of lunisolar acceleration and the rhythms of shoot growth. Also observed were cyclical changes in the direction of rotation of stem apices when gravitational dynamics were at their greatest. After contrasting dark–light cycle experiments, nutational rhythms converged to an identical phase relationship with the Etide and almost immediately their renewed movements commenced. Amplitudes of leaf movements decreased during leaf growth up to the stage when the leaf was fully developed; the periodicity of leaf movements correlated with the Etide rhythms. For the fist time, it was documented that lunisolar acceleration is an independent rhythmic environmental signal capable of influencing the dynamics of plant stem elongation. This phenomenon is synchronised with the known effects of Etide on nutations and leaf movements.

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.

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.

Unique mental abilities have been crucial for evolutionary success of Homo sapiens and for the development of his complex social organization. However, these abilities have also become a target for mental disorders which often result in a reduced fitness and in conflicts between the individual and the conventions of society. To account for this evolutionary maladaptation, we advance a new concept: that of "mis-exaptation", derived from SJ Gould and E Vrba's concept of exaptation. Mis-exaptation is a characteristic which, although it may confer positive effects in one field of activity, may reach an inappropriate degree of specialisation to have deleterious effects in that or in another field thereby leading to a decrease in fitness of the individual. This paper considers "inner speech" as an exaptation. Although inner speech is usually a positive aid to learning and reasoning, it may also favour the emergence of mental disturbances, such as the auditory hallucinations which are characteristic of schizophrenia. There is, nevertheless, a possible evolutionary value in mis-exaptational inner speech; two traits associated with the mis-exapted state would be altruistic behaviour and heightened creativity, the latter being over-expressed in relatives of schizophrenic patients. A possible solution for the evolutionary-genetic paradox posed by altruism and schizophrenia arising from mis-exaptation will be suggested in the light of a cryptic genetic repertoire. A selection of illustrative examples of each of these mental states is presented as they appear in the pages of the European literature. This article is part of a Special Issue entitled: Brain Integration.

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'.

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.

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.

Many facets reflecting the autopoietic process of Life and Living can be found in plant roots at many levels relevant to their organisation, from cells to ecosystems. At each level, there are sub-processes dedicated to both the auto- reproduction and the self-maintenance of that level, these processes being contained within a boundary appropriate for that level. Auto- reproduction and self-maintenance unite with a third sub-process, cognition, and provide the basis of a coherent multi-levelled programme of root-research.

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.

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.

The hypothesis, proposed by the late Gunter Klein, that the autonomous nyctinastic movements of bean leaves are related to the tidal force exerted by the Moon was tested. Using data collected by Dr Klein, a close correspondence was found between the time at which leaves initiated a sudden downward turning movement and the time at which the tidal force changed from either a minimum (AƒÂ‚A‚‘low tideAƒÂ‚A‚Â’) or a maximum (AƒÂ‚A‚‘high tideAƒÂ‚A‚Â’). In many cases the data sets of leaf movements and the changing tidal force gave evidence of correlative patterns of behaviour. Evidence was also adduced for a minimal 6.2-h interval, or multiples thereof, between successively executed leaf movements. Data from an earlier study by A Kleinhoonte were also examined and have been found to show even closer correspondences than do KleinAƒÂ‚A‚Â’s data between bean leaf-movements and changing tidal forces. Thus, KleinAƒÂ‚A‚Â’s hypothesis of coherence between leaf and Moon is upheld.

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.

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.

Les interactions entre conditions environnementales et developpement des tissus vasculaires secondaires ont ete etudiees au cours du developpement de jeunes pousses de tremble hybride (Populus tremula x P. tremuloides) a l'aide d'un modele de regression associe a des equations differentielles. Deux series de donnees ont ete combinees. La premiere concernait le nombre de cellules accumulees de differents types - fibres xylemiennes, vaisseaux, cellules de phloeme, rayons parenchymateux - dans les files radiales de cellules de tiges echantillonnees a intervalles de temps reguliers sur une periode de 16 mois. Etaient aussi pris en compte le nombre de cellules cambiales fusiformes accumulees dans les files radiales et dans le perimetre cambial (cellules initiales). La seconde serie de donnees concernait des variables environnementales externes, dont les valeurs ont ete relevees a intervalles de temps rapproches, tout au long de la periode d'echantillonnage des pousses. Les variables environneinentales prises en compte sont la temperature et l'eclairement, donnee a partir de laquelle est estimee la duree du jour. Elles ont ete utilisees pour definir des unites de « temps de developpement », a partir desquelles se font les regressions contre le nombre de cellules des differents types accumulees dans les tissus vasculaires secondaires. Les analyses de regression permettent d'estimer non seulement le taux de production de cellules, mais aussi les valeurs seuils des parametres environnementaux au dessus et en dessous desquelles les differents types de productions cellulaires sont inities ou arretes en fonction des conditions saisonnieres. De cette maniere on a pu identifier les conditions critiques pour la production de chacun de chacun de ces differents types de cellules.

The radial fusiform cell files of the secondary phloem of conifers and dicots are composed of different cell types – fibres, parenchyma and sieve cells (in conifers), or sieve elements plus companion cells (in dicots). These cell types are arranged in characteristic, species-specific sequences along the radii of the files. The sequences are replicated in adjacent files and this leads to tangential bands of similar cell type. Moreover, the sequences are developed repetitively so that a sequence found in one year's growth increment of phloem is repeated in the next increment. In some species, many repetitions of the same sequence occur within one annual increment. A general hypothesis has been developed to account for the radial sequences of cell types. It is proposed that there is a gradient of a phloem-promoting morphogen, a series of morphogen thresholds for the determination of each phloem cell type, and a particular spatio-temporal pattern of periclinal cell division in the phloem domain of th...

The secondary vascular tissues (xylem and phloem) of woody plants originate from a vascular cambium and develop as radially oriented files of cells. The secondary phloem is composed of three or four cell types, which are organised into characteristic recurrent cellular sequences within the radial cell files of this tissue. There is a gradient of auxin (indole acetic acid) across both the cambium and the immediately postmitotic cells within the xylem and phloem domains, and it is believed that this morphogen, probably in concert with other morphogenic factors, is closely associated with the determination and differentiation of the different cells types in each tissue. A hypothesis is developed that, in conjunction with the positional values conferred by the graded radial distribution of morphogen, cell divisions at particular positions within the cambium are sufficient to determine not only each of the phloem cell types but also their recurrent pattern of differentiation within each radial cell file. BioEssays 27: 533–541, 2005. © 2005 Wiley periodicals, Inc.

There are two main types of arrangement of differentiated cells within the radial cell files of secondary phloem in conifer trees. In the C-type arrangement, characteristic of the Cupressaceae, fibre (F), parenchyma (P) and sieve (S) cells are arranged in recurrent groups, such as the “standard” cellular quartet (FSPS). In the P-type arrangement, characteristic of the Pinaceae, there are no fibres and one of the characteristic recurrent arrangements is the cellular sextet (PSSSSS). In addition, in both C-type and P-type arrangements, similar cell types are often organised into tangential bands. A simulation model, based on the theory of L-systems, was devised to account for the determination of these two types of regular and recurrent patterns of differentiated phloem cells. It was based on the supposition that, in the meristematic portion of the phloem domain, there are specific spatio-temporal patterns of periclinal cell division. When new cells are produced, those already present are displaced along th...

• Background and Aims The impedance to root growth imposed by soil can be decreased by both mucilage secretion and the sloughing of border cells from the root cap. The aim of this study is to quantify the contribution of these two factors for maize root growth in compact soil. • Methods These effects were evaluated by assessing growth after removing both mucilage (treatment I – intact) and the root cap (treatment D – decapped) from the root tip, and then by adding back 2 µL of mucilage to both intact (treatment IM – intact plus mucilage) and decapped (treatment DM – decapped plus mucilage) roots. Roots were grown in either loose (0·9 Mg m−3) or compact (1·5 Mg m−3) loamy sand soils. Also examined were the effects of decapping on root penetration resistance at three soil bulk densities (1·3, 1·4 and 1·5 Mg m−3). • Key Results In treatment I, mucilage was visible 12 h after transplanting to the compact soil. The decapping and mucilage treatments affected neither the root elongation nor the root widening rates when the plants were grown in loose soil for 12 h. Root growth pressures of seminal axes in D, DM, I and IM treatments were 0·328, 0·288, 0·272 and 0·222 MPa, respectively, when the roots were grown in compact soil (1·5 Mg m−3 density; 1·59 MPa penetrometer resistance). • Conclusions The contributions of mucilage and presence of the intact root cap without mucilage to the lubricating effect of root cap (percentage decrease in root penetration resistance caused by decapping) were 43 % and 58 %, respectively. The lubricating effect of the root cap was about 30 % and unaffected by the degree of soil compaction (for penetrometer resistances of 0·52, 1·20 and 1·59 MPa).

Using simple arithmetical formulae, it is shown that, when the meristematic initial cells of a growing plant organ are arranged in a ring, the cellular dimensions predict the relative frequencies of anticlinal and periclinal divisions which these cells undergo. The pattern of cell file branching which appears during the course of development, and which is predicted by this mathematical model, is validated using data pertaining to the numbers and dimensions of initial cells within the secondary vascular cambium of hybrid aspen trees. Data pertaining to a second, simpler set of initial cells which comprises the outer cellular ring of the thallus of the alga Coleochaete orbicularis, and from which all the radial cell files of the circular disc-like thallus are descended, have also been used for model validation. Combining the mathematical approach to division frequencies with data of actual cell sizes permits inferences about the course of the increase of the number of cell files (generated by the anticlinal divisions) and the number of cells within each file (generated by the periclinal divisions) during the earlier stages of secondary tissue or thallus development, and also about how they will develop at future stages. The question whether or not cell division patterns conform to the geometry of the system in which the cells are embedded is also discussed.

Main conclusion Cyclic leaf ascent and descent occur in synchrony and phase congruence with the lunisolar tidal force under a broad range of conditions. Digitized records of the vertical leaf movements of Arabidopsis thaliana were collected under space flight conditions in the International Space Station (ISS). Oscillations of leaf movements with periods of 45 and 90 min were found under light-adapted conditions, whereas in darkness, the periods were 45, 90, and 135 min. To demonstrate the close relationship between these oscillations and cyclical variations of the lunisolar gravitational force, we estimated the oscillations of the in-orbit lunisolar tide as they apply to the ISS, with the aid of the Etide software application. In general, in-orbit lunisolar gravitational profiles exhibited a periodicity of 45 min. Alignment of these in-orbit oscillations with the oscillations of Arabidopsis leaf movement revealed high degrees of synchrony and a congruence of phase. These data corroborate previous results which suggested a correlative relationship and a possible causal link between leaf movement rhythms obtained on ground and the rhythmic variation of the lunisolar tidal force.

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.

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.

A map-L-system is described which simulates the development of the two-dimensional patterns of cell walls displayed at the surfaces of shoot apices of Psilotum nudum. The simulation of these cellular patterns commences with the division of a triangular cell and continues until a complete set of ten different cells, including new triangular cells, is formed amongst the descendants of each merophyte. The triangular cells generated by means of this division pathway, P1, are, in their three-dimensional aspect, four-sided apical cells. In the plant, they have the potentiality to support the development of a shoot apex. The generation of new triangular cells by pathway P1 therefore seems to be a precondition for the branching of the shoot. Observed variations upon the cellular pattern developed by pathway P1 have also been analysed. Two of these variant pathways, P2 and P3, suggest the types of controls which are required to bring about all three (P1–P3) patterns of cells. These controls may involve the participation of the plant cytoskeleton and may also require an influence from the apical cell itself. The triangular shoot apical cells of Psilotum are autoreproductive cells: that is, at each division, one of the daughters is a new triangular cell, the other daughter has some other shape. This example of triangular cell autoreproduction and self-maintenance and its relation to organogenesis is discussed in light of the views on reproduction and self-maintenance expressed by Agnes Arber (1950) in her book The natural philosophy of plant form(Cambridge: Cambridge University Press).

Due to their simple and regular anatomy, root apices represent a unique model object for studying growth, polarity, and morphogenesis. This advantageous anatomy has been exploited to characterize the developmental changes that occur as root cells progress from their origin in the meristem up to their final nongrowing state at the proximal limit of the elongation region. A new growth region located between the apical meristem and the distal portion of the region of rapid cell elongation was discovered and designated as the ‘transition zone.’ Cells of this zone accomplish a developmental transition recently from cytoplasmically driven expansion to vacuome-driven elongation. Cells traversing the transition zone use cytoskeletal elements to regulate both growth polarity and the maintenance of cellular growth per se. Transition zone cells are also sensitive to diverse endogenous clues and exogenous factors such as auxin, ethylene, extracellular calcium, mechanical pressure, aluminum, and microorganisms. This high sensitivity of transition zone cells, which are not engaged in mitotic divisions, seems to be related to their specific cytoarchitecture whereby postmitotic nuclei occupy a central position within the cell, with their radial perinuclear microtubules extending to the cell periphery. Future studies are challenged to identify genes and proteins that determine the various sensory behaviors of cells in this transitional phase of development, and which, in turn, drive directed growth responses (tropisms) of root apices in response to diverse external stimuli.

The cap of the primary root of maize produces several thousand border cells that are shed from the outside of the cap each day. Border cell production is important in the penetration of soil by roots, and in influencing the activity of both beneficial and pathogenic organisms in the rhizosphere. To improve understanding of the dynamics of border cell production, it is desirable to know the number of cells in diAerent parts of the root cap. An image analysis procedure was used to quantify cell dimensions and locations in the median longitudinal section of maize (Zea mays L.) root caps. Calculations based on root symmetry were then used to estimate the number of cells in 3-dimensions. Our estimation procedure was tested initially using regular arrays of identical square and hexagonal shapes to represent cells. It was then tested using two diAerent tissues showing analogous arrays: a transverse section through the maize root cap junction, and a transverse section through a barley root. Good linear correlations were obtained between the number of cells estimated and the number of cells actually counted in the microscope. The numbers of cells in the whole maize root cap (8870+390) were then estimated from longitudinal sections. These numbers of cap cells agreed with values that had been estimated for maize by other methods. In the first tier of the cap meristem, tentimes more meristematic cells were located in the cap flanks (4500 cells) than were present in the columella portion. Similarly, only 7% of cells in the outermost layer of the root were associated with the columella region of the cap, a fraction which compared well with previous measurements of sloughed cells extracted from rhizosphere sand. This present technique can be applied to estimate the numbers of cells in any cylindrically symmetrical tissue from twodimensional sections. # 2001 Annals of Botany Company

Root apical meristems are composed of two zones in which either formative or proliferative cell divisions occur. Within the formative zone, autoreproductive initial cells (a-cells) occupy distinctive locations. By means of graph-L-systems, the behavior of one such type of a-cells has been investigated, with particular reference to root caps within the developing primordia of lateral roots of Lycopersicon esculentum cultivated in vitro. Here, the a-cells constitute the "protoderm initials", cells which are found also in the root cap of many angiosperm species. A set of cuboidal (i.e., six-sided) a-cells develops early in the ontogeny of a lateral-root primordium. Then, according to both anatomical observations and theoretical simulations obtained by the application of graph-L-systems, sequential production of descendents from each a-cell leads to the formation of a new autoreproductive cell (a), a cap columella initial (c), and two mother cells (e and f) whose respective descendents differentiate as root epidermis and cap flank cells. In this graph-L-system, there is specification of the location of sister cells with respect to the three orthogonal directions of a cuboidal. In the early stage of root cap formation, only a few rounds of these formative cell divisions by each a-cell and its four types of descendents are required to provide the basic set of cells necessary for full cap development. After the lateral root emerges from the parent root, there may be a temporary cessation of the formative divisions of the a-cells which give rise to columella initials. Columella production is then supported entirely by its own independent set of autoreproductive c-initials. At the same time, division of the autoreproductive protoderm initial cell is directed towards maintaining the cap flank and the epidermal cell files. The regulation of the types of formative division by the a-cell may be represented by means of a division counter which may be specific for a given species.

Plant root hair formation is initiated when specialized elongating root epidermis cells (trichoblasts) assemble distinct domains at the plasma membrane/cell wall cell periphery complexes facing the root surface. These localities show accumulation of expansin and progressively transform into tip-growing root hair apices. Experimentation showed that trichoblasts made devoid of microtubules (MTs) were unaffected in root hair formation, whereas those depleted of F-actin by the G-actin sequestering agent latrunculin B had their root hair formation blocked after the bulge formation stage. In accordance with this, MTs are naturally depleted from early outgrowing bulges in which dense F-actin meshworks accumulate. These F-actin caps remain associated with tips of emerging and growing root hairs. Constitutive expression of the GFP-mouse talin fusion protein in transgenic Arabidopsis, which visualizes all classes of F-actin in a noninvasive mode, allowed in vivo confirmation of the presence of distinct F-actin meshworks within outgrowing bulges and at tips of young root hairs. Profilin accumulates, at both the protein and the mRNA levels, within F-actin-enriched bulges and at tips of emerging hairs. ER-based calreticulin and HDEL proteins also accumulate within outgrowing bulges and remain enriched at tips of emerging hairs. All this suggests that installation of the actin-based tip growth machinery takes place only after expansin-associated bulge formation and requires assembly of profilin-supported dynamic F-actin meshworks.

Nascent cellulosic cell wall microfibrils and transverse (with respect of cell growth axis) arrays of cortical microtubules (MTs) beneath the plasma membrane (PM) are two well established features of the periphery of higher plant cells. Together with transmembrane synthase complexes, they represent the most characteristic form of a “cell periphery complex” of higher plant cells which determines the orientation of the diffuse (intercalary) type of their cell growth. However, there are some plant cell types having distinct cell cortex domains which are depleted of cortical MTs. These particular cell cortex domains are, instead, typically enriched with components of the actin-based cytoskeleton. In higher plants, this feature is prominent at extending apices of two cell types displaying tip growth - pollen tubes and root hairs. In the latter cell type, highly dynamic F-actin meshworks accumulate at extending tips, and they appear to be critical for the apparently motile character of these subcellular domains. Importantly, tip growth of both root hairs and pollen tubes is immediately stopped when the most dynamic F-actin population is depolymerized with low levels of anti-F-actin drugs. Intriguingly, MTs of tip-growing plant cells are organized in the form of longitudinal arrays, throughout the cytoplasm, which interconnect the extending tips with the subapical nuclei. This suggests that actin-rich cell cortex domains polarize plant “cell bodies” represented by nucleus-MTs complexes. A similar polarization of “cell bodies” is typical of mitotic and cytokinetic plant cells. A further type of MT-depleted and actomyosin-enriched plant cell cortex domain comprises the plasmodesmata. Primary plasmodesmata are formed during cytokinesis as part of the myosin VIII-enriched callosic cell plates, representing “juvenile” forms of the plant “cell periphery complex”. In phylogenetic terms the association between F-actin and the PM may be considered for a more “primitive” form of cellular organization than does the association of cortical MTs with the PM. We hypothesize that the actin cytoskeleton is a natural partner of the PM in all eukaryotic cells. In most plant cells, however, it was replaced by a tubulin-based “cell periphery apparatus” which regulates, via still unknown mechanisms, the spatial deposition of nascent cellulosic microfibrils synthesized by PM-associated synthase complexes.

For walled plant cells, the immunolocalization of actin microfilaments, also known as F-actin, has proved to be much trickier than that of microtubules. These difficulties are commonly attributed to the high sensitivity of F-actin to aldehyde fixatives. Therefore, most plant studies have been accomplished using fluorescent phallotoxins in fresh tissues. Nevertheless, concerns regarding the questionable ability of phallotoxins to bind the whole complement of F-actin necessitate further optimization of actin immunofluorescence methods. We have compared two procedures: (1) formaldehyde fixation and (2) rapid freezing and freeze substitution (cryofixation), both followed by embedding in low-melting polyester wax. Actin immunofluorescence in sections of garden cress (Lepidium sativum L.) root gave similar results with both methods. The compatibility of aldehydes with actin immunodetection was further confirmed by the freeze-shattering technique that does not require embedding after aldehyde fixation. It appears that rather than aldehyde fixation, some further steps in the procedures used for actin visualization are critical for preserving F-actin. Wax embedding, combined with formaldehyde fixation, has proved to be also suitable for the detection of a wide range of other antigens.

Key words: Cell cycle, DNA replication, licensing factor,MCM proteins, plant.A partial cDNA from maize, ROA, encoding a proteinhomologous to the MCM3 family of essential factorsfor the initiation of DNA replication, has been isolated Introduction previously. In the present work, a longer version of theoriginal ROA cDNA, encoding a full-length protein, was The eukaryotic genome is generally replicated exactlyisolated and termed ZmROA1. In addition, three other once, during the S phase of the somatic cell cycle, andclosely related cDNAs, ZmROA2, ZmROA3 and this is essential to maintain the DNA content throughZmROA4, were also isolated. ZmROA2 end ZmROA3 numerous generations of cells. The once-per-cell cycleappear to encode full-length proteins, whereas control over DNA replication ensures that DNA synthesisZmROA4 a partial polypeptide. Two clusters of basic is initiated only once, and that re-replication is inhibitedamino acids comprising putative nuclear localization during S phase (reviewed by Coverly and Laskey, 1994).signals were identified in the N-terminal domain This involves a tight control over replication origins,of these proteins, together with a potential leucine which must be timed to activate upon S phase entry,zipper. Immunofluorescence studies on cycling meris- but then rendered unable to support further rounds oftematic root-tip cells revealed that these proteins are DNA synthesis until cells complete mitosis and enter thelocalized in the nucleus throughout interphase with a next interphase. A complex array of interactions betweenpattern overlapping that of chromatin. However, as initiation factors and chromosomal origins is essential tochromatin condenses at prophase, ZmROA proteins make origins competent for DNA replication, to fire thembecome increasingly distinct from chromatin and during S phase, and to prevent them from firing again inappear totally dissociated from the segregating chro- the same cell cycle (reviewed by Kearsey