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

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.

Leaf movements and their relationship with the lunisolar gravitational force.

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.

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

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.

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

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.

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

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.

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

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.

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

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.

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

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.

Reflections on 'plant neurobiology'.

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.

FAL Clowes, 1921-2016: a Memoir.

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.

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

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.

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.

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.

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

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.

CELLULAR PACKETS, CELL DIVISION AND MORPHOGENESIS IN THE PRIMARY ROOT MERISTEM OF ZEA MAYS L.

Dormant meristematic cells of the unemerged radicle contained within the caryopsis of Zea mays L. are arrested in either the G1 or G2 phase of the mitotic cycle. Following germination and the resumption of root growth, each of these cells divides repeatedly to form multicellular groups, or 'packets'. The thickened cell walls that bound each packet correspond to the walls of the formerly dormant mother cell, while the thinner walls that partition the packet correspond to walls laid down when the successive rounds of division are completed. The relative thickness of these partition walls corresponds to their age, the most recently inserted wall being the thinnest. The packets thus give evidence of not only the number of divisions that have occurred since germination, but also the sequence in which these divisions took place. In addition, the elongation of the packets during root growth allows their displacement away from the root tip into the zone beyond the margin of the meristem to be measured. Using roots fixed at different times during early growth, the kinetics of packet development has been followed in cells occupying different positions within the meristem at the start of root growth. By counting the number of cells in the packets at frequent intervals during root growth, the period between each round of division has been found to be fairly constant, even as the cells are displaced towards the margin of the meristem. Variability in the interdivisional period within a packet is insufficient to cause extensive overlapping of the different rounds of division. Exceptions are found in cortical and stelar cells around the quiescent centre, where the more distal cells in a packet often divide at up to half the rate of the more proximal cells. This is evidence of a steep gradient of cell extension rate near the quiescent centre; such a gradient does not occur along packets elsewhere in the meristem. In the quiescent centre itself, cells of its cortical portion divide more rapidly than cells of its stelar portion. Cells in the cortex (but not in the stele) often divide unequally at their first transverse division; the distal (apical) daughter is usually the longer of the two daughter cells. Asymmetric, transverse division also occurs in some cells during the next rounds of division. The more rapid entry into mitosis of the longer daughter cell results in packets with particular sequences of division. Asymmetric, longitudinal (periclinal) divisions also occur in the cortex, the inner daughter cell being wider than the outer daughter cell. These periclinal divisions occur in the distal portion of the cortex near its inner and outer borders with the stele and epidermis, respectively. At the start of root growth, periclinal divisions commence sooner in the outer cortex than in the inner cortex but do not persist, and the number of cell files across the width of the cortex declines. A concurrent loss of files also occurs in the stele. The first two rounds of periclinal divisions in the innermost file of the cortex show a definite spatial pattern. These divisions intrude into the quiescent centre and may account for the apparently anomalous faster cycling cells that have been reported here. The cellular packets give insights into certain of the fundamental aspects of root morphogenesis, the choice that confronts a cell of whether to divide transversely or longitudinally being of special importance. Particular ranges of values for the ratio between cell length and breadth are associated with these two classes of division.

Root cap structure and cell production rates of maize (Zea mays) roots in compacted sand.

• 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.

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

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.

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

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.