Cell Turgor Pressure Research Articles

干旱胁迫对青藏高原6种植物生理指标的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 干旱胁迫对青藏高原6种植物生理指标的影响 DOI: 10.5846/stxb201306031288 作者: 作者单位: 华南农业大学,华南农业大学,华南农业大学,中国林业科学研究研究院林业研究所 国家林业局林木培育重点实验室 北京,华南农业大学,华南农业大学,甘肃省小陇山林业科学研究所 甘肃天水,甘肃省小陇山林业科学研究所 甘肃天水 作者简介: 通讯作者: 中图分类号: 基金项目: 林业公益性行业科研专项（200904033）；科学技术部农业科技成果转化资金项目（2011GB24320010） Physiological indexes of six plant species from the tibetan plateau under drought stress Author: Affiliation: South China Agricultural University,,South China Agricultural University,,,,, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以青藏高原6种植物：红花岩黄芪（Hedysarum multijugum Maxim.）、西北沼委陵菜（Comarum salesovianum （Steph.）Asch. et Graebn.）、鲜黄小檗（Berberis diaphana Maxim.）、鲜卑花（Sibiraea laevigata （Linn.）Maxim.）、树锦鸡儿（Caragana arborescens（Amm.）Lam.）、砂生槐（Sophora moorcroftiana（Benth.）Baker）为试材进行干旱胁迫模拟盆栽试验，通过对比6种植物叶片中丙二醛（MDA）、脯氨酸、可溶性蛋白质、叶绿素、可溶性糖、淀粉含量的变化，对供选植物进行抗旱性能分析与评价，为在青藏高原地区筛选优良耐旱植物提供参考依据。设置土壤含水量占田间持水量80%以上为正常水平，50%-70%为轻度干旱，30%-50%为中度干旱，低于30%为重度干旱。研究表明，6种供试植物叶片MDA含量逐渐升高，当土壤含水量占田间持水量12%左右时达到最大值，树锦鸡儿的增幅较另5种苗木最小，而峰值最大。脯氨酸含量都呈增加趋势，其中砂生槐最高，为9981.67 mg/g，峰值与对照值相比，砂生槐增加最多为37.43 倍，鲜卑花最小为0.49 倍。苗木叶片中可溶性蛋白质含量总体表现出现增大后减小的规律，且所有测定值都高于正常水分条件下的含量。6种苗木的叶绿素含量在干旱胁迫下总体呈现先降低再升高最后再降低的趋势，24 d时均低于对照值，下降最多的为西北沼委陵菜（15.43 mg/g）。由于干旱下苗木的光合产物转化受抑，以淀粉形式的累积量减少，所以6种苗木的可溶性糖含量呈上升趋势，而淀粉含量呈下降趋势，通过积累可溶性糖以提高细胞的渗透调节能力。砂生槐、树锦鸡儿的可溶性糖含量增幅与淀粉含量的减少明显高于其余苗木，使其在较低叶水势下仍保持较高的细胞膨压，以减缓水分胁迫的不利影响。主成分分析表明，6种苗木抗旱性由强到弱依次为：树锦鸡儿、红花岩黄芪、砂生槐、鲜黄小檗、鲜卑花、西北沼委陵菜。 Abstract:During adaptation to the environment, plants can gradually develop drought resistance via a process of natural selection. Plants are often under water stress in the cold and dry environmental conditions on the Tibetan Plateau, and these conditions can directly affect various physiological activities. The aim of this study was to analyze and evaluate the drought resistance of selected plants from the Tibetan Plateau, and to provide a reference for selecting drought-tolerant plants. We collected six species of plants from the Tibetan Plateau; Hedysarum multijugum Maxim, Comarum salesovianum (Steph.) Asch. et Graebn., Berberis diaphana Maxim., Sibiraea laevigata (Linn.) Maxim., Caragana arborescens (Amm.) Lam. and Sophora moorcroftiana Benth Baker. To protect themselves against drought and low-temperature stress, plants have evolved efficient antioxidant systems to scavenge reactive oxygen species. We evaluated changes in the amounts of malondialdehyde (MDA), proline, soluble protein, chlorophyll, soluble sugars, and starch in leaves of these species subjected to increasingly severe drought conditions in a pot experiment. The soil moisture was greater than 80% of field capacity for the normal level, 50%-70% for mild drought, 30%-50% for moderate drought, and less than 30% for severe drought. In all six plant species, the MDA content increased slowly from day 0 to day 12 of the drought treatment, and then increased significantly after day 16 to reach a peak when the soil water content was approximately 12%. Caragana arborescens showed the smallest increase in MDA content under drought, but had the highest MDA content (4.72 mmol/g) among the six plant species. The proline content increased in all six species under drought, and there were significant differences among species in the amount of proline accumulated. The largest increase in proline content was in S. moorcroftiana (peak value, 9981.67 mg/g; 37.43 times that in CK), and the smallest was in S. laevigata (peak value was 0.49 times that in CK). The leaf soluble protein content increased under drought conditions in all six species, but began to decrease when the drought conditions became more severe. The largest decrease in protein content under severe drought conditions was in S. moorcroftiana (a decrease of 39.22%, compared with the peak protein concentration). The chlorophyll concentrations in the leaves of the six species first increased and then decreased as the drought conditions became more severe. In the moderate drought period, the chlorophyll content of seedling leaves began to recover, probably because of a decrease in leaf water content. In all six species, the chlorophyll content on day 24 of the drought was lower than that on day 0. The largest decrease in chlorophyll concentration was in C. salesovianum (15.43 mg/g). The soluble starch contents in all six species decreased under drought because of a reduction in photosynthesis; however, all species showed an increase in soluble sugars content, which improved the osmotic adjustment capability of cells. The largest increases in soluble sugars contents and the largest reductions in starch contents were in S. moorcroftiana and C. arborescens. These species were able to retain higher cell turgor pressure at lower water potential, compared with the other species. After day 16 of the drought treatment, the decreases in starch and soluble sugar contents in the leaves indicated that prolonged water stress caused decomposition of biomass, reduced biosynthesis, and a weaker ability for osmotic adjustment. The drought resistance of plants is the sum of many physiological factors, and represents complex interactions among these factors. Thus, it is a complicated physiological adjustment mechanism. The six species were ranked differently in terms of each of the physiological indexes measured. Therefore, we used principal component analysis to select the most important physiological indexes of drought resistance: chlorophyll, MDA, and starch contents. The results of the principal component analysis indicated that species could be ranked, in terms of most to least drought resistant, as follows: C. arborescens > H. multijugum > S. moorcroftiana > B. diaphana > S. laevigata > C. salesovianum. 参考文献 相似文献 引证文献

Response of stomatal conductance and osmotic adjustment substances accumulation to rapid drough stress in tomato leaves

本研究采用聚乙二醇(PEG-6000)溶液控制番茄的根际水势和利用光合仪控制叶面的空气湿度, 监测叶片水势、气孔导度、渗透调节物质含量等指标的变化, 揭示快速水分胁迫下番茄的应激性生理响应。结果显示, 当G_s小于120 mmol·m^-2·s^-1时, 水分胁迫处理番茄的叶片净光合速率(<i>P</i>_n)小于对照。空气饱和水汽压差(<i>VPD</i>)与番茄叶片G_s呈显著的负相关(<i>R</i>₂≥0.892)。在同一空气湿度条件下, 水分胁迫处理的番茄叶片Gs仅为对照的43%~51%。快速水分胁迫下番茄叶片的可溶性糖含量呈先增再降的波动, 轻度和中度胁迫下可溶性糖含量比对照(0 min)分别增加61.4%~195.8%和56.0%~167.5%。可见, 番茄叶片Gs为120 mmol·m^-2·s^-1是对<i>P</i>_n影响的一个重要阈值。气孔调节是适应快速干旱胁迫的重要应激性生理响应。可溶性糖对维持番茄叶片细胞膨压和适度气孔开度具有一定的渗透调节作用。

RhNAC3, a stress‐associated NAC transcription factor, has a role in dehydration tolerance through regulating osmotic stress‐related genes in rose petals

Petal cell expansion depends on cell wall metabolism, changes in cell turgor pressure and restructuring of the cytoskeleton, and recovery ability of petal cell expansion is defined as an indicator of dehydration tolerance in flowers. We previously reported that RhNAC2, a development-related NAC domain transcription factor, confers dehydration tolerance through regulating cell wall-related genes in rose petals. Here, we identify RhNAC3, a novel rose SNAC gene, and its expression in petals induced by dehydration, wounding, exogenous ethylene and abscisic acid (ABA). Expression studies in Arabidopsis protoplasts and yeast show that RhNAC3 has transactivation activity along its full length and in the carboxyl-terminal domain. Silencing RhNAC3 in rose petals by virus-induced gene silencing (VIGS) significantly decreased the cell expansion of rose petals under rehydration conditions. In total, 24 of 27 osmotic stress-related genes were down-regulated in RhNAC3-silenced rose petals, while only 4 of 22 cell expansion-related genes were down-regulated. Overexpression of RhNAC3 in Arabidopsis gave improved drought tolerance, with lower water loss of leaves in transgenic plants. Arabidopsis ATH1 microarray analysis showed that RhNAC3 regulated the expression of stress-responsive genes in overexpressing lines, and further analysis revealed that most of the RhNAC3-up-regulated genes were involved in the response to osmotic stress. Comparative analysis revealed that different transcription regulation existed between RhNAC3 and RhNAC2. Taken together, these data indicate that RhNAC3, as a positive regulator, confers dehydration tolerance of rose petals mainly through regulating osmotic adjustment-associated genes.

Physiological limitations in two sugarcane varieties under water suppression and after recovering

Increasing water scarcity and depleted water productivity in irrigated soils are inducing farmers to adopt improved varieties, such as those with high-capacity tolerance. The use of tolerant varieties of sugarcane might substantially avoid the decline of productivity under water deficit. This research aimed to evaluate the harmful effects of drought on the physiology of two sugarcane varieties (RB867515 and RB962962) during the initial development. Young plants were subjected to irrigation suspension until total stomata closure, and then rewatered. Significant reduction on stomatal conductance, transpiration, and net photosynthesis were observed. RB867515 showed a faster stomatal closure while RB962962 slowed the effects of drought on the gas exchanges parameters with a faster recovering after rewatering. Accumulation of carbohydrates, amino acids, proline, and protein in the leaves and roots of the stressed plants occurred in both varieties, substantially linked to reduction of the leaf water potential. Due to the severity of stress, this accumulation was not enough to maintain the cell turgor pressure, so relative water content was diminished. Water stress affected the contents of chlorophyll (a, b, and total) in both varieties, but not the levels of carotenoids. There was a significant reduction in dry matter under stress. In conclusion, RB962962 variety endured stressed conditions more than RB867515, since it slowed down the damaging effects of drought on the gas exchanges. In addition, RB962962 presented a faster recovery than RB867515, a feature that qualifies it as a variety capable of enduring short periods of drought without major losses in the initial stage of its development.

Responses of the Mediterranean seagrass Posidonia oceanica to hypersaline stress duration and recovery

We studied the hypersaline stress responses of the Mediterranean seagrass Posidonia oceanica to determine if the species was tolerant to salinity increases that occur in coastal waters by the desalination industry. Water relations, amino acids, carbohydrates, ions, photosynthesis, respiration, chlorophyll a fluorescence, leaf growth and morphology, and plant mortality were analysed after exposing the mesocosm P. oceanica to a salinity level of 43 for one and three months followed by a month for recovery. One-month saline-stressed plants exhibited sub-lethal effects, including a leaf cell turgor pressure reduction, loss of ionic equilibrium and decreased leaf growth. There were also changes in photoprotective mechanisms, increased concentrations of organic osmolytes in leaves and reduced leaf ageing. All these dysfunctions recovered after removing the stress. After the longer exposure of three months, stress symptoms were much more acute and plants showed an excessive ionic exclusion capacity, increased leaf cell turgor, reduced plant carbon balance, increased leaf aging and leaf decay and increased plant mortality, which indicated that the plant had entered a stage of severe physiological stress. In addition, the long-term saline-stressed plants were not able to recover, still showing sustained injury after the one-month recovery period as reflected by unbalanced leaf ionic content, persistently impaired photosynthesis, decline in internal carbon resources and decreased leaf growth that resulted in undersized plants. In conclusion, P. oceanica was not able to acclimate to the saline conditions tested since it could not reach a new physiological equilibrium or recover after a chronic exposure of 3 months.

In vivo extraction of Arabidopsis cell turgor pressure using nanoindentation in conjunction with finite element modeling

Turgor pressure in plant cells is involved in many important processes. Stable and normal turgor pressure is required for healthy growth of a plant, and changes in turgor pressure are indicative of changes taking place within the plant tissue. The ability to quantify the turgor pressure of plant cells in vivo would provide opportunities to understand better the process of pressure regulation within plants, especially when plant stress is considered, and to understand the role of turgor pressure in cellular signaling. Current experimental methods do not separate the influence of the turgor pressure from the effects associated with deformation of the cell wall when estimates of turgor pressure are made. In this paper, nanoindentation measurements are combined with finite element simulations to determine the turgor pressure of cells in vivo while explicitly separating the cell-wall properties from the turgor pressure effects. Quasi-static cyclic tests with variable depth form the basis of the measurements, while relaxation tests at low depth are used to determine the viscoelastic material properties of the cell wall. Turgor pressure is quantified using measurements on Arabidopsis thaliana under three pressure states (control, turgid and plasmolyzed) and at various stages of plant development. These measurements are performed on cells in vivo without causing damage to the cells, such that pressure changes may be studied for a variety of conditions to provide new insights into the biological response to plant stress conditions.

Responses of epidermal cell turgor pressure and photosynthetic activity of leaves of the atmospheric epiphyte Tillandsia usneoides (Bromeliaceae) after exposure to high humidity

It has been well-established that many epiphytic bromeliads of the atmospheric-type morphology, i.e., with leaf surfaces completely covered by large, overlapping, multicellular trichomes, are capable of absorbing water vapor from the atmosphere when air humidity increases. It is much less clear, however, whether this absorption of water vapor can hydrate the living cells of the leaves and, as a consequence, enhance physiological processes in such cells. The goal of this research was to determine if the absorption of atmospheric water vapor by the atmospheric epiphyte Tillandsia usneoides results in an increase in turgor pressure in leaf epidermal cells that subtend the large trichomes, and, by using chlorophyll fluorescence techniques, to determine if the absorption of atmospheric water vapor by leaves of this epiphyte results in increased photosynthetic activity. Results of measurements on living cells of attached leaves of this epiphytic bromeliad, using a pressure probe and of whole-shoot fluorescence imaging analyses clearly illustrated that the turgor pressure of leaf epidermal cells did not increase, and the photosynthetic activity of leaves did not increase, following exposure of the leaves to high humidity air. These results experimentally demonstrate, for the first time, that the absorption of water vapor following increases in atmospheric humidity in atmospheric epiphytic bromeliads is mostly likely a physical phenomenon resulting from hydration of non-living leaf structures, e.g., trichomes, and has no physiological significance for the plant's living tissues.

Root elongation is restricted by axial but not by radial pressures: so what happens in field soil?

Root distribution determines largely the zone of soil that roots have access to for water and nutrient uptake, and is of great importance especially if water and fertilizer input is restricted. Mechanical impedance is the major limitation to root elongation in many field soils. Until now, experiments have focused largely on the axial resistance to root growth. In a fascinating study of the radial forces exerted by the roots of chickpea, root extension, diameter change, and the radial forces that axially unimpeded roots exert are reported: Kolb et al. (this volume) record radial stresses of about 0.3 MPa that are broadly consistent with cell turgor pressures, but, interestingly, find no restriction to axial elongation. This result is in marked contrast to large decreases in elongation of pea radicles resulting from much smaller axial pressures reported elsewhere in the literature (e.g., an 85 % decrease in root elongation in response to axial pressures of < 0.1 MPa). The situation is different also from that in homogeneous soil, where root penetration resistance pressures of 0.4-1.0 MPa are typically required to halt root elongation. Soil structure and strength properties will determine the balance of axial and radial pressures on an individual root tip, and hence the root elongation response. It appears that a degree of radial confinement may help roots to extend axially into hard soil. This result also complements recent findings that in strong field soils the availability of soil macropores has a large influence on regulating the root-elongation rates of seedlings.

Fission yeast Ags1 confers the essential septum strength needed for safe gradual cell abscission

Fungal cytokinesis requires the assembly of a dividing septum wall. In yeast, the septum has to be selectively digested during the critical cell separation process. Fission yeast cell wall α(1-3)glucan is essential, but nothing is known about its localization and function in the cell wall or about cooperation between the α- and β(1-3)glucan synthases Ags1 and Bgs for cell wall and septum assembly. Here, we generate a physiological Ags1-GFP variant and demonstrate a tight colocalization with Bgs1, suggesting a cooperation in the important early steps of septum construction. Moreover, we define the essential functions of α(1-3)glucan in septation and cell separation. We show that α(1-3)glucan is essential for both secondary septum formation and the primary septum structural strength needed to support the physical forces of the cell turgor pressure during cell separation. Consequently, the absence of Ags1 and therefore α(1-3)glucan generates a special and unique side-explosive cell separation due to an instantaneous primary septum tearing caused by the turgor pressure.

Synergistic action of Galleria mellonella anionic peptide 2 and lysozyme against Gram-negative bacteria

Lysozyme and antimicrobial peptides are key factors of the humoral immune response in insects. In the present work lysozyme and anionic defense peptide (GMAP2) were isolated from the hemolymph of the greater wax moth Galleria mellonella and their antibacterial activity was investigated. Adsorption of G. mellonella lysozyme on the cell surface of Gram-positive and Gram-negative bacteria was demonstrated using immunoblotting with anti-G. mellonella lysozyme antibodies. Lysozyme effectively inhibited the growth of selected Gram-positive bacteria, which was accompanied by serious alterations of the cell surface, as revealed by atomic force microscopy (AFM) imaging. G. mellonella lysozyme used in concentrations found in the hemolymph of naive and immunized larvae, perforated also the Escherichia coli cell membrane and the level of such perforation was considerably increased by GMAP2. GMAP2 used alone did not perforate E. coli cells nor influence lysozyme muramidase activity. However, the peptide induced a decrease in the turgor pressure of the bacterial cell. Moreover, in the samples of bacteria treated with a mixture of lysozyme and GMAP2 the sodium chloride crystals were found, suggesting disturbance of ion transport across the membrane leading to cell disruption. These results clearly indicated the synergistic action of G. mellonella lysozyme and anionic peptide 2 against Gram-negative bacteria. The reported results suggested that, thanks to immune factors constitutively present in hemolymph, G. mellonella larvae are to some extent protected against infection caused by Gram-negative bacteria.

Leaf patch clamp pressure probe measurements on olive leaves in a nearly turgorless state

The non-invasive leaf patch clamp pressure (LPCP) probe measures the attenuated pressure of a leaf patch, P(p) , in response to an externally applied magnetic force. P(p) is inversely coupled with leaf turgor pressure, P(c) , i.e. at high P(c) values the P(p) values are small and at low P(c) values the P(p) values are high. This relationship between P(c) and P(p) could also be verified for 2-m tall olive trees under laboratory conditions using the cell turgor pressure probe. When the laboratory plants were subjected to severe water stress (P(c) dropped below ca. 50 kPa), P(p) curves show reverse diurnal changes, i.e. during the light regime (high transpiration) a minimum P(p) value, and during darkness a peak P(p) value is recorded. This reversal of the P(p) curves was completely reversible. Upon watering, the original diurnal P(p) changes were re-established within 2-3 days. Olive trees in the field showed a similar turnover of the shape of the P(p) curves upon drought, despite pronounced fluctuations in microclimate. The reversal of the P(p) curves is most likely due to accumulation of air in the leaves. This assumption was supported with cross-sections through leaves subjected to prolonged drought. In contrast to well-watered leaves, microscopic inspection of leaves exhibiting inverse diurnal P(p) curves revealed large air-filled areas in parenchyma tissue. Significantly larger amounts of air could also be extracted from water-stressed leaves than from well-watered leaves using the cell turgor pressure probe. Furthermore, theoretical analysis of the experimental P(p) curves shows that the propagation of pressure through the nearly turgorless leaf must be exclusively dictated by air. Equations are derived that provide valuable information about the water status of olive leaves close to zero P(c) .

Direct Measurement of Cell Wall Stress Stiffening and Turgor Pressure in Live Bacterial Cells

We study intact and bulging Escherichia coli cells using atomic force microscopy to separate the contributions of the cell wall and turgor pressure to the overall cell stiffness. We find strong evidence of power-law stress stiffening in the E. coli cell wall, with an exponent of 1.22±0.12, such that the wall is significantly stiffer in intact cells (E=23±8 MPa and 49±20 MPa in the axial and circumferential directions) than in unpressurized sacculi. These measurements also indicate that the turgor pressure in living cells E. coli is 29±3 kPa.

A possible CO2 conducting and concentrating mechanism in plant stomata SLAC1 channel.

Background The plant SLAC1 is a slow anion channel in the membrane of stomatal guard cells, which controls the turgor pressure in the aperture-defining guard cells, thereby regulating the exchange of water vapour and photosynthetic gases in response to environmental signals such as drought, high levels of carbon dioxide, and bacterial invasion. Recent study demonstrated that bicarbonate is a small-molecule activator of SLAC1. Higher CO2 and HCO3 – concentration activates S-type anion channel currents in wild-type Arabidopsis guard cells. Based on the SLAC1 structure a theoretical model is derived to illustrate the activation of bicarbonate to SLAC1 channel. Meanwhile a possible CO2 conducting and concentrating mechanism of the SLAC1 is proposed.MethodologyThe homology structure of Arabidopsis thaliana SLAC1 (AtSLAC1) provides the structural basis for study of the conducting and concentrating mechanism of carbon dioxide in SLAC1 channels. The pKa values of ionizable amino acid side chains in AtSLAC1 are calculated using software PROPKA3.0, and the concentration of CO2 and anion HCO3 – are computed based on the chemical equilibrium theory.ConclusionsThe AtSLAC1 is modeled as a five-region channel with different pH values. The top and bottom layers of channel are the alkaline residue-dominated regions, and in the middle of channel there is the acidic region surrounding acidic residues His332. The CO2 concentration is enhanced around 104 times by the pH difference between these regions, and CO2 is stored in the hydrophobic region, which is a CO2 pool. The pH driven CO2 conduction from outside to inside balances the back electromotive force and maintain the influx of anions (e.g. Cl– and NO3 –) from inside to outside. SLAC1 may be a pathway providing CO2 for photosynthesis in the guard cells.

Measuring Peptidoglycan Elasticity and Stress-Stiffening of Live Bacterial Cells

The mechanical properties of gram-negative bacteria are governed by a rigid peptidoglycan (PG) cell wall and the turgor pressure generated by the large concentration of solutes in the cytoplasm. The elasticity of the PG has been measured in bulk and in isolated sacculi and shown to be very compliant compared to the overall stiffness of the cell itself. However, the stiffness of the cell wall in live cells has not been accurately measured. In particular, the effects that pressure-induced stress might have on the stiffness of the meshlike PG network have not been addressed even though polymeric materials often exhibit large amounts of stress-stiffening. In this study, we use two experimental systems to probe the effects of pressure on the wall stiffness. First, we study blebbing E. coli cells using atomic force microscopy to separate the contributions of the cell wall and turgor pressure to the overall cell stiffness. Second, we study the relationship between cell stiffness and external osmotic pressure which allows us to probe higher turgor pressures. Combining these two types of measurements, we find strong evidence of a power-law stress-stiffening in the E. coli cell wall such that the wall is significantly stiffer in live cells (E∼5 MPa) than the relatively compliant sacculus stiffness (E∼34 MPa).

Actin filaments and microtubules of Arabidopsis suspension cells show different responses to changing turgor pressure

Past decades have brought great advances in understanding the relationship between turgor pressure and plant cell growth. New studies have provided evidence that turgor pressure acts as a stimulus for cell growth, and is also a developmental cue for post-embryonic organogenesis. However, the subcellular mechanisms underlying plant cell turgor pressure sensing remain unclear. Here, using the relatively simple undifferentiated cells from suspension cultures, we report real-time in vivo observations of the reorganization of microtubules and actin microfilaments induced by turgor pressure changes. We found that these two cytoskeletal elements differed in their reorganization patterns. Our results will be useful in the understanding of the relationship between the cytoskeleton, turgor pressure, and stress in plant cell morphogenesis.

Identification of genes involved in bamboo fiber development

Recently bamboo has gained reputation as a major resource of non-wood fiber. The present study was undertaken to generate information about fiber development process in bamboo ( Bambusa balcooa) using PCR-based suppressive subtractive hybridization (PCR-SSH) technique, as molecular mechanism of its fiber development is yet to be explored. SSH was performed between cDNA isolated from leaf (as driver) and internodes (as tester) of B. balcooa which indicated up-regulation of 521 ESTs. Among these 41 were contigs and 65 ESTs were singletons. On the basis of BLASTX search 307 ESTs with known functions were classified into several functional categories including transport, metabolism, information, perception and response to stimuli while others were either non-significant (120) or hypothetical proteins (94). A total of 51 out of 307 functional ESTs were found fiber specific and their global distribution among different plant species like maize, rice, cotton and Arabidopsis ESTs were determined. Net distributions and differential expression patterns of 13 important B. balcooa fiber specific cDNAs among different internodes during bamboo development were studied using RNA slot–blot, semi-quantitative RT-PCR and real time PCR. In-situ localization of mRNA transcript for few selected bamboo fiber ESTs namely, V1Bb147 (protein kinase-like protein) and V1Bb88 (myb domain-containing protein) were detected using Confocal Laser Scanning Microscope. Transcript levels of these genes exhibited an orchestral turn-over during bamboo development, suggesting their close association with fiber development, an event associated with several metabolic and physiological changes. The results clearly suggest that these genes are involved in several concerted mechanisms involving Ca + signaling pathway, cell wall synthesis, hormone regulation, system maintaining cell turgor pressure and cytoskeleton synthesis pathway accountable for bamboo fiber development signifying fiber development as a complex but ordered metabolic process involving differential expression of large scale fiber associated genes. This is the first report on systematic analysis of genes involved in bamboo fiber development.

In situ Turgor Stability in Grape Mesocarp Cells and Its Relation to Cell Dimensions and Microcapillary Tip Size and Geometry

The role of three tip fabrication methods and of tip size in cell pressure probe measurements was investigated. The stability over time of turgor pressure (P) in mesocarp cells of intact grape berries was determined for microcapillary tips of contrasting sizes and methods of production (micro-beveler, micro-grinder, and breaking) at contrasting depths below the berry epidermis. SEM images showed that breaking, and in some cases micro-grinding methods produced tips with irregular, fractured surfaces, compared to relatively smooth surfaces produced with micro-beveling. Finely pointed glass microcapillaries were made with reproducibly small tip dimensions (i.d. 5 μm) and significantly more stable (−0.009 MPa/min) using small tips (i.d. 250 μm), both tip sizes gave relatively stable P values (−0.007 and −0.004 MPa/min for large and small tips, respectively). For tips of comparable size, micro-beveling gave improved P stability compared to breaking, and an improved ability to measure cells closer to the epidermis compared to micro-grinding. Literature values for acceptability of P values as stable in higher plant cells range from −0.001 to −0.05 MPa/min. These data suggest that P stability might be influenced by both tip size/shape and cell dimensions, and that improved tip fabrication techniques should improve the stability and reproducibility of P measurements, particularly for small cells.

UV radiation reduces epidermal cell expansion in Arabidopsis thaliana leaves without altering cellular microtubule organization

Upon chronic UV treatment pavement cell expansion in Arabidopsis leaves is reduced, implying alterations in symplastic and apoplastic properties of the epidermal cells. In this study, the effect of UV radiation on microtubule patterning is analysed, as microtubules are thought to serve as guiding rails for the cellulose synthase complexes depositing cellulose microfibrils. Together with hemicelluloses, these microfibrils are regarded as the load-bearing components of the cell wall. Leaves of transgenic plants with fluorescently tagged microtubules (GFP-TUA6) were as responsive to UV as wild type plants. Despite the UV-induced reduction in cell elongation, confocal microscopy revealed that cellular microtubule arrangements were seemingly not affected by the UV treatments. This indicates an unaltered deposition of cellulose microfibrils in the presence of UV radiation. Therefore, we surmise that the reduction in cell expansion in UV-treated leaves is most probably due to changes in cell wall loosening and/or turgor pressure.

Homologue structure of the SLAC1 anion channel for closing stomata in leaves

SummaryThe plant SLAC1 anion channel controls turgor pressure in the aperture-defining guard cells of plant stomata, thereby regulating exchange of water vapor and photosynthetic gases in response to environmental signals such as drought or high levels of carbon dioxide. We determined the crystal structure of a bacterial homolog of SLAC1 at 1.20Å resolution, and we have used structure-inspired mutagenesis to analyze the conductance properties of SLAC1 channels. SLAC1 is a symmetric trimer composed from quasi-symmetric subunits, each having ten transmembrane helices arranged from helical hairpin pairs to form a central five-helix transmembrane pore that is gated by an extremely conserved phenylalanine residue. Conformational features suggest a mechanism for control of gating by kinase activation, and electrostatic features of the pore coupled with electrophysiological characteristics suggest that selectivity among different anions is largely a function of the energetic cost of ion dehydration.

Comparative monitoring of temporal and spatial changes in tree water status using the non-invasive leaf patch clamp pressure probe and the pressure bomb

Abstract Real-time monitoring of plant water status under field conditions remains difficult to quantify. Here we give evidence that the magnetic-based leaf patch clamp pressure (LPCP) probe is a non-invasive and online-measuring method that can elucidate short- and long-term temporal and spatial dynamics of leaf water status of trees with high precision in real time. Measurements were controlled remotely by telemetry and data transfer to the Internet. Concomitant measurements using the pressure chamber technique (frequently applied for leaf water status monitoring) showed that both techniques yield in principle the same results despite of the high sampling variability of the pressure chamber data. There was a very good correlation between the output pressure signals of the LPCP probe and the balancing pressure values (on average r 2 = 0.90 ± 0.05; n = 8), i.e. the external pressure at which water appears at the cut end of a leaf under pressure chamber conditions. Simultaneously performed direct measurements of leaf cell turgor pressure using the well-established cell turgor pressure probe technique evidenced that both techniques measure relative changes in leaf turgor pressure. The output pressure signals of the LPCP probe and the balancing pressure values were inversely correlated to turgor pressure. Consistent with this, the balancing pressure values and the cell turgor pressure values could be fitted quite well by the same firm theoretical backing derived recently for the LPCP probe ( Zimmermann et al., 2008 ). This finding suggests that use of the LPCP probe technique in agricultural water management can be built up on the knowledge accumulated on spot leaf or stem water potential measurements.