Control Of Plant Water Status Research Articles

Aquaporins facilitate hydrogen peroxide entry into guard cells to mediate ABA- and pathogen-triggered stomatal closure

Stomatal movements are crucial for the control of plant water status and protection against pathogens. Assays on epidermal peels revealed that, similar to abscisic acid (ABA), pathogen-associated molecular pattern (PAMP) flg22 requires the AtPIP2;1 aquaporin to induce stomatal closure. Flg22 also induced an increase in osmotic water permeability (Pf) of guard cell protoplasts through activation of AtPIP2;1. The use of HyPer, a genetic probe for intracellular hydrogen peroxide (H2O2), revealed that both ABA and flg22 triggered an accumulation of H2O2 in wild-type but not pip2;1 guard cells. Pretreatment of guard cells with flg22 or ABA facilitated the influx of exogenous H2O2 Brassinosteroid insensitive 1-associated receptor kinase 1 (BAK1) and open stomata 1 (OST1)/Snf1-related protein kinase 2.6 (SnRK2.6) were both necessary to flg22-induced Pf and both phosphorylated AtPIP2;1 on Ser121 in vitro. Accumulation of H2O2 and stomatal closure as induced by flg22 was restored in pip2;1 guard cells by a phosphomimetic form (Ser121Asp) but not by a phosphodeficient form (Ser121Ala) of AtPIP2;1. We propose a mechanism whereby phosphorylation of AtPIP2;1 Ser121 by BAK1 and/or OST1 is triggered in response to flg22 to activate its water and H2O2 transport activities. This work establishes a signaling role of plasma membrane aquaporins in guard cells and potentially in other cellular context involving H2O2 signaling.

Adapting plant material to face water stress in vineyards: which physiological targets for an optimal control of plant water status?

<p class="Abstract" style="text-align: justify;"><strong>Aims:</strong> Water scarcity, associated with climate change, is a particular threat to the sustainability of viticulture in present areas of cultivation, usually prone to drought. Breeding grapevine for reduced water use, better water extraction and maintained production (i.e., high water use efficiency) is therefore of major interest.</p><p class="Abstract" style="text-align: justify;"><strong>Methods and results:</strong> This requires a comprehensive knowledge of the physiological impacts of drought on yield and quality. Attention should be paid to those mechanisms involved in the regulation of water status in plant tissues, as it is the primary parameter affected by drought. Transpiration rate, which has a major influence on plant water status, should therefore receive special attention in breeding programs. Beyond scions, the role of rootstocks, which have been largely introduced in vineyards, should be investigated further as it determines water extraction capacity and could modify water balance in grafted plants.</p><p class="Abstract" style="text-align: justify;"><strong>Conclusion:</strong> Here we review recent advances in the characterization of genetic variability in the control of water use and water status, whether induced by rootstock or scion.</p><p class="Abstract" style="text-align: justify;"><strong>Significance and impact of the study: </strong>This review should help scientists in choosing the relevant physiological targets in their research on grapevine tolerance to drought, whether for breeding prospects or new management practices.</p>

Adapting plant material to face water stress in vineyards: which physiological targets for an optimal control of plant water status?

Aims: Water scarcity, associated with climate change, is a particular threat to the sustainability of viticulture in present areas of cultivation, usually prone to drought. Breeding grapevine for reduced water use, better water extraction and maintained production (i.e., high water use efficiency) is therefore of major interest.Methods and results: This requires a comprehensive knowledge of the physiological impacts of drought on yield and quality. Attention should be paid to those mechanisms involved in the regulation of water status in plant tissues, as it is the primary parameter affected by drought. Transpiration rate, which has a major influence on plant water status, should therefore receive special attention in breeding programs. Beyond scions, the role of rootstocks, which have been largely introduced in vineyards, should be investigated further as it determines water extraction capacity and could modify water balance in grafted plants.Conclusion: Here we review recent advances in the characterization of genetic variability in the control of water use and water status, whether induced by rootstock or scion.Significance and impact of the study: This review should help scientists in choosing the relevant physiological targets in their research on grapevine tolerance to drought, whether for breeding prospects or new management practices.

PL06 Gasotransmitters in plant signalling: An exciting new field is emerging

Gaseous molecules are nowadays well established signalling components transmitting inter and intracellular information. Gasotransmitters are synthesized and metabolized by specific enzymatic activities, they possess specific cellular targets and regulate a number of physiological responses directed to keep cellular homeostasis in a changing environment. While typical messenger molecules amplify signal cascades, gasotransmitters can act through chemical modification of specific protein targets resulting in a rapid influence on cellular metabolism. In the last decade, findings describing the nitric oxide (NO) functions in plant cell signalling were a breakthrough in plant biology [1] , [2] . Recently, hydrogen sulfide (H2S) has emerged as a critical player in plant physiology acting as NO partner in some cases but within a yet unknown and unexplored scenario [3] , [4] . Plants control the gas exchange with the environment through the regulation of the stomatal pore formed by two specialized cells named guard cells. The size of the stomatal pore is finely regulated by volume changes of the guard cells, driven by the influx and efflux of osmotically active solutes through plasma membrane (PM) ion channels. Abscisic acid (ABA) is the master phytohormone controlling stomatal closure under water deficit conditions. We have demonstrated that ABA induces increases in NO concentration in guard cells [5] . NO, in turn, inactivates inward rectifying K+ K in + channels by increasing cytosolic Ca2+ concentrations [6] contributing to the net loss of solutes from guard cells required for stomatal closure. We have found that the gasotransmitter H2S induces the stomatal closure through a NO-mediated pathway [7] . The mutants of the plant model Arabidopsis are usually used as genetical tools for unravelling gene functions. Stomata of the Arabidopsis mutant atdes1 defective in l -cysteine desulfhydrase (DES), one of the enzymes responsible of H2S synthesis, do not respond to ABA treatment, indicating that H2S is required for ABA-mediated stomatal closure. The Arabidopsis mutant abi1 is impaired in ABA signalling and insensitive to H2S, suggesting that a functional ABA signalling is critical for H2S effect in guard cells. Thus, data support a connection between H2S and NO to operate a fine regulation of gas exchange resulting in a control of plant water status. Experiments are in progress to find experimentally H2S targets among the guard cell PM ion channels. The richness of the redox chemistry of the different NO forms (NO, NO− and NO+) reacting with H2S (H+ and HS−) in guard cells is an intriguing puzzle to decipher ABA crosstalk with NO and H2S. To understand the redox regulation of guard cells in different plant environmental scenarios is necessary to unveil how the physiology of guard cells makes use of NO and H2S as intermediates leading to selective PM ion channels activation/inhibition.

Plant‐Soil Water Relations and Species Border ofClarkia xantianassp.xantiana(Onagraceae)

Low precipitation can limit plant distributions. Soil variation might interact with precipitation gradients to define species borders. Analyzing the eastern species border of the California annual Clarkia xantiana ssp. xantiana, we assessed the following: (1) the geography of plant water status, precipitation, and soil; (2) soil control of plant water status; and (3) water status control of plant performance. Plant water potential declined toward the border in consecutive years. Precipitation declined in parallel and was lower in the year of lower water potential. Many border soils are derived from metasedimentary rock, while igneous rock dominates the species range to the west and unoccupied areas to the east. Compared with igneous soils, metasedimentary soils were found to have greater penetration resistance and finer texture, and they exhibited greater water storage capacity but also stronger restrictions on water release. Within populations, plant water status was inferior on shallow slopes with hard,...

Diurnal and seasonal variation in root xylem embolism in neotropical savanna woody species: impact on stomatal control of plant water status

Vulnerability to water-stress-induced embolism and variation in the degree of native embolism were measured in lateral roots of four co-occurring neotropical savanna tree species. Root embolism varied diurnally and seasonally. Late in the dry season, loss of root xylem conductivity reached 80% in the afternoon when root water potential (psi root) was about -2.6 MPa, and recovered to 25-40% loss of conductivity in the morning when psi root was about -1.0 MPa. Daily variation in psi root decreased, and root xylem vulnerability and capacitance increased with rooting depth. However, all species experienced seasonal minimum psi root close to complete hydraulic failure independent of their rooting depth or resistance to embolism. Predawn psi root was lower than psi soil when psi soil was relatively high (> -0.7 MPa) but became less negative than psi soil, later in the dry season, consistent with a transition from a disequilibrium between plant and soil psi induced by nocturnal transpiration to one induced by hydraulic redistribution of water from deeper soil layers. Shallow longitudinal root incisions external to the xylem prevented reversal of embolism overnight, suggesting that root mechanical integrity was necessary for recovery, consistent with the hypothesis that if embolism is a function of tension, refilling may be a function of internal pressure imbalances. All species shared a common relationship in which maximum daily stomatal conductance declined linearly with increasing afternoon loss of root conductivity over the course of the dry season. Daily embolism and refilling in roots is a common occurrence and thus may be an inherent component of a hydraulic signaling mechanism enabling stomata to maintain the integrity of the hydraulic pipeline in long-lived structures such as stems.

Facing drought in a Mediterranean post-fire community: tissue water relations in species with different life traits

Abstract Bulk shoot water potential, the osmotic component and the bulk modulus of elasticity were measured throughout one growing season in four species co-occurring in a post-fire Mediterranean community in southern Italy: Pinus halepensis, Phillyrea latifolia, Cistus salvifolius and Rosmarinus officinalis. A severe drought occurred throughout the measurement period. Large seasonal fluctuations have been observed for both predawn and afternoon water potential in all species. Although minimum values down to –4 MPa have been measured, plant water potential always recovered to less negative values after drought. Daily amplitude of water potential decreased with increasing plant water stress in all species. In Cistus and Rosmarinus less ability for short-term control of plant water status has been assessed. Osmotic potential at full turgor did not display clear seasonal patterns, with no consistent ranking of species by their osmotic values. In most cases, no osmotic adjustment (lowering of osmotic potentials) and no change in tissue elastic properties were observed in response to increasing summer drought and intensity of water stress.

Modelling water relations of horticultural crops: a review

This paper introduces the basic principles of plant water relations modelling, and reviews some examples of application to horticultural crops. Water relations models are essential components of all crop models because of the critical role that water status has in determining growth, productivity and produce quality. The importance of water to horticultural crops is particularly great because most horticultural produce is sold by weight, with water being the major component, so there is often a marked premium in ensuring that water content is optimised, often through precise control of irrigation. After providing a theoretical background to plant water relations models, the main models for describing and predicting both water flow through plants, and the processes of water uptake from the soil and evaporative loss to the atmosphere are described. The final section then brings together this information in some models that attempt to show how models can either provide insight into the nature of the interactions between the various physiological processes involved in the control of plant water status or which can be used to investigate the optimal plant responses in water limited situations.

98/00184 Review of development of additives for coal water slurry

This paper introduces the basic principles of plant water relations modelling, and reviews some examples of application to horticultural crops. Water relations models are essential components of all crop models because of the critical role that water status has in determining growth, productivity and produce quality. The importance of water to horticultural crops is particularly great because most horticultural produce is sold by weight, with water being the major component, so there is often a marked premium in ensuring that water content is optimised, often through precise control of irrigation. After providing a theoretical background to plant water relations models, the main models for describing and predicting both water flow through plants, and the processes of water uptake from the soil and evaporative loss to the atmosphere are described. The final section then brings together this information in some models that attempt to show how models can either provide insight into the nature of the interactions between the various physiological processes involved in the control of plant water status or which can be used to investigate the optimal plant responses in water limited situations.

Physiological Aspects of the Control of Water Status in Horticultural Crops

Plant water status is arguably the single most-important factor that must be controlled to obtain high yields of good-quality horticultural produce. A clear understanding of how water deficits affect crops and of the natural adaptive processes by which different species respond to limited water availability should enable us to optimize management procedures (e.g., how and when to irrigate) and to breed better cultivars for particular conditions. There have been many reviews in recent years concerned with the techniques of water status measurement; for example, there was a symposium on “Water stress measurement techniques —instrumentation and procedures” at the 81st ASHS Annual Meeting, Vancouver, B.C. (Kanemasu et al., 1985; Spomer, 1985; Syvertsen, 1985), and also another extensive review of techniques for measuring water status (Kirkham, 1985). There has, however, been relatively little emphasis on the relevance of the different methods. I outline in this paper some of the physical and biological processes involved in the control of plant water status and discuss the choice of water status measure for particular purposes. In particular, my objective is to emphasize some problems, often unrecognized, that may be encountered in water relations experimentation. Failure to take into account some of these factors in the past has resulted in many erroneous conclusions being drawn. Examples of areas where a clear understanding of the mechanisms involved in the control of plant water status is important include: the measurement of water status; breeding new cultivars; design of experiments for the field, controlled environments, or glasshouses; and understanding the role of stomata.

Mineral nutrition and water relations of hemiparasitic mistletoes: a question of partitioning. Experiments with Loranthus europaeus on Quercus petraea and Quercus robur.

Hemiparasitic mistletoes thrive on xylem sap diverted from the host through direct xylem connections. There is no phloem link and no exchange of photosynthates. Mineral nutrition is therefore closely coupled with water consumption.Mineral nutrient partitioning between the mistletoe Loranthus europaeus and its host Quercus petraea was studied by monitoring nutrient incorporation into 3-year-old twigs of both species over 1 year. The mistletoes accumulated large amounts of potassium in comparison to other elements. It is hypothesized that this phenomenon is a consequence of the absence of a phloem connection between host and hemiparasite. In the host potassium is cycled between leaves and sites of photosynthate utilization in the wake of photosynthate transport in the phloem. In the hemiparasite it cannot cycle beyond the host-parasite interface and potassium imported with the xylem sap is thus trapped in the hemiparasite phytomass.The control of water partitioning in a host-hemiparasite system is another important aspect. As host and hemiparasite receive water from a common supply the otherwise independent stomatal control systems of both species become linked when transpiration demand exceeds supply. By measuring diurnal curves of transpiration and leaf water status in both species, by use of a special cuff-freezing technique to study stomatal response when water supply is cut off, and by measurements of leaf water capacitance with a pressure-volume curve technique, the fundamental data for a descriptive model of water partitioning in a L. europaeus - Q. robur system were collected. This model may be used to gain deeper insight into stomatal control of plant water status.

Response of cassava to water shortage III. Stomatal control of plant water status

Diurnal measurements of leaf water potential and the diffusive conductance of the abaxial surface of two cassava cultivars, M Col 22 and M Mex 59, were made on three occasions on field grown plants during a 10-week period of rainfall exclusion. Conductances of about 10 mm s −1 were observed in the rainfed plots but generally the mean conductance was in the range 3–5 mm s −1. The minimum water potential of −1.8 MPa was observed in the rainfed plots. Water shortage caused reduction in mean conductance to <1 mm s −1 at which level the control of water loss maintained leaf water potential > −1.5 MPa at all times. Stress plots recovered more slowly during the late afternoon but during the day had higher leaf water potentials than the controls. At the same levels of leaf water potential the conductance of M Mex 59 was less than that of M Col 22 in both control and stress plots. Measurements are also reported of the stomatal distribution, density and pore size for both fully expanded leaves and those whose expansion was seriously restricted by the water shortage.