Hydrogen sulphide regulates inward-rectifying K+ channels in conjunction with stomatal closure

Hydrogen sulphide (H2S) is the third biological gasotransmitter and, in animals, affects many physiological processes by modulating ion channels. H2S has been reported to protect plants from oxidative stress in diverse physiological responses. H2S closes stomata, but the underlying mechanism remains elusive. Here we report the selective inactivation of current carried by inward-rectifying K+ channels (IKIN) of tobacco guard cells and demonstrate its close parallel with stomatal closure evoked by submicromolar concentrations of H2S. Experiments to scavenge H2S suggested an effect that is separable from that of abscisic acid, which is associated with water stress. Thus, H2S appears to associate with a new and as yet unresolved signalling pathway that selectively targets IKIN

Speedy grass stomata: emerging molecular and evolutionary features

No abstract available

Stomatal abundance and distribution in Prosopis strombulifera plants growing under different Iso-Osmotic salt

Changes in several environmental parameters are thought to affect stomatal development. Under salt stress, plants can regulate their transpiration flux through a better control of the stomatal opening (as a short-term response) and through modifications of leaf anatomy (as a long-term response). We investigate how leaf micromorphology (stomatal abundance and distribution) of the halophyte Prosopis strombulifera (a spiny shrub particularly abundant in high-salinity areas of central Argentina) responds to different water status when plants are subjected to different salt treatments (NaCl, Na2SO4 and their iso-osmotic mixture). Different salt treatments on P. strombulifera plants influenced leaf micromorphological traits differently. In this study, Na2SO4-treated plants showed an increase in stomatal density (SD) and epidermal cell density (ECD) (with smaller stomata) at moderate and high salinity (−1.9 and −2.6 MPa), whereas in NaCl and NaCl + Na2SO4 treated plants, a decrease in these variables was observed. In Na2SO4-treated plants, transpiration was the highest at moderate and high salinity, with the highest content of ABA registered. A possible explanation is that, despite of these high ABA levels, there is no inhibition in stomatal opening, resulting in increased water loss, growth inhibition, and acceleration of senescence processes. We demonstrate that P. strombulifera responds to progressive salt stress by different salts changing the leaf development, particularly in Na2SO4-treated plants, leading to structural modifications in leaf size and micro-morphology of leaf cells.Fil: Reginato, Mariana Andrea. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular. Laboratorio de Fisiología Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Reinoso, Herminda Elmira. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales; ArgentinaFil: Llanes, Analia Susana. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular. Laboratorio de Fisiología Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Luna, Maria Virginia. Universidad Nacional de Rio Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Biología Molecular. Laboratorio de Fisiología Vegetal; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Increasing leaf hydraulic conductance with transpiration rate minimizes the water potential drawdown from stem to leaf.

Leaf hydraulic conductance (k leaf) is a central element in the regulation of leaf water balance but the properties of k leaf remain uncertain. Here, the evidence for the following two models for k leaf in well-hydrated plants is evaluated: (i) k leaf is constant or (ii) k leaf increases as transpiration rate (E) increases. The difference between stem and leaf water potential (ΔΨstem-leaf), stomatal conductance (g s), k leaf, and E over a diurnal cycle for three angiosperm and gymnosperm tree species growing in a common garden, and for Helianthus annuus plants grown under sub-ambient, ambient, and elevated atmospheric CO₂ concentration were evaluated. Results show that for well-watered plants k leaf is positively dependent on E. Here, this property is termed the dynamic conductance, k leaf(E), which incorporates the inherent k leaf at zero E, which is distinguished as the static conductance, k leaf(0). Growth under different CO₂ concentrations maintained the same relationship between k leaf and E, resulting in similar k leaf(0), while operating along different regions of the curve owing to the influence of CO₂ on g s. The positive relationship between k leaf and E minimized variation in ΔΨstem-leaf. This enables leaves to minimize variation in Ψleaf and maximize g s and CO₂ assimilation rate over the diurnal course of evaporative demand

An Ecohydrological Perspective on Drought-induced Forest Mortality

Regional‐scale drought‐induced forest mortality events are projected to become more frequent under future climates due to changes in rainfall patterns. The occurrence of these mortality events is driven by exogenous factors such as frequency and severity of drought and endogenous factors such as tree water and carbon use strategies. To explore the link between these exogenous and endogenous factors underlying forest mortality, a stochastic ecohydrological framework that accounts for random arrival and length of droughts as well as responses of tree water and carbon balance to soil water deficit is proposed. The main dynamics of this system are characterized with respect to the spectrum of anisohydric‐isohydric stomatal control strategies. Using results from a controlled drought experiment, a maximum tolerable drought length at the point where carbon starvation and hydraulic failure occur simultaneously is predicted, supporting the notion of coordinated hydraulic function and metabolism. We find qualitative agreement between the model predictions and observed regional‐scale canopy dieback across a precipitation gradient during the 2002–2003 southwestern United States drought. Both the model and data suggest a rapid increase of mortality frequency below a precipitation threshold. The model also provides estimates of mortality frequency for given plant drought strategies and climate regimes. The proposed ecohydrological approach can be expanded to estimate the effect of anticipated climate change on drought‐induced forest mortality and associated consequences for the water and carbon balances

Clathrin Heavy Chain subunits coordinate endo- and exocytic traffic and affect stomatal movement

The current model for vesicular traffic to and from the plasma membrane is accepted but the molecular requirements for this coordination are not well defined. We have identified the has1 mutant, which has a stomatal function defect, as a clathrin heavy chain 1 (CHC1) mutant allele and show that it has a decreased rate of endocytosis and growth defects that are shared with other chc1 mutant alleles. We used chc1 alleles and the related chc2 mutant as tools to investigate the effects clathrin defects have on secretion pathways and plant growth. We show that secretion and endocytosis at the plasma membrane is sensitive to CHC1 and CHC2 function in seedling roots, and that chc mutants have physiological defects in stomatal function and plant growth that have not been previously described. These findings suggest that clathrin supports specific functions of multiple cell types. Stomata movement and gas exchange is altered in chc mutants, indicating clathrin is important for stomatal regulation. The aberrant function of chc mutant stomata is consistent with the growth phenotypes observed under different water and light conditions, which are also similar to those of the secretory SNARE mutant, syp121. The syp121 and chc mutants have impaired endo- and exocytosis compared to wild type, indicating a link between SYP121-dependent secretion and clathrin-dependent endocytosis at the plasma membrane. Our findings provide evidence that clathrin and SYP121 functions are important for the coordination of endo- and exocytosis, and have an impact on stomatal function, gas exchange, and vegetative growth in Arabidopsis

Effects of Ground Level Ozone on Vegetation

All the experiments conducted in this project use ozone exposures that either are already currently occurring or are expected to occur over UK uplands this century, if predictions of increasing „background‟ ozone exposure are correct. Uplands are particularly vulnerable to such increases, because they are windy and wet – conditions which favour ozone uptake by vegetation. Consequently, the observations on ozone effects on upland plant species are likely to occur in the foreseeable future, if they are not already happening. The novel field ozone exposure system at Keenley Fell (Northumberland) has been operating since spring 2007. Seasonal average increases in ozone exposure at 10 m from the release point were very small in 2007, increasing to around 5 ppb above ambient in 2008 and 2009. The effects of the ozone treatments on this conservation-managed grassland should be seen in the context of this very modest increase in annual mean exposure. Average deposition velocity for ozone at Keenley Fell was between 1 mm/s (night) and 5 mm/s (mid-day), varying with weather conditions. These flux data will assist with the modelling of ozone deposition to upland grasslands. Limited flux measurements for CO2 showed uptake during the day and release at night, as expected, and will contribute to modelling interactions between ozone and carbon fluxes under these conditions. The ozone treatments at Keenley Fell had no effect on total above-ground production in any of the three years. However, there was a cumulative decrease in forb biomass, with an associated change in forb species composition, over the three years. This was accompanied by an increase in grass biomass. These effects of ozone are antagonistic to the objectives of the conservation management at this site. The biomass and flowering of a small number of individual forb species were significantly reduced by ozone exposure at Keenley Fell. Importantly, these species included the hemi-parasite Rhinanthus minor which is frequently used to enhance species diversity in this type of conservation management. Hence, the observed effects of ozone on species composition may partly have been caused through its adverse effects on Rhinanthus . Data compiled from several experiments show adverse effects of ozone on semi-natural plant species at concentrations as low as 30 ppb, with 12 of the species studied showing effects at concentrations below 50 ppbv. Effects on roots were greater than on shoots, with potentially significant implications for overwintering, drought tolerance and carbon sequestration

Systems analysis of guard cell membrane transport for enhanced stomatal dynamics and water use efficiency

Stomatal transpiration is at the centre of a crisis in water availability and crop production that is expected to unfold over the next 20-30 years. Global water usage has increased 6-fold in the past 100 years, twice as fast as the human population, and is expected to double again before 2030, driven mainly by irrigation and agriculture. Guard cell membrane transport is integral to controlling stomatal aperture and offers important targets for genetic manipulation to improve crop performance. However, its complexity presents a formidable barrier to exploring such possibilities. With few exceptions, mutations that increase water use efficiency commonly have been found to do so with substantial costs to the rate of carbon assimilation, reflecting the trade-off in CO2 availability with suppressed stomatal transpiration. One approach yet to be explored in any detail relies on quantitative systems analysis of the guard cell. Our deep knowledge of transport and homeostasis in these cells gives real substance to the prospect for ‘reverse engineering’ of stomatal responses, using in silico design in directing genetic manipulation for improved water use and crop yields. Here we address this problem with a focus on stomatal kinetics, taking advantage of the OnGuard software and models of the stomatal guard cell (www.psrg.org.uk) recently developed for exploring stomatal physiology. Our analysis suggests that manipulations of single transporter populations are likely to have unforeseen consequences. Channel gating, especially of the dominant K+ channels, appears the most favorable target for experimental manipulation

Stomatal behavior of cowpea genotypes grown under varying moisture levels

Drought is a major limitation to crop productivity worldwide. Plants lose most of their water through stomata, thus making stomata an important organ in the control of transpiration and photosynthesis. This study assessed the stomatal behavior of four cowpea genotypes grown under four moisture levels under hot semi-arid conditions. Stomatal conductance (gs) was measured at 47, 54, 70 and 77 days after planting (DAP). Biomass and carbon isotope composition (C-13) were also determined at flowering. Genotype and moisture level significantly influenced gs. Genotypes varied in gs at vegetative stages (47 and 54 DAP) only. TVu4607 had higher gs under severe drought conditions at both 47 and 54 DAP. On the other hand, moisture level influenced gs at 54 and 70 DAP only. Stomatal conductance was severely restricted in cowpea under both moderate and severe drought conditions as gs was mostly below the threshold 0.10 mol m(-2) s(-1). Relationships between: biomass and gs, and C-13 and gs were positive under severe drought only. The findings revealed that cowpea genotypes vary in gs under dry conditions and that the variation is more prominent at vegetative stage, suggesting that cowpea productivity in dry areas could be improved through selection of genotypes that maintain higher gs under dry conditions