Rate Of Stomatal Closure Research Articles

Physiological response of winter wheat (Triticum aestivum L.) during vegetative growth to gradual, persistent and intermittent drought

Drought priming at the vegetative growth stage has been demonstrated to be an effective water regulation strategy to enhance drought resistance in wheat. Therefore, exploring the stress response of winter wheat to different soil water changes during this stage can improve the drought priming strategies. This study examined the physiological response of winter wheat during two seasons of greenhouse pot experiments (2018–2019, 2019–2020) in the following four treatments: adequate water supply (control, C), persistent drought (P), intermittent drought (I), and gradual drought (G). An adequate water supply (75–85 % FC, field capacity) was always maintained for treatment C. Before jointing, plants in treatment P were maintained in a drought state (55–65 % FC), while in treatment I, plants underwent a change in soil water status from 55–65% FC to re-watering up to 75–85 % FC and back to 55–65 % FC. After entering the jointing stage, plants in treatments P and I were re-watered to 75–85 % FC. There was no water supplied in treatment G throughout the experiment. The soil water content (SWC) in treatment G gradually decreased with time (100–34 % FC). At the same time, abscisic acid (ABA), and osmotic substances accumulated exponentially with the reduction of SWC, the activity of antioxidant protective enzymes increased significantly, and the change in the stomatal closure rate was faster than the decrease in photosynthetic rate (Pn). Drought priming before jointing in treatments P and I prompted photosynthetic compensation after re-watering at the jointing stage, with the highest Pn in treatment I, followed by treatment P, and lastly, treatment C. The drought-re-watering cycle stimulated the stress response indicators in primed plants; hence, they were significantly higher than the stable levels in non-primed plants. Specifically, the ABA level in the leaves increased faster than the other indicators under repeated drought. Moreover, the relationship between photosynthesis and ABA was stronger than with antioxidative enzymes and osmolytes. Besides, increasing the number of drought-re-watering cycles enabled the primed plants to achieve a higher maximum Pn after re-watering and enhanced the association between soluble sugar and Pn. Overall, increasing the frequency of drought-re-watering enhanced the drought priming effect on the wheat stress response. Besides, there is a time difference in the response of different drought stress indicators to soil water changes. The findings in this study provide an empirical reference for better utilization of drought priming strategies to stimulate crop production.

Physiological and anatomical changes in two rapeseed (Brassica napus L.) genotypes under drought stress conditions

Understanding the mechanisms of drought resistance in crop species is crucial for the selection and breeding of tolerant rapeseed (Brassica napus L.) varieties. The present study aimed to assess the physiological and anatomical responses of two rapeseed genotypes, P287 (drought-tolerant) and T88 (drought-sensitive) under three intensities of drought stress. All physiological and anatomical parameters related to drought acclimation were significantly altered in both genotypes under stress conditions. At the fourth-leaf stage, the relative water content, chlorophyll content, protein content, malondialdehyde content, and the activities of peroxidase and catalase in P287 were significantly higher than those in T88, particularly under severe drought conditions. After rehydration, all physiological indexes recovered rapidly, especially in P287. In addition, under drought stress, compared with T88, P287 had thicker palisade tissue, thinner spongy tissue, higher ratio of chloroplast length to chloroplast width, higher stomatal density and stomatal closure rate. Overall, the interaction between physiological and anatomical features improved the drought tolerance of P287 under drought stress conditions.

Is nitric oxide a critical key factor in ABA-induced stomatal closure?

The role of nitric oxide (NO) in abscisic acid (ABA)-induced stomatal closure is a matter of debate. We conducted experiments in Vicia faba leaves using NO gas and sodium nitroprusside (SNP), a NO-donor compound, and compared their effects to those of ABA. In epidermal strips, stomatal closure was induced by ABA but not by NO, casting doubt on the role of NO in ABA-mediated stomatal closure. Leaf discs and intact leaves showed a dual dose response to NO: stomatal aperture widened at low dosage and narrowed at high dosage. Overcoming stomatal resistance by means of high CO2 concentration ([CO2]) restored photosynthesis in ABA-treated leaf discs but not in those exposed to NO. NO inhibited photosynthesis immediately, causing an instantaneous increase in intercellular [CO2] (Ci), followed by stomatal closure. However, lowering Ci by using low ambient [CO2] showed that it was not the main factor in NO-induced stomatal closure. In intact leaves, the rate of stomatal closure in response to NO was about one order of magnitude less than after ABA application. Because of the different kinetics of photosynthesis and stomatal closure that were observed, we conclude that NO is not likely to be the key factor in ABA-induced rapid stomatal closure, but that it fine-tunes stomatal aperture via different pathways.

Effects of imazethapyr spraying on plant growth and leaf surface microbial communities in Arabidopsis thaliana

Imazethapyr (IM) is an acetolactate synthase (ALS)-inhibiting herbicide that has been widely used in recent years. However, IM spraying can lead to the accumulation of herbicide residues in leaves. Here, we determined the effects of IM spraying on the plant growth and leaf surface microbial communities of Arabidopsis thaliana after 7 and 14 days of exposure. The results suggested that IM spraying inhibited plant growth. Fresh weight decreased to 48% and 26% of the control value after 7 and 14 days, respectively, of 0.035 kg/ha IM exposure. In addition, anthocyanin content increased 9.2-fold and 37.2-fold relative to the control content after 7 and 14 days of treatment, respectively. Furthermore, IM spraying destroyed the cell structures of the leaves, as evidenced by increases in the number of starch granules and the stomatal closure rate. Reductions in photosynthetic efficiency and antioxidant enzyme activity were observed after IM spraying, especially after 14 days of exposure. The diversity and evenness of the leaf microbiota were not affected by IM treatment, but the composition of community structure at the genus level was altered by IM spraying. Imazethapyr application increased the abundance of Pseudomonas, a genus that includes species pathogenic to plants and humans, indicating that IM potentially increased the abundance of pathogenic bacteria on leaves. Our findings increase our understanding of the relationships between herbicide application and the microbial community structures on plant leaves, and they provide a new perspective for studying the ecological safety of herbicide usage.

Responses of individual stomata in Ipomoea pes‐caprae to various CO2 concentrations

The responses of individual stomata to CO2 concentrations ranging from 0 to 900 micromol mol(-1) air were analysed in Ipomoea pes-caprae L. Sweet (Convolvulaceae). The stomata were directly observed using a measurement system that permitted continuous observation of stomatal movement under controlled light and CO2 conditions. A CO2 concentration of 350 micromol mol(-1) or higher induced stomatal closure, whereas concentrations below 350 micromol mol(-1) did not. The time lag before stomatal closure decreased with increasing CO2 concentration, as did the steady-state aperture of the stomata after a change in CO2 concentration. However, the rate of stomatal closure increased with increasing CO2 concentration. Therefore, not only the stomatal closure rate but also the time from the CO2 concentration change to the beginning of stomatal closure changed with increasing CO2 concentration. These results suggest that atmospheric CO2 may be the stimulus for the closure of guard cells. No significant differences were observed between adaxial and abaxial stomata in terms of their responses to CO2. However, heterogeneous responses were detected between neighbouring stomata on each leaf surface.

Comparison of calculated and measured foliar O 3 flux in crop and forest species

We designed a new gas exchange system that concurrently measures foliar H 2O, O 3, and CO 2 flux (HOC flux system) while delivering known O 3 concentrations. Stomatal responses of three species were tested: snapbean, and seedlings of California black oak (deciduous broadleaf) and blue oak (evergreen broadleaf). Acute O 3 exposure (120–250 ppb over an hour) was applied under moderate light and low vapor pressure deficits during near steady state conditions. The rate of stomatal closure was measured when the whole plant was placed in the dark. An adjacent leaf on each plant was also concurrently measured in an O 3-free cuvette. Under some conditions, direct measurements and calculated foliar O 3 flux were within the same order of magnitude; however, endogenously low gs or O 3 exposure-induced depression of gs resulted in an overestimation of calculated O 3 fluxes compared with measured O 3 fluxes. Sluggish stomata in response to light extinction with concurrent O 3 exposure, and incomplete stomatal closure likewise underestimated measured O 3 flux.

The Mutual Effect of Extracellular Ca2+, Abscisic Acid, and pH on the Rate of Stomatal Closure

An analysis of the rate of stomatal closure in epidermal strips of Commelina communis L. induced by different calcium concentrations (10 nM to 1 mM) demonstrated a biphasic dependency, the initial process of closure being more calcium dependent. This dependency was more evident at pH 7 than pH 5 of the bathing medium. Addition of low concentrations of abscisic acid (10 nM) induced a broadening of the Ca(2) dependency, while 10 microM abscisic acid increased the rate of stomatal closure in the whole Ca(2+) range and to a large extent abolished the calcium-induced effects. Such results indicate an interaction of external protons, Ca(2+), and abscisic acid, and possible competition for the membrane associated binding sites of the mechanism(s) responsible for the regulation of stomatal closure.

Interrelationships between water use and growth traits in biomass-producing willows

Water use, drought response and growth were examined under controlled conditions in four interbreeding willow species from different geographical origins (two clones of Salix viminalis L., one clone of S. viminalis × S. schwerenii E. Wolf and one clone of S. purpurea L.). The levels of soil water depletion that plants could sustain without wilting varied markedly between the clones. The level of drought resistance expressed this way was positively related to resistance to xylem cavitation, negatively related to the maximum stomatal conductance, and positively related to early stomatal closure. The rate of stomatal closure, however, was negatively related to the resistance to xylem cavitation. Prior to drought, there were no significant differences between leaf-specific hydraulic conductances of the clones when whole plants were considered. However, there were differences if the roots and shoots were considered separately. Drought resistance was negatively related to maximum growth yields. This is probably because resources were diverted away from leaf production to the production of denser wood (wood density was positively related to cavitation resistance), and, for one clone, to the growth of a larger root system. In addition, because the level of drought resistance was negatively related to the maximum stomatal conductance, growth may have been adversely affected as a result of reduced photosynthesis. Given its high water extraction ability, one of the clones started to wilt sooner than expected, although only lateral shoots were affected. This appeared to indicate a strategy of sacrificing expendable shoots.

Offshore Europe 1983, Aberdeen 6–9 September

Understanding the mechanisms of drought resistance in crop species is crucial for the selection and breeding of tolerant rapeseed (Brassica napus L.) varieties. The present study aimed to assess the physiological and anatomical responses of two rapeseed genotypes, P287 (drought-tolerant) and T88 (drought-sensitive) under three intensities of drought stress. All physiological and anatomical parameters related to drought acclimation were significantly altered in both genotypes under stress conditions. At the fourth-leaf stage, the relative water content, chlorophyll content, protein content, malondialdehyde content, and the activities of peroxidase and catalase in P287 were significantly higher than those in T88, particularly under severe drought conditions. After rehydration, all physiological indexes recovered rapidly, especially in P287. In addition, under drought stress, compared with T88, P287 had thicker palisade tissue, thinner spongy tissue, higher ratio of chloroplast length to chloroplast width, higher stomatal density and stomatal closure rate. Overall, the interaction between physiological and anatomical features improved the drought tolerance of P287 under drought stress conditions.