STOMATAL MOVEMENTS AND RATES OF GASEOUS EXCHANGE IN EXCISED LEAVES OF VICIA FABA

Abstract

SUMMARYSimultaneous measurements of leaf resistance to gaseous flow, rate of transpiration and rate of carbon dioxide exchange were made with the main object of investigating the effects of severing the petiole on stomatal movements and gaseous exchange of leaves of Vida faha of differing initial water content.Extensive stomatal changes occurred on cutting the petioles of illuminated leaves in air. The magnitude and direction of the stomatal movements were strongly influenced by the water relations of the leaf at the time of excision. When the water deficit was small there was a substantial temporary stomiatal opening and corresponding temporary increases in rates of transpiration and photosynthesis. In leaves of moderate water deficit the stomatal opening on leaf excision was much less pronounced and, in leaves under severe water stress at the time of cutting, there was little evidence of any immediate stomatal response. Preliminary stomatal opening and a temporary increase in transpiration rate were also observed in leaves excised in air from plants kept in darkness. In experiments in which the illuminated leaves were severed under water, however, a temporary increase of leaf resistance to gaseous flow was found on leaf excision, and associated declines in rates of transpiration and of photosynthesis.The changes in transpiration rate resulting from leaf severance are clearly associated with stomatal behaviour, and there is evidence of close stomatal control, under these conditions, of rates of transpiration and of photosynthesis. The phenomena involved in leaf excision both in air and under water are discussed and stomatal behaviour shown to depend to a considerable extent on the water relations of the leaf; stomatal movements are interpreted largely in terms of differential turgor changes in the guard cells and neighbouring epidermal cells.

Mitigation of drought stress in rice crop with plant growth‐promoting abiotic stress‐tolerant rice phyllosphere bacteria

“…Similarly, the results of our study elucidate that plants (T 3 ) with the least stomatal aperture size were measured with the maximum soluble sugar content in the leaves. Moreover, stomatal closure positively protects the plant from permanent wilting and restores the plants immediately after rewatering [47]. Drought stress severely damages the chloroplast and reduces the photosynthetic pigment content [48].…”

Fluorometric Measurement of Individual Stomata Activity and Transpiration via a “Brush-on”, Water-Responsive Polymer

“…By providing this fluorometric approach for observing transpiration from individual stomata, we hope to offer this scheme as a valuable addition to field experiments as the sensor coating may easily be applied to the leaf surface prior to excision from the plant. As such, this coating approach may give a more accurate means for determining the stomatal behavior as compared to methods that require acquisition or excision of the leaf prior to the analysis, since this has been known to influence the rates of transpiration 59 60 61 .…”

Water Stress

“…Cummins, Kende & Raschke (52) pointed out that the rapidity and ready reversibility of the action of ABA on stomata would make it a good modulator of stomatal behavior. However, although tissue ABA increases rapidly when water stress sets in (323), stomata possibly close even faster (10,92,272,273,317), thus raising the question of whether the accumulation of ABA from stress is fast enough for it to be the modulator of stomatal response.…”

“…Short-term stomatal oscillation causes strikingly similar and inphase oscillation in CO! assimilation (14,112,295), while leaf water con tent or 'lr oscillates 1800 out of phase (14,112,169 upon a sudden cutoff of the water supply to leaves is associated with a transitory increase in CO2 assimilation in spite of the increase in leaf water defi cit (10).…”