Abstract
Main conclusionStomatal aperture in maize is not affected by exposure to a subtoxic concentration of atmospheric H2S. At least in maize, H2S, thus, is not a gaseous signal molecule that controls stomatal aperture.Sulfur is an indispensable element for the physiological functioning of plants with hydrogen sulfide (H2S) potentially acting as gasotransmitter in the regulation of stomatal aperture. It is often assumed that H2S is metabolized into cysteine to stimulate stomatal closure. To study the significance of H2S for the regulation of stomatal closure, maize was exposed to a subtoxic atmospheric H2S level in the presence or absence of a sulfate supply to the root. Similar to other plants, maize could use H2S as a sulfur source for growth. Whereas sulfate-deprived plants had a lower biomass than sulfate-sufficient plants, exposure to H2S alleviated this growth reduction. Shoot sulfate, glutathione, and cysteine levels were significantly higher in H2S-fumigated plants compared to non-fumigated plants. Nevertheless, this was not associated with changes in the leaf area, stomatal density, stomatal resistance, and transpiration rate of plants, meaning that H2S exposure did not affect the transpiration rate per stoma. Hence, it did not affect stomatal aperture, indicating that, at least in maize, H2S is not a gaseous signal molecule controlling this aperture.
Highlights
Sulfur is an essential macronutrient for plants, which plants usually acquire as sulfate via the root (Hawkesford and De Kok 2006)
It is assumed that H 2S is metabolized into cysteine to stimulate the synthesis of abscisic acid (ABA), which is the canonical trigger for stomatal closure (Batool et al 2018; Rajab et al 2019)
Research with thale cress (Arabidopsis thaliana), maize (Zea mays), cabbage (Brassica olerecea), pumpkin (Curcubita pepo), spruce (Picea abies), and spinach (Spinacea oleracea) showed that exposure to atmospheric H2S did not affect transpiration rates, measured at the whole plant level, at various concentrations and under all exposure periods applied
Summary
Sulfur is an essential macronutrient for plants, which plants usually acquire as sulfate via the root (Hawkesford and De Kok 2006). Sulfate is reduced via several intermediates to sulfide, which is subsequently incorporated in cysteine via the reaction of sulfide with O-acetylserine (OAS), catalyzed by the enzyme O-acetylserine(thiol)lyase (OAS-TL; Hawkesford and De Kok 2006). Cysteine functions as the precursor and reduced sulfur donor for the synthesis of other organic compounds. It is often assumed that sulfur-containing metabolites might modulate physiological processes in plants. It is assumed that H 2S is metabolized into cysteine to stimulate the synthesis of abscisic acid (ABA), which is the canonical trigger for stomatal closure (Batool et al 2018; Rajab et al 2019). Research with thale cress (Arabidopsis thaliana), maize (Zea mays), cabbage (Brassica olerecea), pumpkin (Curcubita pepo), spruce (Picea abies), and spinach (Spinacea oleracea) showed that exposure to atmospheric H2S did not affect transpiration rates, measured at the whole plant level, at various concentrations and under all exposure periods applied (which ranged from minutes to days; De Kok et al 1989; Van der Kooij and De Kok 1998; Stuiver and De Kok 2001; Tausz et al 1998)
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