Abstract
5-Aminolevulinic acid (ALA), a newly proved natural plant growth regulator, is well known to improve plant photosynthesis under both normal and stressful conditions. However, its underlying mechanism remains largely unknown. Stomatal closure is one of the major limiting factors for photosynthesis and abscisic acid (ABA) is the most important hormone in provoking stomatal closing. Here, we showed that ALA significantly inhibited ABA-induced stomatal closure using wild-type and ALA-overproducing transgenic Arabidopsis (YHem1). We found that ALA decreased ABA-induced H2O2 and cytosolic Ca2+ accumulation in guard cells with stomatal bioassay, laser-scanning confocal microscopy and pharmacological methods. The inhibitory effect of ALA on ABA-induced stomatal closure was similar to that of AsA (an important reducing substrate for H2O2 removal), CAT (a H2O2-scavenging enzyme), DPI (an inhibitor of the H2O2-generating NADPH oxidase), EGTA (a Ca-chelating agent), and AlCl3 (an inhibitor of calcium channel). Furthermore, ALA inhibited exogenous H2O2- or Ca2+-induced stomatal closure. Taken together, we conclude that ALA inhibits ABA-induced stomatal closure via reducing H2O2, probably by scavenging, and Ca2+ levels in guard cells. Moreover, the inhibitive effect of ALA on ABA-induced stomatal closure was further confirmed in the whole plant. Finally, we demonstrated that ALA inhibits stomatal closing, but significantly improves plant drought tolerance. Our results provide valuable information for the promotion of plant production and development of a sustainable low-carbon society.
Highlights
5-Aminolevulinic acid (ALA) is an essential precursor in tetrapyrrole biosynthesis in organisms, such as such as chlorophyll and heme in plants
Based on the above findings, we assume that the promoting effect of ALA on stomatal aperture might be universal in plant, and ALA-induced stomatal opening should be a critical mechanism for improvement of plant photosynthesis
To explore the regulatory mechanisms underlying ALA-induced stomatal opening, we examined the effects of ALA on Abscisic acid (ABA)-induced stomatal closure
Summary
5-Aminolevulinic acid (ALA) is an essential precursor in tetrapyrrole biosynthesis in organisms, such as such as chlorophyll and heme in plants. Based on the above findings, we assume that the promoting effect of ALA on stomatal aperture might be universal in plant, and ALA-induced stomatal opening should be a critical mechanism for improvement of plant photosynthesis. It has been demonstrated that increasing H2O2 production and the H2O2activated elevation of cytosolic Ca2+ concentration ([Ca2+]cyt) in guard cells are important mechanisms for ABA-induced stomatal closing (Pei et al, 2000). Based on the above clues, we hypothesized that ALA might inhibit ABA-induced stomatal closure by decreasing H2O2 accumulation and [Ca2+]cyt in guard cells. Effect of ALA on drought tolerance of Arabidopsis was further evaluated to exclude the possibility of increase in plant sensitivity to drought stress by ALA-inhibited stomatal closure. Our results provide valuable information for understanding the function mechanisms of ALA and the promotion of plant production
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