AUTHOR=An Yuyan , Feng Xinxin , Liu Longbo , Xiong Lijun , Wang Liangju 

TITLE=ALA-Induced Flavonols Accumulation in Guard Cells Is Involved in Scavenging H2O2 and Inhibiting Stomatal Closure in Arabidopsis Cotyledons

JOURNAL=Frontiers in Plant Science

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2016.01713

DOI=10.3389/fpls.2016.01713

ISSN=1664-462X

ABSTRACT=<p>5-aminolevulinic acid (ALA), a new plant growth regulator, can inhibit stomatal closure by reducing H<sub>2</sub>O<sub>2</sub> accumulation in guard cells. Flavonols are a main kind of flavonoids and have been proposed as H<sub>2</sub>O<sub>2</sub> scavengers in guard cells. 5-aminolevulinic acid can significantly improve flavonoids accumulation in plants. However, whether ALA increases flavonols content in guard cells and the role of flavonols in ALA-regulated stomatal movement remains unclear. In this study, we first demonstrated that ALA pretreatment inhibited ABA-induced stomatal closure by reducing H<sub>2</sub>O<sub>2</sub> accumulation in guard cells of <italic>Arabidopsis</italic> seedlings. This result confirms the inhibitory effect of ALA on stomatal closure and the important role of decreased H<sub>2</sub>O<sub>2</sub> accumulation in this process. We also found that ALA significantly improved flavonols accumulation in guard cells using a flavonol-specific dye. Furthermore, using exogenous quercetin and kaempferol, two major components of flavonols in <italic>Arabidopsis</italic> leaves, we showed that flavonols accumulation inhibited ABA-induced stomatal movement by suppressing H<sub>2</sub>O<sub>2</sub> in guard cells. Finally, we showed that the inhibitory effect of ALA on ABA-induced stomatal closure was largely impaired in flavonoid-deficient <italic>transparent testa4</italic> (<italic>tt4</italic>) mutant. In addition, exogenous flavonols recovered stomatal responses of <italic>tt4</italic> to the wild-type levels. Taken together, we conclude that ALA-induced flavonol accumulation in guard cells is partially involved in the inhibitory effect of ALA on ABA-induced H<sub>2</sub>O<sub>2</sub> accumulation and stomatal closure. Our data provide direct evidence that ALA can regulate stomatal movement by improving flavonols accumulation, revealing new insights into guard cell signaling.</p>