Abstract
5-aminolevulinic acid (ALA), a new plant growth regulator, can inhibit stomatal closure by reducing H2O2 accumulation in guard cells. Flavonols are a main kind of flavonoids and have been proposed as H2O2 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 H2O2 accumulation in guard cells of Arabidopsis seedlings. This result confirms the inhibitory effect of ALA on stomatal closure and the important role of decreased H2O2 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 Arabidopsis leaves, we showed that flavonols accumulation inhibited ABA-induced stomatal movement by suppressing H2O2 in guard cells. Finally, we showed that the inhibitory effect of ALA on ABA-induced stomatal closure was largely impaired in flavonoid-deficient transparent testa4 (tt4) mutant. In addition, exogenous flavonols recovered stomatal responses of tt4 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 H2O2 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.
Highlights
Stomatal movements regulate plant gas exchange with the environment, and are critical for plant growth and development (Wang et al, 2014)
The time course for stomatal movement illustrated that the inhibition of Aminolevulinic acid (ALA) on abscisic acid (ABA)-induced stomatal closure was initiated after ABA application and lasted for at least 2 h (Figure 1B)
Different letters on the same time point indicate significant differences at P = 0.05 level. It has been well-documented that ALA, a new plant growth regulator, significantly improves plant photosynthesis and growth (Akram and Ashraf, 2013)
Summary
Stomatal movements regulate plant gas exchange with the environment, and are critical for plant growth and development (Wang et al, 2014). Enhancing stomatal aperture to improve the uptake of CO2 by terrestrial plants is an increasingly important problem due to global climate changes (Wang et al, 2014). 5-Aminolevulinic acid (ALA), a natural plant growth regulator, is known to improve plant photosynthesis under both normal (Hotta et al, 1997) and stressful conditions (Hotta et al, 1998; Nishihara et al, 2003; Wang et al, 2004; Liu et al, 2011; Zhang et al, 2012; Ali et al, 2013b). Recent investigations showed that ALA did not affect stomata development, but significantly inhibited stomatal closing (An et al, 2016a), indicating increasing stomatal aperture is an important mechanism of ALA-mediated improvement of photosynthesis. ALA improved plant drought tolerance simultaneously (An et al, 2016a), further suggesting its great application potential in agriculture and forestry
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