Abscisic Acid-Induced Reactive Oxygen Species Are Modulated by Flavonols to Control Stomata Aperture

Abstract

Abscisic acid (ABA) increases reactive oxygen species (ROS) in guard cells to close Arabidopsis (Arabidopsis thaliana) stomata. In tomato (Solanum lycopersicum), we find that ABA-increased ROS is followed by stomatal closure and that both responses are blocked by inhibitors of ROS-producing respiratory burst oxidase enzymes. ABA-induced ROS sensor fluorescence accumulates in the nucleus, chloroplasts, and endomembranes. The accumulation of flavonol antioxidants in guard cells, but not surrounding pavement cells, was visualized by confocal microscopy using a flavonol-specific fluorescent dye. Decreased flavonols in guard cells in the anthocyanin reduced (are) mutant and elevated levels in the anthocyanin without (aw) mutant were quantified by confocal microscopy and in leaf extracts by mass spectrometry. Consistent with flavonols acting as antioxidants, higher levels of ROS were detected in guard cells of the tomato are mutant and lower levels were detected in aw both at homeostasis and after treatment with ABA. These results demonstrate the inverse relationship between flavonols and ROS. Guard cells of are show greater ABA-induced closure than the wild type, reduced light-dependent guard cell opening, and reduced water loss, with aw having opposite responses. Ethylene treatment of wild-type tomato plants increased flavonol accumulation in guard cells; however, no flavonol increases were observed in Neverripe (Nr), an ethylene receptor mutant. Consistent with lower levels of ROS due to elevated flavonols, ethylene treatments decreased ABA-induced stomatal closure in the wild type, but not Nr, with ethylene responses attenuated in the are mutant. Together, these results are consistent with flavonols dampening the ABAdependent ROS burst that drives stomatal closure and facilitating stomatal opening to modulate leaf gas exchange.

Net photosynthetic CO2 assimilation: more than just CO2 and O2 reduction cycles

“…Conversely, ethylene can antagonize abscisic acid (ABA)‐induced stomatal closure under water deficit (Tanaka et al ., ), and in the long‐term, might stimulate plant growth (Pierik et al ., ). Ethylene stimulates antioxidants (flavonols) synthesis in guard cells and thus counteracts ROS accumulation thereby down‐regulating the ABA response in Arabidopsis (Watkins et al ., ) and tomato (Watkins et al ., ). In fact, this effect was not observed in Arabidopsis ethylene‐overproducing1 ( ein1 ) and tomato Neverripe ( Nr ) mutants affected in ethylene signal transduction (Watkins et al ., , ); accordingly, mutants affected in flavonol synthesis have a higher ROS content in guard cells and are more sensitive to ABA.…”

Ethylene Exerts Species-Specific and Age-Dependent Control of Photosynthesis

“…The inhibitory action of ethylene on ABA-induced stomatal closure is mainly regulated by 129 hydrogen peroxide signaling (Desikan, 2005;Desikan et al, 2006;Shi et al, 2015). Ethylene 130 stimulates flavonol production in the guard cells, which subsequently suppresses reactive oxygen 131 species (ROS) accumulation and consequently reduces ABA-induced stomatal closure (Figure 1; 132 Watkins et al, 2014;Watkins et al, 2017). 133…”

A class B heat shock factor selected for during soybean domestication contributes to salt tolerance by promoting flavonoid biosynthesis

“…It has been reported that flavonols can suppress ROS in guard cells (Watkins et al ., ). ROS and DPBA signals were increased after salt treatment (Fig.…”

“…Previous studies have shown that flavonoids are powerful antioxidants involved in abiotic stress responses (Nakabayashi et al ., ; Martinez et al ., ). Flavonols inhibit the ABA‐dependent ROS burst to regulate stomatal movement (Watkins et al ., ). We found that ROS accumulation was decreased in HSFB2b transgenic soybeans under salt treatment (Fig.…”