24-Epibrassinolide positively modulates leaf tissues and antioxidant system attenuating the deleterious effects on photosynthetic machinery in rice plants under simulated acid rain.

Abstract

Acid rain causes significant damages to rice plants, affecting photosynthetic machinery and growth. 24-epibrassinolide (EBR) is an organic steroid that used at low concentrations positively regulates plant growth and mitigates deleterious effects connected to environmental changes. The aim of this study was to investigate whether exogenous treatment with 24-epibrassinolide can alleviate the negative effects of the simulated acid rain (SAR) and the possible tolerance mechanism involved, evaluating the chlorophyll fluorescence, gas exchange, antioxidant system and leaf anatomical variables. The experiment was randomized with four treatments, being two simulated acid rain (0 and 0.5 M H2SO4, described as – SAR and + SAR, respectively) and two concentrations of brassinosteroids (0 and 100 nM EBR, described as – EBR and + EBR, respectively). Our results showed that plants exposed to SAR suffered negative interferences; however, EBR-treated plants presented benefits on chlorophyll fluorescence, alleviating the photoinhibition in the photosystem II and protection against damages caused by the imbalance of the reactive oxygen species. Additionally, EBR promoted increases in gas exchange clearly linked to stomatal regulation, improving uptake and distribution of CO2 in intercellular spaces. This research revealed that EBR attenuated the negative effects of SAR, increasing the activities of the antioxidant enzymes (superoxide dismutase, catalase, ascorbate peroxidase and peroxidase), reducing the damages on tilacoid membrane, confirmed by increases in chlorophylls and carotenoids. Finally, the EBR effects observed in plants under SAR demonstrate that this substance positively modulated important anatomical structures linked to leaf protection, increasing the amount of trichomes, epicuticular wax and aerenchyma area. These results provide evidence that EBR conferred tolerance on rice plants exposed to SAR.