Brassinolide can improve drought tolerance of maize seedlings under drought stress: By inducing the photosynthetic performance, antioxidant capacity and ZmMYB gene expression of maize seedlings

[Purpose] Drought stress is an important abiotic factor that restricts the growth and yield of maize and poses a continuous threat to food security. The purpose of this study was to evaluate the protective effects of three different brassinolide types, 24-epibrassinolide, 28-homobrassinolide, and 28-epihombrassinolide, on the physiological, biochemical, and drought tolerance mechanisms of maize seedlings under two drought stresses. [Methods] The effects of different brassinolide isoforms on photosynthesis (chlorophyll content, photosynthetic parameters (P-n, G(s), T-r, and C-i), chlorophyll fluorescence parameters (F-v/F-m, phi PSII, qP, qN), and the activity and gene expression of phosphoenolpyruvate carboxylase), antioxidants (superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and increase the content of proline), osmotic balance (malonaldehyde (MDA)), and stress tolerance gene expression (ZmMYB48 gene) in maize seedlings after 7 days of drought stress were studied by spraying each kind of brassinolide at the appropriate concentration; the effects of brassinolide on maize yield were studied by simulating drought environment in field under drought shed. [Results] The results showed that the three brassinolides could enhance the photosynthetic performance of maize, induce the increase of antioxidant enzyme activity and proline content, and decrease MDA content; overexpression of drought tolerance gene ZmMYB48 was induced. Among them, 28-homobrassinolide at 0.03 mg center dot kg(-1) had the best regulating activity; The field application of brassinolide can increase the yield of maize during harvest. Compared with the control, the yield of plots under severe drought stress increased by 27.67%, 42.26% and 34.22% respectively after 24-epibrassinolide, 28-homobrassinolide and 28-epihombrassinolide treatments. [Conclusions] These results provide a scientific basis for brassinolide application in maize under drought stress.