Effects of 24-epibrassinolide on photosynthetic parameters in response to different light intensities and CO2 concentrations in maize seedlings under NaCl stress

In order to explore the effect of exogenous 24-epibrassinolide (EBR, 0.1 mu M) application on photosynthetic parameters in response to different light intensities and CO2 concentrations in maize seedlings under NaCl stress (180 mM), this study investigated the light response curve, CO2 response curve, and diurnal variation of photosynthesis of maize seedlings under NaCl stress. Maize cv. Jinlai 318 was used as the material, and the leaves were sprayed with 0.1 mu M EBR. Net photosynthetic rate (PN), stomatal conductance (gs), intercellular CO2 concentration (Ci), and transpiration rate (E) were determined. The results showed that the light response curve, CO2 response curve, and diurnal variation trend under the four treatments (180 mM NaCl, 0.1 mu M EBR, 180 mM NaCl with 0.1 mu M EBR, pure water) were similar. The light saturation point of the leaves under NaCl stress was the lowest (about 1 031 mol m(-2) s(-1)), and that in the control group (without stress) was the highest (about 1 344 mol m(-2) s(-1)). When the light saturation point was reached (1 030 -1 350 mol m(-2) s(-1)), the maximum PN under NaCl stress was the lowest (about 15.15 mu mol m(-2) s(-1)), while that under EBR treatment, it was the highest (about 19.86 mu mol m(-2) s(-1)). NaCl stress significantly reduced chlorophyll a, chlorophyll b, and carotenoid content and chlorophyll a/b ratio, while chlorophyll content significantly increased after EBR treatment. These results showed that exogenous EBR could effectively alleviate the damage to maize seedlings under NaCl stress, delay the light saturation phenomenon, and improve the photosynthetic capacity of maize.