Abstract: We explored the effects of different concentrations of abscisic acid (ABA; 0, 1, 2.5, 5, 10 μmol·L^-1) on the growth characteristics, stomatal morphology, photosynthesis of maize seedlings (Jingke 665) under NaCl stress (100 mmol·L^-1), with the treatment without NaCl solution and ABA as the control. The results showed that exogenous ABA increased plant height, leaf length, root/shoot ratio, aboveground biomass, and total biomass of maize under salt stress (P<0.01). Both stomatal width (P=0.001) and area (P<0.001) on the adaxial surface were decreased, while the width (P=0.001) and area (P=0.012) of the stomata on the abaxial surface reached the maximum at the concentration of 5 μmol·L^-1. Exogenous ABA reduced the L(d) values of stomatal spatial distribution on the abaxial leaf surface than those under salt stress, suggesting exogenous ABA could make the stomatal spatial distribution more regular than those plants under salt stress. The application of ABA released the decline of P_n, T_r, G_s, C_iand WUE of maize leaves under salt stress, and increased the contents of chlorophyll a, chlorophyll b, and total chlorophyll (P<0.01). In addition, exogenous ABA decreased the relative conductivity (P=0.002) and increased the F_v/F_m value (P<0.001). These results indicate that exogenous ABA could optimize gas exchange process by adjusting the stomatal morphological characteristics and spatial distribution pattern of stomata, and alleviate the physiological stress on the growth and development of maize under NaCl stress.

Key words: maize, ABA, NaCl stress, photosynthesis, stomatal trait.