Effects of exogenous zinc on the photosynthesis and carbonic anhydrase activity of millet (Setaria italica L.)

Abstract

This study aimed to evaluate the effects of Zn on the growth safety and activity of carbonic anhydrase (CA) in foxtail millet (Setaria italica L.). The photosynthetic characteristics, CA activity, and relative gene expression of different varieties of millet at the seedling stage were studied by spraying Zn solution under pot experiment and indoor culture conditions. Results showed that spraying low-concentration Zn solution (20, 40, and 60 mg L-1) reduced malondialdehyde content and intercellular CO2 concentration (Ci) but increased antioxidant enzyme activity, pigment content, and photosynthetic gas-exchange parameters (net photosynthetic rate, stomatal conductance, transpiration rate, except for Ci); meanwhile, spraying high Zn concentration (80 and 100 mg L-1) exerted opposite effects. The optimal growth of millet was achieved when the Zn concentration was 40 mg L-1. At this concentration, CA activity increased and β-CA family expression was upregulated, which exerted little or no effect on other CA families. Compared to Zhangzagu 10 (zinc-resistant variety), Jingu 21 (zinc-sensitive variety) showed a more significant change. This study may serve as a reference for further research on the function of CA and physiological processes, such as photosynthesis in millet, and a theoretical basis for the effective use of Zn fertilizer in millet.