Regulations of 6-Benzyladenine (6-BA) on Leaf Ultrastructure and Photosynthetic Characteristics of Waterlogged Summer Maize

A field experiment was performed to study the effects of spraying exogenous 6-benzyladenine (6-BA) after waterlogging for 6 days at the third leaf stage on the leaf mesophyll cell ultrastructure, chlorophyll content, gas exchange parameters, chlorophyll fluorescence, and malondialdehyde (MDA) content of summer maize (Zea mays L.) hybrids Denghai605 (DH605) and Zhengdan958 (ZD958), to determine the photosynthetic mechanism for the regulation of 6-BA to waterlogged summer maize. Results showed that exogenous application of 6-BA effectively alleviated the adverse effects of waterlogging on photosynthetic characteristics by increasing leaf area index and chlorophyll content. Treatment with spraying exogenous 6-BA resulted in significant and substantial (in the range of 9-37%) increases of the net photosynthetic rate compared to waterlogging treatments. In addition, spraying 6-BA effectively alleviated the adverse effects of waterlogging on leaf ultrastructure by increasing the numbers of grana and grana lamella, decreasing MDA content, and improving membrane structure and chloroplast structure. Visibly, spraying exogenous 6-BA effectively alleviated the adverse effects of waterlogging on leaf ultrastructure of summer maize led to the improvement of photosynthetic performance, resulting in significant and substantial (around 20%) increases in grain yield compared to those of the waterlogging treatments.