PJB-2019-580
RESPONSES OF PHOTOSYNTHESIS, ANTIOXIDANT ENZYMES AND GENES TO NICOSULFURON STRESS IN TWO GENOTYPES OF SWEET MAIZE (ZEA MAYS L.) WITH DIFFERING NICOSULFURON TOLERANCE
JIAN WANG
Abstract
Weed control in maize (Zea mays L.) crops is usually undertaken using the postemergence herbicide nicosulfuron. The toxicity of nicosulfuron on maize, especially sweet maize, has been widely reported. In order to examine the effect of nicosulfuron on seedling photosynthetic characteristics, chlorophyll fluorescence, reactive oxygen species (ROS) production, antioxidant enzyme activities and gene expressions on sweet maize, nicosulfuron-tolerant ‘HK310’ and nicosulfuron-sensitive ‘HK320’ were studied. All experiment samples were subjected to a water or nicosulfuron treatment when the fourth leaves on the plants were fully developed. After treatment with nicosulfuron, results for HK301 were significantly higher than those of HK320 for net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E), leaf maximum photochemical efficiency of PSII (Fv/Fm), photochemical quenching of chlorophyll fluorescence (qP), and the electron transport rate (ETR). These results were contrary to intercellular CO2 concentration (Ci) and nonphotochemical quenching (NPQ). As higher O2－ and H2O2 accumulations were observed in HK320 than in HK301, an increase in oxidative stress may have resulted in the reduction of photosynthetic capacity in HK320. Serious damage may have occurred to lipids and proteins, resulting in a reduction of the stability of the membrane. As exposure time increased, associated effects also increased. Both O2·－ and H2O2 detoxificationare is modulate by antioxidant enzymes. Compared to HK301, SOD, POD, and CAT activities of HK320 were significantly reduced as exposure time increase. Compared to HK320, the gene expression for the majority of SOD genes, except for SOD2, increased due to inducement by nicosulfuron, and it significantly upregulated the gene expression of CAT in HK301. Results from this study indicate that plants can improve photosynthesis, scavenging capabilities of ROS, and protective mechanisms to alleviate phytotoxic effect of nicosulfuron. Future research is needed to further elucidate the important role antioxidant systems and gene regulation play in herbicide detoxification in sweet maize.
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