Effects of Sigma Broad on Photosynthesis Characteristics and Soluble Substances Content in Leaves of Foxtail Millet

To better understand the physiological mechanism behind the phenomenon of decreased photosynthetic rate when foxtail millet seedlings are treated with Sigma Broad, different concentrations (0, 7.5, 15.0, 30.0, 60.0 mg · L^-1) of 3.6% Sigma Broad were sprayed at the five-leaf stage of Zhangzagu 5 and Jingu 21, and gas exchange parameters, photosynthetic key enzyme activities and soluble matter content were determined and analyzed after 7 days later. The results showed that the net photosynthetic rate (Pn), ETR, the activities of phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPDK), NADP-malate dehydrogenase (NADP-MDH), were reduced with the increasing of Sigma Broad at 15 mg · L^-1. The NAD-malic enzyme (NAD-ME), Ribulose-1, 5-bisphosphate carboxylase oxygenase (Rubisco) activities and soluble substances content increased first and then decreased with the increased concentration of Sigma Broad in the two varieties, and the maximum values of NAD-ME, reducing sugar, sucrose and soluble protein were all appeared at the treatment of 15 mg · L^-1 for both varieties. In summary, Sigma Broad making the obvious damages to the net photosynthetic rate in leaves of foxtail millet is partially due to that the activities of PSII photochemical, PEPC, NADP-MDH, and PPDK were reduced, and the activities of Rubisco and NAD-ME and the metabolism of sugar were affected. (authors)