ANTIOXIDATIVE DEFENSES OF SOYBEAN [Glycine max (L.) Merr. cv. Grobogan] AGAINST PURPLE NUTSEDGE (Cyperus rotundus L.) INTERFERENCE DURING DROUGHT STRESS

Various biotic and abiotic stresses are responded by plants through the production of large amounts of Reactive Oxygen Species (ROS). This condition creates oxidative stress and as the result reduces plant cell function, inhibits growth and development and in the worst case, it may cause plant death. However, the plant develops antioxidative defence mechanisms to control ROS to a harmless level. Every plant will give different responses toward various stresses, so it is possible that the response of soybean [Glycine max (L.) Merr. cv. Grobogan] plant to multiple stresses will be different when compared to its response to a single stress factor. The objective of this research was to study the antioxidative defenses of soybean towards multiple stresses, i.e. purple nutsedge (Cyperus rotundus L.) interference and drought treatment. This research was designed factorially using Completely Randomized Design (CRD), i.e. purple nutsedge interference (control, three and six purple nutsedge) and drought stress (control / fraction of transpirable soil water 1 / FTSW 1, mild / FTSW 0.5 and severe / FTSW 0.25). The results showed that enzyme activity of superoxide dismutases (SOD), ascorbate peroxidases (APX) and catalase (CAT) increased under mild and severe drought stresses. In contrast, activity of those three enzymes decreased under interference of three and six purple nutsedge treatments. Moreover, SOD activity increased under the combined treatments of interference by three purple nutsedge with mild drought stresses, whereas other combined treatments decreased SOD activity. Activity of APX and CAT decreased under all combination treatments of purple nutsedge interference and drought stress. The content of non-enzymatic antioxidant, i.e. glutathione, ascorbic acid, and total phenol increased under all treatments with interference of purple nutsedge, drought stress and combination of both stresses, whereas carotenoid content decrease on same treatments.