Variation in free-radical damage in rice cell suspensions with different embryogenic potentials

Levels of free-radical-mediated lipid peroxidation were monitored in cell-suspension cultures of Oryza sativa L. possessing different embryogenic potentials. Oxidative stress was evaluated using assays which sequentially assessed the stages of lipid peroxidation (diene conjugation, peroxidation, and the formation of secondary lipid-peroxidation products). Lipid peroxidation was significantly higher in a cell line which had lost embryogenic ability compared with lines which still retained this capacity. Superoxide dismutase (EC 1.15.1.1) activity did not vary significantly between the embryogenic and previously embryogenic lines; however, catalase (EC 1.11.1.6) and peroxidase (EC 1.11.1.7) activities were significantly lower in the line which had lost embryogenic ability. Metabolic activity as estimated by reduction of triphenyl tetrazolium chloride decreased with diminishing embryogenic potential and was especially low in cell lines which never exhibited embryogenic capabilities. The possible involvement of free radicals in the loss of embryogenic potential of rice cells is discussed.