WATER-STRESS AND FREE-RADICAL MEDIATED CHANGES IN SUNFLOWER SEEDLINGS

Sunflower seedlings were grown in well watered and dryland conditions obtained by withholding water. In the stressed seedlings the leaf water potential was 1.0 MPa lower than the control and the relative water content decreased as well. The reduction in the osmotic potential at full turgor following water stress indicated that an osmotic adjustment came into play. Water deficit conditions resulted in reduced growth of the plants and in increased membrane permeability. In comparison to the control, the unwatered seedlings showed lower chlorophyll and soluble protein amounts, as well as a reduction in total and polar lipid contents. Neither decrease in the unsaturation of lipids nor increase in the malondialdehyde level were observed upon water stress. In the sunflower subjected to drought, ESR spectra showed a 17% higher free radical production; moreover, reduced superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) activities were also found.