ACTIVATED OXYGEN PRODUCTION AND DETOXIFICATION IN WHEAT PLANTS SUBJECTED TO A WATER-DEFICIT PROGRAM

Wheat plants (Trificum durum L. cv. Ofanto) were grown in a controlled environment. In one set, control plants were regularly watered; the o ther set of plants was subjected to two water deficit periods obtained by withholding water and rewatering to field capacity at the end of t he first period. After both periods of stress, water potential (Psi(w) ), pressure potential (Psi(p)) and relative water content (RWC) decrea sed; osmotic potential (Psi(pi)) decreased by 0.3 MPa only after the s econd period of stress. In both treatments no osmoregulation mechanism occurred, however, an elastic adjustment took place and turgor was ma intained at positive levels. Following the first treatment the good fu nctionality of the ascorbate/glutathione cycle allowed the plants to m aintain hydrogen peroxide to the control level despite a greater capac ity of the thylakoid membranes to leak electrons towards oxygen; moreo ver, the ascorbate (AsA)/dehydroascorbate (DHA) ratio was unchanged wh ile reduced glutathione (GSH)/oxidized glutathione (GSSG) increased in comparison with the control. Following the second period of stress, t he decreased enzyme defence activities of the glutathione reductase (G R), dehydroascorbate reductase (DHAR) and ascorbate peroxidase (AsAP) together with a minor glutathione content might be a consequence of a reduced rate of activated oxygen production.