Activated oxygen production and detoxification in wheat plants subjected to a water deficit programme

Wheat plants (Triticum durum L. cv. Ofanto) were grown in a controlled environment. In one set, control plants were regularly watered; the other set of plants was subjected to two water deficit periods obtained by withholding water and rewatering to field capacity at the end of the first period. After both periods of stress, water potential (Ψw), pressure potential (Ψp) and relative water content (RWC) decreased; osmotic potential (Ψπ decreased by 0.3 MPa only after the second period of stress. In both treatments no osmoregulation mechanism occurred, however, an elastic adjustment took place and turgor was maintained at positive levels. Following the first treatment the good functionality of the ascorbate/glutathione cycle allowed the plants to maintain hydrogen peroxide to the control level despite a greater capacity of the thylakoid membranes to leak electrons towards oxygen; moreover, the ascorbate (AsA)/dehydroascorbate (DHA) ratio was unchanged while reduced glutathione (GSH)/oxidized glutathione (GSSG) increased in comparison with the control. Following the second period of stress, the decreased enzyme defence activities of the glutathione reductase (GR), 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.