Influence of water deficit and rewatering on the components of the ascorbate-glutathione cycle in four interspecific Prunus hybrids

The activities of ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2), as well as the levels of ascorbate pool, glutathione pool and H2O2 were studied in plants of four interspecific Prunus hybrids subjected to water deficit and shade conditions. After 70 days of water shortage, plants were subjected to a rewatering treatment. During water recovery, leaves fully exposed to sunlight and leaves in shade conditions of about 30% of environmental irradiance were sampled. After 70 days without irrigation, mean pre-dawn leaf water potential of all the hybrids fell from 0.34 to 3.30 MPa and marked decreases in net photosynthesis and transpiration occurred. The activities of APX, MDHAR, DHAR and GR increased in relation to the severity of drought stress in all the clones studied. Generally, APX, MDHAR, DHAR and GR were down-regulated during the rewatering phase and their activities decreased faster in shaded leaves than in non-shaded leaves. The levels of total ascorbate, total glutathione and H2O2 were directly related to the increase of drought stress and subsequently decreased during rewatering. This response could limit cellular damage caused by active oxygen species during periods of water deficit. The ability of Prunus hybrids to regulate the enzymatic antioxidant system during different water and irradiance conditions might be an important attribute linked to drought tolerance.