Variation in antioxidant metabolism of young and mature leaves of Arabidopsis thaliana subjected to drought

Young and mature leaves of 4-week-old Arabidopsis plants were exposed to drought stress up to -2.54MPa of water potential (ψ_w) by withholding water supply for 7 days. The efficiency of photosystem (PS) II photochemistry, F_v/F_m, and chlorophylls (Chls) remained unaltered and quantum yield of PSII electron transport (Φ_PSII) decreased slightly in drought-stressed young leaves, whereas F _v/F_m decreased slightly and Φ_PSII and Chls decreased by 40 and 24%, respectively, in drought-stressed mature leaves. Both young and mature leaves exhibited a considerable increase in non-photochemical quenching (NPQ) and xanthophyll-mediated photoprotection capacity in response to drought stress, with a greater level of NPQ in mature leaves. Although the drought-induced increase in non-enzymatic antioxidants in young and mature leaves, enzymatic antioxidants including catalase, peroxidase (POD), superoxide dismutase (SOD) and glutathione reductase (GR) substantially increased only in drought-stressed mature leaves. Plants recovered rapidly 24h after resupplying water, as indicated by that ψ_w, F_v/F_m and pigment contents returned to well-watered control levels, however, the activities of POD, SOD and GR remained high. The fact that drought-stressed mature leaves suffer more stress than drought-stressed young leaves suggests that developmental stages of leaves might contribute to the differential prevention of oxidative damage in plants exposed to drought.