Abstract
A comparative study on contribution of photoprotective and anti-oxidative mechanisms to combined drought and high radiation intensity stress adaptation was conducted on two grapevine varieties (Vitis vinifera L., cvs Sabatiano and Mavrodafni), differing in their ability for drought adaptation. Plants of both varieties were subjected to two different deficit irrigation regimes receiving either 50% (DI50) or 25% (DI25) of fully irrigated control plants. Sabatiano, which is considered as more drought resistant variety, maintained significant higher values of photosynthetic rate (PN), stomatal conductance (gs) and predawn water potential (ΨPD) compared to Mavrodafni at the beginning of the drought period. Furthermore, Sabatiano showed significantly lower electron transport rate (ETR), PSII maximum (Φexc) efficiency and significantly higher non-photochemical quenching (NPQ) values for the same values of ΨPD and gs respectively, which implies a more efficient dissipation of excess energy via the xanthophyll cycle. On the other hand, photorespiration was higher in Mavrodafni suggesting a possible contribution of this mechanism in this variety photoprotection. Drought-induced hydrogen peroxide (H2O2) concentration increased rapidly in Mavrodafni resulting in higher lipid peroxidation. No significant differences in the up-regulation of ascorbic peroxidase (APX, EC 1.11.1.11) and superoxidase dismutase (SOD, EC 1.15.1.1) enzyme activities in response to drought were observed whereas catalase (CAT, EC 1.11.1.6) activity changes in response to gs followed completely different patterns in two varieties. The similarity between nitric oxide (NO) accumulation and CAT activity increase at the early stages of drought suggests a positive role of NO in catalase up-regulation.
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