Heat acclimation induced acquired heat tolerance and cross adaptation in different grape cultivars: relationships to photosynthetic energy partitioning

Several mechanisms on acquired heat tolerance and cross adaptation have been proposed; however, relationships to photosynthetic energy partitioning remain unknown. The effects of heat pretreatment on cold and heat tolerance in grapevine leaves of two cultivars ('Jingxiu', cold sensitive; 'Beta', cold tolerant) were evident in changes in the antioxidant system, lipid peroxidation, net photosynthesis rate and also in chlorophyll fluorescence according : Y(II) + Y(NPQ) + Y(NO) = 1, where Y(II) is the effective PSII quantum yield; Y(NPQ) is regulated energy dissipation as a protective mechanism; and Y(NO) is non-regulated energy dissipation as a damaging mechanism. Heat pretreatment enhanced heat tolerance in the two cultivars, which was associated with less energy partitioned in non-regulated energy dissipation, less lipid peroxidation and higher antioxidant enzyme (catalase, ascorbate peroxidase and guaiacol peroxidase) activities compared with control plants under heat stress. Heat pretreatment also induced cold tolerance in 'Jingxiu' and 'Beta' leaves. This cross adaptation seemed to be attributable in part to less non-regulated energy dissipation in pretreated 'Jingxiu' and 'Beta' than the controls under cold stress. The evidence that lipid peroxidation was less and antioxidant enzyme activities were higher in pretreated plants under cold stress further corroborated the results from energy partitioning.