Effects of short-term heat stress on PSII and subsequent recovery for senescent leaves of Vitis vinifera L. cv. Red Globe
Heat stress occurs frequently in energy-saving sunlight greenhouses (ESSG) at the late growth stage. Three-year delayed cultivation (DC) of the Red Globe cultivar of Vitis vinifera L. was used to clarify the physiological mechanisms of short-term heat stress on PSII and subsequent recovery from heat stress. By November, the photosynthetic function had declined and the fall in transpiration rate (E) with heating time increased the possibility of heat damage. In July, the most obvious increase was in the relative variable fluorescence at J point at 40°C, and in November it changed to K point. The 5 min of heat treatment resulted in a significant increase of the relative variable fluorescence at 0.3 ms (Wk), and after 10 min of heat treatment, the number of reactive centres per excited cross section (RC/CSo), probability that a trapped exciton moves an electron into the electron transport chain beyond QA− (at t=0) (ψo) and quantum yield of electron transport at t=0 (ϕEo) decreased significantly (P<0.05), suggesting that the reaction centre, donor and acceptor side of photosystem II (PSII) were all significantly inhibited (P<0.05) and that the thermal stability of the photosynthetic mechanism was reduced. The inhibition of energy fluxes for senescent leaves in November was earlier and more pronounced than that for healthy leaves, which did not recover from heat stress of more than 15 min after 2 h recovery at room temperature.
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