ISHS Acta Horticulturae 493: I ISHS Workshop on Water Relations of Grapevines
HIGH LIGHT AND WATER STRESS IN GRAPEVINES: PHOTOINHIBITION AND PHOTOPROTECTION |
| Author: | H. Düring |
| Keywords: | chlorophyll fluorescence, photosynthesis, quantum yield, xanthophyll |
| Abstract:
Determination of quantum yield and electron transport rate by measurements of chlorophyll fluorescence in leaves exposed to increasing light and water stress indicates that excessive light surpassing the photosynthetic demand causes photoinhibition of photosynthesis in shade-adapted vines, water stress (water logging or drought) intensifying this process. Symptoms of photoinhibition are shown to be transient, i.e. they disappeared within 24 h. Photoprotection can be achieved - inter alia - by carotenoids of the xanthophyll cycle. In dark-adapted leaves, high light very rapidly induced a conversion of violaxanthin to zeaxanthin, a process known to protect thylakoid membranes against destructive overexcitation. Darkening of leaves reversed this process. Under field conditions, diurnal levels of violaxanthin and zeaxanthin were shown to vary counter-currently in leaves according to sunlight intensity. The xanthophyll pool size was higher in leaves at the outer part of the canopy compared to the inner part indicating a higher maximum capacity for nonradiative energy dissipation. | |
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