Photoprotection in leaves of grapevines: Responses of the xanthophyll cycle to alterations of light intensity

Under conditions of light intensities exceeding the photosynthetic use carotenoids of the xanthophyll cycle have been shown to be involved in the dissipation of excess energy. When, after a period of darkness, low light-adapted leaves (400 mu mol m-2 s-1) of cv. Orion vines were suddenly exposed to high light (800 mu mol m-2 s-1) the zeaxanthin (Z) content of the leaves increased significantly within 3 min at the expense of violaxanthin (V); a steady state was reached after ca. 20 min. On the contrary, when high light-adapted leaves were abruptly exposed to darkness the Z content decreased and the V content increased to a steady state within 2.5 h. In both trials, the intermediate substance of the xanthophyll cycle, antheraxanthin (A), remained almost constant at a relative low level. In field experiments with cv. Gf.Ga-47-42 an increase of sunlight in the morning was accompanied by increases of A+Z and decreases of V while a decline of sunlight in the afternoon was associated with decreases of A+Z and an increase of V. In laboratory and field experiment the xanthophyll-irradiance relation showed hysteresis. The epoxidation state (EPS, V+0.5A / V+A+Z) decreased in the morning to a minimum at noon and then increased again in the afternoon reflecting a distinct depression of photosynthesis at midday