Developmental changes of primary processes of photosynthesis in sun- and shade-adapted berries of two grapevine cultivars

Abstract

Light utilisation and thermal dissipation of field-grown sun- and shade-adapted berries of cvs Kerner (white) and Portugieser (red) were investigated during berry development by determining chlorophyll fluorescence parameters. In stages I and H of berry development for both cultivars the maximum quantum yield of photochemical energy conversion of dark-adapted berries (Fv/Fm) was close to the maximum (0.75-0.80). It decreased significantly in sun- and shade-adapted berries of cv. Kerner two weeks after veraison indicating damage of photosystem 11 (PSII) during ripening. When at veraison anthocyanins accumulated in the skin of berries chlorophyll fluorescence of cv. Portugieser berries could no longer be determined. In both cultivars the linear electron transport rate at light saturation (ETRmax) increased in stage I and reached maxima in stage 11, sun-adapted berries showing higher rates than shade-adapted. After high values in stage I non-photochemical quenching at light saturation (NPQmax) decreased in light- and shade-adapted Kerner berries in stage 11 indicating a lowering of the thermal dissipation efficiency. The pool size of the xanthophyll cycle pigments diverged significantly in sun- and shade-adapted berries during their development: under clear, warm and dry weather conditions in shade-adapted berries the xanthophyll pool size decreased to low levels, while in sun-adapted berries it increased to maximum values shortly before (cultivar Kerner) or at veraison (cultivar Portugieser) and subsequently declined. Unripe, sun-adapted berries of both cultivars showed a transient decline of the xanthophyll pool size during a rain period suggesting pool size adjustment to changes of ambient conditions in the longer term. It is concluded that unripe, sun-adapted berries are better adapted to high light than shade-adapted berries due to their higher capacity of photosynthetic energy consumption and thermal energy dissipation; at the onset of ripening these photoprotective mechanisms appear to loose importance.