Plant stress is usually diagnosed via physiological measurements on leaves such as water potential,
photosynthetic rate or chlorophyll fluorescence. Since stress in the case of grapevines is of concern with respect
to the quality of the fruit, we attempted to use one of the above mentioned techniques, chlorophyll fluorescence,
directly on the fruit itself in order to investigate stress responses in vivo. Berry fluorescence was measured in an
experiment with different levels of UV-B and UV-A radiation in the field in 2000 in Geisenheim with the variety
Riesling. UV radiation has been shown to affect chlorophyll and was thus likely to show differences in
fluorescence signals. Berry fluorescence was measured periodically between veraison and harvest on darkadapted
berries (20min). For each berry, a light response curve was recorded followed by a recovery phase in the
dark. The maximum quantum yield of PSII (qY) was determined after a saturation pulse at each light intensity.
The qY decreased exponentially with increasing light intensity. The response level of the quantum yield of PSII
decreased during ripening indicating a loss in chlorophyll and/or PSII capacity for all treatments. Effects of the
different levels of UV-radiation on the light curve were only detected at the end of the ripening period, with
higher quantum yield values recorded for the treatments protected against UV-A and UV-A+UV-B. Similar
results were obtained after recovery in the dark. Changes in fluorescence signals were accompanied by a visual
change in berry colour indicating changes in skin pigmentation, which may also have some effect on fruit
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