
TY  - JOUR
A1  - Flexas, J. 
A1  - Escalona, J. M. 
A1  - Medrano, H. 
T1  - Down-regulation of photosynthesis by drought under field conditions in grapevine leaves
JF  - Functional Plant Biology
JO  - Functional Plant Biol.
Y1  - 1999
VL  - 25
IS  - 8
SP  - 893
EP  - 900
KW  - Vitis vinifera L., Vitaceae, grapevines, water stress, irrigation, photosynthesis, photoinhibition.
UR  - https://doi.org/10.1071/PP98054 
N2  - The importance of both stomatal closure and reduced carboxylation efficiency on the photo- synthesis decline in response to long term water stress was previously measured in field-grown grapevines. Here we address the question of whether water stress affects the photochemical capacity of leaves, measuring gas-exchange rates and chlorophyll fluorescence under drought and moderate irrigat- ion at intervals through the summer season during three consecutive years. We conclude that usually water stress does not induce photoinhibition in field-grown grapevines, even when stomatal conductance and photosynthesis are reduced to very low values. Moreover, down-regulat- ion of photochemical reactions is low, leading to a general pattern of photosynthetic response to drought consistent in large reductions of stomatal conductance (g), followed by a consistent decrease of CO2 assimilation (A) but with a much lower effect on electron transport rate (ETR). In consequence, the intrinsic water-use efficiency (A/g) increased, as well as the ratio ETR/A. It is suggested that increased electron transport to alternative pathways, such as photorespiration, prevented further down-regulation of ETR under drought conditions. These results are in agreement with our previous reports for potted plants. However it is clear that, under field conditions with a much more slowly developed water stress, ETR reductions are more attenuated than in potted plants, reducing their incidence in carbon assimilation, which seems to be mainly regulated by stomatal closure. 
ER  -

