Water stress decreases the availability of the gaseous substrate for
ribulose-1,5-bisphosphate carboxylase/
oxygenase (
Rubisco) by decreasing leaf conductance to CO(2). In spite of limiting photosynthetic
carbon assimilation, especially in those environments where drought is the predominant factor affecting plant growth and yield, the effects of water deprivation on the mechanisms that control
Rubisco activity are unclear. In the present study, 11 Mediterranean species, representing different growth forms, were subject to increasing levels of drought stress, the most severe one followed by rewatering. The results confirmed species-specific patterns in the decrease in the initial activity and activation state of
Rubisco as drought stress and leaf
dehydration intensified. Nevertheless, all species followed roughly the same trend when
Rubisco activity was related to stomatal conductance (g(s)) and chloroplastic CO(2) concentration (C(c)), suggesting that deactivation of
Rubisco sites could be induced by low C(c), as a result of
water stress. The threshold level of C(c) that triggered
Rubisco deactivation was dependent on leaf characteristics and was related to the maximum attained for each species under non-stressing conditions. Those species adapted to low C(c) were more capable of maintaining active
Rubisco as drought stress intensified.