Vulnerability to cavitation of leaf minor veins: any impact on leaf gas exchange?
Plant, Cell and Environment, (2001)Abstract
Vulnerability to cavitation of leaf minor veins and stems of Laurus nobilis L. was quanti?ed together with that of leaf- lets, rachides and stems of Ceratonia siliqua L. during air- dehydration of 3-year-old branches. Embolism was esti- mated by counting ultrasound acoustic emissions (UAE) and relating them to leaf water potential (YL). The thresh- old YL for cavitation was less negative in L. nobilis than in C. siliqua according to the known higher drought resis- tance of the latter species. Leaf minor vein cavitation was also quanti?ed by in?ltrating leaves with ?uorescein at dif- ferent dehydration levels and observing them under micro- scope. Distinct decreases in the functional integrity of minor veins were observed during leaf dehydration, with high correlation between the two variables. The relation- ship between leaf conductance to water vapour (gL) and YL showed that stomata of L. nobilis closed in response to stem and not to leaf cavitation. However, in C. siliqua, gL decreased in coincidence to the leaf cavitation threshold, which was, nevertheless, very close to that of the stem. The hypothesis that stem cavitation acts as a signal for stomatal closure was con?rmed, while the same role for leaf cavita- tion remains an open problem.