A Highly Embryogenic Line of the Legume Model Medicago truncatula, M9–10a: Performance Under Water Deficit

Abstract

We examined relationships between conductance to CO2 diffusion from stomatal cavities to the chloroplasts (mesophyll conductance, gm) and plasma membrane aquaporin contents in tobacco leaves acclimated to the long-term drought and those grown under enough irrigation. gm was determined from simultaneous analyses of CO2 gas exchange and chlorophyll fluorescence. Relative plasma membrane aquaporin content was immunochemically determined with an antibody of radish PIP2-type aquaporins. Leaf hydraulic conductivity was measured as a relative weight loss of leaf disks in 1 M sorbitol solution. gm in drought-acclimated plants was about two-third that in well-watered plants. On the other hand, relative aquaporin content on a leaf area basis was about 1.5 times lager in drought-acclimated than well-watered plants. When leaves were fed with 0.5 mM HgCl2, an inhibitor of aquaporins, gm and leaf hydraulic conductivity in well-watered plants were reduced by 20–30% while those in drought-acclimated plants were not significantly affected. These results suggest that a decrease in aquaporin activity leads to the reductions of gm in the long-term drought.