Epicuticular-wax removal influences gas exchange and water relations in the leaves of an exotic and native species from a Brazilian semiarid region under induced drought stress

The primary physiological function of the leaf cuticle is to limit water loss. Thus, in the present study, we examined the hypothesis that variation in the quality and content of the epicuticular wax between different species influences leaf gas exchange. Plants of Jatropha mollissima (Pohl) Bailon, a Brazilian semiarid native, and Jatropha curcas L. (Euphorbiaceae), an exotic species, were subjected to a water deficit in the presence or absence of epicuticular wax. Plants were grown in 10-L pots under greenhouse conditions. The relative water content, gas-exchange parameters and primary carbon metabolism were measured at 21 days after the irrigation was reduced to induce a water deficit. The well-watered plants of both species showed recovery of gas exchange days after the removal of epicuticular wax. Furthermore, under drought, a gradual increase in transpiration rates was observed only in the leaves of native species without wax, although the stomatal conductance did not differ between the species. High relative water content was maintained, except in the leaves under drought and without wax from Day 13 onward, when compared with all other treatments. The wax production was induced in both species under water shortage. Nevertheless, the native species showed a higher content of long-chain n-alkanes. In fact, the barrier to water vapour under reduced stomatal conductance was highest in the native species.