LOPEZ-SANTILLAN, JOSE ALBERTO1, ALFREDO J HUERTA2*, and SERGIO CASTRO-NAVA1. 1UAM Agronomia y Ciencias - UAT, CU Victoria, Cd. Victoria, Tam. Mexico CP 87149; 2Dept. of Botany - Miami University, Oxford, Ohio 45056. - Epicuticular leaf wax load on isogenic lines of sorghum (Sorghum bicolor L. Moench) and its contribution to water stress resistance.
High concentrations of leaf epicuticular waxes are thought to enhance
water stress resistance in plants because of a reduction in leaf
temperature and also reduced water vapor loss from the leaves.
However, even though this phenomenon has been studied for some time,
much remains to be understood about the relationship between leaf wax
load and leaf responses under varied environmental conditions. In this
study, we report the effects of leaf epicuticular wax load on leaf
temperature (LT), stomatal conductance (g), transpiration (E), and
total water potential (Psi) in four isogenic lines of sorghum
(obtained from the sorghum research program at Purdue University, West
Laffayette, Indiana), which varied with respect to epicuticular wax
load. For this research, plants were grown in the field in
northeastern Mexico (Ciudad Victoria, Tamaulipas), under both
irrigated and non-irrigated conditions and sampled at 42, 58, 73, and
89 days after planting. Our results showed that LT was not affected by
the amount of leaf epicuticular waxes and on average the LT was about
4 C higher under drought conditions than under irrigation. We found
that g, E, and Psi were significantly correlated with leaf
epicuticular wax load, but the degree of significance depended on
sampling date. In general, we found that the isogenic lines with the
greatest amounts of leaf epicuticular waxes showed the greatest
reductions in g and E under non-irrigated conditions and also had the
highest values for Psi. Under irrigated conditions, the effects of the
leaf epicuticular waxes on the parameters measured were much reduced.
In summary, we conclude from this study that under non-irrigated
conditions, high epicuticular wax loads reduce water loss and hence
allow the leaves to maintain a higher water potential.
Key words: epicuticular leaf wax, Sorghum bicolor, stomatal conductance, transpiration, water stress