Change in epicuticular wax levels in wheat lines in response to heat stress.                            Cuticular wax protects the shoot from pathogen attack as well as water loss through transpiration. Intracuticular waxes determine epidermal conductance and epicuticular wax is associated with water transpiration and spectral reflectance. Recent studies in our lab identified natural variation in leaf wax thickness among wheat varieties. Some of these varieties have shown increased wax deposition prior to stress, while others increased their deposition when exposed to heat stress at 10 DAP (days after pollination). The epicuticular wax was extracted at three developmental stages, 10 DAP, 11 DAP and 13 DAP. Australith, Debeira and Fang 60 showed significant increase in wax levels from 10 DAP to 13 DAP. Halberd, Kauz, and Ogallala showed a slight increase, and Cutter and Tam 110 showed no significant difference in wax levels. Relative expression analysis of the wheat lines showed that Kauz and Halberd have a high expression levels of the ABC transporter that corresponded to the high level of wax found in these lines while those lines with low wax levels had a relatively low level of ABC transporter gene expression. Currently, thirteen winter and spring lines that includes heat susceptible and heat tolerant lines are being used to determine epicuticular wax concentration and expression of candidate wax regulatory genes in response to heat stress. Leaf samples will be collected during the course of the day for three days after the plants reach 10 DAP. The results from this study will provide important information on the role of wax in heat tolerance and help plant breeders develop new heat tolerant wheat cultivars.