| Understanding the basis of water use efficiency in plants will be the first step toward manipulating the plant's physiology to improve drought tolerance, yield, and ultimately reduce the costs associated with irrigation. The cuticle, a thin, extracellular coating on the aerial surfaces of the plant, provides a protective barrier between the plant and its environment. The most distal layer of the cuticle, the epicuticular wax, is the primary determinant of the permeability of the plant cuticle and, thus, is the primary factor in regulating rates of cuticular transpiration. Cuticular transpiration is the principal form of water vapor loss when stomata are closed. As such, it is important to understand the mechanisms by which the epicuticular wax is produced and regulated in plants. In this research, Nicotiana glauca, a plant that produces a wax bloom when subjected to periodic drying events, has been used as a model system to study wax deposition. Lipid transfer proteins (LTPs) are small, basic proteins thought to be involved in the transfer of lipids through the cell wall during the formation of the cuticle. Five putative members of the N. glauca LTP family have been identified by screening a guard cell cDNA library and a genomic library. NgLTP gene expression is upregulated by dehydration stress and NgLTP2 is upregulated upon wounding. Neither wax load nor composition were altered in transgenic hybrid poplar plants expressing a CaMV35S promoter: NgLTP1 gene fusion, when compared to wild type, suggesting that the level of expression of LTP does not regulate wax formation. To begin assessing the variability among genotypes of hybrid poplar and willow, the diversity in wax composition and load was determined throughout one growing season for five clones previously selected for their high biomass production in short rotation intensive culture systems. There was little difference in the epicuticular wax from two hybrid poplar clones, while epicuticular wax from three species of willow displayed significant variability. |
