PHYSIOLOGICAL CHARACTERIZATION OF TRANSGENIC ALFALFA (MEDICAGO SATIVA) PLANTS FOR IMPROVED DROUGHT TOLERANCE

WXP1 is an ethylene-responsive element-binding transcription factor that has been shown to lead to improved drought tolerance and increased wax accumulation when overexpressed in transgenic alfalfa under the control of the CaMV35S promoter. In this study, alfalfa was transformed with the WXP1 gene, driven by the epidermis-specific promoter CER6. The transgenic CER6::WXP1 alfalfa plants and a previously tested CaMV35S:: WXP1 line were subjected to water stress for 3 d and then rewatered. Gas exchange, chlorophyll fluorescence, relative water content, and water potential were measured. Compared with the controls, the transgenic lines showed higher net photosynthetic rate, transpiration rate, and stomatal conductance and higher efficiency of photosystem II, quantum yield of photosystem II, coefficient of photochemical quenching, and apparent electron transport rate under water stress and after rewatering. The transgenic lines also showed higher relative water content and leaf water potential under water deficit conditions. The growth and development of CER6:: WXP1 plants were normal, and the plants showed enhanced drought tolerance. Gas exchange and chlorophyll fluorescence data provided consistent evidence that the WXP1 transgenic lines experienced less damage underwater stress conditions. This study revealed that increased wax accumulation did not have a negative impact on photosynthesis. The physiological analyses indicated that WXP1 is involved not only in wax biosynthesis but also in other physiological responses associated with enhanced drought tolerance that warrant further investigation.