Physiological and molecular responses of Aeluropus lagopoides (Poaceae) to water deficit

As a stoloniferous perennial grass, Aeluropus lagopoides (L.) Trin. is a candidate of choice to elucidate the physiological and molecular aspects of acclimation to adverse environmental conditions. Vegetatively propagated plants were subjected to drought stress by withholding water for 5, 11 or 18 days. Indicators such as relative water content (RWC), relative growth rate and net photosynthesis rate as well as free proline, soluble sugars, the levels of potassium, total protein and chlorophyll contents were monitored for the duration of the drought treatment and subsequent re-watering. Close correlations between RWC and the other indicators of drought stress were evident. When RWC was reduced to 5%, plants looked healthy, net photosynthesis and leaf biomass decreased only slightly and total protein content was relatively higher than the control plants. Moderate reduction in RWC to 10% reduced relative growth rate and net CO2 assimilation but remarkably increased total protein content. In this state, plants recovered shortly after re-watering. When RWC was reduced severely to more than 20%, the dry weight, net photosynthesis rate and chlorophyll and total protein contents decreased while the levels of free proline and soluble sugars increased significantly. Re-watering helped in the partial recovery of the plants. Although total protein contents of severely drought-stressed plants were significantly reduced, alterations in the expression of only a few proteins were detected. Also, the expression of about 1.5% of transcripts was affected by severe drought. Using DD-AFLP methodology, several differentially expressed genes were identified. These genes are predicted to be involved in signaling, regulation of gene expression and osmotic adjustment processes. Altogether, these data indicate that drought tolerance is well programmed in A. lagopoides allowing adaptation to harsh environmental conditions in the natural habitat.