Monday, June 18, 2007
Physiological and Biochemical Responses of Field Grown Alfalfa to Water Deficit.
Janakiraman Maruthavanan1, Ian Ray2, and Tracy Sterling1. (1) Entomology, Plant Pathology and Weed Science, New Mexico State University, MSC 3BE, Skeen Building, PO Box 30003, Las Cruces, NM 88003, (2) PO Box 30003 Dept. 3Q, New Mexico State University, New Mexico State University, Plant & Environmental Sciences Dept., Las Cruces, NM 88003-0003
Water deficit is a major environmental factor limiting crop production. The effect of water deficit on alfalfa (Medicago sativa L. var. ‘Peruvian’) grown at the Leyendecker Plant Science Research Center near Las Cruces, NM was characterized by withholding irrigation. Physiology and biochemical measurements were taken overtime at 10 A.M. everyday 7 to 20 (Experiment 1) and 7 to 30 (Experiment 2) days after irrigation (DAI). Diurnal measurements were sampled hourly from 5: 30 A.M. through 5: 30 P.M. at 10 (baseline) and 20 (drought) DAI for both experiments. Trifoliate leaves were harvested from the top of the canopy and frozen immediately to quantify antioxidants and pigments using HPLC. Plant RWC decreased in the time course and diurnal studies with exposure to water deficit and corresponded to increased ambient temperature. The time course study (Experiment 2) showed that prolonged drought stress (> 20 DAI) induced antioxidants like α-tocopherol. In the diurnal studies, conversion of violaxanthin to zeaxanthin through antheraxanthin increased gradually during the morning, reaching a maximum around solar noon and declining in the later part of the day. An inverse relationship between chlorophyll a:b ratio and xanthophyll cycle conversion was also observed in the diurnal studies. Results from this preliminary study characterizing the ecophysiological and biochemical responses of alfalfa to water deficit was important to targeting optimal sampling times for studies comparing multiple progeny of alfalfa genotypes which differ in their water stress tolerance.