Comparative Analysis of Alfalfa Mutants in Response to Drought Stress Applied After First Cutting

The purpose of this study was to determine the agro-morphological, physiological, and transcriptional characteristics of ethyl methane sulfonate (EMS)-mutagenized M₃ alfalfa (Medicago sativa L.) mutants grown for 24 days under water deficit conditions following the first cutting at the blooming bud stage. Drought stress generally reduced all agro-morphological parameters measured. Cutting stress significantly reduced total chlorophyll contents of all genotypes, with the exception of mutant X20. Significant changes occurred in the levels of ascorbate peroxidase (APX), lipid peroxidation (TBARS), glutathione reductase (GR), superoxide dismutase (SOD) and crude protein levels. Drought stress considerably elevated GR levels in irrigated control (C1) and unirrigated control (C2) plants. In contrast to the other genotypes studied, mutant X20’s crude protein level increased significantly after the first cutting under 24 days of water deficit conditions, compared to the level found before cutting. The expression profiles of Medicago truncatula Response to Desiccation 2 (MtRD2) and Medicago sativa proline dehydrogenase (MsProDH) genes differed based on the plant genotype and duration of drought stress. Drought stress increased MsProDH gene expression in X20, X50, and C2 plants by 4.57, 14.8, and 20.65 times, respectively. The findings of the expression study indicated that the MtRD2 gene may play a key role in stress reduction rather than drought stress per se. The results of this study revealed that cutting and drought are two independent stress variables that should be evaluated separately when evaluating genotype response to both irrigated and unirrigated growing environments in alfalfa.