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Arabidopsis ABSCISIC ACID-RESPONSIVE ELEMENT-BINDING FACTOR 3 ( ABF3 ), a bZIP transcription factor, plays an important role in regulating multiple stress responses in plants. Overexpressing AtABF3 increases tolerance to various stresses in several plant species. Alfalfa ( Medicago sativa L.), one of the most important perennial forage crops worldwide, has high yields, high nutritional value, and good palatability and is widely distributed in irrigated and semi-arid regions throughout the world. However, drought and salt stress pose major constraints to alfalfa production. In this study, we developed transgenic alfalfa plants (cv. Xinjiang Daye) expressing AtABF3 under the control of the sweetpotato oxidative stress-inducible SWPA2 promoter (referred to as SAF plants) via Agrobacterium tumefaciens -mediated transformation. After drought stress treatment, we selected two transgenic lines with high expression of AtABF3 , SAF5 and SAF6, for further characterization. Under normal conditions, SAF plants showed smaller leaf size compared to non-transgenic (NT) plants, while no other morphological changes were observed. Moreover, SAF plants exhibited enhanced drought stress tolerance and better growth under drought stress treatment, which was accompanied by a reduced transpiration rate and lower reactive oxygen species contents. In addition, SAF plants showed an increased tolerance to salt and oxidative stress. Therefore, these transgenic AtABF3 alfalfa plants might be useful for breeding forage crops with enhanced tolerance to environmental stress for use in sustainable agriculture on marginal lands. [ABSTRACT FROM AUTHOR]

In this study, we generated and evaluated transgenic alfalfa plants ( Medicago sativa L. cv. Xinjiang Daye) expressing the Arabidopsis nucleoside diphosphate kinase 2 ( AtNDPK2 ) gene under the control of the oxidative stress-inducible SWPA2 promoter (referred to as SN plants) to develop plants with enhanced tolerance to various abiotic stresses. We selected two SN plants (SN4 and SN7) according to the expression levels of AtNDPK2 and the enzyme activity of NDPK in response to methyl viologen (MV)-mediated oxidative stress treatment using leaf discs for further characterization. SN plants showed enhanced tolerance to high temperature, NaCl, and drought stress on the whole-plant level. When the plants were subjected to high temperature treatment (42 °C for 24 h), the non-transgenic (NT) plants were severely wilted, whereas the SN plants were not affected because they maintained high relative water and chlorophyll contents. The SN plants also showed significantly higher tolerance to 250 mM NaCl and water stress treatment than the NT plants. In addition, the SN plants exhibited better plant growth through increased expression of auxin-related indole acetic acid (IAA) genes ( MsIAA3 , MsIAA5 , MsIAA6 , MsIAA7 , and MsIAA16 ) under normal growth conditions compared to NT plants. The results suggest that induced overexpression of AtNDPK2 in alfalfa will be useful for increasing biomass production under various abiotic stress conditions. [ABSTRACT FROM AUTHOR]

Abstract: To understand the adaptability of alfalfa (Medicago sativa L.) to environmental stresses, we analyzed the activity of several antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and catalase (CAT), in alfalfa shoots and roots subjected to salt and drought stresses during germination. The germination rate of six alfalfa cultivars was comparatively studied under 200 mM NaCl or 35% PEG treatment. Alfalfa Xinmu No. 1 and Northstar varieties were selected as stress-tolerant and -sensitive cultivars, respectively, and were used for further characterization. After NaCl or PEG treatment, Xinmu No. 1 showed enhanced seedling growth, compared with Northstar. Xinmu No. 1 also exhibited low levels of hydrogen peroxide (H2O2) production and lipid peroxidation, compared with Northstar. In addition, Xinmu No. 1 showed higher enzymatic activity of SOD, APX, CAT, and POD in its shoots and roots than Northstar. These results seem to indicate that Xinmu No. 1 cultivar''s tolerance to salt or drought stresses during germination is associated with enhanced activity of antioxidant enzymes. This study highlights the importance of antioxidant enzymes in the establishment of alfalfa seedlings under drought and salinity conditions typical of desertification. [Copyright &y& Elsevier]