Citrate synthesis and exudation confer Al resistance in alfalfa (Medicago sativa L.)

Aims Alfalfa is the most important forage legume but sensitive to aluminum (Al), which largely limits its growth in acid soils. To improve Al resistance in alfalfa, responses to Al toxicity were investigated for understanding of the mechanisms of Al resistance in alfalfa. Methods Growth performance and Al resistance in forty-two cultivars was evaluated. Organic acids synthesis and exudation as well as the key genes in response to Al were investigated. Results Alfalfa cultivars showed diversity in Al resistance. Compared to the sensitive cultivar ‘Magnum 801’, the Al resistant cultivar ‘WL414’ had higher relative root elongation in response to Al toxicity, with less accumulation of Al. Al activated citrate and malate exudation in alfalfa, with higher citrate exudation and concentration as well as higher levels of citrate synthase (CS) activity, MsCS , MsALMT1 , and MsMATE22 transcripts in root apex in WL414 than in Magnum 801. Citrate exudation is the major mechanism in Al resistance in alfalfa. Conclusions Alfalfa cultivars had diversity in Al resistance. Citrate synthesis and exudation plays a key role in Al resistance in alfalfa. Higher levels of citrate concentration and exudation are associated with Al resistance in Al resistant cultivar as compared with the sensitive cultivar.