Differential strategies of the model legumes Lotus japonicus and Medicago truncatula in the adaptation to salt stress: Photo synthetic and nutritional responses

Abstract

In this research, Lotus japonicus and Medicago truncatula plants, forming determined and indeterminate nodules respectively, were subjected to NaCl stress to study changes in plant growth, nitrogen fixation, photosynthetic parameters and distribution and/or accumulation of organic and inorganic solutes. NaCl produced a significant inhibition of shoot growth in both legumes; meanwhile Nitrogen Fixation Rate (NFR) only was significantly inhibited in L. japonicus, indicating higher sensitivity of determined nodules to salinity. Optimum quantum yield of photosystem II (PSII), represented by the Fv/Fm ratio and pigments content, decreased in both legumes, mainly with 50 mM NaCl. The Na+ percentage augmented in M. truncatula and L. japonicus shoot with 50 mM NaCl. NaCl also altered the K+ concentration that decreased resulting in a decrease of K+/Na+ ratio in both legumes, more severe in M. truncatula. The results found in this study led us to conclude that the strategy against salt stress was different between these species, since amino acids and sugars accumulation can alleviate the effects of high Na+ and low K+/Na+ in M. truncatula shoot, while in L. japonicus, the transport restriction of Na+ to the shoot could be a strategy to avoid shoot Na+ toxicity. © 2008 Academic Journals Inc.