Research article Modulation of polyamine balance in Lotus glaber by salinity and arbuscular mycorrhiza Analı ´a I. Sannazzaro a , Mariela Echeverrı ´a a , Edgardo O. Alberto ´ a , Oscar A. Ruiz a , Ana B. Mene ´ndez a,b, * a Instituto Tecnolo ´gico de Chascomu ´s (IIB-INTECH), CONICET, 1428 Buenos Aires, Argentina b University of Buenos Aires, Biodiversity and Experimental Biology, DBBE, Piso 4, PAB II, CIUDAD UNIV, 1428 Buenos Aires, Argentina Received 22 March 2006 Available online 28 December 2006 Abstract In this work we investigated the involvement of Glomus intraradices in the regulation of plant growth, polyamines and proline levels of two Lotus glaber genotypes differing in salt tolerance, after longterm exposure to saline stress. The experiment consisted of a randomized block design with three factors: (1) mycorrhizal treatments (with or without AM fungus); (2) two salinity levels of 0 and 200 mM NaCl; and (3) L. glaber genotype. Experiments were performed using stem cuttings derived from L. glaber individuals representing a natural population from saline lowlands. One of the most relevant results was the higher content of total free polyamines in mycorrhized plants compared to non-AM ones. Since polyamines have been proposed as candidates for the regulation of root development under saline situations, it is possible that AM plants (which contained higher polyamine levels and showed improved root growth) were better shaped to cope with salt stress. Colonization by G. intraradices also increased (Spd þ Spm)/Put ratio in L. glaber roots. Interestingly, such increment in salt stressed AM plants of the sensitive genotype, was even higher than that produced by salinization or AM symbiosis separately. On the other hand, salinity but not mycorrhizal colonization influenced proline levels in both L. glaber genotypes since high proline accumulation was observed in both geno- types under salt stress conditions. Our results suggest that modulation of polyamine pools can be one of the mechanisms used by AM fungi to improve L. glaber adaptation to saline soils. Proline accumulation in response to salt stress is a good indicator of stress perception and our results suggest that it could be used as such among L. glaber genotypes differing in salt stress tolerance. Ó 2006 Elsevier Masson SAS. All rights reserved. Keywords: Lotus; Salinity; Arbuscular mycorrhiza; Polyamine; Proline 1. Introduction Lotus glaber Mill. (narrow-leaf trefoil; syn L. tenuis Waldst et Kit. Ex Wild.) is a glycophytic, perennial legume of Euro- pean origin that occurs frequently in saline habitats. Previous observations indicate the occurrence of genotypes highly tolerant to salinity in different populations of L. glaber [34], which is the best-adapted forage species used for cattle pro- duction in the Salado River basin (9  10 6 Ha). Mendoza and Pagani [33] showed this species has a high dependence of arbuscular mycorrhizal (AM) colonization in P-deficient soils. More recently, highly diverse AM fungal colonization patterns in roots of L. glaber were found in saline fields [43]. Several researchers have shown AM fungi can protect the plant against adverse effects of salinity. For instance, salt tolerance of banana plants was enhanced in the presence of Glomus isolates [52]. In cotton, improvement of plant growth, * Corresponding author. University of Buenos Aires, Biodiversity and Ex- perimental Biology, DBBE, Piso 4, PAB II, CIUDAD UNIV, 1428 Buenos Aires, Argentina. Tel.: þ54 11 4542 7396. E-mail address: anamen@bg.fcen.uba.ar (A.B. Mene ´ndez). 0981-9428/$ - see front matter Ó 2006 Elsevier Masson SAS. All rights reserved. doi:10.1016/j.plaphy.2006.12.008 Plant Physiology and Biochemistry 45 (2007) 39e46 www.elsevier.com/locate/plaphy