Effect of salt stress on polyamine metabolism in two bean cultivars

"In agricultural areas, salinity affects plant growth, development and productivity, causing loss of economically important crops. Nitrogenderived compounds such as polyamines (PAs) are differentially accumulated in diverse plants species in response to salinity. PA and chlorophyll (Chl) contents, as well as water potential (w), were assessed in leaves of two common bean cultivars subjected to salt stress for one and seven days; these bean cultivars, ‘Pinto Villa’ and ‘Canario 60’, differ in their drought tolerance phenotype. Salt stress induced a phenotypic behaviour similar to that of drought in which the sensitive ‘Canario 60’ showed a pronounced decrease in w, in comparison to the tolerant ‘Pinto Villa’. Regarding PAs, after the first day of treatment, the levels of all of them (putrescine (Put), spermidine (Spd) and spermine (Spm)) increased in tolerant cultivar (‘Pinto Villa’) while in the sensitive one (‘Canario 60’) the levels of Spd and Spm only increased at 400 mM NaCl. At the seventh day, the tolerant cultivar showed an accumulation of Spm at the higher concentrations of NaCl used (150 and 400 mM), whereas a decrease in PA content occurred in the sensitive cultivar at all concentrations assayed. Furthermore, the effect of salt stress on the expression of the main genes involved in PA biosynthesis, including a new S-adenosylmethionine decarboxylase (SAMDC) gene identified in this work, was analysed. It is suggested that Spm accumulation in ‘Pinto Villa’ might be part of the mechanism conferring salt tolerance.