Diverse response of three sweetpotato cultivars to abiotic stresses and adjustment of free polyamine levels

THREE SWEETPOTATO cultivars, Abees, Mogamba and Santo Amaro, were subjected to moderate (-0.5MPa) and severe drought stress (-2.5MPa) or to salt treatments up to 200mM NaCl, respectively. Patterns of leaf polyamine contents were analyzed to verify whether these metabolites could be used as early traits of tolerance. Physiological parameters like leaf relative water content, total chlorophyll content, leaf electron conductance, stomata resistance and transpiration rate were used to indicate stress conditions of the plants and growth parameters were applied to identify the level of tolerance among the used cultivars. In all three cultivars, drought led to an increase of putrescine (Put) and decrease of spermidine (Spd) concentrations while spermine (Spm) was decreased only in the Santo Amaro cultivar. The most tolerant cultivar was Mogamba followed by Santo Amaro and Abees. However, this descending order was not reflected by the specific changes in polyamine levels but it is altered under drought as well as under salinity in both sensitive and tolerant cultivars. More investigations are needed to figure out if polyamines behave as a response of stress and/or a protective mechanism.