Involvement of jasmonates in responses of sunflower (Helianthus annuus) seedlings to moderate water stress

Jasmonates (JAs), a type of phytohormone, are involved in sensing and signaling of several environmental stresses (biotic and abiotic). Jasmonic acid (JA) has been suggested to function in plant responses to drought, because this type of stress induces expression of several genes that also respond to JA. We investigated the involvement of JA and its precursor (12-oxo-phytodienoic acid; OPDA) on seedling morphological and physiological characteristics of two sunflower (Helianthus annuus) inbred lines with contrasting responses (sensitive vs. tolerant) to water stress. Our experimental treatments were based on moderate water stress (simulated by application of mannitol 400 mM) and on blocking of JA biosynthesis (by the chemical inhibitor salicylhydroxamic acid; SHAM). Water stress resulted in reduction of primary root (PR) growth and lateral root (LR) growth, but in increased LR number. SHAM treatment increased PR length, LR number, and LR length, thus strongly affecting root architecture. Water stress had differential effects on various physiological parameters, including relative water content (RWC), stomatal conductance, and content of photosynthetic pigments (chlorophylls, carotenoids). OPDA and JA accumulation in aerial part and roots induced by water stress was reversed by combined water stress plus SHAM treatment at day 14. Our findings suggest that SHAM effectively inhibits de novo JA biosynthesis induced by water stress, and that JAs play a protective role in responses of sunflower seedlings to this stress. JAs, particularly OPDA, are highly effective signaling molecules in mediation of sunflower seedling responses to water stress.