Syringaldazine Peroxidase Stimulates Lignification by Enhancing Polyamine Catabolism in Wheat during Heat and Drought Stress

Six wheat cultivars, namely PBW 343, PBW 550 (stress susceptible), PBW 621, PBW 175 (drought tolerant), C 306 and HD 2967 (heat tolerant), were used in this study to evaluate the effect of heat and drought stress on the activities of peroxidases (POXs), diamine oxidase (DAO), polyamine oxidase (PAO) and arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) in relation to contents of polyamines (PAs), lipid peroxide and lignin. High temperature (HT) elevated activities of syringaldazine peroxidase (SPX), guaiacol peroxidase (GPX) and coniferyl alcohol peroxidase (CPX) in heat tolerant cultivars while, drought stress accentuated ADC/ODC activities in drought tolerant cultivars. Both heat and drought stress enhanced activities of DAO and PAO alongwith contents of H2O2 in PBW 175 and C 306. Amongst studied POXs, SPX activity was relatively more and coincided well with lignin content under HT stress while, the levels of ADC/ODC paralleled with putrescine and spermidine contents under drought stress. Higher build up of thiobarbituric acid reactive substances in cultivars PBW 343 and PBW 550 indicated their membrane instability during both the stresses. Our results revealed that SPX mediated lignification leading to higher cell wall rigidity under heat stress and drought increased PAs involved in ROS scavenging due to presence of positive charges which can bind strongly to the negative charges in cellular components such as proteins and phospholipids and thereby stabilize the membranes under stress conditions.