Polyamine catabolism influences antioxidative defense mechanism in shoots and roots of five wheat genotypes under high temperature stress

Effect of high temperature stress on polyamine catabolism and antioxidant enzyme activity in relation to glutathione, ascorbate and proline accumulation was studied in five wheat (Triticum aestivum L.) genotypes (differently susceptible to temperature stress). High temperature significantly increased the activities of superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR) and glutathione S-transferase (GST) in shoots of all genotypes. Higher activities of GPX in C 306, C 273 and APX in PBW 550, PBW 343 and PBW 534 demonstrate their important role in scavenging H₂O₂. Conversely, high temperature stress led to a significant decline in SOD, CAT, APX and GPX activities of roots with a subsequent increase in diamine oxidase (DAO) and polyamine oxidase (PAO) activities especially in PBW 550 and PBW 343. The concentration of ascorbic acid declined with the imposition of heat stress, however, polyamines responded to high temperature stress by increasing spermidine and spermine levels and decreasing putrescine levels. After exposure to high temperature, proline accumulation was significantly decreased in roots and increased in shoots though maximum concentration was achieved in C 306 genotype. Apparently, the wheat seedlings respond to high temperature mediated increase in reactive oxygen species (ROS) production by altering antioxidative defense mechanism and polyamine catabolism though differentially in five wheat genotypes. Among five genotypes studied, C 306 and C 273 seem to be better protected against temperature stress. The results suggested that shoots were more resistant against the destructive effects of ROS as is indicated by low levels of thiobarbituric acid reactive substances under high temperature stress.