NONOPTIMAL GROWTH TEMPERATURES AND ANTIOXIDANTS IN THE LEAVES OF SORGHUM-BICOLOR (L.) MOENCH - I - LONG-TERM ACCLIMATION

The foliar antioxidant status and the photosynthetic capacity were com pared in two sorghum [Sorghum bicolor (L.) Moench] cultivars of differ ent agroclimatic provenance, namely Aralba and ICSV 112, which were gr own at near-optimal, 27+/-0.3 degrees C, suboptimal, 17+/-0.4 degrees C, or supraoptimal, 37+/-0.1 degrees C, temperatures. Both non-optimal growth temperatures, although unable to cause visible symptoms of str ess, affected gas exchange parameters and antioxidant levels both in c v. Aralba and in cv. ICSV 112. Compared to controls, plants grown at 1 7+/-0.4 degrees C or at 37+/-0.1 degrees C had higher contents of phot osynthetic pigment, an increased size of the ascorbate pool and an enh anced monodehydroascorbate reductase activity. On the other hand, subo ptimal and supraoptimal growth temperatures, respectively, decreased a nd increased the glutathione pool and on the capacities of ascorbate-a nd guaiacol peroxidases, and of catalase. In cv. Aralba, but not in cv . ICSV 112, the expression of superoxide dismutase, in terms of both e nzymic activity and mRNA transcripts abundance, was downregulated by t he growth at non-optimal temperature. Adaptation to nonoptimal growth temperature might involve antioxidant responses which could be differe nt in part from those evoked by genuine temperature stress.