THE BIOCHEMICAL RESPONSES OF 6 COTTON CULTIVARS TO HEAT-STRESS

The response of cotton leaves to heat stress was investigated using triphenyltetrazolium chloride in a viability assay, comparing absorbances at 485 nm of control (29 degrees C) and acclimated (40 degrees C) plants. The cotton cultivars used were Selati, Nik 2, Letaba, Delta Pine Acala 90, Acala 1517-70 and Acala OR3. Results indicated that this assay can be used as a measurement of heat tolerance in cotton. The incorporation of C-14-protein hydrolysate into proteins during heat stress was also examined. The efficiency of protein synthesis increased from control treatment (29 degrees C) to moderate stress (40 degrees C) and decreased during a severe stress (43 degrees C). A protein-DNA binding study indicated that hear shock proteins visualized in this study do not have a regulatory function. Letaba performed as heat-tolerant and Acala 1517-70 and Selati as heat-sensitive cultivars. The proven thermotolerance for these cultivars is nor known, but our findings correlate with yield data observed in hot and dry areas.