Heat stress tolerance studies in callus cultures of Gossypium hirsutum L. cv. Acala SJ2.

Heat stress tolerance was studied in cotton (Gossypium hirsutum L.). Callus cultures of two cotton cultivars viz., Coker 312 (cotyledonary-derived) an d Acala SJ2 (leaf and petiole-derived) showed significant stimulation in gr owth at stress temperature of 44 degrees C for 2 hours after 2 days of pre- incubation at 28 degrees C followed by 26 days of incubation at 28 degrees C. Reduction in callus growth at 47 and 50 degrees C, was higher in Acala S J2 compared to Coker 312. Petiole-derived callus exhibited more heat tolera nce than leaf-derived callus. At 50 degrees C callus tissue turned brown. T he relative significance of increases in growth rate at 44 degrees C and dr astic reduction in growth rate at temperatures above 44 degrees C is discus sed in the light of heat induced production of proline, glycinebetaine, hea t-shock proteins and killing of some viruses which have been reported to pr otect plant tissues from damage caused by heat stress.