ACCUMULATION OF FREE PROLINE IN SORGHUM (SORGHUM-BICOLOR) POLLEN

Suboptimal temperatures cause grain yield reductions generally associa ted with low seed-set in sorghum [Sorghum bicolor (L.) Moench]. Low pr oline concentration in pollen has been associated with cold-induced ma le sterility. This study was done to (i) determine free proline concen trations in grain sorghum pollen after low temperature exposure, (ii) determine the relationship between seed-set and proline concentration in pollen, and (iii) determine the association of proline concentratio n in pollen with grain yield in sorghums of different maturity. Eleven sorghum genotypes, grown in a greenhouse at 27/22 degrees C (day/nigh t) until the early boot stage were transferred to 20/10 degrees C in g rowth chamber until physiological maturity. Concentration of proline i n pollen was determined at anthesis and related to seed number and gra in yield. Proline concentrations in pollen increased from 19 to 36 mu g . mg(-1) fresh wt. to 30 to 49 mu g . mg(-1) fresh wt. at low temper atures. Seed number and grain yield were reduced by low temperature in most of the genotypes. Percent seed-set in male sterile lines was sig nificantly correlated (r = 0.45*) with free proline concentrations in the pollen from 13 fertile hybrids grown under cold or control condit ions. Higher concentrations of proline in pollen under cool and also c ontrol temperatures seemingly contribute to greater pollen viability i n grain sorghum. In 21 sorghum hybrids grown under control temperature s, seed number per panicle was found correlated (r = 0.42) to free pr oline concentrations in pollen. Genotypic differences in pollen prolin e concentration were not associated with differences between maturity groups.