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Proline level in floral parts and its role in protecting pollen from high temperature stress in groundnut

The effects of high temperature on the proline contents in the floral parts, in vitro pollen germination, pollen vigor and role of proline in protecting pollen from heat stress in three groundnut (Arachis hypogaea L.) genotypes (ICG 1236, ICGS 44 and Chico) differing in their sensitivity to high temperature were examined. The plants, raised in a glasshouse maintained at 25/25 °C day/night temperature (LT), were exposed to 35/30 °C (HT) after the appearance of 3 r d leaf. The most sensitive floral bud stage to HT was found to be 5 days before anthesis (DBA). Anthers of ICG 1236 (relatively HT tolerant) accumulates more proline at 3 and 5 DBA, while it decreases in susceptible genotypes (ICGS 44 and Chico) at these stages under HT as compared to LT. However, a decrease in proline concentration in anthers and corresponding increase in pollen were observed just before anthesis under HT in ICG 1236, but not in ICGS 44. HT did not affect the in vitro pollen germination (PG), but rate of pollen tube growth (PTG) were reduced in susceptible genotypes. Further, when pollens obtained from LT were heat stressed for 40 or 45 °C for 30 minutes on a germination media, the PG and PTG were reduced in all the genotypes, with minimum reduction in ICG 1236. Addition of proline (100-125 pmol) in the incubation media of sensitive genotypes neutralized the effects of heat stress. It is concluded that heat injury during floral development of sensitive genotypes may be due to the decline in proline concentration during the early floral bud development stage and inhibition in the transportation of proline from anther walls to pollen.