Pollen development in cotton (Gossypium hirsutum) is highly sensitive to heat exposure during the tetrad stage

The development of gametes in plants is acutely susceptible to heatwaves as brief as a few days, adversely affecting pollen maturation and reproductive success. Pollen in cotton (Gossypium hirsutum) was differentially affected when tetrad and binucleate stages were exposed to heat, revealing new insights into the interaction between heat and pollen development. Squares were tagged and exposed to 36/25 degrees C (day/night, moderate heat) or 40/30 degrees C (day/night, extreme heat) for 5 days. Mature pollen grains and leaves were collected for physiological and proteomic responses. While photosynthetic competence was not compromised even at 40 degrees C, leaf tissues became leakier. In contrast, pollen grains were markedly smaller after the tetrad stage was exposed to 40 degrees C and boll production was reduced by 65%. Sugar levels in pollen grains were elevated after exposure to heat, eliminating carbohydrate deficits as a likely cause of poor reproductive capacity. Proteomic analysis of pure pollen samples revealed a particularly high abundance of 70-kDa heat shock (Hsp70s) and cytoskeletal proteins. While short-term bursts of heat had a minor impact on leaves, male gametophyte development was profoundly damaged. Cotton acclimates to maxima of 36 degrees C at both the vegetative and reproductive stages but 5-days exposure to 40 degrees C significantly impairs reproductive development.

Automated summary

The development of plant gametes is highly sensitive to heatwaves, even lasting for just a few days, adversely affecting pollen maturation and reproductive success. Exposure to heat at 40 degrees Celsius can significantly reduce pollen size after the tetrad stage and decrease cotton boll production by 65%. Interestingly, levels of sugar in pollen grains increase after exposure to heat, ruling out carbohydrate deficits as a likely cause of poor reproductive capacity.