Heat Injury During Floral Development in Cowpea (Vigna Unguiculata, Fabaceae)

Abstract

High night temperatures during floral development induce male sterility in cowpea (Vigna unguiculata [L.] Walp.). The objectives of this study were to determine: the possible causes of the male sterility; the stage of floral development when damage due to heat stress occurs; and whether specific tissues are damaged during the period of sensitivity to heat. Plants were grown under controlled temperatures in both greenhouses and growth chambers in separate experiments. Floral development was normal under a night temperature of 20 C, whereas flowers developed under high night temperature (30 C) set no pods due to low pollen viability and anther indehiscence. Anthers developed under 33/30 C day/night temperatures did not exhibit endothecial formation, whereas anthers developed under 33/20 C day/night temperatures exhibited normal development of the endothecial layer. Reciprocal transfers of plants between chambers with high or optimum night temperature demonstrated that the stage of floral development most sensitive to heat stress occurs 9 to 7 d before anthesis. Anthers developed under either optimal or high night temperatures were compared cytologically. Development was similar through meiosis, but after tetrad release, which occurred 8 d before anthesis, the tapetal layer degenerated prematurely under high night temperature. Premature degeneration of the tapetal layer and lack of endothecial development may be responsible for the low pollen viability, low anther dehiscence, and low pod set under high night temperatures.

Climate Change and Heat Stress Tolerance in Chickpea

“…In chickpea, development of male (pollen/anther) and female (stigma, style, and ovary) reproductive organs is most sensitive to abiotic stress [52]. High temperature has a particularly detrimental effect on two stages of pollen development: meiosis in the microspore mother cell and mature microspores [53][54][55]. Heat stress could also affect the development of tapetal cells, resulting in degeneration and premature development of pollen in the case of cowpea and snapbean [54,55].…”

“…High temperature has a particularly detrimental effect on two stages of pollen development: meiosis in the microspore mother cell and mature microspores [53][54][55]. Heat stress could also affect the development of tapetal cells, resulting in degeneration and premature development of pollen in the case of cowpea and snapbean [54,55]. Pollen germination in chickpea is optimal at 25 C and germination is reduced under heat stress conditions, leading to reduced fertilization [56,57].…”

Breeding Cowpea for Future Climates

“…Artificial pollination studies demonstrated that pistil viability was not affected by high night temperatures (Warrag and Hall 1983). Reciprocal transfers of plants between growth chambers with high or optimal night temperatures demonstrated that the stage of floral development most sensitive to heat stress occurred 9-7 days before anthesis (Ahmed et al 1992). This is after meiosis, which occurs 11 days before anthesis and about the same time that the tetrads are released from the microspore mother cell sac (Warrag and Hall 1984b;Ahmed et al 1992;Mutters and Hall 1992).…”

“…Reciprocal transfers of plants between growth chambers with high or optimal night temperatures demonstrated that the stage of floral development most sensitive to heat stress occurred 9-7 days before anthesis (Ahmed et al 1992). This is after meiosis, which occurs 11 days before anthesis and about the same time that the tetrads are released from the microspore mother cell sac (Warrag and Hall 1984b;Ahmed et al 1992;Mutters and Hall 1992). Premature degeneration of tapetal tissue and lack of endothecium formation were observed, which could have been responsible for the low pollen viability, low anther dehiscence, and low pod-set under high night temperatures (Ahmed et al 1992).…”

“…This is after meiosis, which occurs 11 days before anthesis and about the same time that the tetrads are released from the microspore mother cell sac (Warrag and Hall 1984b;Ahmed et al 1992;Mutters and Hall 1992). Premature degeneration of tapetal tissue and lack of endothecium formation were observed, which could have been responsible for the low pollen viability, low anther dehiscence, and low pod-set under high night temperatures (Ahmed et al 1992). Tapetal tissue plays an important role in providing nutrients to developing pollen grains and its premature degeneration could thereby stunt pollen development.…”