Relationship between phytohormones and male sterility in thermo-photo-sensitive genic male sterile (TGMS) wheat

Fertility alternation normally occurs in a novel type of thermo-photo-sensitive genic male sterile (TGMS) wheat whose recessive genes in the nucleus are expressed as virtually complete sterility under lower temperature and shorter daylight conditions, but as normal fertility under higher temperature and longer daylight conditions during the developmental period from meiosis of pollen mother cells (PMCs) to the early mononucleate stage of microsporogenesis. In order to provide more information about the mechanism(s) of fertility alternation in TGMS wheat, the relationship between fertility alternation and levels of phytohormones was analyzed by endogenous hormone quantification and exogenous hormone treatments in the present research. Sown at an earlier date with a relatively low temperature and short daylight, TGMS wheat was male sterile phenotypically. Pollen abortion mainly occurred at the mononucleate to bi-nucleate stages of microsporogenesis and pollen abortion was mainly of the spherical type. Levels of endogenous indole-3-acetic acid (IAA), abscisic acid (ABA) and gibberellic acid (GA(3)) in the anthers were at lower levels, and zeatin riboside (ZR) was higher. Sown at a later date, when the temperature during the critical period for fertility alternation was relatively high and the daylight was long, TGMS wheat was almost as fertile as the normal genotype and the contents of endogenous IAA, ABA and GA(3) in anthers were at higher levels, and the content of ZR was at a lower level. At the critical period for fertility alternation, treatments with exogenous IAA, ABA, GA(3) or aminoethoxy vinylglycine (AVG), an inhibitor of ethylene biosynthesis, decreased the frequency of sterile pollen grains and increased the frequency of self-pollinated fertile florets. Treatment with exogenous 2-chloroethyl phosphonic acid (CEPA), a releaser of ethylene, increased the frequency of sterile pollen grains and decreased the frequency of self-pollinated fertile florets. It was thus suggested that the fertility alternation of TGMS wheat was closely related to levels of phytohormones in the anthers, and changes of endogenous hormone levels were among the important factors responsible for the fertility alternation of TGMS wheat.