To determine the relationship between female sterility of Pinus tabulaeformis Carr. and plant hormones, content changes of several endogenous plant hormones in a female-sterile clone and a normal clone were analyzed during the key period of female gametophyte abortion in mutant clones. The change of ABA content showed a similar pattern between normal and mutant clones, but the ABA content of the mutant clone was always much higher than that of the normal clone. In the normal clone, the IAA content decreased significantly at the early stage of the period and reached its minimum during the first ten days of April and stabilized thereafter. The endogenous ZR levels increased sharply at the early stages and reached a maximum in the middle of April, then decreased dramatically. The IAA and ZR contents of the mutant clone did not change perceptively through the entire period. We conclude that the high levels of ABA and the deficit of IAA and ZR may be the reasons of female gametophyte abortion in the female-sterile clones of P. tabulaeformis.
