Pollen tube growth is affected by exogenous hormones and correlated with hormone changes in styles in Torenia fournieri L.

In the present report, we described the effects of indole-3-acetic acid (IAA), zeatin (ZT), gibberellin (GA(3)), and abscisic acid (ABA) on in vitro pollen germination and pollen tube growth in Torenia fournieri L. The results showed that IAA and GA(3) stimulated in vitro pollen tube growth, ABA inhibited pollen tube growth, and ZT had no significant effect on the process. The stimulating effect of exogenous IAA was particularly distinct, and led to synchronous growth of straighter and more slender pollen tubes compared with the controls. However, no significant changes were found in the germination of the treated pollen. The auxin efflux inhibitor, 10 mu M 1-N-naphthylphthalamic acid (NPA), was also found to stimulate pollen tube growth. We measured the content of hormones (free IAA, ZT, GA(3), and ABA) in the stigmas and styles before and after pollination. The hormone contents of stigmas measured 0.5 h after pollination (0.5 HAP) showed that ABA content decreased, whereas the content of IAA, ZT, or GA(3) did not change significantly. The hormone level in pollinated styles (4 HAP) when pollen tubes had grown into the middle part of style was characterized by an increase in free IAA and GA(3) and a decrease in ABA, which was in agreement with the results that IAA and GA(3) promoted but ABA inhibited pollen tube growth in vitro. Furthermore, the change of IAA level in styles was most notable, which was accordant to the fact that auxin stimulated significantly pollen tube growth in vitro. Using immunoenzyme and immunogold labeling techniques and an anti-IAA monoclonal antibody, we confirmed that free IAA was present throughout style tissues, and distributed in the nucleus and cytoplasm of style cells. All these results suggested that hormones, especially IAA, play important roles in pollen tube growth of T. fournieri.