Distribution of Ca2+ in the stigma and style of Robinia pseudoacacia during pollen germination and pollen tube elongation.

We used antimonate precipitation in combination with transmission electron microscope (TEM) in order to investigate the distribution of Ca2+ in stigma and style of black locust (Robinia pseudoacacia) and its effect on pollen germination and pollen tube growth. Experimental materials were emasculated flowers of black locust with artificial pollination and non-pollination as control. Our findings were as follows. Before germination, a lot of Ca2+ was observed on and near the germinal pore. Pollination could increase the amount of Ca2+ in exudate vesicles and extracellular matrix on stigma. With the finishing of most pollen germination, the amount of Ca2+ in exudate vesicles started to decline; however, no obvious decrease occurred in extracellular matrix, indicating that the amount of Ca2+ in vesicles might promote pollen germination. A hollow stylar canal surrounded by a layer of canal cells was inside the style of black locust. Whether pollinated or not, lots of Ca2+ accumulated in the vacuoles and on cell walls of canal cells. Those Ca2+ may promote the pollen tube growth in vivo. Gradient distribution of Ca2+ in the style of black locust could not be observed. The results of this study are beneficial to revealing the distribution of Ca2+ in the stigma and style of black locust as well as other leguminous plants on pollen germination and tube elongation.