Putrescine modifies the pollen tube growth of tea (Camellia sinensis) by affecting actin organization and cell wall structure

The aim of the current study was to examine the effect of different exogenous putrescine concentrations (200, 400, 600, and 800 mu M) on the tea pollen performance. It was shown that putrescine has a dose-dependent effect on pollen performance. Results exhibited that pollen germination and tube elongation were induced by 200 and 400 mu M putrescine treatment, especially, 400 mu M putrescine-enhanced pollen performance. However, pollen performance was inhibited by higher concentrations of putrescine. Putrescine concentrations above 400 mu M changed the actin filament distribution in pollen tubes by affecting the distribution of sucrose synthase enzyme. Alterations of the distribution on sucrose synthase enzyme also caused the alterations in the dispersion of cellulose and callose in the cell wall, and morphological alterations such as balloon-shaped and snake-shaped pollen tube tip accompanied them. Moreover, putrescine concentrations above 400 mu M caused a decrease of ROS level in apex and led to chromatin condensation of the generative nucleus. In conclusion, exogenous putrescine application can be used as a pollen performance enhancer at low concentrations while the high concentrations cause adverse effects reducing fertilization success.