Ca²⁺ dynamics in a pollen grain and papilla cell during pollination of Arabidopsis thaliana

Abstract

In order to examine the role of Ca²⁺ during pollination, we expressed yellow cameleon, a Ca²⁺ indicator based on green fluorescent protein (GFP), in the pollen grains and papilla cells of Arabidopsis thaliana and monitored Ca²⁺ dynamics during pollination. In the pollen grain, [Ca²⁺]_cyt increased at the potential germination site soon after hydration and remained augmented until germination. As in previous in vitro germination studies, [Ca²⁺]_cyt oscillations were observed in the tip region of the growing pollen tube, but the oscillation frequency was faster and [Ca²⁺]_cyt was higher than had been observed in vitro. In the pollinated papilla cell, remarkable increases in [Ca²⁺]_cyt occurred three times in succession, just under the site of pollen-grain attachment. [Ca²⁺]_cyt increased first soon after pollen hydration, with a second increase occurring after pollen protrusion. The third and most remarkable [Ca²⁺]_cyt increase took place when the pollen tube penetrated into the papilla cell wall.