The activity of plasma membrane hyperpolarization-activated Ca2+ channels during pollen development of Pyrus pyrifolia

Abstract

Calcium (Ca2+) plays crucial roles in regulation of pollen tube growth. The influx of Ca2+ into the pollen tube is mediated by ion channels, and the density and activity of Ca2+ channels in pollen plasma membranes critically determines their electrical properties. In this report, using whole-cell and single-channel patch-clamping techniques, we investigated developmental changes of hyperpolarization-activated Ca2+ channel activity in pear (Pyrus pyrifolia) pollen and its relationship with pollen viability. For both pollen and pollen tubes, hyperpolarization-activated Ca2+ channels had the same conductance and cAMP sensitivity, indicating that they were the same channels. However, the Ca2+ current density in pollen tube protoplasts was greater than that in pollen protoplasts. Compared with day-3 flowers’ pollen, hyperpolarization-activated Ca2+ current density was significantly lower in day 0 and day 3 flowers’ pollen, which was consistent with the pollen germination and pollen tube growth, indicating that pollen protoplasts’ increased Ca2+ current density may have enhanced the pollen viability. During pollen tube elongation, pollen tube plasma membrane Ca2+ current density increased with increased length pollen tubes up to 300 μm. All of these results indicated that hyperpolarization-activated Ca2+ channel activity was associated with in pear pollen development and may have a causal link between Ca2+ channel activity and pollen viability.