Heterotrimeric G‐protein participation in Arabidopsis pollen germination through modulation of a plasmamembrane hyperpolarization‐activated Ca2+‐permeable channel

Summary •  The role of heterotrimeric G proteins in pollen germination and tube growth was investigated using Arabidopsis thaliana plants in which the gene (GPA) encoding the G-protein a subunit (Ga) was null or overexpressed. •  Pollen germination, free cytosolic calcium concentration ([Ca2+]cyt) and Ca2+ channel activity in the plasma membrane (PM) of pollen cells were investigated. •  Results showed that, compared with pollen grains of the wild type (ecotype Wassilewskija, ws), in vitro germinated pollen of Ga null mutants (gpa1-1 and gpa1-2) had lower germination percentages and shorter pollen tubes, while pollen from Ga overexpression lines (wGa and cGa) had higher germination percentages and longer pollen tubes. Compared with ws pollen cells, [Ca2+]cyt was lower in gpa1-1 and gpa1-2 and higher in wGa and cGa. In whole-cell patch clamp recordings, a hyperpolarization-activated Ca2+-permeable conductance was identified in the PM of pollen protoplasts. The conductance was suppressed by trivalent cations but insensitive to organic blockers; its permeability to divalent cations was Ba2+ > Ca2+ > Mg2+ > Sr2+ > Mn2+. The activity of the Ca2+-permeable channel conductance was down-regulated in pollen protoplasts of gpa1-1 and gpa1-2, and up-regulated in wGa and cGa. •  The results suggest that Ga may participate in pollen germination through modulation of the hyperpolarization-activated Ca2+ channel in the PM of pollen cells.