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

Wu, Yansheng; Xu, Xiaodong; Li, Sujuan; Liu, Ting; Ma, Ligeng; Shang, Zhonglin

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

2007

• 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.

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