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

Abstract

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 α subunit (G α ) was null or overexpressed.• Pollen germination, free cytosolic calcium concentration ([Ca 2 + ] cyt ) and Ca 2 + 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 G α null mutants ( gpa1-1 and gpa1-2 ) had lower germination percentages and shorter pollen tubes, while pollen from G α overexpression lines (wG α and cG α ) had higher germination percentages and longer pollen tubes. Compared with ws pollen cells, [Ca 2 + ] cyt was lower in gpa1-1 and gpa1-2 and higher in wG α and cG α . In whole-cell patch clamp recordings, a hyperpolarization-activated Ca 2 + -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 Ba 2 + > Ca 2 + > Mg 2 + > Sr 2 + > Mn 2 + . The activity of the Ca 2 + -permeable channel conductance was down-regulated in pollen protoplasts of gpa1-1 and gpa1-2 , and up-regulated in wG α and cG α .• The results suggest that G α may participate in pollen germination through modulation of the hyperpolarization-activated Ca 2 + channel in the PM of pollen cells.

Plant extracellular ATP signalling by plasma membrane NADPH oxidase and Ca2+channels

“…channel conductance (Figure 2a), similar to those characterized previously in this and other cell types, including guard cells (Pei et al, 2000;Foreman et al, 2003;Demidchik et al, 2007;Wu et al, 2007b). An increase in inwardly-directed current was observed 1-3 min after the addition of ATP, and was evident over the physiological voltage range for this cell type (Maathuis and Sanders, 1993).…”

The Apical Actin Fringe Contributes to Localized Cell Wall Deposition and Polarized Growth in the Lily Pollen Tube

“…Given the tip-focused Ca 2+ gradient, which will have profound effects on the apical actin, possibly through specific actin-binding proteins such as villin/gelsolin Zhang et al, 2010a;Qu et al, 2013), it becomes apparent that any mechanism that modulates intracellular Ca 2+ could induce a cascade of events crucial to the targeted delivery of vesicles and polarized growth. Candidate Ca 2+ channels include those that are activated by mechanical forces or stretch (Dutta and Robinson, 2004), by changes in the membrane potential (Wang et al, 2004;Shang et al, 2005;Qu et al, 2007;Wu et al, 2007Wu et al, , 2010, or by the presence of a ligand Figure 9. KCN and BFA affect both cell wall deposition and actin structure.…”

Pollen Tube Growth Regulation by Free Anions Depends on the Interaction between the Anion Channel SLAH3 and Calcium-Dependent Protein Kinases CPK2 and CPK20

“…A difference in electric polarization of the plasma membrane of growing pollen tubes has recently been reported (Breygina et al, 2009) using spectroscopic techniques and could explain the differential channel activity of voltage-dependent K + and Ca 2+ channels, reported to exist in the pollen tube plasma membrane (Fan et al, 2001;Mouline et al, 2002;Wang et al, 2004;Shang et al, 2005;Qu et al, 2007;Wu et al, 2007). This is a tantalizing hypothesis, because it would permit the generation of the biophysical conditions necessary for differential plasma membrane polarization domains, a mechanism we are currently trying to address.…”