Dynamics of Pollen Activation and the Role of H+-ATPase in Pollen Germination in Blue Spruce (Picea pungens).

Pollen is a highly specialized structure for sexual plant reproduction. Early stages of pollen germination require the transition from dormant state to active metabolism. In particular, an important role during this early phase of angiosperm pollen germination is played by H+-ATPase. Very little is known about pollen activation in gymnosperm species, and information on the involvement of H+-ATPase is lacking. We tracked four indicators characterizing the physiological state of pollen: membrane potential, intracellular pH, anion efflux and oxygen uptake, in order to monitor the dynamics of activation in Picea pungens. Based on pH dynamics during activation, we assumed the important role of H+-ATPase in spruce pollen germination. Indeed, germination was severely suppressed by P-type ATPase inhibitor orthovanadate. In spruce pollen tubes, a pronounced pH gradient with a maximum in the apical zone was found, which was different from the pollen tubes of flowering plants. Using orthovanadate and fusicoccin, we found that the proton pump is largely responsible for maintaining the gradient. Immunolocalization of the enzyme in pollen tubes showed that the distribution of H+-ATPase generally coincides with the shape of the pH gradient: its maximum accumulation is observed in the apical zone.