Abstract
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.
Highlights
Pollen is a highly specialized haploid organism representing the crucial stage of the life cycle in seed plants; polar growth is the most studied feature of this life form
Male gametophytes of angiosperms and conifers correspond in general terms to a similar structure plan but typical conifer pollen exhibits a wide range of features [3,4], among which are: a solid pollen wall, ability for bipolar germination [5] and different shape and size of the apical compartment, as well as the trajectory of organelle movement in pollen tubes [6,7,8,9], a rather sloping calcium gradient and membrane potential gradient [10,11], participation of microtubules in cyclosis [12] and specific arrangement of cell wall layers [13]
The dynamics of oxygen consumption in Picea pungens is different from that reported previously for tobacco [15]: instead of a sharp rise in the respiration level with saturation, we observe a curve with a maximum at the tube exit point (9 h)
Summary
Pollen is a highly specialized haploid organism representing the crucial stage of the life cycle in seed plants; polar growth is the most studied feature of this life form. Another important feature of pollen is physiological dormancy which is typical for the majority of species, both angiosperms and gymnosperms [1]. Male gametophytes of angiosperms and conifers correspond in general terms to a similar structure plan but typical conifer pollen exhibits a wide range of features [3,4], among which are: a solid pollen wall, ability for bipolar germination [5] and different shape and size of the apical compartment, as well as the trajectory of organelle movement in pollen tubes [6,7,8,9], a rather sloping calcium gradient and membrane potential gradient [10,11], participation of microtubules in cyclosis [12] and specific arrangement of cell wall layers [13].
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