Extracellular ATP is involved in the initiation of pollen germination and tube growth in Picea meyeri

Key message Gymnosperm pollen grains release ATP to the extracellular matrix which is essential for the initiation of pollen germination and tube growth. Abstract Extracellular ATP (eATP) is an important signaling compound involved in various processes of animal and angiosperm cells. However, the role played by eATP in gymnosperm cells remains unclear. Using a bioluminescence assay, we found that pollen grains of Picea meyeri released ATP to the extracellular matrix before germination and during tube elongation. The addition of further exogenous ATP or an apyrase inhibitor to pollen suspensions inhibited germination and pollen tube elongation. Exogenous apyrase (which hydrolyzes eATP released from pollen per se) exerted a similar inhibitory effect. Moreover, incubation of pollen suspensions with purinoceptor inhibitors prevented germination. ATP intensified the influx of Ca 2+ after germination, which was abrogated by purinoceptor inhibitors. Confocal microscopy revealed that the microfilament pattern became disorganized in pollen tubes when exposed to ATP. Together, our findings suggest that optimum concentration of eATP is essential for initiation of pollen germination, and eATP signaling regulates pollen tube growth by activating purinoceptors to increase Ca 2+ influx, thus modulating microfilament organization, which, in turn, is essential for pollen germination and tube growth. Hence, we provide a mechanistic framework for the role played by eATP in pollen germination and tube growth.