Pollen Tube Development and Characteristics of the Protein Emission in Conifers

When ripe, viable pollen of Pinus contorta, Pinus nigra, Picea sitchensis, Abies alba and Cedrus deodara is germinated on a suitable artificial substrate, the process of pollen tube growth begins 12–36 h later, according to the species. The tube emerges at the leptoma, a structurally specialized site in the pollen wall, and the early tube wall is continuous with the two microfibrillar intine strata within the grain. Later in pollen tube development, when cytoplasmic zonation has been established, only the inner of these two wall layers is differentiated. Cytochemical methods show that, during hydration and throughout the period of tube growth in culture, proteins are released from the pollen grains; before germination most conspicuously from the leptoma, subsequently from the tube itself. The emission contains a number of hydrolytic enzymes and a non-catalytic moiety. Gel-electrofocusing reveals that the hydrolases released from germinating Pinus contorta pollen include several acid phosphatase and esterase isozymes, and that there are differences between the composition of the emission and the spectrum of soluble proteins extracted from the pollen grains before germination. Analysis by immunodiffusion demonstrates that two components with antigenic characteristics present in the quiescent pollen grains are represented in the emission. The possible utility of the released components in the biology of conifer reproduction is discussed.