The Lily Pollen Tube: Aspects of Chemistry and Nutrition in Relation to Fine Structures

William V. Dashek


The structure of pollen grains and the growth of pollen tubes have been investigated for almost a century. However, only within the last decade has an intensive interest in pollen physiology emerged. The areas of current pollen research include: incompatibility, chemistry, metabolism, nutrition and, recently, fine structure. In addition, biologists are examining the responses exhibited by pollen tubes to chemotropic stimulation. Chemotropically active substances have been isolated from pistil tissues. To determine the mechanism by which these substances regulate the directional growth of pollen tubes, cytochemical and fine structural analyses of lily pollen tubes grown in vitro have been in progress in this laboratory. Attention has been focused on the tip of the tube which appears to be the site of perception as well as response to the chemotropic stimulus and which is the region of rapid growth, The present study attempts to relate the cytochemical findings to the fine structure of the tube. To determine the chemical composition of the ultrastructural components of the growing tip, chemical and enzymatic extractions and autoradiography at the electron microscope level have been employed. In addition, a limited exploration was made of the effects of exogenous supplies of certain of the tube constituents and related compounds on germination and tube growth in vitro. The present study also attempts to establish if changes occur in the levels of some of the chemical constituents of the tube during growth.