LIPIDS IN THE STIGMATIC SECRETION OF DATUR STRAMONIUM L (SOLANACEAE)

The chemical nature of secretion by the stigma and transmitting tissue in Datura stramonium was studied by light microscopy using Sudan black B, Coomasie brilliant blue (CBB), Toluidine blue, Safranin, and PAS. The stigmatic secretion reacted positively for lipids. During development, stigmatic cells became separated and intracellular lipids were transferred to intercellular spaces where they gradually migrated to the stigma surface. Excretion of the lipids was a continuous process and persisted during maturity and even in pollinated and opened flowers (post-pollinated). Lipid secretion was associated with cell autolysis in papillae and in secretory cells of the stigma, particularly in superficially located ones. The transmitting tissue cells also showed glandular activity with the release of a polysaccharide rich substance. The pollen germination and pollen tube growth seem to be closely dependent upon these secretions in Datura stramonium. The different nature of the secretion of the stigma (lipids) versus secretion of the transmitting tissue of the style (carbohydrates), supports the hypothesis that the pollen tube metabolism changes from autotrophic to the heterotrophic upon entering the transmitting tissue from the stigma surface.