Compatible and incompatible pollen tubes growing on detached Lilium longiflorum pistils which had been prelabeled with myoinositol-U-14C take up a portion of the label and utilize it for biosynthesis of tube wall substance. The label is transferred from pistil to pollen tubes apparently via the secretion products (exudate) of the pistil.The exudate thus appears to have a major nutritional role in pollen tube growth in vivo.Pollen tabes produced in vitro seldom achieve the length needed for fertilization in vivo. One may assume that pollen tubes growing in vivo obtain additional substances necessary for their development from the pistil. A study of the nutritional role of the pistil in pollen tube development is described in this paper. We were interested especially in the utilization of pistil material for tube wall synthesis. Myoinositol, a precursor of uronosyl and pentosyl units of cell wall polysaccharides of higher plants, is utilized by detached Lilium longiflorum pistils for cell wall polysaccharide formation and for biosynthesis of exudate, the secretion product found on the stigma and in the style canal of pollinated pistils (2). As pollen tubes grow through the style canal, they are surrounded by this exudate, which may provide the tubes with carbohydrate material for wall synthesis. To explore this possibility, we have pollinated pistils that were previously labeled with myoinositol-U-'4C and examined the growing pollen tubes for uptake and incorporation of label into tube wall substance.

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The pistil of Lilium longiflorum secretes two forms of exudate, one from the stigma surface and the other from the canal cavity. Electrophoretic studies of these exudates have revealed quantitative and qualitative differences in protein profiles. The exudatic components which are transferred to the cell wall by endoplasmic reticulum and Golgi vesicles, are stored within the cell wall of the secretive tissues and secreted from the cell walls directly. The cell wall structure of these secretive tissues differs. The canal cell wall has thick characteristic ingrowths that are supplied mainly from Golgi vesicles, while the papilla cell wall of the stigma is thinner, lacks ingrowths, and is supplied from ER vesicles.

Large quantities of intact generative cells and their protoplasts were isolated from pollen protoplasts of four liliaceous plants, and their structural features were investigated. The generative cells, liberated from the vegetative cell cytoplasm of the pollen protoplasts, were initially spindle-shaped with two long, oppositely oriented extensions, and were surrounded by two cell membranes, one on each side of a wall of uniform thickness. The generative nuclei, stained with 4',6-diamidino-2-phenylindole (DAPI), showed ellipsoidal and highly condensed chromatin, whereas the generative cell cytoplasm, whose quantity was widely different from species to species, showed no fluorescence, suggesting the absence of plastid and mitochondrial DNA, although many mitochondria were present. The isolated generative cells, which were spindle-shaped at first, became spherical in shape in vitro. Immunocytochemistry and transmission electron microscopy revealed that this change was associated with the depolymerization of an axial array of microtubules present in generative cells in situ. These results are discussed in relation to the function of the generative cell within the bicellular pollen of angiosperms.