Pistil Exudate Production and Pollen Tube Growth in Lilium longiflorum Thunb.

Exudate production in the pistil of Lilium longiflorum was studiedin relation to pollen tube growth, using scanning electron microscopy(SEM), transmission electron microscopy and light microscopy.In contrast with conventional fixation for SEM, during whichthe exudate of L. longiflorum largely washes away, the exudateremains present through freezing in case of cryo-SEM. Usingthe latter method we observed that exudate production on thestigma and in the style started before anthesis. Just underneaththe stigma the exudate was first accumulated at the top of eachsecretory cell, followed by a merging of those accumulationsas exudate production proceeded. Exudate is also produced bythe placenta. It was however not possible to determine whetherany of this fluid originated from the micropyle. Apart fromthe cell shape and the cuticle present in between the secretorycells, the ultrastructure of the secretory cells covering theplacenta was comparable to those of the stylar canal. The transferwall of the secretory cells of the placenta originated fromfusing Golgi vesicles but the endoplasmic reticulum seemed tohave an important role as well. After pollination the pollen tubes grew across the stigma andentered the style through one of the slits in the three stigmalobes. The pollen tubes grew straight downward through the styleand were covered by exudate. As the pollen tubes approachedthe ovary their growth was restricted to the areas with secretorycells. In the cavity the pollen tubes formed a bundle and theybent from this bundle in between the ovules towards the micropylarside. There they bent again to stay close to the secretory cells.After bud pollination the pollen tube growth was retarded. Laterarriving pollen tubes had a tendency to grow close to the secretorycells of the style, which resulted in a growth between thesecells and preceding pollen tubes. If there was still a littleexudate produced, it resulted in a lifting up of the pollentubes, out of the exudate. The relationship between exudateproduction and pollen tube growth is discussed. Both the speedand the guidance of the pollen tube seemed determined by theproperties of the exudate.Copyright 1994, 1999 Academic Press Cryo-scanning electron microscopy, exudate, Lilium longiflorum, lily, ovary, pollination, pollen tube growth, secretory cell, stigma, style