Growth of barley pollen tubes in vivo. I. Ultrastructural aspects of early tube growth in the stigmatic hair

Abstract

Barley styles were examined with transmission electron microscopy (TEM) and scanning electron microscopy (SEM) before and after pollination. Pollen tube penetration of a stigmatic hair may follow initial missing of the hair and (or) a period of growth on the hair surface. Changes in hair cell walls occur at penetration sites. Absence of demonstrable reserve carbohydrate in hair cells and styles and its abundance in pollen tubes suggest that early tube growth is largely dependent on endogenous substrates relative to its carbohydrate requirement. The pollen tube wall has an inner, somewhat reticular region and an outer, multilayered fibrillar region. Membrane-bound pollen tube vesicles containing reticular material fuse with the pollen tube membrane, contributing to development of the pollen tube wall. Vesicles and tube wall are stained by Ruthenium Red; this staining is compared with results of periodic acid–silver proteinate treatment. Two types of tube growth anomalies are reported. In the first, a tube may grow out of a hair and discharge its cytoplasm onto the hair surface through an aperture. Discharged, naked tube cytoplasm often remains appressed to hair surfaces. In the second, a tube may grow into a hair cell and discharge its contents therein through an apparently similar aperture. Vegetative nuclei appear unaltered during early pollen tube growth, but there are minor structural alterations in sperms and vegetative cell cytoplasm.