Fine Structure of Pollen Tubes Grown in Vitro
The growth in pollen tubes is exclusively restricted to the tip. Cytochemical analysis reveals the pollen tip zone to be rich in RNA and protein. This zone has numerous vesicles and an elaborate network of smooth membranes. The vesicles appear to rise from the ends of dictyosome cisternae. They coalesce with one another and ultimately contribute their membrane and contents to the compartmented cap covering the growth zone at the tip. The cap and the vesicles contain pectin and the RNA resides in the smooth membranes.
In the region behind the tip the tube contains those organelles present in pollen before germination, as well as numerous amyloplasts. The tube wall is thin (tubes growing in pistil have complex wall). Cellulose is the primary wall component. The cytoplasm of pollen tubes growing in vitro lack microtubules. EM shows that the generative cell is surrounded by its own distinct wall and the cytoplasm is different from the grain proper. It contains a small number of poorly developed organelles which possess little storage material.