Directional secretion by the Golgi bodies in maize root cells.

In the root caps of many plant species, the outer few layers of cells secrete a polysaccharide mucus. This mucus probably derives from the breakdown of the starch in the amyloplasts. Is then fed through the Golgi bodies and, in vesicular form, reaches and is discharged through the plasmamembrane. Once in the wall it accumulates briefly between the plasmalemma and the wall and finally passes through the wall to the outside of the root. Its function is probably to facilitate the passage of the root through the soil by lubricating the movement of the root tip around and between the soil particles. Our observations show that the pattern of this discharge is not random, but that the mucus accumulates only against that wall which is or will be the outer tangential. The implication of this directional movement and possible suggestions for its control are discussed.