Fine Structure and Formation of Cell Wall of Developing Cotton Fiber

Abstract

In the stage of elongation growth of cotton fiber, there is a plenty of amoeboid plastids, lipid droplets and rough-surfaced endoplasmic reticulum (RER) in the cytoplasm. On the other hand, in the stage of secondary wall thickening, cytoplasm is poor in amoeboid plastids and lipid droplets, but rich in smooth- and rough-surfaced ER. The fact that microtubules alter their orientation from perpendicular to parallel to the cell axis in the course of transition from primary to. secondary wall deposition suggests that microtubules are responsible for the orientation of microfibril. Through secondary wall growth, vesicle-secreting ability of Golgi bodies seems to be very poor. In view of almost all cellulose that composes the cell wall components of cotton fiber, Golgi-derived vesicles could not excrete cellulose precursor to the wall. It was found that smooth-surfaced ER (SER) is derived from RER during the secondary wall thickening. In addition, vesicles (larger than Golgi-derived vesicles) and cisternae of SER appear most frequently near the plasmalemma and seems to be incorporated into the cell wall. Consequently, a close correlation between SER and wall synthesis is presumed in the development of cotton fiber. The occurrence of intensively electron dense substances in a vacuole and paramural bodies is also discussed in relation to the formation of cell wall.