| Abstract: | The giant stacked rough endoplasmic reticulum(S-RER)is discovered in the study of cotton microsporogenesis. These giant S-RER are randomly dispersed in the outerpart of the microspore cytoplasm and are easily visualized ,because they have sufficient number and are large enough for examination under light microscope. The diameters of those stacks attain to a range of 2.0—4.5μm. Specific characteristics of S-RER vary with the developmental stage and metabolic state, but they may be included into two main types :one is small and simple, the other is large and complex. The giant stacks may be composed of more than 50 parallel cisternae. Of course, between the main types there are many transitional forms. In addition, a few special configurations of S-RER was observed which the cisternae always become vesicularized at the peripheral portion of the stacks occurring near the plasma membrane (PM). In this case,the S-RER itself may be further lost its own structural property,instead of substituted a lot of small vesicles at its original site. It may also be called vesicular RER. Those vesicles derived from RER cisternae bear ribosomes on the outer surface. On the other hand,vesicles as a major vesicle may be directly formed at the ends of RER cisternae, which, in fact, serve as transition elements. The dynamic activities of those vesicles during the spore metabolic processes are conducted via two pathways operative:(1)the vesicles detach from the RER end and migrate towarss PM,then the vesicle membrane fuses with PM and the contents of the vesicles are discharged, (2) vesicles fuse together among themselves to form provacuolar bodies in the outer part of the spore cytoplasm. Several provacuolar bodies may further converge more and more to form small vacuoles. From the data studied the following conclusions may be drawn: (1)although the S-RER presented during cotton microsporogenesis is much the same as that in mature pollen grains of some plants,yet in this study S-RER always shows functional activities. So that S-RER is not limitted to represent an inactive RER configuration. (2)During the development of cotton microspore,the enlargement of the cell size is bound to follow a rapid increase and great extension of the vacuoles. It indicates that a rapid synthesis of endomembrane materials must be involved in the growth of microspore. The supply of membrane materials is one of the important functions of S-RER. |
