ULTRASTRUCTURE OF OOGENESIS IN PENAEUS-KERATHURUS (CRUSTACEA, DECAPODA) - II - VITELLOGENESIS

The ultrastructure of vitellogenesis in Penaeus kerathurus is presente d. Early vitellogenesis is characterized by the predominance of recept or mediated endocytosis, forming dense vesicles that rapidly loose the ir coating. This exogenous sourer of yolk is, however, directly used t o form yolk vesicles that also receive components of the Golgi apparat us and the endoplasmic reticulum. These mixed-type yolk vesicles then fuse together and form large dense yolk resides. During this stage, so me of the rough endoplasmic reticulum vesicles also give rise to large yolk vesicles that have an intermediate dense content and whose limit ing membrane appears rather labile. Midvitellogenesis is a brief perio d with dramatic changes occurring within the endoplasmic reticulum. Fi rst, rough endoplasmic reticulum vesicles give rise to large amounts d f rough endoplasmic reticulum tubules filled with a fine fibrillar mat rix. After this phase, rough endoplasmic reticulum vesicles fuse and e xpand, forming a large anastomotic reticulum that encircles and assist s formation of a large number of intermediate dense yolk vesicles. Thi s type of yolk vesicles represents the yolk stock of mature oocytes, a nd their labile limiting membrane will allow engulfment of several dif ferent oocyte structures, namely, smooth endoplasmic reticulum tubules , dense (mixed origin) yolk vesicles, Golgian vesicles and vacuoles, a nd numerous concentrical arrays of smooth endoplasmic reticulum derive d membranes. In conclusion, yolk production in P. kerathurus has a mix ed (endogenous and exogenous) origin, and shows rather infrequent endo plasmic reticulum activities.