Laticifer Ultrastructural and Immunocytochemical Studies of Papain in Carica papaya

Cotyledons of germinating papaya (Carica papaya L. ) seeds and exocarp of young fruits were used as materials for study. The ultrastructural changes occurring during differentiation of laticifer and the ultrastructural environment of papain synthesis were studied by means of TEM and immunocytochemistry. Electron microscopic observations showed that the differentiating laticiferous cells were rich in ribosomes and mitochondria. Endoplasmic reticulum (ER) was well developed and apparently active, forming secretory vesicles of various sizes. With further development, organelles were gradually degenerated and autophagy of cytoplasm within vacuole was evident. ER was dilated and split into fragments. Cell wall perforations occurred at several sites of adjacent laticifer elements. Towards maturity, laticifer was fully filled with vesicles containing electron-dense materials. Organelles disappeared thoroughly but plasmalemma remained. Sections were incubated with anti-chymopapain antibodies followed by goat-anti-rabbit IgG-gold. Labeled gold was found predominantly in ER and the associated vesicles of differentiating laticifer. Several controls were used to establish the specificity of the immunolaheling pattern. Investigations led to the conclusions that ER and polyribosomes were involved in papain synthesis. Papain was stored in the vesicles of ER origin temporally before reorganized into laticiferous vesicles with other components of latex.