ULTRASTRUCTURAL STUDIES ON THE ONTOGENY OF GRAPEFRUIT JUICE VESICLES (CITRUS-PARADISI MACF CV STAR RUBY)

The ultrastructure of juice vesicle development and maturation was investigated in cv Star Ruby grapefruit. Juice vesicle primordia were initiated by divisions of epidermal and subepidermal cells on the adaxial surface of the carpel wall at least 2 d before anthesis. Development occurred in three distinct stages: cell division, cell elongation, and cell maturation. Development of juice vesicles in the first 3 wk postanthesis occurred by cell division of a subterminal meristem and resulted in the formation of a main juice vesicle body subtended by highly vacuolate stalk cells connected to the carpel wall. Cells of the main body were characteristic of meristematic cells. Between 4 and 10 wk postanthesis, oil gland/oil cavity development occurred in the center of the main juice vesicle body and began with a single electron-dense cell. Surrounding cells exhibited characteristics of intense metabolic and secretory activity, culminating in the synthesis of lipid and osmiophilic material. A schizogenous and/or lysigenous cavity developed in the central area of the main juice vesicle body, where fibrillar-oil material and lysed cell remnants were observed, respectively. Expansion of surrounding cells resulted in further lysigeny of the central electron-dense cells. The mature juice' vesicle body contained highly vacuolate central cells surrounded by a hypodermis and epidermal layer. The central cavity remained even after 12 mo of juice vesicle development.