Growth and metabolic activity of lemon juice vesicle explants in vitro

Actively growing juice-vesicle explants, established from small lemon (Citrus limon L. Burm. f. var. ;Eureka') fruits, were cultured in vitro on defined media. The juice vesicles continued to enlarge in culture for several months, without callus proliferation, and their initial growth was promoted by indoleacetic acid, gibberellic acid, and N(6)-benzyladenine.The metabolic competence of the explants, and its relevance to whole fruit development, was further investigated. Juice vesicles continued to accumulate protein on all media, for at least 16 days, but sugars did not change much during culture. Acid invertase increased dramatically during the first days of culture, and its specific activity was markedly promoted by indoleacetic acid, and to a lesser degree by gibberellic acid. Total peroxidase of juice vesicles increased progressively up to the 11th day of culture, and its specific activity was promoted by all three hormones, especially by N(6)-benzyladenine. Explant growth was accompanied by appearance of several cathodic and anodic isoperoxidases.The results suggest that the study of this unique juice vesicle system may contribute to a better understanding of fruit development.