Growth and Metabolic Activity of Lemon Juice Vesicle Explants in Vitro

Abstract

Actively growing juice-vesicle explants, established from smaDl lemon (Cits lmon 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 caDlus proliferation, and their initial growth was promoted by indoleacetic acid, gibberellic acid, and N-benzyladenine.The metabolic competence of the explants, and its relevance to whole fruit development, was further investigated. Juice vesicles continued to accumulate protein on al 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 gibberelic acid. Total peroxidase ofjuice vesicles increased progressively up to the 11th day of culture, and its specific activity was promoted by all three hormones, especially by N-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.Apart from their extensive use in rapid clonal propagation and in genetic research (25), plant tissue culture methods may be useful in development and physiological studies. The advantage of in vitro tissue and organ culture stems from the possibility of minimizing undefined variables and carefully controlling medium composition, and from the continuous availability of plant material. Such in vitro studies are, however, dependent on: (a) establishment of a long term growing culture; (b) elucidation of the physiological and metabolic competence in vitro; and (c) a substantial resemblance between physiological and biochemical patterns of tissue cultures and those of their parent, intact, plants.Our earlier studies have established the suitability of tissue culture studies with citrus bud explants (1, 2). We found it desirable to extend these findings to fruits and fruit explants. Three different in vitro culture systems have been attempted in the past for the study of fruit development: the culture of floral buds, of fertilized ovules and ovaries, and of fruit explants (3,17,21,23,28,30 Former studies with citrus fruit explants, employing either separated juice vesicles (7, 17) or peel tissues (7, 9, 21), all resulted in callus proliferation. Thus, they are irrelevant for the study of the unique physiology ofjuice vesicles. Recently, we were able to culture juice vesicles with potentially unlimited and undisturbed growth (15). In the following, we described the in vitro growth of lemon juice vesicle explants and their metabolic competence as evidenced by protein and sugar accumulation and the activities of invertase and peroxidase.MATERIALS AND METHODS Plant Material. Small fruits (about 12.5 mm in diameter) were harvested during December-January from orchard-grown 15-yearold 'Eureka' lemon (Citrus limon L.Burm. f., var. 'Eureka'). The fru...

In vitro culture of lemon juice vesicles

“…The order of juice vesicle stimulation (i.e. fresh weight increases) was GA3 > 6-BAP > IAA > basal medium [2]. In contrast, we found the order of benefit using growth regulators was as follows: IAA > ABA > basal medium > GA3 > 6-BAP (Table 2).…”

“…Altman, Gulsen and Goren [2] and Gulsen, Altman and Goren [6] reported that juice vesicles could be cultured several months on nutrient medium containing MS salts, 5% sucrose, and 0.01 mM GA3, 6-BAP, or IAA. The order of juice vesicle stimulation (i.e.…”

“…A fruit tissue culture system would be useful to study fruit physiology and differentiation [2,3,6,14]. Few sterile fruit culture studies have been performed with either whole organs or isolated tissues [2,6,10,16].…”

“…Few sterile fruit culture studies have been performed with either whole organs or isolated tissues [2,6,10,16]. Unfortunately, once isolated tissues (even complex fruit tissues) are introduced into a sterile environment, they often immediately lose structural integrity and dedifferentiate into a rapidly dividing callus mass [9,10,12].…”

“…Attempts to proliferate whole plantlets and organized structures from fruit sources usually fail. Citrus juice vesicle tissue readily produces callus on a variety of media [2,3,6,8,9,12,15,16,17]. Kordan [9,12] has extensively used mature lemon juice vesicles to study basic plant mitotic activities and callus formation.…”