Abstract:The mRNA accumulation of two endo-l,4-P-o-glucanase genes, Cell and Cel2, was examined in the pericarp and locules throughout the development of normal tomato (Lycopersicon esculentum) fruit and the ripening-impaired mutants rin and Nr. Both Cell and Cel2 were expressed transiently at the earliest stages of fruit development during a period corresponding to cell division and early cell expansion. In the pericarp, the mRNA abundance of both genes increased markedly at the breaker stage; the leve1 of Cell mRNA d… Show more
“…Xyloglucan represents the predominant hemicellulose in many fruit including tomato, where degradation is apparent during ripening in wild-type fruit but not in fruit of the rin (ripening inhibitor) tomato mutant that soften extremely slowly (16). Fruit ripening has been associated with both endo-1,4--glucanases (15,17) and xyloglucan endotransglycosylases (16,18); however, the importance of these and other as yet uncharacterized enzymes in modifying hemicellulose abundance, distribution, and interaction with other cell wall components in fruit has yet to be determined.…”
Expansins are proteins that induce extension in isolated plant cell walls in vitro and have been proposed to disrupt noncovalent interactions between hemicellulose and cellulose microfibrils. Because the plant primary cell wall acts as a constraint to cell enlargement, this process may be integral to plant cell expansion, and studies of expansins have focused on their role in growth. We report the identification of an expansin (LeExp1) from tomato that exhibits high levels of mRNA abundance and is specifically expressed in ripening fruit, a developmental period when growth has ceased but when selective disassembly of cell wall components is pronounced. cDNAs closely related to LeExp1 were also identified in ripening melons and strawberries, suggesting that they are a common feature of fruit undergoing rapid softening. Furthermore, the sequence of LeExp1 and its homologs from other ripening fruit define a subclass of expansin genes. Expression of LeExp1 is regulated by ethylene, a hormone known to coordinate and induce ripening in many species. LeExp1 is differentially expressed in the ripening-impaired tomato mutants Nr, rin, and nor, and mRNA abundance appears to be inf luenced directly by ethylene and by a developmentally modulated transduction pathway. The identification of a ripening-regulated expansin gene in tomato and other fruit suggests that, in addition to their role in facilitating the expansion of plant cells, expansins may also contribute to cell wall disassembly in nongrowing tissues, possibly by enhancing the accessibility of noncovalently bound polymers to endogenous enzymic action.
“…Xyloglucan represents the predominant hemicellulose in many fruit including tomato, where degradation is apparent during ripening in wild-type fruit but not in fruit of the rin (ripening inhibitor) tomato mutant that soften extremely slowly (16). Fruit ripening has been associated with both endo-1,4--glucanases (15,17) and xyloglucan endotransglycosylases (16,18); however, the importance of these and other as yet uncharacterized enzymes in modifying hemicellulose abundance, distribution, and interaction with other cell wall components in fruit has yet to be determined.…”
Expansins are proteins that induce extension in isolated plant cell walls in vitro and have been proposed to disrupt noncovalent interactions between hemicellulose and cellulose microfibrils. Because the plant primary cell wall acts as a constraint to cell enlargement, this process may be integral to plant cell expansion, and studies of expansins have focused on their role in growth. We report the identification of an expansin (LeExp1) from tomato that exhibits high levels of mRNA abundance and is specifically expressed in ripening fruit, a developmental period when growth has ceased but when selective disassembly of cell wall components is pronounced. cDNAs closely related to LeExp1 were also identified in ripening melons and strawberries, suggesting that they are a common feature of fruit undergoing rapid softening. Furthermore, the sequence of LeExp1 and its homologs from other ripening fruit define a subclass of expansin genes. Expression of LeExp1 is regulated by ethylene, a hormone known to coordinate and induce ripening in many species. LeExp1 is differentially expressed in the ripening-impaired tomato mutants Nr, rin, and nor, and mRNA abundance appears to be inf luenced directly by ethylene and by a developmentally modulated transduction pathway. The identification of a ripening-regulated expansin gene in tomato and other fruit suggests that, in addition to their role in facilitating the expansion of plant cells, expansins may also contribute to cell wall disassembly in nongrowing tissues, possibly by enhancing the accessibility of noncovalently bound polymers to endogenous enzymic action.
“…Tomato flowers can also be induced to abscise even if they are pollinated when flowers are excised from the plant and exposed to ethylene (Valdovinos and Jensen, 1967). In tomato there is a family of EGase genes of at least six members, and the expression of two members of this family, Cell and Ce12, overlaps in ripening fruit and in flower abscission zones de1 Campillo and Bennett, 1996;Gonzalez-Bosch et al, 1996). Although both Cell and Ce12 mRNA are present in abscission zones and in ripening fruit, Cell mRNA is more abundant than Ce12 mRNA in abscission zones, whereas Ce12 mRNA is most abundant in ripening fruit.…”
Cell wall disassembly accompanies many physiological processes. The disassembly can range from discrete modifications of cell wall architecture that take place during cell growth and expansion to major cell wall breakdown, which occurs in processes such as fruit ripening and abscission of plant organs. These degradative processes are mediated by cell wall hydrolases, which are regulated in a developmental and tissue-specific manner (Fischer and Bennett, 1991). The process of abscission takes place at precisely determined positions in a plant and is the result of cell separation mediated by cell wall dissolution (Sexton and Roberts, 1982). In many plants, organ abscission is associated with an increase in ethylene production and involves ethylenerelated changes in gene expression (Sexton and Roberts, 1982;Reid, 1985). Ethylene induces cell wall hydrolases and, in particular, EGase (Horton and Osborne, 1967;Lewis and Varner 1970;Tucker et al., 1988) and polygalacturonase (Tucker et al., 1984;Taylor et al., 1990;Kalaitzis et al.,
“…These results are in agreement with those of Amrani on grapes [10] and of Agravante and his collaborators [33] and Lohani and his collaborators [34] on the banana ripening. Furthermore, the study of gene expression encoding the parietal hydrolases showed that most of them are induced during ripening and regulated by ethylene [35][36][37][38]. These physiological processes allow embrittlement of the olives' cell walls, which has the consequence of facilitating the release of the phenolic compounds and the enrichment of the virgin olive oil by these compounds.…”
Background:The effect of the ethephon application at fruit set and veraison on cell maturity of Olea europaea L. olives and on the extractability of phenolic compounds (PC) in virgin olive oil has been studied.
Methods:The ethephon was sprayed on olive trees of the Moroccan Picholine at the fruit set stage and on other olive trees at the veraison stage at a concentration of 100 mg/L. The effect of these treatments was evaluated by the fruit yield and the determination of the period of olives growth and ripening. The extractability of the olive oil and the diffusion of the PCs in the fat as well as the embrittlement of the parietal structures are also monitored.
Results and conclusions:A chemical thinning is entrained out by ethephon when applied at fruit set (16%) or veraison (12%). It also results in precocious ripening of fruits treated at fruit set (about 2 weeks) and a precocity of the harvest similar to that induced in olives treated at veraison (estimated at 6 weeks). At this stage, a significant increase in the fat accumulation (more than 26 g/100 g in the olives treated compared to 7.7 g/100 g olive pulp in the control) and quantities of extracted oils (87 and 83%, respectively, in the olives treated at fruit set and those treated at veraison compared to 70% in the control) as well as a significant improvement in the extractability of the diffusible PCs in these oils at maturity (540 and 590 mg/kg, respectively, in the treated olives at fruit set and those treated at veraison compared to 216 mg/kg in the control oil).
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