Abstract
Cell cultures derived from strawberry fruit at different developmental stages have been obtained to evaluate their potential use to study different aspects of strawberry ripening. Callus from leaf and cortical tissue of unripe-green, white, and mature-red strawberry fruits were induced in a medium supplemented with 11.3 µM 2,4-dichlorophenoxyacetic acid (2,4-D) under darkness. The transfer of the established callus from darkness to light induced the production of anthocyanin. The replacement of 2,4-D by abscisic acid (ABA) noticeably increased anthocyanin accumulation in green-fruit callus. Cell walls were isolated from the different fruit cell lines and from fruit receptacles at equivalent developmental stages and sequentially fractionated to obtain fractions enriched in soluble pectins, ester bound pectins, xyloglucans (XG), and matrix glycans tightly associated with cellulose microfibrils. These fractions were analyzed by cell wall carbohydrate microarrays. In fruit receptacle samples, pectins were abundant in all fractions, including those enriched in matrix glycans. The amount of pectin increased from green to white stage, and later these carbohydrates were solubilized in red fruit. Apparently, XG content was similar in white and red fruit, but the proportion of galactosylated XG increased in red fruit. Cell wall fractions from callus cultures were enriched in extensin and displayed a minor amount of pectins. Stronger signals of extensin Abs were detected in sodium carbonate fraction, suggesting that these proteins could be linked to pectins. Overall, the results obtained suggest that fruit cell lines could be used to analyze hormonal regulation of color development in strawberry but that the cell wall remodeling process associated with fruit softening might be masked by the high presence of extensin in callus cultures.
Highlights
Ripening of fleshy fruits is a complex developmental process involving changes in color, flavor, and texture that make the tissue edible to seed-dispersing animals [1]
Most studies have focused on the cell wall disassembly process taking place during fruit ripening; despite the large amount of information available, a general model of cell wall remodeling leading to fruit softening remains elusive [9]
To optimize the generation of callus from strawberry tissue, leaf explants from micropropagated plants were cultured in N30 K medium supplemented with a combination of benzyladenine (BA)
Summary
Ripening of fleshy fruits is a complex developmental process involving changes in color, flavor, and texture that make the tissue edible to seed-dispersing animals [1]. Fruit texture is one of the main attributes for the acceptance in the market from the consumer’s point of view [2] Soft fruits such as strawberry acquire an undesirable melting texture very soon after ripening, increasing their susceptibility to pathogen attack and reducing their shelf life to a few days [4,5]. It is generally accepted that the modification of the mechanical properties of the primary cell walls due to cell wall disassembly, the reduction of intercellular adhesion as a result of middle lamella dissolution, and the reduction in cell turgor are the major causes of fruit softening [6,7,8,9] Among these three factors, most studies have focused on the cell wall disassembly process taking place during fruit ripening; despite the large amount of information available, a general model of cell wall remodeling leading to fruit softening remains elusive [9]. Functional analyses of genes encoding pectinases such as polygalacturonase and pectate lyase point to the pectin fraction as a key factor involved in strawberry softening [10,11]
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