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    Effect of gibberellic acid on cell wall degradation and softening in postharvest okras
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    Abstract:
    The effect of postharvest gibberellic acid (GA) treatment on fruit softening, cell wall components, and cell wall metabolic genes in postharvest okras was explored. GA effectively slowed the softening of postharvest okras. In comparison to the control, okras treated with GA displayed higher levels of protopectin (PP) and cellulose (CEL), but lower level of water-soluble pectin (WSP). GA treatment could block cell wall degradation via the downregulation of multiple cell wall-degrading genes, such as AePME, AeCX, AePG, AePL, AeGAL, and AeARF. Collectively, our study revealed that GA treatment postponed softening of postharvest okras by retarding cell wall degradation during storage.
    Keywords:
    Gibberellic acid
    Pectin
    Degradation
    Pectin, an enriched component in primary cell walls and middle lamellae, is an essential polysaccharide in all higher plants. Homogalacturonans (HGs), a major form of pectin, are synthesized and methyl-esterified by enzymes localized in the Golgi apparatus and transported into the cell wall. Depending on cell type, the degree and pattern of pectin methylesterification are strictly regulated by cell wall-localized pectin methylesterases (PMEs) which are governed by multiple pectin methylesterase inhibitors (PMEIs) in vivo. Pectin methylesterases (PMEs, EC 3.1.1.11), belonging to carbohydrate esterase family 8, cleave the ester bond between a galacturonic acid and an methyl group and the resulting change in pectin methylesterification status from which clearly impacts diverse plant developmental processes and stress responses. PMEs play major roles in modification of pectin properties, such as the stiffening by forming Ca2+-pectate cross-link complexes or loosening by triggering cell wall degrading enzymes (CWDE)s to break out cell wall components including pectin and its interactiors. The action of PMEIs results in opposite consequences to PMEs on pectin properties. Optimal pectin methylesterification status in each cell type is determined by the balance between PME activity and post-translational PME inhibition by PMEIs.
    Pectin
    Pectinesterase
    Pectate lyase
    Esterase
    Citations (3)
    The effect of postharvest gibberellic acid (GA) treatment on fruit softening, cell wall components, and cell wall metabolic genes in postharvest okras was explored. GA effectively slowed the softening of postharvest okras. In comparison to the control, okras treated with GA displayed higher levels of protopectin (PP) and cellulose (CEL), but lower level of water-soluble pectin (WSP). GA treatment could block cell wall degradation via the downregulation of multiple cell wall-degrading genes, such as AePME, AeCX, AePG, AePL, AeGAL, and AeARF. Collectively, our study revealed that GA treatment postponed softening of postharvest okras by retarding cell wall degradation during storage.
    Gibberellic acid
    Pectin
    Degradation
    Citations (9)
    Mango fruit cv. 'Namdokmai' at the mature-green stage were heat-treated by dipping in 50°C or 55°C water for 5 min and stored at 25°C with 90-95% relative humidity. Fruit dipped in ambient water served as control. Softening slowed down in response to heat treatment. The effect of the two heat treatments did not considerably differ. Concomitant with softening, the heat-treated fruits exhibited reduced pectin methylesterase (PME) and polygalacturonase (PG) activities in both peel and pulp tissues. Heat treatment at 55°C generally resulted to lower PME and PG activity than at 50°C. These results indicate that heat inhibition of ripening-associated softening is due to inhibition of pectin-degrading enzymes.
    The softening of Japanese radishes and the decomposition of pectin (0.5% pectin solution in 1/10 M phosphate buffer, pH 6.5) during the thermal process (100°C-110°C) under atmospheric and high pressures (100 MPa-400 MPa) were investigated. High pressure decreased the rates of softening for Japanese radishes and the decomposition of pectin during the thermal process. The activation volumes for the softening of Japanese radishes were 4.3 cm3/mol at 100°C and 3.1 cm3/mol at 110°C, and those for the decomposition of pectin were 10.4 cm3/mol (100°C) and 8.1 cm3/mol (110°C). Though the values indicated that the pressure lowered the pectin decomposition more than the softening of the radish, the ratios of the activation volume at 110°C to that at 100°C for both phenomena were nearly the same. These results suggested that the resistance to softening of the radish by pressure is closely related to the inhibition of the pectin decomposition in the radish by pressure.
    Pectin
    Flower longevity of ornamental alliums depending on cutting stage and postharvest treatment. The postharvest longevity of infl orescences evaluated till the drying up of the fl orets amounted 15–20 days for Allium afl atunense, 21–29 days for Allium christophii, 28–35 days for Allium giganteum and 15–19 days for Allium rosenbachianum. The postharvest longevity of infl orescences was the longest when fl owers were harvested at the beginning of fl owering or when 1/4 of the fl orets were open in an infl orescence. Applying 8-hydroxyquinoline sulphate for conditioning improved only the longevity of cut infl orescences of A. giganteum till drying up when they were kept in 100 mg⋅dm–3 and 200 mg⋅dm–3 gibberellic acid solutions. The postharvest longevity of cut infl orescences of A. christophii improved when they were kept in gibberellic acid. This was the case for A. afl atunense only in non-conditioned infl orescences treated with 100 mg⋅dm–3 gibberellic acid solution and in conditioned infl orescences treated with 100 mg⋅dm–3 and 200 mg⋅dm–3 gibberellic acid solutions. Gibberellic acid improved the postharvest longevity of A. giganteum till drying up only in conditioned infl orescences and of A. rosenbachianum in conditioned infl orescences treated with 200 mg⋅dm–3 solution.
    Gibberellic acid
    Ornamental plant
    Vase life
    Cut flowers
    Citations (5)