桃果实成熟前后细胞壁成分和降解酶活性的变化及其与果实硬度的关系

比较桃品种‘双久红’和‘川中岛白桃’果实成熟前后20 d内果肉硬度、细胞壁成分和细胞壁降解酶活性变化的结果表明,桃果实成熟5 d后,‘双久红’桃果实的硬度、纤维素含量和原果胶含量均极显著高于‘川中岛白桃’:从成熟前15 d开始,‘双久红’的水溶性果胶含量、多聚半乳糖醛酸酶活性和纤维素酶活性均极显著低于‘川中岛白桃’;整个成熟期间,‘双久红’的果胶甲酯酶活性明显低于‘川中岛白桃’。相关分析表明,果实硬度与原果胶、纤维素含量呈极显著正相关,而与可溶性果胶含量、多聚半乳糖醛酸酶活性和纤维素酶活性呈极显著负相关。     

细胞壁代谢与琯溪蜜柚果实成熟过程汁胞粒化的关系

以易发生汁胞粒化的老龄树和不易发生汁胞粒化的适龄树的琯溪蜜柚（Citrus grandis（L．）Osbeck‘Guanximiyou’1果实为材料，研究了果实成熟过程中汁胞粒化发生与细胞壁代谢的关系。结果表明：老龄树果实的汁胞粒化指数随着果实成熟而上升。在汁胞粒化发生过程中，汁胞维持较低的细胞壁降解酶[果胶甲酯酶（PE）、多聚半乳糖醛酸酶（PG）、纤维素酶（Cx）]活性，保持较高的细胞壁物质（原果胶、纤维素、半纤维素）含量；尤其在汁胞粒化的起动阶段和加快阶段，纤维素、半纤维素含量极显著增加。相反，适龄树果实的汁胞粒化指数在果实成熟过程中变化不大，汁胞中细胞壁降解酶活性较高，促进原果胶、纤维素、半纤维素等细胞壁物质的降解，保持较低的细胞壁物质含量，使汁胞发育正常、柔软多汁。这说明PE、PG、Cx活性和原果胶、纤维素、半纤维素含量与錧溪蜜柚汁胞粒化密切相关。     

柿果实采后软化过程中细胞壁组分代谢和超微结构的变化

柿果实采后果胶酯酶活性迅速上升,其活性与果实硬度的下降呈明显的负相关。多聚半乳糖醛酸酶活性增加缓慢,但其活性与果实硬度的下降无明显相关性。β-半乳糖苷酶活性迅速增加,其活性与果实硬度的下降呈明显的负相关。纤维素酶活性呈逐渐上升趋势,与果实硬度的下降也呈明显的负相关。伴随着细胞壁水解酶活性的增加,果实原果胶和纤维素含量迅速下降,而水溶性果胶含量则迅速上升。柿果刚采收时细胞壁结构完整,3d后细胞壁中胶层基本被溶解,甚至初生壁也局部发生降解。     

柿果实采收后软化生理分析（简报）

柿子(乾县火柿)采后的粗纤维、原果胶、单宁和可溶性固形物含量都随硬度的降低而降低,可溶性果胶则升高。多聚半乳糖醛酸酶和纤维素酶活性逐渐升高,果胶甲酯酶活性和蛋白质含量逐渐降低,都在果实变软时同时出现高峰;随后出现呼吸峰和乙烯峰。     

高压静电场对草莓采后一些生理指标的影响

草莓果实经-50和-100 kV*m-1高压静电场处理后,呼吸速率受到明显抑制,果实中可溶性固形物含量较高,多聚半乳糖醛酸酶和羧甲基纤维素酶活性降低,果实硬度下降缓慢.     

真菌多聚半乳糖醛酸酶研究进展

真菌多聚半乳糖醛酸酶是降解植物细胞壁果胶的主要降解酶之一,是植物病原真菌的致病因子之一。文中对真菌多聚半乳糖醛酸酶及其序列特征、多聚半乳糖醛酸酶的基因及其序列特征、多聚半乳糖醛酸酶的表达调控以及与病原真菌致病力之间的关系等方面进行了综述。     

向日葵花盘水提物对硫色镰刀菌及其细胞壁降解酶活性抑制特性

通过抑菌及细胞壁降解酶活性试验,研究向日葵花盘(sunflower disc,SFD)水提物对引起马铃薯干腐病主要病原菌——硫色镰刀菌(Fusarium sulphureum)生长及其侵染不同马铃薯品种时分泌的多聚半乳糖醛酸酶(polygalacturonase,PG)、果胶甲基半乳糖醛酸酶(polymethyl-ga...     

荔枝果实采后钙处理对三种酶活性的影响

用不同浓度的Ｃａ（Ⅱ）对荔枝果实采后处理,测定果实中的果胶酯酶、多聚半乳糖醛酸酶和纤维素酶的活性变化,发现用４％的钙处理,对上述各酶活性都有一定的抑制作用;在冷藏条件下,还能推迟这三种酶活性高峰的来临,甚至使之不出现,从而延缓了果实的衰老。     

果实成熟软化原因新探

五十多年来,科学家一直认为果实在成熟时变软,是由于聚半乳糖醛酶分解细胞壁的果胶所致。一些果实成熟时聚半乳糖醛酶的数量和活性均增加,实验室也证明聚半乳糖醛酶能破坏细胞壁的结构。然而某些果实,如草莓、苹果等的果实中不含聚半乳糖醛酶,将具活性的聚半乳糖醛酶注入未成熟的果实,不能促进其软化,说明软化还有其它原因。     

不同温度下后熟香蕉果实果皮生理与颜色变化

香蕉果实经乙烯利处理后，比较20℃和30℃下后熟期间的果皮色泽、淀粉转化及几种细胞壁降解相关酶活性的变化。在20℃下，香蕉果实能正常褪绿和软化，而30℃高温则明显抑制了褪绿转黄，加速了果皮软化。与20℃后熟比较，30℃促进了香蕉果皮中淀粉向可溶性糖的转化，提高了多聚半乳糖醛酸酶、纤维素酶、果胶甲酯酶等的活性。讨论了香蕉果皮可溶性糖含量与青皮熟形成之间的可能关系。     

间歇低温胁迫对桃果实细胞壁代谢的影响

桃果实在成熟过程中细胞壁干物质不断减少,随着共价结合果胶质和离子结合果胶质减少,水溶性果胶质明显增加,纤维素也逐渐减少,但半纤维素含量变化较小.低温胁迫造成果胶质和纤维素的降解过程受阻,从而造成较高分子量果胶质的积累,果汁粘度升高.中途加温则能促进果胶质和纤维素的增溶和解聚,引导细胞进行与果实成熟有关的细胞壁代谢.14C-蔗糖标记试验表明,在细胞壁不断降解的同时,也进行着合成.在果实成熟的启动阶段,细胞壁的合成能力加强.果实衰老过程与细胞壁合成减少有着直接的联系.受到低温伤害的果实细胞壁物质含量高于正常果实的原因,并不是其合成水平的升高,而是其降解的减慢.     

Pectin methylesterases induce an abrupt increase of acidic pectin during strawberry fruit ripening

The decrease of strawberry (Fragariaxananassa Duch.) fruit firmness observed during ripening is partly attributed to pectolytic enzymes: polygalacturonases, pectate lyases and pectin methylesterases (PMEs). In this study, PME activity and pectin content and esterification degree were measured in cell walls from ripening fruits. Small green, large green, white, turning, red and over-ripe fruits from the Elsanta cultivar were analyzed. Using the 2F4 antibody directed against the calcium-induced egg box conformation of pectin, we show that calcium-bound acidic pectin was nearly absent from green and white fruits, but increased abruptly at the turning stage, while the total pectin content decreased only slightly as maturation proceeded. Isoelectrofocalisation performed on wall protein extracts revealed the expression of at least six different basic PME isoforms. Maximum PME activity was detected in green fruits and steadily decreased to reach a minimum in senescent fruits. The preliminary role of PMEs and subsequent pectin degradation by pectolytic enzymes is discussed.     

番茄果实中乙烯与多聚半乳糖醛酸酶的关系

乙烯与多聚半乳糖醛酸酶(PG)都是果实成熟过程中关键的调节因子.一方面,在有乙烯合成缺陷的转反义ACS番茄和乙烯感受缺陷的Nr突变体番茄果实中PG基因表达量都明显下降,PG酶活性明显降低;用外源乙烯(100 μL/L)处理绿熟期番茄果实使PG基因的表达明显增强,而1-甲基环丙烯(1-MCP,1 μL/L)处理转色期番茄果实明显抑制PG基因表达.另一方面,转反义PG基因番茄果实乙烯释放量在授粉后低于其野生型,番茄乙烯受体基因LeETR4和乙烯反应因子LeERF2基因表达量比野生种低.PG降解果胶的产物D-GA(100 mg/L)促进未熟期番茄果实中的乙烯生成和LeETR4、LeERF2基因的表达.     

Pectin methylesterase activity in vivo differs from activity in vitro and enhances polygalacturonase-mediated pectin degradation in tabasco pepper

Polygalacturonase (PG) and pectin methylesterase (PME) activities were analyzed in ripening fruits of two tabasco pepper (Capsicum frutescens) lines that differ in the extent of pectin degradation (depolymerization and dissolution). Ripe 'Easy Pick' fruit is characterized by pectin ultra-degradation and easy fruit detachment from the calyx (deciduous trait), while pectin depolymerization and dissolution in ripe 'Hard Pick' fruit is limited. PG activity in protein extracts increased similarly in both lines during fruit ripening. PME activity in vivo assessed by methanol production, however, was detected only in fruit of the 'Easy Pick' line and was associated with decreased pectin methyl-esterification. In contrast, methanol production in vivo was not detected in fruits of the 'Hard Pick' line and the degree of pectin esterification remained the same throughout ripening. Consequently, a ripening specific PME that is active in vivo appears to enhance PG-mediated pectin ultra-degradation resulting in cell wall dissolution and the deciduous fruit trait. PME activity in vitro, however, was detected in protein extracts from both lines at all ripening stages. This indicates that some PME isozymes are apparently inactive in vivo, particularly in green fruit and throughout ripening in the 'Hard Pick' line, limiting PG-mediated pectin depolymerization which results in moderately difficult fruit separation from the calyx.     

Manipulation of strawberry fruit softening by antisense expression of a pectate lyase gene

Strawberry (Fragaria x ananassa, Duch., cv Chandler) is a soft fruit with a short postharvest life, mainly due to a rapid lost of firm texture. To control the strawberry fruit softening, we obtained transgenic plants that incorporate an antisense sequence of a strawberry pectate lyase gene under the control of the 35S promoter. Forty-one independent transgenic lines (Apel lines) were obtained, propagated in the greenhouse for agronomical analysis, and compared with control plants, non-transformed plants, and transgenic lines transformed with the pGUSINT plasmid. Total yield was significantly reduced in 33 of the 41 Apel lines. At the stage of full ripen, no differences in color, size, shape, and weight were observed between Apel and control fruit. However, in most of the Apel lines, ripened fruits were significantly firmer than controls. Six Apel lines were selected for further analysis. In all these lines, the pectate lyase gene expression in ripened fruit was 30% lower than in control, being totally suppressed in three of them. Cell wall material isolated from ripened Apel fruit showed a lower degree of in vitro swelling and a lower amount of ionically bound pectins than control fruit. An analysis of firmness at three different stages of fruit development (green, white, and red) showed that the highest reduction of softening in Apel fruit occurred during the transition from the white to the red stage. The postharvest softening of Apel fruit was also diminished. Our results indicate that pectate lyase gene is an excellent candidate for biotechnological improvement of fruit softening in strawberry.