钙处理对葡萄柚果实细胞壁物质代谢及其相关基因表达的影响

Effects of calcium treatments on cell wall material metabolism and related enzyme activities and gene expression in grapefruit (Citrus paradisi Macf.)

【目的】研究采前、采后钙处理对葡萄柚果实细胞壁组分、细胞壁降解酶活性变化及其相关基因表达的影响,可为了解钙与果实细胞壁物质代谢之间的关系,揭示钙对果实软化的作用机理,为调控葡萄柚果实膳食纤维含量,提高果实质地品质提供理论依据。【方法】试验于2011年2月至11月在云南省玉溪市葡萄柚果园进行,供试品种为‘里约红’葡萄柚,该品种于2005年嫁接于当地砧木,株行距为3 m×3 m。试验由采前和采后钙处理两部分组成。采前钙处理在幼果初期、幼果末期、膨大初期、膨大末期、转色期,叶面喷施2%Ca Cl2;采后钙处理在果实成熟采后浸于2%Ca Cl2溶液5 min,室温贮藏。之后每15天取样一次,每次取10个果实,测定葡萄柚果肉细胞壁组分、细胞壁降解酶活性及其基因表达量。【结果】随葡萄柚果实后熟软化,紧密结合型果胶(共价结合型果胶)解聚为松散结合型果胶(水溶性果胶、离子结合型果胶),紧密结合型半纤维素(24%KOH可溶性半纤维素)解聚使其含量下降,而松散结合型半纤维素含量增加(4%KOH可溶性半纤维素)。果实PG、PME、Cx、α-L-Af和β-Gal酶活性及其基因表达量均随果实软化呈不同程度增加。PME活性在果实采收后表现出较高含量,而PG活性在果实贮藏前期急剧增加,其酶基因的表达量与酶活性变化趋势基本一致。Cx、α-L-Af和β-Gal活性在贮藏中、后期上升较快,相关酶基因的表达量亦明显增加。钙处理显著地降低果实细胞壁降解酶活性和基因表达水平,其中采后钙处理对α-L-Af和β-Gal活性和基因表达在贮藏中、后期的调控作用较显著,酶活性和基因表达均维持在较低水平。【结论】外源钙处理降低细胞壁降解酶活性及其基因表达,抑制了细胞壁物质的解聚,采后钙处理对细胞壁物质代谢的调控效果优于采前钙处理。外源钙处理抑制了细胞壁降解酶基因表达水平,降低了细胞壁降解酶活性,减缓了果胶、半纤维素的解聚,从而达到调控果实膳食纤维含量、维持果实质地品质、延长果实货架期寿命的目的。

【Objectives】Study on the effect of Ca treatment on the cell wall components,the variations of cell wall degrading enzyme activities and the expression of relevant genes will help to understand the relationship between the Ca and metabolism of cell wall materials,explore the mechanisms of Ca to fruit softening,and provide base for the improvement of fruit benching time. 【Methods】A field experiment was carried out in grapefruit orchard in Yuxi City,Yunnan Province in 2012. Grapefruit cultivar ‘Rio red ＇ was used as tested crop. The rootstock of the cultivar was grafted in 2005 on a local cultivar in density of 3 m × 3 m. The Ca treatments were composed of two parts： during fruit growing and after harvest. Growing treatment was foliar spraying 2% Ca Cl2 solution at very young fruit,end of young fruit,early fruit expansion,end of fruit expansion and color developing stage. After harvest treatment： the harvested fruits were soaked in 2% Ca Cl2 solution for 5 min,then stored at room temperature. Fruitsamples were taken every 15 days and each time with 10 fruits during the storage for the measurement of relative items.【Results】The tightly bound pectins（ covalent bound pectin） were dissembled into loosely bound pectins（ water soluble pectin,ion bound pectin） with grapefruit fruit ripening. The contents of tightly bound hemicelluloses（ 24% KOH-soluble fraction） decreased while loosely bound hemicelluloses（ 4% KOH-soluble fraction） increased.The activity and the expression of cell wall enzymes genes increased as fruit softened. PME expressed high levels after harvest. The level of PG activity increased in the early stage of storage while PG expression changed similar to enzyme tendency. The activities of Cx,α-L-Af and β-Gal accelerated in the middle and later stage of storage respectively,and their expression were obviously enhanced during storage. Calcium treatment had significantly inhibited cell wall enzyme activities and gene expression. Calcium treatment dramatically regulated the activity of α-L-Af,β-Gal activity in middle stage of storage and later stage, respectively. The enzyme activities, gene expressions of α-L-Af and β-Gal had noticeably lower levels in calcium treatments. 【Conclusions 】Calcium treatments could reduce the activities of wall-degrading enzymes,the expression of relevant genes,and inhibit the dissembling of wall materials. Therefore,calcium treatment is effective in maintaining fruit texture quality and prolonging the benching period.