网纹甜瓜发育果实糖分积累与蔗糖代谢参与酶的关系

随着网纹甜瓜果实的发育,果实中葡萄糖和果糖的含量增加,蔗糖的快速积累发生在果实发育的中后期,高蔗糖积累型果实中蔗糖积累速率明显快于低蔗糖积累型.蔗糖磷酸合成酶活性在果实发育的前期短暂下降, 而后稳步上升,在果实发育的中后期高蔗糖积累型果实中该酶的活性显著高于低蔗糖积累型果实;随着果实发育,蔗糖合成酶的分解活性降低而合成活性升高.酸性和中性转化酶在未成熟果实中活性较高,而在成熟果实中很低; 高蔗糖积累型果实中酸性转化酶活性显著低于同期低蔗糖积累型果实.合成蔗糖的酶活性小于分解蔗糖的酶活性时蔗糖几乎没有积累.根据这些结果推测,转化酶活性的下降、蔗糖磷酸合成酶活性的增加以及蔗糖合成酶分解活性的下降和合成活性的增加,是引起果实蔗糖积累的主要内在因子.

The Relationship Between Sugar Accumulation and Enzymes Related to Sucrose Metabolism in Developing Fruits of Muskmelon

Sugar accumulation and activities of enzymes related to sucrose metabolism were compared between muskmelon genotypes with high and low sucrose contents. It was observed that glucose and fructose were the predominant soluble sugars in the flesh of muskmelon during early or mid stages of developing fruits, and maintained at high level throughout development (Figs.2-4). Sucrose accumulated obviously quicker in genotype with high sucrose content than that with low sucrose in the late developing stage (Fig.3). Sucrose synthase activity in the cleavage direction (SS c) was very high at early developing fruit, and its activity declined and sucrose synthase activiy in the synthesis direction (SS s) increased concomitant with fruit ripening (Fig.7). Sucrose phosphate synthase (SPS) activity was significantly higher in genotype with high sucrose content than that with low sucrose level in 35 DAP(Fig.6). However, it was found that no or less sucrose accumulation occurred when net activities were negative in terms of the arithmatic differences between the enzymatic capacity to synthesize and to degrade sucrose. The genotype with high sucrose content had an earlier decrease in activities of both invertase and SS c, and earlier increase in SPS activity. We deduced that a reduction in invertase and SS c, and an increment in SPS activity, and SS s as well are responsible for sucrose accumulation in developing fruits of netted melons.