Effects of light intensity on sucrose accumulation and sucrose metabolizing enzyme activities of melon fruits | 遮阴对甜瓜果实蔗糖积累及其代谢酶活性的影响

中国人. 分析光照强度对果型大小不同的甜瓜果实蔗糖积累量及其代谢酶活性的影响，以期更好地理解甜瓜果实糖分积累的内在生理机制。以“玉金香”、“银帝”、“黄河蜜”3个果型大小不同的甜瓜品种为试材，分析了透光率100%（自然光照，对照）、52%（一层黑色遮阳网遮阴）、26%（一层黑色遮阳网+一层白色防虫网遮阴）3个光照水平，对甜瓜果实蔗糖积累量及其代谢酶(酸性转化酶（AI）、中性转化酶（NI）、蔗糖磷酸合成酶（SPS）、蔗糖合成酶（SS））活性变化的影响。果实发育初期，蔗糖分解酶（AI，NI）活性较高，蔗糖积累很少；随着果实发育，蔗糖分解酶活性大幅度下降，蔗糖合成酶（SS，SPS）活性逐渐升高；甜瓜果实定个后进入蔗糖快速积累期，蔗糖分解酶活性降到最低。遮阴降低了甜瓜果实蔗糖含量， 52%透光率条件下，“黄河蜜”果实的蔗糖含量降幅（21.6%）显著大于“银帝”（10.1%）和“玉金香”（11.5%）；26%透光率条件下，“黄河蜜”的蔗糖含量降幅（30.7%）大于“银帝”（25.8%），且二者均显著大于“玉金香”（16.7%）。遮阴对转化酶活性的影响相对较小，主要是降低了蔗糖合成酶（特别是SPS）的活性：透光率52%条件下，“玉金香”和“银帝”SPS活性分别比对照下降了18.7%和20.5%；透光率26%条件下，“银帝”的SPS活性降幅（32.7%）显著大于“玉金香”（26.2%）；“黄河蜜”在2个光强水平下SPS活性降幅（30.5%和36.7%）均显著大于“银帝”和“玉金香”。蔗糖合成酶活性降低是遮阴条件下甜瓜果实蔗糖积累量减少的主要原因，SPS是甜瓜果实蔗糖积累的关键酶；遮阴条件下蔗糖积累量和代谢酶活性降低具有果型依赖性：大果型品种（“黄河蜜”）＞中果型品种（“银帝”）＞小果型品种（“玉金香”）。

英语. The study analyzed the sucrose accumulation and the activities of sucrose-metabolizing enzymes of melon fruit under different light intensities for better understanding of the physiological mechanism of sugar accumulation in melon fruit. Three cultivars of Cucumis melo L. with different fruit sizes (Yujinxiang, Yindi and Huanghemi) were employed to study the effects on sucrose accumulation and the changes of sucrose-metabolizing enzymes activities of melon fruit under three levels of light intensities (26%, 52% and 100% of natural light respectively). The results showed that the activities of sucrose decomposing enzyme increased at early stages of fruit development, but sugar didn’t accumulate much. With the development of fruits, the activities of sucrose decomposing enzymes rapidly decreased, the activities of sucrose syntheses gradually increased; While sucrose rapid accumulation took place at later stage, the activities of sucrose decomposing enzyme were at a minimum. Shading reduced the sucrose content. Under 52% light intensity, the sucrose content decrease percentage of Huanghemi (21.6%）was remarkably higher than that of Yindi (10.1%) and Yujinxiang (11.5%); under 26% light intensity, the sucrose content decrease percentage of Huanghemi (30.7%) was slightly higher than that of Yindi(25.8%), and they were both significantly higher than that of Yujinxiang (16.7%).Shading decreased the activities of melon sucrose metabolism enzymes, especially sucrose phosphate synthases, while the activities of invertase were affected rarely. Under 52% light intensity, the activities of sucrose phosphate synthases of Yujinxiang and Yindi decreased by 18.7% and 20.5% respectively compared to that of CK; under 26% light intensity, the decrease of sucrose phosphate synthase activity of Yindi (32.7%) was remarkably higher than that of Yujinxiang(26.2%); Under the two shading levels, the activities of sucrose phosphate synthase in Huanghemi decreased by 30.5% and 36.7% respectively compared to that of CK, and the decrease rates were significantly greater than that of Yindi and Yujinxiang. Sucrose phosphate synthase was the key enzyme of sucrose accumulation in melon fruit and the decrease of sucrose synthase activity was the main reason of sucrose accumulation reduction under shading condition. The decrease percentage of sucrose accumulation and the sucrose-metabolizing enzyme activities positively depended on melon fruits size.