Zhu Xudong, Zhang Chaobo, Wu Weimin, Li Xiaopeng, Zhang Chuan, Fang Jinggui
College of Horticulture, Nanjing Agricultural University, No 1 weigang, Nanjing 210095, China.
Institute of Horticulture, Jiangsu Academy of Agricultural Sciences, No 50 Zhongling road, Nanjing 210014, China.
Hortic Res. 2017 May 10;4:17018. doi: 10.1038/hortres.2017.18. eCollection 2017.
Grapes are categorized as a non-climacteric type of fruit which its ripening is not associated to important rises in respiration and ethylene synthesis. The starch metabolism shares a certain role in the carbohydrate metabolic pathways during grape berry development, and is regarded as an important transient pool in the pathway of sugar accumulation. However, the comprehensive role of starch and its contribution to the quality and flavor of grape berry have not been explored thoroughly. In this study, the expression levels of genes enzyme activities and carbohydrate concentrations related to starch metabolism, were analyzed to understand the molecular mechanism of starch accumulation during grape berry development. The results indicated that starch granules in grape berry were located at the chloroplast in the sub-epidermal tissues, acting as the temporary reserves of photosynthetic products to meet the needs for berry development, and relatively high starch contents could be detected at véraison stage. Moreover, both ADP-glucose pyrophosphorylase (EC 2.7.7.27) and sucrose phosphate synthase (EC 2.3.1.14) involved in starch synthesis displayed elevated gene expression and enzymes activities in the sub-epidermal tissue, while α- and β-amylases involved in its degradation were highly transcribed and active in the central flesh, explaining the absence of starch in this last tissue. Change in the gene expression and activities of ADP-glucose pyrophosphorylase, β-amylase and sucrose phosphate synthase revealed that they were regulated by the circadian rhythms in the fruitlets compared with those in the leaves. Both the morphological, enzymological and transcriptional data in this study provide advanced understandings on the function of starch during berry development and ripening that are so important for berry quality. This study will further facilitate our understanding of the sugar metabolism in grape berry as well as in other plant species.
葡萄被归类为非跃变型果实，其成熟与呼吸作用和乙烯合成的显著增加无关。淀粉代谢在葡萄浆果发育过程中的碳水化合物代谢途径中发挥着一定作用，被视为糖积累途径中的一个重要临时库。然而，淀粉的综合作用及其对葡萄浆果品质和风味的贡献尚未得到充分研究。在本研究中，分析了与淀粉代谢相关的基因表达水平、酶活性和碳水化合物浓度，以了解葡萄浆果发育过程中淀粉积累的分子机制。结果表明，葡萄浆果中的淀粉粒位于表皮下组织的叶绿体中，作为光合产物的临时储备以满足浆果发育的需求，在转色期可检测到相对较高的淀粉含量。此外，参与淀粉合成的ADP - 葡萄糖焦磷酸化酶（EC 2.7.7.27）和蔗糖磷酸合酶（EC 2.3.1.14）在表皮下组织中均表现出基因表达升高和酶活性增强，而参与其降解的α - 和β - 淀粉酶在中央果肉中高度转录且活性较高，这解释了该组织中不存在淀粉的原因。与叶片相比，ADP - 葡萄糖焦磷酸化酶、β - 淀粉酶和蔗糖磷酸合酶的基因表达和活性变化表明它们受幼果昼夜节律的调节。本研究中的形态学、酶学和转录数据为淀粉在浆果发育和成熟过程中的功能提供了更深入的理解；而淀粉对浆果品质非常重要。这项研究将进一步促进我们对葡萄浆果以及其他植物物种中糖代谢的理解。
