Nebauer Sergio G, Renau-Morata Begoña, Lluch Yolanda, Baroja-Fernández Edurne, Pozueta-Romero Javier, Molina Rosa-Victoria
Departamento de Producción Vegetal, Universitat Politécnica de València, Edificio 3K-2 planta, Camino de vera s.n., 46022 Valencia, Spain.
Departamento de Producción Vegetal, Universitat Politécnica de València, Edificio 3K-2 planta, Camino de vera s.n., 46022 Valencia, Spain.
Plant Physiol Biochem. 2014 Jul;80:105-13. doi: 10.1016/j.plaphy.2014.03.032. Epub 2014 Apr 5.
The fruit is the main sink organ in Citrus and captures almost all available photoassimilates during its development. Consequently, carbohydrate partitioning and starch content depend on the crop load of Citrus trees. Nevertheless, little is known about the mechanisms controlling the starch metabolism at the tree level in relation to presence of fruit. The aim of this study was to find the relation between the seasonal variation of expression and activity of the genes involved in carbon metabolism and the partition and allocation of carbohydrates in 'Salustiana' sweet orange trees with different crop loads. Metabolisable carbohydrates, and the expression and activity of the enzymes involved in sucrose and starch metabolism, including sucrose transport, were determined during the year in the roots and leaves of 40-year-old trees bearing heavy crop loads ('on' trees) and trees with almost no fruits ('off' trees). Fruit altered photoassimilate partitioning in trees. Sucrose content tended to be constant in roots and leaves, and surplus fixed carbon is channeled to starch production. Differences between 'on' and 'off' trees in starch content can be explained by differences in ADP-glucose pyrophosphorylase (AGPP) expression/activity and α-amylase activity which varies depending on crop load. The observed relation of AGPP and UGPP (UDP-glucose pyrophosphorylase) is noteworthy and indicates a direct link between sucrose and starch synthesis. Furthermore, different roles for sucrose transporter SUT1 and SUT2 have been proposed. Variation in soluble sugars content cannot explain the differences in gene expression between the 'on' and 'off' trees. A still unknown signal from fruit should be responsible for this control.
果实是柑橘的主要库器官，在其发育过程中捕获几乎所有可用的光合产物。因此，碳水化合物的分配和淀粉含量取决于柑橘树的结果量。然而，关于在树木水平上与果实存在相关的淀粉代谢调控机制，人们了解甚少。本研究的目的是找出‘萨卢斯蒂亚纳’甜橙树在不同结果量下，参与碳代谢的基因表达和活性的季节性变化与碳水化合物的分配和分布之间的关系。在一年中，对40年树龄、结果量重的树（‘结果’树）和几乎不结果的树（‘不结果’树）的根和叶，测定了可代谢碳水化合物以及参与蔗糖和淀粉代谢（包括蔗糖转运）的酶的表达和活性。果实改变了树木中光合产物的分配。根和叶中的蔗糖含量趋于恒定，多余固定碳被导向淀粉合成。‘结果’树和‘不结果’树在淀粉含量上的差异可以通过ADP - 葡萄糖焦磷酸化酶（AGPP）表达/活性和α - 淀粉酶活性的差异来解释，这两种酶的活性因结果量而异。观察到的AGPP和UGPP（UDP - 葡萄糖焦磷酸化酶）之间的关系值得注意，表明蔗糖和淀粉合成之间存在直接联系。此外，还提出了蔗糖转运蛋白SUT1和SUT2的不同作用。可溶性糖含量的变化无法解释‘结果’树和‘不结果’树之间基因表达的差异。果实发出的一个仍未知的信号应该负责这种调控。
