Carbohydrate metabolism in two apple genotypes that differ in malate accumulation
Carbohydrate metabolism in two apple genotypes that differ in malate accumulation
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DOI：
10.1016/j.jplph.2003.12.008
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发表时间：
2004-09-01
影响因子：
4.3
通讯作者：
Berüter, J
中科院分区：
文献类型：
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作者：
Berüter, J
在苹果品种'Usterapfel'中，有两种已知的基因型，其苹果酸含量不同。开花后100天，低酸型（LA-果）含有125 μ mol g（-1）干物质（DW）的苹果酸，白色高酸型（HA-果）达到627 μ mol g（-1）DW的水平。参与苹果酸代谢的酶，如PEP羧化酶、苹果酸脱氢酶和NADP苹果酸酶的催化活性没有差异。在[C-14]葡萄糖掺入任一基因型的切除组织中后，有机酸部分被标记至大致相同的程度。此外，[C-14]苹果酸的吸收显着塔在离体组织的LA-果实。这些研究结果表明，LA果实中苹果酸含量较低是苹果薄壁细胞积累苹果酸能力有限的结果，苹果酸积累能力的不同对总体碳分配有显着影响。然而，两种基因型的呼吸速率和苹果酸合成速率相似。在HA-果实，通过丙酮酸激酶的糖酵解通量增加，以补偿积累在液泡中的苹果酸的碳。由于LA果实中的苹果酸储存受到限制，因此它更容易用于异源发生，并且与PEP羧激酶活性高出3倍相关。LA果实显示出较高浓度的ATP，这刺激了GLc 6P和果糖-6-磷酸的形成。在更成熟的果实中，磷酸己糖含量的升高导致碳分配到淀粉（+40%）、半纤维素（+104%）和蔗糖（+40%）中的增强。碳水化合物合成的激活导致葡萄糖-1-磷酸（Glc 1 P）的显着下降。为了满足对Glc 1 P需求的增加，中性和酸性转化酶、己糖激酶和磷酸葡萄糖变位酶的活性在LA果实中较高。葡萄糖是一种比果糖更通用的代谢途径底物。这也是显而易见的，糖酵解通量在苹果是依赖于葡萄糖水平，和葡萄糖磷酸变位酶催化的反应有助于苹果酸和碳水化合物聚合物之间的碳分配的调节。(C)2004年Elsevier GmbH。All rights reserved.
In the apple variety 'Usterapfel', there are two known genotypes, which differ in malic acid content. One hundred days after full bloom, low-acid fruit (LA-fruit) contained 125 mumol g(-1) dry matter (DW) of malate, white the high-acid genotype (HA-fruit) reached levels up to 627 mumol g(-1) DW. There was no difference in the catalytic activity of enzymes involved in malate metabolism, such as PEPcarboxylase, malate dehydrogenase, and NADP malic enzyme. After [C-14] glucose incorporation into the excised tissue of either genotype, the organic acid fraction was labeled to approximately the same extent. Furthermore, uptake of [C-14] malate was significantly tower in excised tissue of LA-fruit. These findings suggest that tow malate content in LA-fruit is the result of a restricted ability to accumulate malate in apple parenchyma cells.The different ability to accumulate malate had a pronounced effect on overall carbon partitioning. However, the rate of respiration and the rate of malate synthesis was similar in both genotypes. In HA-fruit, the gtycolytic flux through pyruvate kinase was increased to compensate for the carbon that accumulated in the vacuole as malate. Since malate storage in the LA-fruit was restricted, it was more easily available for gluconeogenesis, and was correlated with a three-times higher activity of PEPcarboxykinase.LA-fruit showed higher concentrations of ATP, which stimulated GLc6P and fructose-6-phosphate formation. The elevated hexosephosphate content led to an enhanced partitioning of carbon into starch (+40%), hemicellulose (+104%), and sucrose (+40%) in more mature fruit. The activation of carbohydrate synthesis resulted in a significant drop in glucose-1-phosphate (Glc1P). To meet the increased demand for Glc1P, the activities of neutral and acid invertase, hexokinase, and phosphoglucomutase were higher in LA-fruit. Glucose was a more versatile substrate for this metabolic route than was fructose. It was also evident that glycolytic flux in apple was dependent on glucose level, and that the reaction catalysed by phosphoglucomutase contributed to the regulation of carbon partitioning between malate and carbohydrate polymers. (C) 2004 Elsevier GmbH. All rights reserved.