Wu Alex Chi, Ral Jean-Philippe, Morell Matthew K, Gilbert Robert G
Tongji School of Pharmacy, Huazhong University of Science and Technology, Wuhan, Hubei province, China; Centre for Nutrition and Food Sciences, Queensland Alliance for Agricultural and Food Innovation, The University of Queensland, Brisbane, Queensland, Australia.
Food Futures National Research Flagship, CSIRO, Canberra, Australian Capital Territory, Australia; Plant Industry, CSIRO, Canberra, Australian Capital Territory, Australia.
PLoS One. 2014 Jun 27;9(6):e100498. doi: 10.1371/journal.pone.0100498. eCollection 2014.
Transient starch in leaves is synthesized by various biosynthetic enzymes in the chloroplasts during the light period. This paper presents the first mathematical model for the (bio)synthesis of the chain-length distribution (CLD) of transient starch to aid the understanding of this synthesis. The model expresses the rate of change of the CLD in terms of the actions of the enzymes involved. Using this to simulate the experimental CLD with different enzyme combinations is a new means to test for enzymes that are significant to the rate of change of the CLD during synthesis. Comparison between the simulated CLD from different enzyme combinations and the experimental CLD in the leaves of the model plant Arabidopsis thaliana indicate α-amylase, in addition to the core starch biosynthetic enzymes, is also involved in the modification of glucans for the synthesis of insoluble starch granules. The simulations suggest involvement of β-amylase, in the absence of α-amylase in mutants, slows the rate of attaining a crystalline-competent CLD for crystallization of glucans to form insoluble starch. This suggests a minor role of β-amylase in shaping normal starch synthesis. The model simulation predicts that debranching of glucans is an efficient mechanism for the attainment of crystalline-competent CLD; however, attaining this is still possible, albeit slower, through combinations of α- and β-amylase in the absence of isoamylase-type debranching enzyme. In Arabidopsis defective in one of the isoamylase-type debranching enzymes, the impact of α-amylase in starch synthesis is reduced, while β-amylase becomes significantly involved, slowing the rate of synthesis in this mutant. Modeling of transient starch CLD brings to light previously unrecognized but significant effects of α- and β-amylase on the rate of transient starch synthesis.
叶片中的暂态淀粉是在光照期间由叶绿体中的各种生物合成酶合成的。本文提出了第一个用于暂态淀粉链长分布（CLD）（生物）合成的数学模型，以帮助理解这种合成过程。该模型根据所涉及酶的作用来表达CLD的变化速率。利用这个模型来模拟不同酶组合下的实验CLD，是一种测试对合成过程中CLD变化速率有重要影响的酶的新方法。对模式植物拟南芥叶片中不同酶组合模拟得到的CLD与实验CLD进行比较表明，除了核心淀粉生物合成酶外，α-淀粉酶也参与了葡聚糖的修饰以合成不溶性淀粉颗粒。模拟结果表明，在突变体中缺乏α-淀粉酶的情况下，β-淀粉酶的参与会减缓葡聚糖结晶形成不溶性淀粉所需的具备结晶能力的CLD的达到速率。这表明β-淀粉酶在正常淀粉合成过程中作用较小。模型模拟预测，葡聚糖的去分支是达到具备结晶能力的CLD的有效机制；然而，在缺乏异淀粉酶型去分支酶的情况下，通过α-淀粉酶和β-淀粉酶的组合仍有可能达到这一目标，尽管速度较慢。在一种异淀粉酶型去分支酶存在缺陷的拟南芥中，α-淀粉酶在淀粉合成中的作用减弱，而β-淀粉酶则显著参与其中，减缓了该突变体的合成速率。暂态淀粉CLD的建模揭示了α-淀粉酶和β-淀粉酶对暂态淀粉合成速率此前未被认识但却很重要的影响。
