Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth, W-8580, Bayreuth, Germany.
Planta. 1991 Dec;183(1):31-9. doi: 10.1007/BF00197564.
We have investigated the regulation of sucrose storage in cell-suspension cultures of sugarcane. When grown in batch culture, sucrose accumulation commences after about 5 d, when the nitrogen supply is exhausted. Sucrose storage is also induced by decreasing the nitrogen supply to cells growing in a chemostat. The measured activity of sucrose-phosphate synthase is high enough to account for the rate of sucrose accumulation, provided precautions are taken to avoid the hydrolysis of UDP during the assay. The cells contained high sucrose-synthase activity but pulsing experiments with [(14)C]glucose and unlabelled fructose indicated that this enzyme did not contribute substantially to the synthesis of sucrose, because the glucosyl and fructosyl moieties of sucrose were equally labelled. Several lines of evidence demonstrate the presence of a cycle in which sucrose is synthesized and degraded simultaneously; sucrosephosphate-synthase activity doubles during the phase when the cells are actively storing sucrose but activity is also high after storage has ceased, or when the sucrose is being remobilised; pulse experiments with [(14)C]fructose also showed that sucrose synthesis occurs not only during the storage phase, but also after storage has stopped and during the rapid mobilisation of sucrose; the cells contain high activities of sucrose synthase and alkaline invertase and these are both at a maximum when sucrose storage is occurring; even during the storage phase. [(14)C]fructose pulses lead to labelling of free glucose which is evidence for rapid synthesis and degradation of sucrose. It is proposed that the rate and extent of sucrose storage is regulated by this cycle of synthesis and degradation. Measurements of enzyme activities and metabolite levels are presented, and it is discussed which factors could contribute to the regulation of these two opposing fluxes and, hence, the rate of net sucrose storage and mobilisation.
我们研究了甘蔗悬浮细胞培养中蔗糖的储存调节。当在分批培养中生长时，当氮源耗尽时，约在 5 天后开始积累蔗糖。通过减少恒化器中细胞的氮供应也可以诱导蔗糖储存。只要在测定中采取措施避免 UDP 的水解，测量的蔗糖磷酸合酶活性就足以解释蔗糖的积累速率。细胞中含有高的蔗糖合酶活性，但用 [(14)C]葡萄糖和未标记的果糖进行脉冲实验表明，该酶并没有大量参与蔗糖的合成，因为蔗糖的葡萄糖基和果糖基部分的标记程度相等。有几条证据表明存在一个同时合成和降解蔗糖的循环；当细胞积极储存蔗糖时，蔗糖磷酸合酶活性增加一倍，但在储存停止后或蔗糖被重新动员时，活性仍然很高；用 [(14)C]果糖进行的脉冲实验还表明，蔗糖合成不仅发生在储存阶段，而且在储存停止后和蔗糖快速动员期间也会发生；细胞中含有高活性的蔗糖合酶和碱性转化酶，当蔗糖储存发生时，这两种酶都达到最大值；即使在储存阶段也是如此。[(14)C]果糖脉冲导致游离葡萄糖的标记，这证明了蔗糖的快速合成和降解。提出蔗糖的储存速率和程度受到这种合成和降解循环的调节。本文提出了一些酶活性和代谢物水平的测量方法，并讨论了哪些因素可能有助于调节这两种相反的通量，从而调节净蔗糖的储存和动员速率。
