Uptake of leucine by Chlorella symbionts of green hydra
Uptake of leucine by Chlorella symbionts of green hydra
复制标题
绿水螅小球藻共生体对亮氨酸的摄取
DOI：
10.1098/rspb.1988.0051
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
P. McAuley
中科院分区：
文献类型：
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作者：
P. McAuley
与绿色水螅共生的小球藻的细胞能够在从共生体分离后通过高亲和力的转运机制摄取亮氨酸，并将螯合的氨基酸掺入蛋白质中。在完整的共生体系中，小球藻细胞摄取亮氨酸的时间过程是在水螅被喂食用放射性亮氨酸标记的卤虫无节幼体后进行的。摄取分两个阶段进行，第一个阶段比第二个阶段更快，间隔很短，其中每个细胞的放射性量持续下降。虽然亮氨酸从卤虫游离氨基酸池中积累不成比例的共生小球藻细胞，这是不足以解释的初始快速阶段的吸收，也不能解释的小球藻细胞的性质的变化后，随着时间的推移，摄取率的变化。相反，在第二阶段的吸收较慢，以及在此之前每个细胞的放射性量的减少，可能是由于小球藻细胞的氨基酸供应的变化。由相同的系统作为亮氨酸运输的氨基酸引起积累的亮氨酸从孤立的小球藻细胞外排时，存在于高的外部浓度。因此，所观察到的共生放射性的积累可能是单向流入和单向流出的亮氨酸依赖于外部浓度的变化，从卤虫或水螅池的差异。这是讨论参考宿主控制藻类细胞分裂，这已被证明是依赖于供应的“分裂因子”从宿主食物。
Cells of a Chlorella sp. symbiotic with green hydra were able to take up leucine via a high-affinity transport mechanism after isolation from the symbiosis, and to incorporate sequestered amino acid into protein. The time course of uptake of leucine by Chlorella cells in the intact symbiosis was followed after hydra were fed with nauplii of the brine shrimp Artemia salina that had been labelled with radioactive leucine. Uptake proceeded in two stages, the first more rapid than the second, separated by a short interval in which there was a consistently observed decrease in the amount of radioactivity per cell. Although leucine from Artemia free amino acid pools was accumulated disproportionately by Chlorella cells in symbiosis, this was not sufficient to explain the initial rapid phase of uptake, nor could changes in rate of uptake with time after feeding be explained by changes in properties of the Chlorella cells. Rather, slower uptake in the second phase, and the decrease in amount of radioactivity per cell which preceded it, were probably due to changes in supply of amino acids to the Chlorella cells. Amino acids transported by the same system as leucine caused efflux of accumulated leucine from isolated Chlorella cells when present in high external concentrations. Thus the observed accumulation of radioactivity in symbiosis may have been the difference between unidirectional influx and unidirectional efflux of leucine dependent upon changes in external concentrations of unlabelled amino acids from Artemia or from hydra pools. This is discussed with reference to host control of algal cell division, which has been shown to be dependent upon supply of a ‘division factor’ from host food.