CARBON ASSIMILATION PATTERN IN THE SUBMERGED LEAVES OF THE AQUATIC ANGIOSPERM: VALLISNERIA SPIRALIS L.
CARBON ASSIMILATION PATTERN IN THE SUBMERGED LEAVES OF THE AQUATIC ANGIOSPERM: VALLISNERIA SPIRALIS L.
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DOI：
10.1111/j.1438-8677.1982.tb01635.x
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发表时间：
1982-08
期刊：
影响因子：
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通讯作者：
R. Helder;M. V. Harmelen
中科院分区：
文献类型：
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作者：
R. Helder;M. V. Harmelen
摘要苦草叶片节段在光照或黑暗条件下均能吸收CO2和HCO3-离子并吸收无机碳。C4的固定发生在黑暗中，产生苹果酸和天冬氨酸作为第一个化合物，但也可以检测到Calvin循环的一些残余活性。C4和C3的固定都受到光的刺激，在当时的条件下，C4的固定占总固定率的20-25%。通过延长暗固定时间，可以获得几乎不偏离光固定实验中发现的图案的标记分布图案。标记从天冬氨酸转移到其他氨基酸和有机酸，其中柠檬酸-异柠檬酸是最明显的。草酸是苦艾叶中含量最丰富的酸，在草酸中没有检测到活性。相反，苹果酸会积累，不会发生翻转。根据苹果酸分子内标记分布的初步数据，我们推断只有单标记分子在黑暗中形成。标记物倾向于均匀分布在第四个和第一个C原子之间。然而，在光照下，有一种逐渐统一标记的趋势，即更多的C原子被标记。标记原子在C3和C4产物之间的转移必须是双向的。然而，没有检测到标记的PEP的量，这似乎是转移反应中的一种可信的中间体，无法证明。积累的苹果酸可以用作二氧化碳储存库，可以在从介质减少的二氧化碳供应的条件下利用，这反过来又是二氧化碳在液体介质中的高度减少扩散的结果，这导致接触叶片的溶液迅速耗尽。
SUMMARY Segments of leaves of Vallisneria spiralis L. were allowed to take up CO2 and HCO3-ions and assimilate the inorganic carbon either in the light or in the dark. C4-fixation occurred in the dark producing malate and aspartate as the first compounds, but some residual activity of the Calvin cycle could be detected, too. Both C4 and C3 fixation were stimulated by light, the C4 fixation amounting to 20–25% of total fixation rate under the prevailing conditions. By extending the dark fixation period a label distribution pattern could be obtained which hardly deviated from the pattern found in a light fixation experiment. Label from aspartate was transferred to other amino acids and to organic acids, citrate-isocitrate being the most apparent one. No detectable activity could be demonstrated in oxalic acid, which is the most abundant acid in Vallisneria leaves. In contrast, malate is accumulated and no turn-over could be demonstrated. From preliminary data on label distribution within the malate molecules we deduced that only single-labelled molecules were formed in the dark. The label tended to be distributed evenly among the fourth and first C-atom. However, in the light there was a gradual tendency to uniform labelling, i.e. more C-atoms became labelled. Transfer of labelled atoms between C3 and C4 products must have occurred in both directions. However, no detectable amounts of labelled PEP, which seemed to be a plausible intermediate in the transfer reactions, could be demonstrated. The accumulated malic acid may function as a CO2-reservoir that can be drawn on under conditions of reduced CO2 supply from the medium, which is, in turn, the results of the highly reduced diffusion of CO2 in a liquid medium which leads to rapid depletion of the solution contacting the leaves.