為維持有效的碳攝取，植物於陰暗環境下會產生較薄的蔭生葉葉片，
以有效吸收陽光與二氧化碳；然而當光照增強時，蔭生葉溫度上升易導致
光呼吸作用，而降低碳的合成效率。C4 植物能克服光呼吸作用的影響，但
卻需耗費較多的能量，因此能在陰暗環境中生存的C4 植物並不多。而柔
枝莠竹(Microstegium vimineum (Trin.) A. Camus)即為一種不受陰暗環境影
響的C4 植物。
本研究藉由觀察柔枝莠竹在不同光強度下葉部解剖特性的變化，來了
解其環境適應上的優勢。實驗結果顯示柔枝莠竹在全日照及全日照3%這
兩種光照強度下，蔭生葉的顏色比陽生葉深，束鞘細胞的澱粉粒較少，葉
部的細胞形狀變扁但數量及層數沒有改變，有較多的異型細胞的排列在維
管束間，兩種葉片的葉綠體，無明顯不同。此外，原生質聯絡絲中的腫脹(稱
為sphincters)僅在蔭生葉發現，推測其功能應與調控光合作用之中間產物
於葉肉細胞與束鞘細胞間的移動有關。
綜合上述結果，本研究推測柔枝莠竹藉由控制成熟葉片內葉肉細胞和
束鞘間的通透性，以達到C4 光合作用的可塑性，而可生長於陰暗環境下。

To maintain an effective carbon uptake, plants in the dark environment
usually possess a thinner shade leaves for efficiently absorbing sunlight and
carbon dioxide. However, when the light intensity is increased, the high
temperatures lead shade leaves to act photorespiration and reduce the synthetic
rates of carbon. C4 plants can avoid photorespiration, while need to consume
energy. Therefore they hardly survive in the dark environments. Unexpectedly,
Microstegium vimineum (Trin.) A. Camus a C4 plant, can grow well under dark
environments.
Through observing M. vimineum under different light intensities, changes
in leaf anatomy were found. Results showed that leaves of M. vimineum
growing under 3% of sunlight yielded dark-color leaves, fewer starch grains in
bundle sheath, while no differences in cell number or chloroplast structure and
density distinctive cell than full sunlight. In addition, the enlargement of
electron-dense elements(sphincters) were only found in plasmodesmata of
shade leaves, suggesting that its function should be regulate the shuttle of C4
pathway intermediates between bundle sheath and mesophyll.
This study suggest that in order to achieve the plasticity of C4
photosynthesis M. vimineum mediates the permeabilitits of between mesophyll
and bundle sheath in mature leaves.

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