Programmed Cell Death of the Mung Bean Cotyledon during Seed Germination

在綠豆發芽過程中，其子葉進行細胞凋亡。細胞貯存物質之流失及大量液泡化造成了子葉貯藏薄壁細胞的死亡，當細胞凋亡進入細胞瓦解之階段，貯藏薄壁細胞逐漸自動溶解，形成巨大的中心液泡，細胞質、細胞核完全溶解，原生質體由細胞壁向內萎縮，進入了細胞凋亡的最後階段。在此凋亡過程中，細胞色素C由粒線體釋放至細胞質中，細胞核DNA片段化亦明顯發生。細胞凋亡過程中核酸酶之活性可由體外測試証明，此核酸酶之活性可被caspase-3抑制劑Ac-DEVD-fmk所抑制。Caspase-like protease (CLP)之活性亦可在子葉凋亡過程中偵測到。CLP之活性在種子發芽第三天之子葉中活性最高，此CLP之活性可被caspase-3專一抑制劑所抑制，對caspase-1專一抑制劑則有抗性。

關鍵字

Caspase-like protease ；細胞色素c釋放； Internucleosomal DNA片段化；線粒體；程序性細胞凋亡；貯藏物質之溶解和液泡化

並列摘要

The cotyledon of the mung bean (Vigna radiata) undergoes programmed cell death (PCD) during seed germination. Death of the cotyledon storage parenchyma cells was preceded by reserve mobilization and vacuolation. During the dismantling phase of PCD, the storage parenchyma cells exhibited progressive autolysis, resulting in the formation of a large central vacuole. Complete lysis of the cytoplasm and nucleus occurred, and condensation of the protoplast away from the cell wall appeared at the final stage of cell death. Cytochrome c translocation from the mitochondria to the cytosol and internucleosomal DNA fragmentation were also observed in cotyledon senescence during seed germination. Nuclease activity was detected in vitro during mung bean cotyledon PCD, and the activity of this nuclease was repressed by the caspase-3 inhibitor Ac-DEVD-fmk. Caspase-like protease (CLP) activity was detected in cotyledons during seed imbibition and after seed germination. CLP activity reached a peak in day 3 cotyledons. These CLP activities were inhibited by a caspase-3-specific inhibitor but were resistant to caspase-1-specific inhibitors. This study demonstrates that the programmed cell death in mung bean cotyledons involves nuclease induction, nuclear DNA fragmentation, cytochrome c releasing and CLP participation. These PCD hallmarks establish the important paradigm for further understanding of PCD in higher plant.

並列關鍵字

Caspase-like protease ； Cytochrome c releasing ； Internucleosomal DNA fragmentation ； Mitochondria ； Programmed cell death ； Reserve mobilization and vacuolation

國際替代計量

Programmed Cell Death of the Mung Bean Cotyledon during Seed Germination

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