杜仲次生木质部分化和脱分化过程中酸性磷酸酶的超微细胞化学定位

Ultracytochemical Localization of Acid Phosphatase During Differentiation and Dedifferentiation of the Secondary Xylem in Eucommia ulmoides Trunk

杜仲（EucommiaulmoidesOliv．）次生木质部分化过程中，在形成层刚衍生的木薄壁细胞中，酸性磷酸酶（APase）主要分布于核膜边缘和高尔基体；在分化程度较高的木薄壁细胞中，APase散布于整个核中，进而，在各种细胞器残体上聚集；在成熟的木薄壁细胞中，APase沿细胞壁内侧分布。在未成熟导管分子中，核、质膜及纹孔上明显存在APase聚集，进而，核解体；在即将分化成熟的导管分子中，APase主要集中于初生壁；在已分化成熟的导管分子中，APase集中于次生壁。脱分化过程中，只在细胞质中可见分散的APase活性，而细胞核和细胞壁上未见此酶的分布；更深层的即将分化成熟和已分化成熟的导管分子，未见有细胞分裂，其上APase的分布与剥皮前相同。通过比较分化和脱分化过程中APase的分布，推测不同的APase同工酶可能分别参与了次生木质部细胞程序性死亡过程中原生质体的解体和次生壁的建成。APase的聚集程度可能是决定细胞能否脱分化的一个重要特征。

The role of acid phosphatase (APase) played in the differentiation and dedifferentiation of the secondary xylem in Eucommia ulmoides Oliv. in respect of enzyme localization was studied. APase was initially prominent along the nuclear membrane and in the dictyosomes of the young xylem parenchyma cells,and present in the whole nucleus in the highly differentiated cells. At a later stage of differentiation of the xyem penchyma cells, APase was concentraed in the debris of other ompelles and along the cell wall in the mature cells. APase aggregated in the nucleus, plasma membare and pits of the immature vessel element,from which part of the plasma membrane became indistinct or disappeared and the nucleus eventually degenerated. APase mainly aggregated along the primary cell wall of the nearly maure vessel element, and in the secondary cell wall in the mature vessel element. On the 1st and 2nd day after girdling, the enzyme was sparsely scattered in the cytopasm during the dedifferentiation of the xylem parenchyma cells. On the 4th and 7th day after girdling, APase was present in the cytoplasm of the dilated xylem parenchyma cells in the surface layer and also that of the adjacent dedifferentiating parenchyma cell. On the 14th and 21st day after girdling, few APase was found in the cytoplasm and none in the cell wall of the inner immature dedifferentiating vessel element. The localization of APase in the secondary xylem formed form the new cambium was as similar as that in the normal vascular tissue, and that in the mature and nearly mature vessel element that could not dedifferentiate after girdling was the same as that before girdling. Comparison of the distribution of Apase activity between the differentiation and dedifferntiation stages of the secondary xylem indicates that different isoforms of APase may respectively play functions in the protoplast degeneration and the secondary wall formation during programmed cell death of the secondary xylem. The intensity of APase activity may be an important decisive characteristic in cell dedifferentiation.