镉诱导的茶树苗膜脂过氧化和细胞程序性死亡

在含镉的营养液中，茶树幼苗生长受到抑制。随培养时间延长，膜脂过氧化产物丙二醛含量持续升高；超氧物岐化酶（SOD）和过氧化氢酶（CAT）活性初期升高，而后分别在第4天和第2天开始下降。镉胁迫的第5-7天，一部分细胞陆续发生程序性死亡。其特征是：线粒体聚集于核周围，个数增加，嵴发达，而后衰亡。核仁消失，染色质凝结在核膜边缘，核萎缩，外层核膜局部扩张，形成胀泡。核以外溢、出芽和崩裂三种方式溃解。核是最后消亡的细胞器。程序性死亡的细胞局限于某些区域。镉胁迫下，幼苗膜脂过氧化可能是诱发PCD的主要原因。

Cadmium-induced Membrane Lipid Peroxidation and Programmed Cell Death in Tea Seedling

The relation between oxidative stress and programmed cell death(PCD )in stem apex cell of tea Camellia sinensis (L.)O. Kuntze]seedlings cultured in Hoagland nutrient solution containing Cd 2+ 0.50 mmol/L was studied. The biomass of tea seedling dropped significantly after Cd 2+ treatment(Fig.1). The malonyl dialdehyde(MDA)content in the seedling increased slightly at first and then very fast (Fig.2). At the same time the superoxide dismutase(SOD)and catalase(CAT)activity in the seedling increased slightly to reach their peaks on the 4th and 2th day respectively after treatment, then declined markedly(Figs. 3 and 4). MDA content, SOD and CAT activity in control were stable with prolonged culture time. PCD was observed from 5 d to 7 d after treatment with transmission electron microscopy. As PCD proceeded the protoplasmic components degenerated progressively and in a well orderly way and finally disintegrated. The ultrastructural changes in the cell as follows: Number of mitochondria increased with many cristae and thick matrix and came near to the nucleus at the early stage of PCD(Fig.5- 4- 6), then the matrix in the mitochondria formed vesicles which eventually disintegrated(Fig.5-7 and 8). At the onset of degeneration of nucleus, the nucleolus disintegrated and chromatin formed a dense layer at the periphery(Fig.5-9). In some nuclei the expanded perinuclear membrane contained nuclear materials, then the inner membrane of nucleus ruptured and outer membrane formed puffs. Partly nuclear material was expelled from the puff into vacuole(Fig.5-10 and 11). The degeneration of nucleus at the late stage can proceed in three ways: scattering(Fig.5-14), protrusion to form buds(Fig.5-16) and bursting(Fig.5-18). Nucleus was the last organelle to disappear. These characteristics were similar to characteristics PCD in animal cells. The debris formed after autotysis might be used in two ways: to be transported to adjacent cells( Fig.5-13 and 17), or to be used in the formation of cell wall(Fig.5-19). PCD occurred compartmentally in some cells, with the contiguous cells remaining intact(Fig.5-19). We suggested that oxidative stress might play an important role in the induction of PCD by Cd 2+.