Auxin-dependent gene expression of ascorbate oxidase and cell-elongation in plants.

抗坏血酸氧化酶（AAO）的生物学功能尚未阐明，尽管AAO已被认为参与细胞生长。我们研究了烟草BY-2细胞在非同步、同步和伸长培养过程中AAO的表达。在非同步培养中，AAO mRNA在对数生长期大量表达。在同步分裂培养中，AAO mRNA在各时相均有表达，但在G1期表达量很低。在伸长培养中，AAO mRNA的水平随着细胞的伸长而增加。培养基中的AAO活性以及细胞中的抗坏血酸和脱氢抗坏血酸含量也在伸长过程中增加。我们认为AAO的表达和脱氢抗坏血酸的产生受细胞周期的控制，AAO可能在细胞伸长过程中起抗坏血酸氧化剂的作用。将南瓜AAO cDNA导入烟草BY-2（Nicotiana tabacum L.）CV.通过农杆菌介导的转化方法，将重组南瓜AAO基因表达到转化细胞中，并分泌到培养基中。这些转基因细胞显示与野生型细胞没有形态学差异。然而，在应用激素的存在下，从转基因细胞制备的原生质体比野生型细胞更迅速地伸长。我们认为AAO可能通过控制质膜的运输过程而不是通过影响细胞壁来调节细胞膨胀。

The biological function of ascorbate oxidase (AAO) has not been clarified yet, although AAO has been suggested to be involved in cell growth. We investigated AAO expression during non-synchronous, synchronous and elongation cultures of tobacco BY-2 cells. In non-synchronous culture, AAO mRNA was abundant in logarithmic growth phase. In synchronous division culture, AAO mRNA was detected in all phases but the levels were quite low in G1 phase. In elongation culture, the levels of AAO mRNA increased during elongation of cells. AAO activity in the culture medium, as well as ascorbate and dehydroascorbate contents in the cells, also increased during the elongation. We propose that AAO expression and production of dehydroascorbate is under the control of cell cycle, and that AAO may function as an ascorbate oxidizer apoplastically in the process of cell elongation. When pumpkin AAO cDNA was introduced into tobacco BY-2 (Nicotiana tabacum L. cv. Bright Yellow No. 2) cultured cells by Agrobacterium-mediated transformation, the transgenic cells expressed and secreted the recombinant pumpkin AAO into the culture medium. These transgenic cells showed no morphological difference from wild-type cells. However, in the presence of applied hormones protoplasts prepared from the transgenic cells elongated more rapidly than those of wild-type cells. We propose that AAO may play a key role in the regulation of cell expansion perhaps by controlling transport processes through plasma membrane, but not by affecting the cell wall.