Higuchi T, Suga S, Tsuchiya T, Hisada H, Morishima S, Okada Y, Maeshima M
Laboratory of Biochemistry, Graduate School of Bioagricultural Sciences, Nagoya University, Japan.
Plant Cell Physiol. 1998 Sep;39(9):905-13. doi: 10.1093/oxfordjournals.pcp.a029453.
A major membrane intrinsic protein (VM23) in vacuoles of radish (Raphanus) tap root was investigated. The cDNAs for two isoforms of VM23, gamma- and delta-VM23, encode polypeptides of 253 and 248 amino acids, respectively. gamma- and delta-VM23 correspond to the gamma- and delta-TIP (tonoplast intrinsic protein) of Arabidopsis. The deduced amino acid sequences of the two VM23 isoforms were 60% identical. The amino-terminal sequence of gamma-VM23 showed agreement with the direct sequence of the purified VM23, suggesting that gamma-VM23 is the most abundant molecule among the VM23 isoforms. When mRNAs of gamma- and delta-VM23 were injected into Xenopus oocytes, the osmotic water permeability of oocytes increased 6-fold (60 to 200 microns s-1) of the control oocytes. The transcripts of both isoforms were detected in a high level in growing hypocotyls and young leaves, but delta-VM23 was not detected in seedling roots. Light illumination enhanced the transcription of two genes of VM23 in cotyledons and roots but suppressed their expression in hypocotyls the growth of which was inhibited by light. These findings suggest that the expression of VM23 is tightly related to cell elongation.
对萝卜（Raphanus）主根液泡中的一种主要膜内在蛋白（VM23）进行了研究。VM23的两种同工型γ-VM23和δ-VM23的cDNA分别编码253和248个氨基酸的多肽。γ-VM23和δ-VM23分别对应拟南芥的γ-TIP（液泡膜内在蛋白）和δ-TIP。两种VM23同工型的推导氨基酸序列有60%的同源性。γ-VM23的氨基末端序列与纯化的VM23的直接序列一致，表明γ-VM23是VM23同工型中含量最丰富的分子。当将γ-VM23和δ-VM23的mRNA注射到非洲爪蟾卵母细胞中时，卵母细胞的渗透水通透性增加到对照卵母细胞的6倍（从60到200微米/秒）。在生长的下胚轴和幼叶中高水平检测到两种同工型的转录本，但在幼苗根中未检测到δ-VM23。光照增强了子叶和根中VM23两个基因 的转录，但抑制了它们在下胚轴中的表达，而下胚轴的生长受到光照的抑制。这些发现表明，VM23的表达与细胞伸长密切相关。
