Cho H T, Kende H
Michigan State University-Department of Energy Plant Research Laboratory, East Lansing 48824-1312, USA.
Plant Physiol. 1997 Apr;113(4):1137-43. doi: 10.1104/pp.113.4.1137.
Cell walls of deepwater rice (Oryza sativa L.) internodes undergo long-term extension (creep) when placed under tension in acidic buffers. This is indicative of the action of the cell wall-loosening protein expansin. Wall extension had a pH optimum of around 4.0 and was abolished by boiling. Acid-induced extension of boiled cell walls could be reconstituted by addition of salt-extracted rice or cucumber cell wall proteins. Cucumber expansin antibody recognized a single protein band of 24.5-kD apparent molecular mass on immunoblots of rice cell wall proteins. Expansins were partially purified by concanavalin A affinity chromatography and sulfopropyl (SP) cation-exchange chromatography. The latter yielded two peaks with extension activity (SP20 and SP29), and immunoblot analysis showed that both of these active fractions contained expansin of 24.5-kD molecular mass. The N-terminal amino acid sequence of SP20 expansin is identical to that deduced from the rice expansin cDNA Os-EXP1. The N-terminal amino acid sequence of SP29 expansin matches that deduced from the rice expansin cDNA Os-EXP2 in six of eight amino acids. Our results show that two expansins occur in the cell walls of rice internodes and that they may mediate acid-induced wall extension.
深水水稻（Oryza sativa L.）节间的细胞壁在置于酸性缓冲液中受拉时会经历长期伸展（蠕变）。这表明细胞壁松弛蛋白扩展素的作用。细胞壁伸展的最适pH约为4.0，煮沸后则被消除。通过添加盐提取的水稻或黄瓜细胞壁蛋白，可以重建煮沸细胞壁的酸诱导伸展。黄瓜扩展素抗体在水稻细胞壁蛋白的免疫印迹上识别出一条表观分子量为24.5-kD的单一蛋白带。通过伴刀豆球蛋白A亲和层析和磺丙基（SP）阳离子交换层析对扩展素进行了部分纯化。后者产生了两个具有伸展活性的峰（SP20和SP29），免疫印迹分析表明这两个活性组分都含有分子量为24.5-kD的扩展素。SP20扩展素的N端氨基酸序列与从水稻扩展素cDNA Os-EXP1推导的序列相同。SP29扩展素的N端氨基酸序列在八个氨基酸中的六个与从水稻扩展素cDNA Os-EXP2推导的序列匹配。我们的结果表明，水稻节间细胞壁中存在两种扩展素，它们可能介导酸诱导的细胞壁伸展。
