Nakamura T, Vrinten P, Hayakawa K, Ikeda J
Tohoku National Agriculture Experimental Station, Akahira 4, Morioka 020-01, Japan.
Plant Physiol. 1998 Oct;118(2):451-9. doi: 10.1104/pp.118.2.451.
Waxy wheat (Triticum aestivum L.) lacks the waxy protein, which is also known as granule-bound starch synthase I (GBSSI). The starch granules of waxy wheat endosperm and pollen do not contain amylose and therefore stain red-brown with iodine. However, we observed that starch from pericarp tissue of waxy wheat stained blue-black and contained amylose. Significantly higher starch synthase activity was detected in pericarp starch granules than in endosperm starch granules. A granule-bound protein that differed from GBSSI in molecular mass and isoelectric point was detected in the pericarp starch granules but not in granules from endosperm. This protein was designated GBSSII. The N-terminal amino acid sequence of GBSSII, although not identical to wheat GBSSI, showed strong homology to waxy proteins or GBSSIs of cereals and potato, and contained the motif KTGGL, which is the putative substrate-binding site of GBSSI of plants and of glycogen synthase of Escherichia coli. GBSSII cross-reacted specifically with antisera raised against potato and maize GBSSI. This study indicates that GBSSI and GBSSII are expressed in a tissue-specific manner in different organs, with GBSSII having an important function in amylose synthesis in the pericarp.
糯小麦（普通小麦）缺乏蜡质蛋白，蜡质蛋白也被称为颗粒结合淀粉合酶I（GBSSI）。糯小麦胚乳和花粉中的淀粉颗粒不含直链淀粉，因此用碘液染色呈红棕色。然而，我们观察到糯小麦果皮组织中的淀粉染成蓝黑色且含有直链淀粉。在果皮淀粉颗粒中检测到的淀粉合酶活性显著高于胚乳淀粉颗粒。在果皮淀粉颗粒中检测到一种在分子量和等电点上与GBSSI不同的颗粒结合蛋白，但在胚乳颗粒中未检测到。这种蛋白被命名为GBSSII。GBSSII的N端氨基酸序列虽然与小麦GBSSI不同，但与谷物和马铃薯的蜡质蛋白或GBSSI具有很强的同源性，并且包含基序KTGGL，这是植物GBSSI和大肠杆菌糖原合酶的假定底物结合位点。GBSSII与针对马铃薯和玉米GBSSI产生的抗血清发生特异性交叉反应。这项研究表明，GBSSI和GBSSII在不同器官中以组织特异性方式表达，GBSSII在果皮直链淀粉合成中具有重要功能。
