The Macaulay Institute for Soil Research, Craigiebuckler, AB9 2QJ, Aberdeen, UK.
Planta. 1975 Jan;122(3):227-38. doi: 10.1007/BF00385270.
Excised root segments of Pisum sativum (L.) cut from the region 2-4 mm behind the root tip were cultured in a 2% sucrose medium containing analogues of uracil and proline. Of several uracil analogues tested only those containing a thiol group (2-thiouracil and 2-thio-6-azauracil) markedly stimulated the growth rate and prolonged the duration of growth of the segments, whereas other uracil analogues which enhanced growth affected only its duration. Uracil had no effect on cell elongation and did not completely prevent the effects of 2-thiouracil and 2-thio-6-azauracil; it did, however, prevent the stimulation by those analogues without a thiol group. Two analogues of proline, thioproline and hydroxyproline, also enhanced cell elongation but whereas the effect of hydroxyproline was completely prevented by proline, the stimulation produced by thioproline was not.During cell elongation, [(14)C]thiouracil was incorporated into RNA, where it replaced uracil, and into a non-nucleotide fraction of the cell wall from which it could not be removed with perchloric acid, sodium hydroxide, ribonuclease or pronase. Experiments using labelled thiouracil, orotic acid, leucine, proline and hydroxyproline strongly suggest that 2-thiouracil stimulates the growth rate of segments by becoming attached to cysteine in cell-wall proteins and delaying an increase in wall rigidity caused by the formation of disulphide bridges between proteins.
从根尖后 2-4 毫米处切下的豌豆（L.）的根段在含有尿嘧啶和脯氨酸类似物的 2%蔗糖培养基中培养。在所测试的几种尿嘧啶类似物中，只有含有巯基的那些（2-硫代尿嘧啶和 2-硫代-6-氮杂尿嘧啶）明显刺激了片段的生长速度并延长了生长时间，而其他增强生长的尿嘧啶类似物仅影响其持续时间。尿嘧啶对细胞伸长没有影响，也不能完全阻止 2-硫代尿嘧啶和 2-硫代-6-氮杂尿嘧啶的作用；然而，它阻止了没有巯基的类似物的刺激。脯氨酸的两种类似物，硫代脯氨酸和羟脯氨酸，也增强了细胞伸长，但羟脯氨酸的作用被脯氨酸完全阻止，而硫代脯氨酸产生的刺激则没有。在细胞伸长过程中，[(14)C]硫代尿嘧啶掺入 RNA，在其中取代尿嘧啶，并掺入细胞壁的非核苷酸部分，用高氯酸、氢氧化钠、核糖核酸酶或蛋白酶不能将其从细胞壁中去除。使用标记的硫代尿嘧啶、乳清酸、亮氨酸、脯氨酸和羟脯氨酸的实验强烈表明，2-硫代尿嘧啶通过与细胞壁蛋白中的半胱氨酸结合并延迟由蛋白质之间形成二硫键引起的细胞壁刚性增加，从而刺激片段的生长速度。
