Department of Biology, State University of New York, Buffalo, New York 14214.
Plant Physiol. 1968 Jun;43(6):979-89. doi: 10.1104/pp.43.6.979.
The metabolism of myo-inositol-2-(14)C, d-glucuronate-1-(14)C, d-glucuronate-6-(14)C, and l-methionine-methyl-(14)C to cell wall polysaccharides was investigated in excised root-tips of 3 day old Zea mays seedlings. From myo-inositol, about one-half of incorporated label was recovered in ethanol insoluble residues. Of this label, about 90% was solubilized by treatment, first with a preparation of pectinase-EDTA, then with dilute hydrochloric acid. The only labeled constituents in these hydrolyzates were d-galacturonic acid, d-glucuronic acid, 4-O-methyl-d-glucuronic acid, d-xylose, and l-arabinose, or larger oligosaccharide fragments containing these units. Medium external to excised root-tips grown under sterile conditions in myo-inositol-2-(14)C contained labeled polysaccharide.When label was supplied in the form of d-glucuronate, the pattern of labeled uronic acid and pentose units in cell wall polysaccharides resembled that obtained from labeled myo-inositol, indicating that both substances were metabolized along a common path during polysaccharide formation, and that methylation occurred at a step subsequent to uronic acid formation. When label was supplied in the form of l-methionine-methyl-(14)C, 4-O-methyl-d-glucuronic acid was the only labeled monosaccharide component that survived enzymatic or acid hydrolysis.Zea mays endosperm, a known source of phytin, developed maximal phytase activity after the third day of germination. Results obtained here suggest that myo-inositol released by hydrolysis of phytin represents the initial precursor of a normal, possibly predominant pathway for the formation of uronic acids in plants.
采用离体 3 天大的玉米根尖研究了肌醇-2-（14）C、D-葡萄糖醛酸-1-（14）C、D-葡萄糖醛酸-6-（14）C 和 L-蛋氨酸甲硫基-（14）C 向细胞壁多糖的代谢。从肌醇中，约一半的掺入标记物回收于乙醇不溶残渣中。该标记物的约 90%可先用果胶酶-EDTA 制剂处理，然后用稀盐酸溶解。这些水解物中仅有的带标记的成分是 D-半乳糖醛酸、D-葡萄糖醛酸、4-O-甲基-D-葡萄糖醛酸、D-木糖和 L-阿拉伯糖，或含有这些单位的更大寡糖片段。在无菌条件下于离体根尖中生长的介质中，含有标记的多糖。当以 D-葡萄糖醛酸盐形式供应标记物时，细胞壁多糖中带标记的糖醛酸和戊糖单位的模式类似于从标记肌醇获得的模式，表明这两种物质在多糖形成过程中沿共同途径代谢，并且甲基化发生在糖醛酸形成之后的步骤。当以 L-蛋氨酸甲硫基-（14）C 形式供应标记物时，4-O-甲基-D-葡萄糖醛酸是唯一可耐受酶或酸水解的带标记的单糖成分。玉米胚乳，一种已知的植酸来源，在发芽后的第三天达到最大植酸酶活性。此处获得的结果表明，植酸水解释放的肌醇代表了植物中糖醛酸形成的正常、可能主要途径的初始前体。
