Hancock Robert D, Chudek John A, Walker Paul G, Pont Simon D A, Viola Roberto
Scottish Crop Research Institute, Plant Products and Food Quality, Invergowrie, Dundee DD2 5DA, United Kingdom.
Phytochemistry. 2008 Jun;69(9):1850-8. doi: 10.1016/j.phytochem.2008.03.022. Epub 2008 May 9.
Analysis of phloem exudates from the fruit of Cucurbitaceae revealed the presence of several compounds with UV-visible absorption spectra identical to that of l-ascorbic acid. In Cucurbita pepo L. (zucchini), the compounds could be isolated from phloem exudates collected from aerial parts of the plant but were not detected in whole tissue homogenates. The compounds isolated from the phloem exudates of C. pepo fruit were eluted from strong anion exchange resin in the same fraction as l-ascorbic acid and were oxidised by ascorbate oxidase (E.C. 1.10.3.3). The major compound purified from C. pepo fruit exudates demonstrated similar redox properties to l-ascorbic acid and synthetic 6-O-glucosyl-l-ascorbic acid (6-GlcAsA) but differed from those of 2-O-glucosyl-l-ascorbic acid (2-GlcAsA) isolated from the fruit of Lycium barbarum L. Parent and fragment ion masses of the compound were consistent with hexosyl-ascorbate in which the hexose moiety was attached to C5 or C6 of AsA. Acid hydrolysis of the major C. pepo compound resulted in the formation of l-ascorbic acid and glucose. The purified compound yielded a proton NMR spectrum that was almost identical to that of synthetic 6-GlcAsA. A series of l-ascorbic acid conjugates have, therefore, been identified in the phloem of Cucurbitaceae and the most abundant conjugate has been identified as 6-GlcAsA. The potential role of such conjugates in the long-distance transport of l-ascorbic acid is discussed.
对葫芦科果实韧皮部渗出液的分析表明，存在几种化合物，其紫外可见吸收光谱与L-抗坏血酸相同。在西葫芦（Cucurbita pepo L.）中，这些化合物可以从植物地上部分收集的韧皮部渗出液中分离出来，但在全组织匀浆中未检测到。从西葫芦果实韧皮部渗出液中分离出的化合物与L-抗坏血酸在同一级分从强阴离子交换树脂上洗脱下来，并被抗坏血酸氧化酶（E.C. 1.10.3.3）氧化。从西葫芦果实渗出液中纯化得到的主要化合物表现出与L-抗坏血酸和合成的6-O-葡萄糖基-L-抗坏血酸（6-GlcAsA）相似的氧化还原特性，但与从宁夏枸杞果实中分离出的2-O-葡萄糖基-L-抗坏血酸（2-GlcAsA）不同。该化合物的母离子和碎片离子质量与己糖基抗坏血酸一致，其中己糖部分连接在抗坏血酸的C5或C6位上。西葫芦主要化合物的酸水解产生L-抗坏血酸和葡萄糖。纯化后的化合物产生的质子核磁共振谱与合成的6-GlcAsA几乎相同。因此，在葫芦科植物的韧皮部中鉴定出了一系列L-抗坏血酸共轭物，其中最丰富的共轭物被鉴定为6-GlcAsA。文中讨论了这些共轭物在L-抗坏血酸长距离运输中的潜在作用。
