The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture and the Otto Warburg Minerva Center for Agricultural Biotechnology, The Hebrew University of Jerusalem, The Robert H. Smith Faculty of Agriculture, Food and Environment, Rehovot 76100, Israel.
Plant J. 2011 Apr;66(2):366-74. doi: 10.1111/j.1365-313X.2011.04498.x. Epub 2011 Mar 1.
Based on the high density of plasmodesmata interconnecting the intermediary cells and their neighboring phloem parenchyma or bundle-sheath cells, and based on the insensitivity to the sucrose transport inhibitor p-chloromercuribenzenesulfonic acid (PCMBS), cucurbits have been concluded to be symplastic loaders. In the present study, we identified and characterized the full-length sequence of sucrose transporter gene (CmSUT1) from melon (Cucumis melo L. cv. Hale's best jumbo). In vitro experiments confirmed that the identified gene product has sucrose transporter activity in baker's yeast. Healthy and cucumber mosaic virus (CMV)-infected melon plants were employed to examine sucrose transporter activity in planta. Pretreatment with PCMBS inhibited loading of newly fixed ¹⁴CO₂ into minor veins of CMV-infected plants. Moreover, CMV infection caused significant increase in CmSUT1 transcripts expression, mainly in vascular bundles of minor veins, which was associated with elevated sucrose content in phloem sap collected from source-leaf petioles. We propose that cucurbit plants contain the machinery for apoplastic phloem loading and that CMV infection causes a quantitative shift in the mode by which photoassimilates are loaded into the sieve tube.
基于中间细胞与其邻近韧皮部薄壁细胞或束鞘细胞之间连接的胞间连丝密度高，以及对蔗糖转运抑制剂对氯汞苯甲酸（PCMBS）不敏感这两个特点，葫芦科被认为是共质体装载者。在本研究中，我们从甜瓜（Cucumis melo L. cv. Hale's best jumbo）中鉴定并表征了蔗糖转运基因（CmSUT1）的全长序列。体外实验证实，所鉴定的基因产物在面包酵母中有蔗糖转运活性。我们用健康的和感染黄瓜花叶病毒（CMV）的甜瓜植株来检测植株体内的蔗糖转运活性。用 PCMBS 预处理会抑制 ¹⁴CO₂向 CMV 感染植株的小脉中的重新固定。此外，CMV 感染导致 CmSUT1 转录本表达显著增加，主要发生在小脉的维管束中，这与从小叶叶柄采集的韧皮部汁液中的蔗糖含量升高有关。我们提出，葫芦科植物含有质外体韧皮部装载的机制，而 CMV 感染导致同化产物装载到筛管的方式发生了定量变化。
