Bick J A, Neelam A, Smith E, Nelson S J, Hall J L, Williams L E
School of Biological Sciences, University of Southampton, UK.
Plant Mol Biol. 1998 Oct;38(3):425-35. doi: 10.1023/a:1006040306581.
This study describes the expression of a sucrose carrier at various developmental stages in Ricinus communis. A partial-length cDNA clone, RcSUT1, was isolated by RT-PCR from Ricinus seedling RNA. This is almost identical to a sucrose carrier cDNA, Rscr1, which has previously been isolated by library screening. However, we have observed a very different expression pattern in the seedling to that previously reported. Northern analysis, with RcSUT1 as a probe, revealed high expression of a 2 kb transcript in the cotyledons of the germinating seedling; transcript levels were similar in cotyledons harvested 3-6 days after germination. A much lower level of this transcript was detected in the root, hypocotyl and endosperm RNA of the seedling and very low levels were also present in the sink and source leaves of the mature plant. This pattern of expression was also reflected at the protein level with an antipeptide antibody raised to part of the RcSUT1 deduced amino acid sequence. Tissue print hybridisation analysis of the hypocotyl revealed that the sucrose carrier transcripts were localised to the phloem cells of the vascular bundles. A more detailed analysis of sucrose carrier gene expression in the cotyledons of the germinating seedling was carried out by in situ hybridisation; the strongest signals were observed from the lower epidermal layer and the phloem, consistent with an active loading role for these cells. An ultrastructural study of the cells in the lower epidermis showed that they have wall ingrowths which are characteristic of transfer cells. The results are discussed in relation to the physiological role of the sucrose carrier in the Ricinus seedling and to the pathways of sucrose movement from endosperm to the sieve elements in the cotyledons.
本研究描述了蓖麻不同发育阶段蔗糖载体的表达情况。通过RT-PCR从蓖麻幼苗RNA中分离出一个部分长度的cDNA克隆RcSUT1。它与之前通过文库筛选分离出的蔗糖载体cDNA Rscr1几乎完全相同。然而，我们观察到其在幼苗中的表达模式与之前报道的有很大不同。以RcSUT1为探针进行Northern分析，发现在萌发幼苗的子叶中有一个2 kb转录本的高表达；在萌发后3 - 6天收获的子叶中，转录本水平相似。在幼苗的根、下胚轴和胚乳RNA中检测到该转录本的水平要低得多，在成熟植株的库叶和源叶中也非常低。这种表达模式在蛋白质水平上也有体现，使用针对RcSUT1推导氨基酸序列的一部分产生的抗肽抗体进行检测。下胚轴的组织印迹杂交分析表明，蔗糖载体转录本定位于维管束的韧皮部细胞。通过原位杂交对萌发幼苗子叶中的蔗糖载体基因表达进行了更详细的分析；在下表皮层和韧皮部观察到最强的信号，这与这些细胞的活跃装载作用一致。对下表皮细胞的超微结构研究表明，它们具有壁内突，这是转移细胞的特征。本文将结合蔗糖载体在蓖麻幼苗中的生理作用以及蔗糖从胚乳向子叶筛管分子移动的途径对这些结果进行讨论。
