Pathway of sugar transport in germinating wheat seeds
Pathway of sugar transport in germinating wheat seeds
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DOI：
10.1104/pp.106.082719
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发表时间：
2006-08-01
期刊：
影响因子：
7.4
通讯作者：
Furbank, Robert T.
中科院分区：
文献类型：
--
作者：
Aoki, Naohiro;Scofield, Graham N.;Furbank, Robert T.
在六倍体小麦（Triticum aestivum）中，编码蔗糖转运蛋白（SUT）的三个同源基因TaSUT1A、1B和1D在发芽种子中表达，其功能尚不清楚。通过与酿酒酵母（Saccharomyces cerevisiae）突变株SUSY7/ura3的互补试验，证实了这三种TaSUT1蛋白都能够运输蔗糖和麦芽糖。通过原位杂交、免疫定位、荧光染料示踪运动和代谢物分析等方法，研究了这些转运体在籽粒萌发中的作用。TaSUT1转录本和SUT蛋白均在黄芩、茎部和根部的粉粉层、黄芩表皮、黄芩底细胞和筛元-伴细胞复合体中检测到。将膜不渗透荧光染料羧基荧光素酯加载到萌发种子的黄芩表皮细胞中，表明黄芩通过韧皮部与茎和根形成了同质通路。然而，肩胛骨表皮为卵乳组织的溶质运动提供了一个质外屏障。对根、芽、胚乳和鳞茎中的糖的测量表明，随着胚乳淀粉的降解，产生的己糖在鳞茎中转化为苏。在萌发早期胚乳中发现了主要的糖，而麦芽糖和葡萄糖在后期阶段占主导地位。提出小麦种子萌发过程中籽粒韧皮部的装载可通过同质和胞质两种途径进行，胞质通过SUT活性促进。此外，SUTs还可能在萌发初期将麦芽糖从胚乳转运到胚乳，并在萌发后期转运麦芽糖。
Three homeologous genes encoding a sucrose (Suc) transporter (SUT) in hexaploid wheat ( Triticum aestivum), TaSUT1A, 1B, and 1D, were expressed in germinating seeds, where their function is unknown. All three TaSUT1 proteins were confirmed to be capable of transporting both Suc and maltose by complementation tests with the SUSY7/ura3 yeast ( Saccharomyces cerevisiae) mutant strain. The role of Suc transporters in germinating grain was examined by combining in situ hybridization, immunolocalization, fluorescent dye tracer movement, and metabolite assays. TaSUT1 transcript and SUT protein were detected in cells of the aleurone layer, scutellar epidermis, scutellar ground cells, and sieve element-companion cell complexes located in the scutellum, shoot, and root. Ester loading of the membrane-impermeable fluorescent dye carboxyfluorescein into the scutellum epidermal cells of germinating seeds showed that a symplasmic pathway connects the scutellum to the shoot and root via the phloem. However, the scutellar epidermis provides an apoplasmic barrier to solute movement from endosperm tissue. Measurements of sugars in the root, shoot, endosperm, and scutellum suggest that, following degradation of endosperm starch, the resulting hexoses are converted to Suc in the scutellum. Suc was found to be the major sugar present in the endosperm early in germination, whereas maltose and glucose predominate during the later stage. It is proposed that loading the scutellar phloem in germinating wheat seeds can proceed by symplasmic and apoplasmic pathways, the latter facilitated by SUT activity. In addition, SUTs may function to transport Suc into the scutellum from the endosperm early in germination and later transport maltose.