Fallahi Hossein, Scofield Graham N, Badger Murray R, Chow Wah Soon, Furbank Robert T, Ruan Yong-Ling
CSIRO Plant Industry, PO Box 1600, Canberra, ACT 2601, Australia.
J Exp Bot. 2008;59(12):3283-95. doi: 10.1093/jxb/ern180. Epub 2008 Jul 16.
This study investigated the roles of sucrose synthase (SUS) in developing seeds and siliques of Arabidopsis thaliana. Enzyme activity assays showed that SUS activity was highest in developing whole siliques and young rosette leaves compared with other tissues including mature leaves, stems, and flowers. Surprisingly, quantitative PCR analyses revealed little correlation between SUS activity and transcript expression, which indicated the importance of examining the role of SUS at the protein level. Therefore, immunolocalization was performed over a developmental time course to determine the previously unreported cellular localization of SUS in Arabidopsis seed and silique tissues. At 3 d and 10 d after flowering (daf), SUS protein localized to the silique wall, seed coat, funiculus, and endosperm. By 13 daf, SUS protein was detected in the embryo and aleurone layer, but was absent from the seed coat and funiculus. Starch grains were also present in the seed coat at 3 and 10 daf, but were absent at 13 daf. Co-localization of SUS protein and starch grains in the seed coat at 3 and 10 daf indicates that SUS may be involved in temporary starch deposition during the early stages of seed development, whilst in the later stages SUS metabolizes sucrose in the embryo and cotyledon. Within the silique wall, SUS localized specifically to the companion cells, indicating that SUS activity may be required to provide energy for phloem transport activities in the silique wall. The results highlight the diverse roles that SUS may play during the development of silique and seed in Arabidopsis.
本研究调查了蔗糖合酶（SUS）在拟南芥发育中的种子和角果中的作用。酶活性分析表明，与包括成熟叶片、茎和花在内的其他组织相比，SUS活性在发育中的整个角果和幼嫩莲座叶中最高。令人惊讶的是，定量PCR分析显示SUS活性与转录本表达之间几乎没有相关性，这表明在蛋白质水平上研究SUS的作用很重要。因此，在发育时间进程中进行了免疫定位，以确定拟南芥种子和角果组织中SUS以前未报道的细胞定位。在开花后3天和10天（daf），SUS蛋白定位于角果壁、种皮、珠柄和胚乳。到13 daf时，在胚和糊粉层中检测到SUS蛋白，但种皮和珠柄中没有。在3和10 daf时，种皮中也存在淀粉粒，但在13 daf时不存在。3和10 daf时种皮中SUS蛋白与淀粉粒的共定位表明，SUS可能参与种子发育早期的临时淀粉沉积，而在后期SUS在胚和子叶中代谢蔗糖。在角果壁内，SUS特异性定位于伴胞，这表明可能需要SUS活性为角果壁中的韧皮部运输活动提供能量。这些结果突出了SUS在拟南芥角果和种子发育过程中可能发挥的多种作用。
