Jeongyeo Lee1,2, Xiangshu Dong1,3, Kwan Choi1, Hayong Song1, Hankuil Yi1, Yoonkang Hur4. 1. Department of Biological Sciences, Chungnam National University, Daejeon, 34134, Republic of Korea. 2. Korea Research Institute of Bioscience and Biotechnology, Daejeon, 34141, Republic of Korea. 3. School of Agriculture, Yunnam University, Kunming, 650091, China. 4. Department of Biological Sciences, Chungnam National University, Daejeon, 34134, Republic of Korea. ykhur@cnu.ac.kr.
Abstract
BACKGROUND: A leaf of Chinese cabbage (Brassica rapa ssp. pekinensis) is composed of a photosynthetic blade and a non-photosynthetic large midrib; thus each leaf contains both source and sink tissues. This structure suggests that, unlike in other plants, source-sink metabolism is present in a single leaf of Chinese cabbage. OBJECTIVE: This study was designed to identify the transport route of photosynthetic carbon and to determine whether both source and sink tissues were present in a leaf. METHODS: Plant samples were collected diurnally. Their carbohydrate contents were measured, and a genome-wide transcriptome analysis was performed using the Br300K microarray. Expression profiles of selected genes were validated using qRT-PCR analysis. RESULTS: The presence of two contrasting tissues (blade as source and midrib as sink) in a leaf was demonstrated by (1) diurnal distribution patterns of starch and sucrose content; (2) Gene Ontology (GO) enrichment analysis of microarray data; (3) expression profiles of photosynthetic and sucrose biosynthetic genes; and (4) expression patterns of a variety of sugar transporter genes. CONCLUSION: Source and sink tissues were both present in Chinese cabbage leaves, but the midrib functioned as a sink tissue as well as a site exporting to roots and other sink tissues. Function of most genes discriminating between source and sink tissue appeared to be regulated largely at the post-transcriptional level, not at the transcriptional level.
BACKGROUND: A leaf of Chinese cabbage (Brassica rapa ssp. pekinensis) is composed of a photosynthetic blade and a non-photosynthetic large midrib; thus each leaf contains both source and sink tissues. This structure suggests that, unlike in other plants, source-sink metabolism is present in a single leaf of Chinese cabbage. OBJECTIVE: This study was designed to identify the transport route of photosynthetic carbon and to determine whether both source and sink tissues were present in a leaf. METHODS: Plant samples were collected diurnally. Their carbohydrate contents were measured, and a genome-wide transcriptome analysis was performed using the Br300K microarray. Expression profiles of selected genes were validated using qRT-PCR analysis. RESULTS: The presence of two contrasting tissues (blade as source and midrib as sink) in a leaf was demonstrated by (1) diurnal distribution patterns of starch and sucrose content; (2) Gene Ontology (GO) enrichment analysis of microarray data; (3) expression profiles of photosynthetic and sucrose biosynthetic genes; and (4) expression patterns of a variety of sugar transporter genes. CONCLUSION: Source and sink tissues were both present in Chinese cabbage leaves, but the midrib functioned as a sink tissue as well as a site exporting to roots and other sink tissues. Function of most genes discriminating between source and sink tissue appeared to be regulated largely at the post-transcriptional level, not at the transcriptional level.
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