1994 Fiscal Year Final Research Report Summary
Studies on the structure and expression of genes that governs leaf senescence
| Project/Area Number |
03404002
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| Research Category |
Grant-in-Aid for General Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
植物生理学
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| Research Institution | The University of Tokyo (1993-1994)
Nagoya University (1991-1992) |
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Principal Investigator |
WATANABE Akira The University of Tokyo, Graduate School of Science, Professor, 大学院・理学系研究科, 教授 (70023471)
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| Co-Investigator(Kenkyū-buntansha) |
ITO Masaki The University of Tokyo, Graduate School of Science, Assistant Professor, 大学院・理学系研究科, 助手 (10242851)
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| Project Period (FY) |
1991 – 1994
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| Keywords | Plant Senescence / cDNA Cloning / Branched-Chain alpha-Ketoacid Dehydrogenase / Protease / Direct Display RT-PCR / Glutamine Synthetase / Pyruvate Dehydrogenase |
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| Research Abstract |
We were successful in isolating several cDNA clones for senescence-related genes by newly developed procedures. One of the procedures is that cDNA sequences are selected by proteins expressed in vitro if they have ability to be imported by isolated intact chloroplasts. By this procedure a sequence was found to code for a new protein which has similarity to a stress protein expressed in E.coli cells when they are infected by a phage. Another one is a modified direct display RT-PCR.Three independent cDNA clones were isolated, one of which codes for protein which has homology to branched-chain alpha-ketoacid dehydrogenase. This enzyme is one of the three subunits of pyruvate dehydrogenase complex known in mammals. Another clone had a sequence homologous to the second subunit of this complex. These observations suggest that senescing leaf cells become deficient in supply of energy from photosynthesis and are preparing to utilized branched chain amino acids such as Leu, Val, and Ile release
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d from degraded protein for a energy source by burning their carbon skeleton in TCA cycle. The last clone showed similarity in amino acid sequence to glucosidases known in plants. Expression of the gene in senescing leaf cells may suggest that the encoded enzyme converts various glucosides to glucose which can also used to generate energy.
Expression of several known protease genes were also examined by northern hybridization with cDNA probes. Genes for proteasome subunits were not found to be specifically expressed in senescing cells, but a nuclear gene for the regulatory subunit of chloroplast Clp protease and a gene for cathepsin-like protease know to localize in vacuoles are expressed at high levels in those cells.
Two out of the three genes for cytosolic glutamine synthetase had been shown to be expressed in the later stage of leaf senescence. By examining the effects of inhibitors of the enzyme and of feeding amino acids, one on the two was found to be regulated by the level of Glu/Gln in the cell. Less
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