1993 Fiscal Year Final Research Report Summary
Molecular Basis for Nitrogen Remobilization with Leaf Senescence
| Project/Area Number |
03454061
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
土壌・肥料
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| Research Institution | TOHOKU UNIVERSITY |
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Principal Investigator |
MAE Tadahiko Tohoku Univ., Faculty of Agriculture, Professor, 農学部, 教授 (60134029)
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| Co-Investigator(Kenkyū-buntansha) |
MAKINO Amane Tohoku Univ., Facuty of Agriculture, Associate Professor, 農学部, 助教授 (70181617)
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| Project Period (FY) |
1991 – 1993
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| Keywords | Leaf Senescence / Nitrogen metabolism / Protein degradation / Remobilization / Rubisco |
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| Research Abstract |
Changes in the amounts of chloroplast proteins were examined in the leaves of rice grown under average and low irradiances during senescence. Clear differences were observed in Rubisco and LHCII between the leaves senesced under the two irradiances. The decrease of LHC II occurred much later than that of Rubisco in the leaves with the low irradiance, while it follwed soon after the decrease of Rubisco in the leaves with the average irradiances. These results suggested that ratio of capacity of light harvesting to that of RuBP carboxylation can be regulated in the manner to adapt to a given irradiance even in the senscing leaves as in growing leaves and that the adaptation can be mainly controled by the levels of protein degradation.
Changes in the levels of enzymes related to nitrogen metabolism and remobilization such as GSI,GSII,Fd-GOGAT,and NADH-GOGAT were examined during the life span of a rice leaf. GSII and Fd-GOGAT changed coordinately with Rubisco throughout the life span of the
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leaf, while the levels of GSI changed little during senescence. NADH-GOGAT was relatively more active in the developing leaves than the mature and senescing leaves. GSI and NADH-GOGAT were located abundantly in vascular-bundle tissues, suggesting that these enzymes are involved in loading and unloading of nitrogen compounds in the tissues.
Accumulation of nitrogen, dry matter, glutelin and its mRNA were compared between superior spikelets and inferior spikelets during ripening of rice ear. Accumulation of glutelin and its mRNA started much later in the inferior spikelets than the superior spike lets. It was suggested that the retardation of the accumulation in the inferior spikelets was attributed to the late development of endosperm tissues.
Proteolytic activity against Rubisco was assayd with the lysates of the purified chloroplasts from wheat leaves. The activity was higher in acidic pH ranges than alkaline pH ranges. About 40% of the total-leaf endopeptidase activity against CBZ-Gly-Pro-Gly-Gly-Pro-Ala was found in the chloroplast fraction. Less
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