| Budget Amount *help |
¥7,000,000 (Direct Cost: ¥7,000,000)
Fiscal Year 1986: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1985: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1984: ¥5,700,000 (Direct Cost: ¥5,700,000)
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| Research Abstract |
We have shown for years that in response to Fe deficiency, roots of barley secrete a large amount of mugineic acid(MA) family phytosiderophores to extract and acquire Fe from the soil. In this study, we dealt with the following 4 subjects in order to collect further information on the Fe-acquiring mechanism in barley roots.
(1) HPLC analysis of MA family phtosiderophores(MAs) in barley root exudates A HPLC for amino acids (instrument: Shimadzu LC-4A equipted with an ion-exchageer column and a fluorescence spectro-monitor) proved to give high sensitivity and fairly good resolution when applied to MAs analysis, and was used in many of the experiments described below.
(2) Biosynthetic pathway of MAs in barley roots Results of tracer experiments, using <^(15)N> -labelled ammonia and <^(14)C> -labelled amino acids as nitrogen sources of nutrient solution, suggested that aspartic acid and methionine may situate in the MAs synthetic pathway as intermediate precursor. It was suggested also that
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in barley roots 2'-deoxy -MA is first synthesized from some amino acid precursor, followed by its conversion into MA and 3-epi-hydroxy-MA.
(3) Characterization of MA-secreting system in barley roots Under natural day-length in Japan, MA secretion from barley roots occurs exclusively within a few or several hours in the morning every day. Experimental evidence indicated that this periodic secretion is due to the operation of a MAs-specific transport system, the operation of which is dependent on metabolic energy, accompanied by co-transport of equimoler <K^+> ions, and under the control of both circadian rhythm and cyclic changes in environmental temperature.
(4) Efficiency of MAs in soil iron extraction and effect of microbial decomposition As compared with EDTA, DTPA, EDDHA and deferri-ferrioxamine B, MA and 2'-deoxy-MA exhibited much higher efficiency of Fe extraction when added to high-pH soils; this is due to the exceptionally low affinity of MAs for Al and Ca, the major metallic elements in soils. Mugineic acids were rapidly decomposed by microbes, particularly when added to rhyzosphere soils. Less
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