| Research Abstract |
The aim of this research project was to clarify the biosynthetic pathway of mugineic acid family of phytosiderophores (MAs), which is secreted by the roots of grasses and solubilizes iron in rhizosphere under iron-deficient condition.
At first, the experiment was conducted to investigate the pathway of MAs biosynthesis which is derived from glucose. In the experiment, it was indicated that ^<14>C of glucose was converted to MAs rapidly. The rate for conversion of glucose into MAs was as high as that into organic acids in TCA cycle or amino acids in protein. The feeding experiments of excised barley roots was conducted using glucose whose carbons were specifically labeled by stable isotope ^<13>C or radio isotope ^<14>C.The results suggested that all of 6 carbons in a glucose molecule were incorporated specifically into a MAs molecule.
The feeding experiment with ^<14>C-homoserine suggested that homoserine may not be a precursor of MAs. In the subsequent experiment about the relationship between sulfur metabolism and MAs biosynthesis, glucose was suggested to be converted to MAs by way of methionine bypassing homoserine. In addition, the valuable result was obtained which shows that glycerol is converted to MAs rapidly.
In the experiments using inhibitors of metabolism, it was noted that DTNB,PCBA and beta-cyanoalanine increase the incorporation of ^<14>C of methionine into MAs.
As a preliminary step for purification of enzymes catalyzing MAs biosynthesis, cell free system derived from roots of iron-deficient barley was prepared and used for feeding experiments with ^<14>C-labeled compounds. The results showed that homocysteine strongly inhibited the incorporation of ^<14>C of methionine into MAs. It was suggested that homocysteine may competitively inhibit MAs biosynthesis as an analogue of methionine. It may be a useful information for the succeeding experiment to purify the enzymes of MAs biosynthesis.
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