Some compounds capable of solubilizing ferric chloride as the iron source were released into the growth medium from cultured rice cells in the latter half of the growth cycle. This exudation of iron-solubilizing compounds was repressed by an addition of ammonium ion, which, of five cations, was taken up most rapidly. These iron-solubilizing compounds from cultured rice cells were identified by chromatography to be principally malic acid and some citric acid. In the medium containing almost insoluble ferric chloride as the iron source, the growth rate of the cultured cells decreased when cells were inoculated at a low population density. This iron deficiency at the low initial population was rectified by an addition of a small amount of conditioned medium or malic acid.
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