Partial Purification of a Growth Factor from Orange Juice Which Affects Citrus Tissue Culture and Its Replacement by Citric Acid

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Abstract
Orange (Citrus sinensis L. Osbeck) tissue cultures required a supply of orange juice to the medium for their vigorous growth. The growth-promoting activity of juice seemed to involve both cell division and cell enlargement. Juice had no promotive activity in bioassays for auxins, gibberellins, and cytokinins. The growth promoting activity of juice was mostly transferred into 1-butanol upon partition at pH 2. Gas chromatographic analysis of this acid 1-butanol fraction revealed large amounts of citric acid and negligible amounts of other organic acids. Supply of pure citric acid to the medium, alone or in combination with different concentrations of juice, indicated that citric acid replaces most of the requirement for juice.It seems that citric acid, which is a natural component of citrus juice, is responsible for the major part of the growth-promoting activity of the juice. The significance of citric acid as a growth factor in tissue cultures and the reasons for the dependence of citrus tissue cultures on external supply of citric acid are discussed.