Iron Nutrition of Nicotiana Tabacum L. in Relation to Riboflavin, Riboflavin-5-phosphate, and Flavin Adenine Dinucleotide Content.

Under normal conditions of growth, riboflavin is synthesized by all higher plants and is utilized as a prosthetic group by various flavoprotein enzymes (12). Pound and Welkie (11) observed the presence of a yellow pigment in the nutrient solution of tobacco plants grown in the absence of iron. Physical and chemical tests indicated that the pigment was riboflavin, and it was suggested that the deficiency of iron interferes with the utilization of the riboflavin as a prosthetic group of flavoprotein enzymes, which results in the accumulation of riboflavin in the plant and excretion by the roots. Increased synthesis of riboflavin by yeast (Candida quilliermiondia) grown under conditions of low iron nutrition has been reported by Tanner et al (16) and Burkholder (2). This research was initiated to investigate further the relation of iron nutrition and flavin concentration in tobacco plants. The appearance and disappearance of riboflavin in nutrient solutions was studied in relation to iron concentration in the nutrient solution and the concentration of riboflavin within whole plants, roots, and leaves. Concentrations of riboflavin, flavin adenine dinucleotide (FAD), and flavinmonophosphate (FMN) in normal and iron-deficient plant parts were determined. Enzyme assays of a noniron, flavoprotein enzyme. nitrate reductase (10), and a possible iron, flavoprotein enzymi-e, cytochrome reductase (10), were determined.