Extracts from primary leaves of Little Club wheat, prepared under anaerobic conditions, gave oxidationndash;reduction potentials in the range of minus;180ensp;mv to minus;140ensp;mv at pH 6 when measured potentiometrically with prepolarized platinum electrodes. These poorly poised potentials are believed to represent a flavin system. By mixing mediators (e.g. methylene blue and riboflavin) with the extracts stable average potentials were achieved. These ranged from minus;70 to +70ensp;mv. Coleoptiles and very young primary leaves exhibited relatively low average potentials, which climbed to a steady level in 8 to 10 days after sowing. This change was accompanied by a quantitative shift between three poising systems found in the leaves by redox titrations. The results suggested that ascorbic acid becomes the dominating redox system in extracts from mature leaves. At senescence, indicated by yellowing, a new system dominates the redox background. This exhibited quinonic properties.
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