Nutritional Control of Regreening and Degreening in Citrus Peel Segments

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Abstract
A method for reversibly regreening and degreening citrus epicarp in vitro using peel segments was developed. Peel segments from mature degreened fruit promptly regreened when kept in light upon agar medium containing low (15 mM) concentrations of sucrose. Higher concentrations of sucrose inhibited this regreening, but NO3- and certain amino acids included in the media overcame the inhibition by sucrose. However, L-serine strongly inhibited regreening. In the presence of N, sucrose promoted regreening. Peel segments from green fruit remained green on media with low concentrations of sucrose and on media with high concentrations of sucrose and 60 mM KNO3, but degreened in response to high concentrations of sucrose in the absence of N. Nitrate overcame the degreening effects of high sucrose concentrations in both light and dark. Peel segments were reversibly degreened and regreened by transferring the segments between appropriate media. Nitrate in the media markedly reduced the levels of endogenous sugars in the epicarp and increased endogenous amino acid levels. Sucrose in the media increased endogenous sugar levels and, in the presence of nitrate, increased endogenous amino acid levels. In the absence of N, high sucrose concentrations reduced endogenous amino acid concentrations.