Nutritional Control of Regreening and Degreening in Citrus Peel Segments

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 millimolar) concentrations of sucrose. Higher concentrations of sucrose inhibited this regreening, but N03-and certain amino acids included in the media overcame the inhibition by sucrose. However, L-erine strongly inhibited regreening. In the presence of nitrogen, sucrose promoted regreening.Peel (14), Chrysosoplenium alternifolium and Chr. oppositifolium (29), the spathe of Zantedeschia elliottiana Eng. (14), and subepidermal tissues of Cucurbita pepo fruit (9).In addition to temperature, the degreening and regreening of citrus fruit are affected by nitrogen fertilization (18, 19), exogeneously applied gibberellins (7), and certain internal factors such as variety, rootstocks, and number of seeds per fruit (11).An in vitro method of studying this interconversion ofchromoplasts and chloroplasts in citrus peels has been developed and a preliminary report presented (15). Further in vitro studies have shown that the degreening and regreening of citrus peels can be regulated nutritionally. An abundance of nitrogen promotes the chloroplast form, whereas an abundance of sugars promotes the chromoplast form. A nutritional explanation for the degreening and regreening of certain citrus fruit is proposed. MATERIALS AND METHODSFruit ofCitrus sinensis L. Osbeck (cv Valencia) and C. paradisi Macf. (cv Marsh) were surface-sterilized by a 5-min soak in 1% (w/v) NaOCI and rinsed in sterile water. A wide section of peel was cut from the equatorial region (usually) with a razor blade and held submerged in a shallow tray of sterile water while discs were cut out with a 10-mm-diameter cork borer.Peel segments thus prepared were placed epicarp side up on 8 ml of agar media in covered 18-x 150-mm culture tubes and placed under continuous fluorescent lighting (Sylvania Cool White) of between 4 and 12 w m-2 the following morning.

Physiology of citrus fruiting

“…The process of external citrus fruit ripening is mostly dependent upon the conversion of chloro-to chromoplasts and involves the progressive loss of chlorophylls and the gain of carotenoids, thus changing peel color from green to orange (Huff, 1983(Huff, , 1984. The changes associated with external ripening are essentially comparable to the senescence of vegetative chlorophyllous tissues and in citrus fruits are influenced by environmental conditions, nutrient availability and hormones (Goldschmidt, 1988;Iglesias et al, 2001).…”

“…It has also been suggested that color break of citrus fruit is controlled by nutrients. Based on data collected from in vitro studies on citrus epicarp, Huff (1983Huff ( , 1984 suggested that citrus fruit might partially de-green in response to the accumulation of sugars. It has specifically been shown that the chloroto chromoplast conversion in citrus fruit epicarps is stimulated by sucrose accumulation after an initial decrease in peel nitrogen content (Iglesias et al, 2001).…”

Improvement of N fertilization by using the nitrification inhibitor DMPP [3,4-dimethylpirazole phosphate] in drip-irrigated citrus trees

“…Lower fruit colour index values in the DMPP-treated trees were also observed by Serna et al (1992) when decreasing the NO 3 -/NH 4 + ratio. NH 4 + nutrition could be responsible for greener fruit colour, since NH 4 + applied on citrus fruit peel delays chlorophyll degradation (Huff, 1983). The slight delay in the time colour break found in the DMPP-treated fruits could be an economical advantage for mead-season and late varieties.…”

Accumulation of Chlorophyll, Chloroplastic Proteins, and Thylakoid Membranes during Reversion of Chromoplasts to Chloroplasts in Citrus sinensis Epicarp

“…Reversible interconversions between chloroplasts and chromoplasts can be conveniently studied by culturing pericarp segments from citrus fruit on agar media (11). Media with high sugar concentrations and lacking N promote differentiation of chloroplasts into chromoplasts, while media with low sugar concentrations or any of several sources of N promote redifferentiation of chromoplasts into chloroplasts.…”