In vivo sucrose stimulation of colour change in citrus fruit epicarps: Interactions between nutritional and hormonal signals

Abstract

During ripening, citrus fruit-peel undergoes 'colour break', a process characterized by the conversion of chloroplast to chromoplast. The process involves the progressive loss of chlorophylls and the gain of carotenoids, changing peel colour from green to orange. In the present work, the in vivo and in vitro effects of supplemented nutrients (sucrose and nitrogen) and phytohormones (gibberellins [GA] and ethylene) on colour change in fruit epicarp of Satsuma mandarin (Citrus unshiu (Mak.) Marc., cv. Okitsu), were studied. The rate of colour break was correlated positively with sucrose content and negatively with nitrogen content. The removal of leaves blocked natural sucrose build-up and nitrogen reduction in the peel. Defoliation also inhibited chlorophyll disappearance and carotenoid accumulation, thereby preventing colour break. In vivo sucrose supplementation promoted sucrose accumulation and advanced colour break. In both in vivo and in vitro experiments, colour change promoted by sucrose was unaffected by ethylene but delayed by GA3. In non-supplemented plants, ethylene accelerated colour break while GA3 had no detectable effects. Ethylene inhibitors effectively counteracted the sucrose effects on colour change. Collectively, these results suggest that the chloroplast to chromoplast conversion in citrus fruit epicarps is stimulated by sucrose accumulation. The sugar regulation appears to operate via ethylene, whereas GA may act as a repressor of the sucrose-ethylene stimulation.

Physiology of citrus fruiting

“…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). In this work it is proposed that sugar regulation may operate via ethylene, whereas GA functions as a repressor of the ethylene-sucrose stimulation.…”

“…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). Color break in subtropical areas generally takes place in midautumn when temperatures go down and day length diminishes (Figure 4).…”

Caracterização de frutos do tangor TMxLP 290 para mercado de fruta fresca

“…Embora seus frutos sejam semelhantes às da laranja Pera, possivelmente apresenta maturação mais precoce, já que de acordo comacordo com Schinor et al (2010) A coloração é o atributo de qualidade mais atrativo para o consumidor, sendo um dos fatores determinantes na aquisição dos frutos, pois é associada com a maturação, frescor e também com o sabor. A cor externa dos frutos cítricos é o parâmetro fundamental para o mercado de frutos frescos, pois o consumidor prefere frutas semimaduras, para prolongar o período de durabilidade, além de julgar a fruta verde de forma negativa (EDAGI et al, 2010;IGLESIAS et al, 2001;BADENES et al, 1998).…”

Control endógeno y exógeno de la maduración externa de los frutos cítricos

“…El proceso de desverdizado natural se puede modificar con aplicaciones exógenas de reguladores de crecimiento, tales como ácido giberélico (Goldschmidt y Eilati, 1970, Kuraoka et al, 1977 y etileno (Pons et al, 1992;Goldschmidt et al, 1993); sustancias nitrogenadas (Jones y Embleton, 1959;Sala et al, 1992;Quiñones et al, 2004) y carbohidratos (Iglesias et al, 2001). …”

“…La sacarosa se incrementó hasta el inicio del cambio de color de los frutos y, posteriormente, se mantuvo relativamente estable, con pequeñas variaciones entre cultivares, lo que sugiere que a partir de ese momento el aumento de los restantes azúcares es producto de su hidrólisis. Se ha señalado que el suplemento de sacarosa in vitro (Huff, 1983) o in vivo (Iglesias et al, 2001) promueve el desverdizado del flavedo de los cítricos.…”