Plastid ultrastructure, chlorophyll contents, and colour expression during ripening of cavendish banana (Musa acuminata ’williams') at 18°c and 27°c

Abstract

When Cavendish banana (Musa acuminata ’Williams') is ripened at tropical ambient temperature (27°C) the peel fails to degreen although the pulp has softened. However, the peel will degreen to a yellow colour when the fruit is ripened at 18°C. The inability of the peel to degreen could be because of the retention of thylakoid membranes in the plastids and chlorophyll during the ripening process. A study was carried out to investigate the relationships between plastid ultrastructure, chlorophyll content, and peel colour of Cavendish banana ripened at 18±2°C (C18) and 27±2°C (C27). The peel of Cavendish banana underwent complete degreening when the fruit was ripened at a temperature of 18°C to produce a yellow fruit at ripening stage (RS) 6, after 9 days of treatment. In contrast, bananas exposed to 27°C failed to degreen. By day 5 after ripening initiation, the pulp had softened to eating-ripe in those fruit and brown specks appeared on the fruit peel indicating that senescence had begun. Transmission electron microscopy revealed that the grana-thylakoid membranes of peel chromoplasts had lysed by RS 6 in C18 fruit and only 40% of the total chlorophyll content from RS 1 was retained. In contrast, the grana-thylakoid membranes in C27 at day 5 were retained, along with retention of 57% of total chlorophyll content. Total chlorophyll content of C27 fruit correlated significantly with L*, C*, and h° colour values. The higher percentage of total chlorophyll retained in C27 compared with C18 fruit did not fully unmask the existing peel carotenoids, thus producing a pale-green fruit. © 2007 Taylor & Francis Group, LLC.