INHIBITION OF DEGREENING IN THE PEEL OF BANANAS RIPENED AT TROPICAL TEMPERATURES .5. CHLOROPHYLL BLEACHING ACTIVITY MEASURED INVITRO

A linolenate‐dependent chlorophyll oxidase activity resembling the activity considered responsible for chlorophyll bleaching in senescing leaves has been studied in thylakoids isolated from the peel of bananas (Musa AAA, Subgroup Cavendish). While the degreening of bananas is inhibited as the temperature was raised above 24°C, chlorophyll oxidase activity increased linearly as the temperature was raised from 20°C to 40°C. Cyanide inhibits the chlorophyll oxidase activity in vitro, but the increased amounts of cyanide produced by banana peel ripened at high temperatures do not accumulate, despite the fact that β‐cyanoalanine synthase activity, which effectively traps the cyanide, remains relatively unaffected by the increased temperature. The association of chlorophyll oxidase activity with the functional and structural organisation of the light‐harvesting complexes and photosystems is discussed in relation to the inhibition of degreening in the peel of Cavendish bananas ripened at tropical temperatures. Copyright © 1990, Wiley Blackwell. All rights reserved