Inhibition of degreening in the peel of bananas ripened at tropical temperatures. IV, Photosynthetic capacity of ripening bananas and plantains in relation to changes in the lipid composition of ripening banana peel

SUMMARY Functional and structural changes in peel tissue have been followed by analysing fluorescence induction curves and the lipid composition during the ripening of bananas (Musa AAA, Subgroup Cavendish) at 20°C and 35°C. Changes in the fluorescence induction curves indicated that electron transport capacity was lost more rapidly at 35°C than at 20°C, thus revealing that the chlorophyll retained by bananas ripened at 35°C soon becomes non-functional photosynthetically, probably because of serious disturbances in thylakoid organisation during ripening at tropical temperatures. By contrast, in plantains (Musa Group AAB, Plantain Subgroup), where degreening is complete at both 20°C and 35°C, the loss of electron-transport capacity closely corresponds to the loss of chlorophyll. The lipid composition of unripe banana peel resembled other photosynthetic tissue in possessing a high proportion of mono- and digalactosyl diacylglycerols, containing predominantly polyunsaturated fatty acids, particularly linolenic acid. Following ripening for four days at 20°C, when degreening was complete, some 50% of the galactolipids had broken down, and the polyunsaturated fatty acids were recovered in the neutral lipid fraction. By comparison, after ripening at 35°C there was a greater loss of galactolipids, and a lower overall recovery of linolenic acid. The significance of these findings for the stability of the chlorophyll-protein complexes during the incomplete degreening of bananas at tropical temperatures is discussed.