Profiling photosynthetic competence in mango fruit.
Hetherington S. E.
Author Affiliation: Department of Agriculture, University of Queensland, St Lucia, Brisbane, Qld 4072, Australia.
Journal of Horticultural Science 72 : 755-763
Abstract : Photosynthetic competence was investigated in mature, unripened fruits of 11-year-old mango trees. Fruits of several cultivars were compared, so as to include a range of intense, moderate or no anthocyanin coloration. Intrinsic efficiency of photosystem II, measured as Fv/Fm, the ratio of variable to maximal chlorophyll fluorescence emission in dark-adapted fruits, was not uniform around the fruit surface. Surfaces exposed to low or moderate sunlight showed high intrinsic efficiencies (range 0.76-0.81) comparable with leaves, whereas surfaces exposed to full sunlight showed lower intrinsic efficiencies (range 0.52-0.78 at the equator on the exposed side of fruits) indicating that some degree of photoinhibition had occurred. More severe photoinhibition and photodestruction of pigments was seen on a localized area on the shoulder of fruits exposed to full sunlight. Although previous studies of CO2 fixation in mango put photosynthetic rates in mature fruit peel at about 1% of rates in leaves, fluorescence measurements indicated that except for the shoulder area of some fruits, actual efficiencies during photosynthesis and photosynthetic rates of fruits on a surface area basis were high and comparable with those typical of leaves. Purple fruits consistently showed higher actual efficiencies of photosystem II than green fruits. As susceptibility to photoinhibition decreases when the efficiency of photosystem II increases, it is postulated that anthocyanins may be effective in protecting the photosynthetic system in mango fruits against photoinhibition.