Vol. 72 No: 5

Title:
Profiling Photosynthetic Competence in Mango Fruit

Author:
SUZAN E. HETHERINGTON

pp: 755-764

Abstract:
Photosynthetic competence was investigated in mature, unripened fruit of eleven year old trees of mango (Mangifera indica L.). Fruit of several cultivars were compared, so as to include a range of fruit showing intense, moderate or no anthocyanic coloration. Intrinsic efficiency of photosystem II, measured as F_v/F_m, the ratio of variable to maximal chlorophyll fluorescence emission in dark-adapted fruit, was not uniform around the fruit surface. Surfaces exposed to low or moderate sunlight showed high intrinsic efficiencies (range 0.76 to 0.81) comparable with leaves, whereas surfaces exposed to full sunlight showed lower intrinsic efficiencies (range 0.52 to 0.78 at the equator on the exposed side of fruit) 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 fruit 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 fruit on a surface area basis were high and comparable with those typical of leaves. Purple fruit consistently showed higher actual efficiencies of photosystem II than green fruit. 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 fruit against photoinhibition.

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