Significance of skin flavonoids for UV-B-protection in apple fruits.
An attempt has been made to assess the UV-B-protective capacity of phenolic compounds accumulated in superficial structures of plants using apple fruit as a model. Two apple (Malus domestica Borkh.) cultivars (Braeburn and Granny Smith) differing in response to high fluxes of solar radiation were selected and exposed to increasing doses of UV-B radiation. The extent of UV-B-induced damage to photosystem II of apple skin correlated with its quercetin glycoside (but not anthocyanin) content. Granny Smith apples did not demonstrate a pronounced response to high sunlight in terms of the accumulation of phenolic substances in the skin and exhibited similar patterns of Fo, Fm, and Fv/Fm changes in the course of UV-B irradiation both on sun-exposed and shaded surfaces of a fruit. Unlike Granny Smith, Braeburn fruits were characterized by a significant accumulation of quercetin glycosides in sun-exposed skin, however, shaded skin contained these compounds in similar amounts to those in Granny Smith. Accordingly, photosystem II in sun-exposed skin of Braeburn apples was resistant to high doses of UV-B radiation (up to 97 kJ m-2), whereas the susceptibility of the photosynthetic apparatus in shaded skin of Braeburn to UV-B-induced damage was much higher and similar to that of both sun-exposed and shaded skin of Granny Smith fruits. Anthocyanins, at least in the amounts found in Braeburn, did not show an additional effect in UV-B protection.
Solovchenko
Alexei
A
Department of Physiology of Microorganisms, Faculty of Biology, Moscow State University, GSP-2 Moscow 119992, Russia.
Schmitz-Eiberger
Michaela
M
D002734:Chlorophyll / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D005453:Fluorescence; D005638:Fruit / Q000737:chemistry / Q000502:physiology* / Q000528:radiation effects*; D045342:Light-Harvesting Protein Complexes; D027845:Malus / Q000737:chemistry / Q000502:physiology* / Q000528:radiation effects*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological / Q000032:analysis; D019441:Plant Epidermis / Q000737:chemistry* / Q000528:radiation effects; D011794:Quercetin / Q000031:analogs & derivatives / Q000378:metabolism*; D014466:Ultraviolet Rays
D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010860:Pigments, Biological; D002734:Chlorophyll; D011794:Quercetin