title: Regulation of tomato fruit ascorbate content is more highly dependent on fruit irradiance than leaf irradiance.
abstract: OBJECTIVE
  The mechanisms involving light control of vitamin C content in fruits are not yet fully understood. The present study aimed to evaluate the impact of fruit and leaf shading on ascorbate (AsA) accumulation in tomato fruit and to determine how fruit sugar content (as an AsA precursor) affected AsA content.
  
  
  METHODS
  Cherry tomato plants were grown in a glasshouse. The control treatment (normally irradiated fruits and irradiated leaves) was compared with the whole-plant shading treatment and with leaf or fruit shading treatments in fruits harvested at breaker stage. In a second experiment, the correlation between sugars and AsA was studied during ripening.
  
  
  RESULTS
  Fruit shading was the most effective treatment in reducing fruit AsA content. Under normal conditions, AsA and sugar content were correlated and increased with the ripening stage. Reducing fruit irradiance strongly decreased the reduced AsA content (-74 %), without affecting sugars, so that sugar and reduced AsA were no longer correlated. Leaf shading delayed fruit ripening: it increased the accumulation of oxidized AsA in green fruits (+98 %), whereas it decreased the reduced AsA content in orange fruits (-19 %), suggesting that fruit AsA metabolism also depends on leaf irradiance.
  
  
  CONCLUSIONS
  Under fruit shading only, the absence of a correlation between sugars and reduced AsA content indicated that fruit AsA content was not limited by leaf photosynthesis or sugar substrate, but strongly depended on fruit irradiance. Leaf shading most probably affected fruit AsA content by delaying fruit ripening, and suggested a complex regulation of AsA metabolism which depends on both fruit and leaf irradiance and fruit ripening stage.
authors.affiliation: INRA, UR1115 Plantes et systèmes de culture horticoles, Domaine St Paul, Avignon, France. helene.gautier@avignon.inra.fr
authors.forename: Hélène
authors.initials: H
authors.lastname: Gautier
authors.forename: Capucine
authors.initials: C
authors.lastname: Massot
authors.forename: Rebecca
authors.initials: R
authors.lastname: Stevens
authors.forename: Sylvie
authors.initials: S
authors.lastname: Sérino
authors.forename: Michel
authors.initials: M
authors.lastname: Génard
mesh_terms: D001205:Ascorbic Acid / Q000032:analysis*; D002241:Carbohydrates / Q000032:analysis; D005638:Fruit / Q000737:chemistry* / Q000502:physiology / Q000528:radiation effects*; D008027:Light; D018551:Solanum lycopersicum / Q000737:chemistry* / Q000502:physiology / Q000528:radiation effects*; D010084:Oxidation-Reduction / Q000528:radiation effects; D010858:Pigmentation / Q000528:radiation effects; D018515:Plant Leaves / Q000528:radiation effects*; D012995:Solubility / Q000528:radiation effects; D013696:Temperature
chemical_list: D002241:Carbohydrates; D001205:Ascorbic Acid