Regulation of tomato fruit ascorbate content is more highly dependent on fruit irradiance than leaf irradiance.
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.
Gautier
Hélène
H
INRA, UR1115 Plantes et systèmes de culture horticoles, Domaine St Paul, Avignon, France. helene.gautier@avignon.inra.fr
Massot
Capucine
C
Stevens
Rebecca
R
Sérino
Sylvie
S
Génard
Michel
M
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
D002241:Carbohydrates; D001205:Ascorbic Acid