In order to understand a mechanism regulating sugar accumulation in peach fruit under water stress condition, 13C-photoassimilates partitioning to fruit and the other organs in container-grown peach trees were examined under water stress condition during fruit maturation stage. Under moderate water stress condition [ψmax(predawn leaf water potential): -0.85MPa], 13C content per unit dry matter, corresponding to sink activity for photoassimilates, increased in fruit, although photosynthetic rate

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... decreased to 83%. On the other hand, under severer water stress condition (ψmax: -1.65MPa), both the photosynthetic rate and the photoassimilates partitioning to fruit were decreased. These results suggest that photoassimilate partitioning to fruit are accelerated under moderate water stress condition, although the severe water stress exerts an opposite effect.