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The effect of day temperature on photoassimilate translocation in three tomato ecotypes (Japanese cultivar ´Ogata Zuiko´ ; North European cultivar ´Moneymaker´ ; South European cultivar ´Roma´) was studied. Greenhouse-grown plants with young fruits at the first trusses (15 d after flowering) were transferred into artificially illuminated growth cabinet and raised for 10 d at 15 / 20, 25 / 20 and 30 / 20℃, 12 h day / 12 h night temperatures. After the acclimation to temperature regimes, plants were fed with 700㎕ ℓ^(-1) ^(13)CO₂ for 1 h photosynthetically. At 0 h, 6 h (end of day time) and 18 h (end of night time) from the termination of the feeding, plants were harvested, sorted into 9∼12 fractions and oven dried. After the measurements of ^(13)C and ^(12)C by an infrared absorption method, the ^(13)C atom % excess and relative content of ^(13)C were calculated. ´Moneymaker´ showed the high ^(13)C concentration in the fruit, irrespective of high or low temperature during the growth, which indicated the low sensitivity of photoassimilate translocation to temperature. ´Ogata Zuiko´ showed a similar response as ´Moneymaker´ at optimal temperature (25 / 20℃), but at suboptimal range, its sensitivity decreased more than ´Moneymaker´. ´Roma´ showed a marked decline of photoassimilate translocation to the fruit at 30 / 20℃, suggesting that the important limiting factor of fruit production was reduced translocation at high temperatures. The relationship between organ to organ with respect to the current photoassimilate translocation was the most intimate between the upper leaves and the fruit. Together with our previous results on night temperature regime, it was concluded that photoassimilate translocation of ´Moneymaker´ was heattolerant and that of ´Roma´ was heat-sensitive. The character observed in ´Moneymaker´ may be applicable to tomatoes in tropical and subtropical areas.
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