Abstract: In order to investigate the effect of tomato rootstock，scion and their potential interaction on chilling tolerance，we grafted chilling-sensitive tomato cultivar‘060911’（S）and chilling-resistant tomato cultivar‘060112’（R）. We then selectively removed rootstock or scion from the grafted seedlings RS/RS，and incubated the newly formed 6 varieties of seedlings，i.e. R/R，R/RS，R/S，S/R，S/RS，S/S in the growth chamber with light intensity of 22 klx and photoperiod 12 h/12 h. The seedlings were treated with low temperature at 10 ℃/3 ℃ for 9 days and recovered at 25 ℃/15 ℃ for 3 days. Photosynthetic parameters and indexes related to nitrogen metabolism were measured after the chilling treatment and after the recovery. The results showed that low temperature stress reduced the photosynthesis of tomato grafted seedlings. Among these 6 varieties of grafted seedlings，S/S seedlings displayed the lowest photosynthetic rate（Pn）while R/R seedlings displayed the highest. Meanwhile，R/R seedlings showed the highest pigment，water content，stomatal conductance（Gs）and stomatal limitation（Ls）. While RS/R，S/R，R/S，RS/S seedlings were intermediate between R/R and S/S regarding the pigment，water content，Pn，Gs and Ls，indicating that the photosynthetic assimilatory power of grafted seedlings with R as root or scion was significantly higher than that of S. Meanwhile，the content of NO3--N and the activities of nitrate reductase（NR），glutamine synthetase（GS）and glutamate synthase （GOGAT）were significantly decreased in low temperature stress，while the content of free amino acids and NH4+-N was significantly increased. However，in addition to NH4+-N content，the content of NO3--N and the activities of NR，GS and GOGAT in leaves of RS/R，S/R，R/S，RS/S seedlings were lower than that of R/R，but higher than S/S. The results showed that the nitrogen assimilatory power of R root or scion was higher than that of S. Moreover，the photosynthesis and nitrogen assimilatory power of RS-R was significantly higher than those of RS-S，and the P value of interaction was less than 0.05. The results showed that rootstock and scion had significant interaction effect on photosynthesis and nitrogen metabolism of grafted seedlings.

Key words: tomato, rootstock, grafting, low temperature stress, photosynthesis, nitrogen metabolism