Abstract: Variations in salicylic acid (SA) and hydrogen peroxide (H₂O₂) were analyzed in different resistance poplars (Populus tomentosa and Populus × beijingensis) inoculated with Botryosphaeria dothidea. The results showed that the SA content increased in P. tomentosa, the concentration of endogenous free SA peaked (191.41 μg·g^-1 FW) at 72 h, which was accompanied with the reduction of CAT activity and increase in H₂O₂ content. However, in P. X beijingensis the SA content did not significantly arose (7.83 μg·g^-1 FW), and was not accompanied by decreases in CAT activity and H₂O₂ content. The H₂O₂ peak occurred earlier with lower values compared with P. tomentosa (306.99 nmol·g^-1 FW vs 737.52 nmol·g^-1 FW). The above results indicated there were significant differences in SA and H₂O₂ in different poplars interacted with B. dothidea. Meanwhile, we isolated and identified full-length coding sequence of PtSABP and PbSABP from P. tomentosa and P. × beijingensis stem cDNAs. The proteins of PtSABP and PbSABP belong to the Catalase_like superfamily, and their sequences are 90% identical to that of tobacco SABP at the amino acid level based on NCBI blast and phylogenetic tree analysis. RT-PCR analysis showed that gene expression of CAT was inhibited in 6～24 h after inoculated with B. dothidea, suggesting that SA was bound with SABP at this time, inhibiting CAT activity, thus promoting significant increase in H₂O₂ content at 24 h after inoculation. The experiments determined that the difference of content of SA and H₂O₂ in poplars was due to inoculated with B. dothidea, SABP was involved in the disease resistance of poplar, and suggested that the resistance of poplars to B. dothidea would be relevant to the accumulation of SA and H₂O₂.

Key words: Populus spp., Botryosphaeria dothidea, salicylic acid(SA), H₂O₂