Histochemical observation and HPLC analysis of phenolic compounds at the graft union of dwarf peach trees grafted onto Prunus tomentosa

Phenolic compounds extracted from the graft union of heterograft trees (Pru nus peisica / tomentosa) were analyzed by histochemistry and HPLC methods: and compared with those on homograft trees (P. persica/P. persica). A DMACA (p-dimethylamino-cinnamaldehyde) staining method showed that at early stag es after budding the phenols were localized mainly in the callus cells, in the new xylem and in the cortical tissues of the heterograft combination an d persisted even 6 months after budding. These phenolic compounds frequentl y surrounded necrotic tissues which seemingly impeded the union between the scion and rootstock. From the HPLC analysis, four phenolic compounds were found as major components in both rootstocks, but two of them were not dete cted in the phloem of dwarfing P. tomentosa. The chemical nature of these p eaks was unknown, except one was identified as catechin; however, based on their UV spectrum, behavior in TLC and retention time, our assignments are tentative. In general, the phenolic content in the phloem tissues was highe r in homograft than in heterograft trees, particularly peaks # 1 and # 3, w hich we suppose are prunin and naringenin respectively. However,in the xyle m tissues on heterograft trees the phenolic concentration was much smaller and the patterns from the stock to the scion were different from those obse rved on homograft trees. Peak # 1, prunin and. Peak # 2 accumulated in the phloem above the heterograft union; whereas in the xylem, Peak # 1, prunin, and Peak # 3, naringenin, were present at low amounts. Catechin, a low mol ecular weight flavan occurred in similar amounts in the xylem of both combi nations, accumulating at the graft union, whereas the phloem, of the homogr aft contained a larger amount of catechin.