Abstract: 【Objective】 β-aminobutyric acid (BABA) can effectively induce defense responses in potato against late blight disease by means of spray in field or on detached leaves. The objective of this study is to investigate the histochemical aspects of BABA induced resistance (BABA-IR) and signaling pathway involved in BABA-IR in potato. The present study will provide knowledge for further elucidating the mechanisms of BABA-IR.【Method】Potato plants were sprayed with 4 mmol?L-1 BABA or distilled water (Mock, as control). Three days after treatment, the sprayed leaves were detached and inoculated with Phytophthora infestans. Then leaf discs were punched out from attached leaves at different time points after inoculation and used for histochemical staining and hypersensitive response (HR) observation. Diaminobenzidine (DAB) staining method was used to detect hydrogen peroxide (H2O2) generation around inoculated site. Callose deposition and HR were detected by aniline blue staining combined with fluorescence microscopic observation. For investigating the signaling pathway in which BABA induced late blight resistance involved, transgenic potato plants which disturbed the jasmonic acid (JA) or salicylic acid (SA) signaling pathway by interferencing StCOI1 or overexpressing NahG were used. 【Result】 No deposition of H2O2 was observed when Mock and BABA pretreated leaves were inoculated with water. While H2O2 deposition appeared around inoculation sites on both Mock and BABA pretreated leaves 24 h after P. infestans inoculation. It was obvious that BABA pretreated potato leaves accumulate H2O2 strongly and early ahead of Mock (control) 12 h after P. infestans inoculation. No obvious callose deposition was observed when Mock and BABA pretreated leaves were inoculated with water. But strong callose deposition was observed around the P. infestans inoculation sites in BABA pretreated potato leaves compared to that of Mock leaves. Fluorescence microscopic observation showed that HR occurred around the P. infestans inoculation sites on BABA pretreated leaves as early as 24 h. Although HR appeared on both Mock and BABA pretreated leaves, high frequency (85%) of HR occurred around the inoculation sites on BABA pretreated leaves, which was about 55% higher than it occurred on the Mock leaves. Treatment with BABA could not effectively induce late blight resistance in the potato leaves overexpressing NahG, while it was capable of inducing resistance in the StCOI1 silenced potato leaves, which meant that BABA-IR needs SA signaling pathway. 【Conclusion】 Various of defense responses, including H2O2 accumulation, callose deposition and HR, were rapidly and strongly activated in BABA pretreatment potato leaves after P. infestans inoculation. SA signaling pathway involved in BABA-IR in potato against P. infestans.

Key words: Solanum tuberosum , β-aminobutyric acid induced resistance , late blight , histochemical assays , SA signaling pathway