We examined the role of salicylic acid (SA) accumulation in the tobacco hypersensitive response (HR) and systemic acquired resistance (SAR) induced by PB90, a 90 kDa protein elicitor that is secreted by Phytophthora boehmeriae. The elicitor induced HR of a consistent shape and size on tobacco plants expressing the bacterial gene nahG. Salicylate hydroxylase is encodec by nahG and inactivates SA by converting it into catechol. The mutant NahG does not accumulate SA. In contrast, infiltration with of a wild type tobacco (cv. Xanthi nc) leaves with the elicitor caused the increase of SA levels. The same SA levels were observed in leaves not treated by the elicitor. HR appears to be mediated by a SA-independent signaling pathway. PB90 treatment resulted in enhanced resistance of wild-type plants to infection by black shank fungus, P. nicotianae, and TMV, but not in NahG plants. Moreover, the elicitor-induced expression of an SAR marker gene encoding PR-1a was suppressed in NahG plants. These results indicate that SA mediates SAR but not HR in tobacco treated with PB90. During plant-elicitor interactions, HR and SAR may be regulated by distinct signal pathways, or SA may function as an intermediate signal upstream of SAR but downstream of HR, and HR may not be a direct defense mechanism against pathogen infection.

为了确定Ca2+信号途径是否参与、在哪一时期参与稻瘟病菌分生孢子萌发及附着胞形成过程的调控，用四种可从不同位点阻断Ca2+信号途径的抑制剂分别处理分生孢子，观察抑制剂对孢子萌发及附着胞形成过程的抑制作用。结果表明：Ca2+螯合剂EGTA、Ca2+通道抑制剂Verapamil、抑制磷脂酶C活性的抑制剂U-73122、影响钙调素与钙调素依赖蛋白激酶作用位点的抑制剂KN-93，随着浓度的增加，对孢子萌发和附着胞形成过程的抑制作用明显增强；同一浓度下，抑制剂对附着胞形成过程的抑制作用大于孢子萌发过程；抑制剂影响孢子萌发和附着胞形成过程在萌发早期（1～4h）最有效；在完全被抑制、不能萌发的孢子内出现了许多颗粒状囊泡；抑制剂可使附着胞形态明显变小甚至不能形成。以上结果表明钙信号途径参与了稻瘟病菌孢子萌发及疏水条件下附着胞形成过程的调控。