A NEW PARTNER IN THE DANSE MACABRE: THE ROLE OF NITRIC OXIDE IN THE HYPERSENSITIVE RESPONSE

Abstract

Summary. Plant responses to abiotic and biotic stress are to a great extent coordinated by similar chemical signals. Thus, salicylic acid (SA) and reactive oxygen intermediates (ROIs) influence tolerance to heat and chilling as much as resistance to pathogens during the hypersensitive response (HR) form of cell death. We have shown that following elicitation the generation of SA and ROI is biphasic and each signal influences the production of the other in a positive feedback mechanism. When SA is applied alone this “potentiates” plant responses to be more effective following elicitation by either pathogenic challenge or abiotic stress. Nitric oxide (NO) has also been proposed to contribute towards plant defence. Using photoacoustic laser (PLA) detection NO generation was detected in tobacco following challenge with bacterial pathogens but was not produced in a biphasic manner. In contrast PLA measurements showed that C2H4 production during the HR was biphasic. This pattern of C2H4 production could be mimicked with the NO-donor sodium nitroprusside (SNP), acting part through the initiation of SA synthesis. A model is proposed