The inhibition of the hypersensitive response of potato tuber tissues by cytokinins, similarities between senescence and plant defence responses

It has been found that cytokinins (CKs) are able to inhibit the hypersensitive response (HR) and to induce susceptibility in plants. It has also been argued that the ability of CKs to delay the senescence of detached leaves and flowers may be due to an inhibition of the peroxidation of lipids observed during senescence. Recently, the work of numerous groups has implicated the peroxidation of lipids in the HR. Therefore, it was of interest to investigate the effect of CKs on plant defences further. In this work, the effect of 6-furfurylaminopurine (kinetin) on the HR of potato tubers challenged with Phytophthora infestans was investigated. The characterization of the host-pathogen interaction was achieved via the measurement of hypersensitive cell death (electrolyte leakage), secondary defences (phytoalexin accumulation), and fungal growth in planta (fungal biomass measured by enzyme-linked immunosorbent assay). Kinetin inhibited electrolyte leakage at concentrations from 15-240 μm, depressed phytoalexin accumulation at 120-240 μm, and induced susceptibility at concentrations greater than 60 μm. In this regard, kinetin mimics the action of salicylhydroxamic acid, an inhibitor of CN^--insensitive respiration and lipoxygenase. A hypothetical model linking senescence and HR physiology via oxidative damage is briefly presented.