THE INHIBITION OF THE HYPERSENSITIVE RESPONSE OF POTATO-TUBER TISSUESBY CYTOKININS - SIMILARITIES BETWEEN SENESCENCE AND PLANT DEFENSE RESPONSES (VOL 44, PG 33, 1994)

It has been found that cytokinins (CKs) are able to inhibit the hypers ensitive response (HR) and to induce susceptibility in plants. It has also been argued that the ability of CKs to delay the senescence of de tached leaves and flowers may be due to an inhibition of the peroxidat ion of lipids observed during senescence. Recently, the work of numero us groups has implicated the peroxidation of lipids in the HR. Therefo re, it was of interest to investigate the effect of CKs on plant defen ces further. In this work, the effect of 6-furfurylaminopurine (kineti n) on the HR of potato tubers challenged with Phytophthora infestans w as investigated. The characterization of the host-pathogen interaction was achieved via the measurement of hypersensitive cell death (electr olyte leakage), secondary defences (phytoalexin accumulation), and fun gal growth in planta (fungal biomass measured by enzyme-linked immunos orbent assay). Kinetin inhibited electrolyte leakage at concentrations from 15-240 mu M, depressed phytoalexin accumulation al 120-240 mu M, and induced susceptibility at concentrations greater than 60 mu M. In this regard, kinetin mimics the action of salicylhydroxamic acid, an inhibitor of CN--insensitive respiration and lipoxygenase. A hypotheti cal model linking senescence and HR physiology via oxidative damage is briefly presented.