Effect of systemic tobacco mosaic virus infection on endogenous cytokinin concentration in tobacco ( Nicotiana tabacum L.) leaves: consequences for the control of resistance and symptom development

Abstract

Capillary gas chromatography (GC) with nitrogen-specific detection was used to measure cytokinin concentration in White Burley tobacco ( Nicotiana tabacum L.) systemically-infected with tobacco mosaic virus (TMV). Infected plants developed a mosaic of distinct light-green and darkgreen areas in syslemically-infected leaves. Virus infection reduced the concentration of zeatin (Z) in dark-green areas of infected leaves. Zeatin riboside (ZR) concentration was unchanged by infection. Both healthy and TMV-infected leaves contained the cytokinin glycosides, zeatin-O-glucoside (ZOG) and zeatin-O-glucoside riboside (ZROG). The concentration of ZOG in uninfected leaves was typically 1·7 to 2·4 times that of Z on a molar basis while ZROG occurred at approximately the same level as ZR. Virus infection increased the concentration of ZOG and ZROG by up to 1·7 and 4·5-fold respectively in dark-green areas of infected leaves while glucosioe concentration in light-green areas of leaves was largely unchanged. Treatment with exogenous abscisic acid (ABA) stimulated cytokinin catabolism in both healthy control and infected plants, reducing the concentration of Z and increasing markedly the concentration of cytokinin glucosides. The role of the observed changes in cytokinin concentration and their interaction with ABA metabolism in control of symptom development and resistance are discussed.