Effect of systemic and local-lesion-forming strains of tobacco mosaic virus on abscisic acid concentration in tobacco leaves: consequences for the control of leaf growth

Abstract

Abscisic acid (ABA) is a plant hormone which inhibits growth. Its concentration increased 2- to 6-fold in leaves of White Burley tobacco systemically-infected with the vulgare strain of tobacco mosaic virus (TMV). The concentration of “bound” ABA (presumed to be the glucosyl ester) was not affected by infection. TMV strain flavum produced necrotic lesions and localized infection. Commencing at the time of lesion appearance, free ABA increased by up to 18-fold, and “bound” ABA by up to 3-fold. The increase in ABA occurred in or very close to the lesions. ABA concentration also increased in uninfected leaves of flavum-infected plants, probably by ABA transport from inoculated leaves. The means by which systemic and localized TMV infection might stimulate ABA synthesis are discussed. Virus infection reduced leaf growth. Healthy plants were sprayed with ABA to test whether growth inhibition could be caused by the raised ABA concentration after infection. Both infection and application of ABA to healthy plants decreased leaf growth by inhibiting cell division: neither affected cell expansion. The 2 treatments had similar effects when applied at different stages of leaf development. Quantitatively, raising the ABA concentration of healthy leaves by an amount similar to the increase caused by TMV gave a similar inhibition of leaf growth. It is concluded that raised ABA concentration after infection is a major cause of the inhibited growth of infected plants.