Interactions between tobacco mosaic virus and chloroplast functions during photoacclimation of tobacco leaves

The effects of infection of two strains of tobacco mosaic virus on photoacclimation of Nicotiana tabacum cv Xanthi were investigated. The capacity for photoacclimation was influenced by N nutrition and developmental stage of leaves. Low N nutrition accentuated susceptibility to photoinhibition and led to impaired photoacclimation. The masked strain tobacco mosaic virus (strain PV42) which produces no or mild symptoms, had little additional inhibitory effect on photoacclimation of tobacco plants. Indeed, infection actually enhanced photosynthetic acclimation in low light in all leaf types and during low light to high light transfer in low nitrogen developed and mature leaves. Tobacco leaves infected with TMV strain PV42 were no more susceptible to photoinhibition than uninfected controls grown in the same light and N nutrition regimes.;The severe strain of tobacco mosaic virus (strain PV230) which produces chlorotic-mosaic symptoms in expanding leaves, drastically impaired photosynthetic acclimation in high light. The inhibition of photoacclimation by strain PV230 was shown to result from photoinhibitory damage to chloroplasts. The efficiency of PSII, measured with in vivo fluorescence, was reduced before overt symptoms developed. Photosynthetically functional area was subsequently reduced in expanding leaves through formation of chlorotic mosaic tissue and reduced Rubisco content. Thus, I conclude that exposure of infected expanding leaves to high light leads to photoinhibitory damage which increases the rate and extent of development of chlorotic-mosaic symptoms and impairs photoacclimation.;On a whole leaf basis, decreased Rubisco content is associated with impaired photoacclimation in expanding leaves. Developed and mature leaves which are symptomless when infected with TMV strain PV230, showed impaired photoacclimation under low N nutrition (mature leaves) and during low light to high light transfer conditions (developed leaves) and are susceptible to photoinhibition.;Studies on photoacclimation of transgenic plants, expressing the coat protein of TMV, generally showed unaffected photoacclimation. Even though plants expressing the movement protein of the virus showed reduced Rubisco content strengthening the involvement of more specific effects of the virus on impaired photoacclimation.