Alterations in RNA and protein metabolism in uninoculated half-leaves of cowpea adjacent to tobacco necrosis virus infected halves

Abstract

Following inoculation of half-leaves of cowpea with tobacco necrosis virus (TNV, R 1 : 1.5 19 : S S : S Fu), two major protein fractions, termed α and β appear in soluble extracts, which are absent from sham-inoculated (control) tissue. The origin and role of these proteins are unknown, but they appear coincidently with hypersensitivity 3 days after inoculation. The same proteins appear 3 days later in apparently healthy tissue directly adjacent to necrotic half-leaves. Virus is absent from the apparently healthy tissue. During this time-course the ratios of the amounts of radiolabelled precursors incorporated into both total RNA and protein, between apparently healthy and healthy tissue were compared. No significant alterations in either were seen. However, alterations in 'early' polyadenylate (poly(A)) mRNA were observed reproducibly. Increases in 'early' mRNA up until 1 day postinfection of the adjacent half-leaf are not thought to be concerned with the synthesis of either the α or β fractions as these appear much later in apparently healthy tissue. Novel synthesis of the α and β fractions has not been demonstrated. The role of host-adaptation either by the amplification of small proteins or the degradation of larger proteins to produce the α and β fractions is discussed.