SUMMARY To understand the phenomenon by which
infection of seed-transmitted Barley stripe mosaic virus (BSMV) alters membrane structures and inhibits
protochlorophyllide biosynthesis of dark-grown barley (Hordeum vulgare L.) plants, we analysed the presence of
NADPH:protochlorophyllide oxidoreductase (POR, EC 1.3.1.33) and the
galactolipid content and
fatty acid composition. The amount of POR in etioplasts of infected leaves, compared with non-infected leaves, was reduced, as measured by immunoelectron microscopy and Western blot. These results are in agreement with the previously described reduction of the ratio of the photoactive 650 nm to non-photoactive 630 nm absorbing
protochlorophyllide forms (Harsányi et al., 2002. Physiol. Plant 114, 149-155). The
galactolipid content was lower in infected leaves. Monogalactosyl-
diacylglycerol (MGDG) content was reduced to 40% and digalactosyl-
diacylglycerol to 55% of control plants on a fresh weight basis. In infected plants, the proportion of
linolenic acid decreased in both
galactolipids. The lower amount of highly
unsaturated fatty acids and the reduced abundance of MGDG correlated well with the previously detected reduction in the membrane ratio of prolamellar body (PLB) to prothylakoid (Harsányi et al., 2002. Physiol. Plant 114, 149-155). The reduced amount of POR and the above described alterations in the
lipid composition resulted in a disturbed structure of PLBs. As a consequence, pigment synthesis and the greening process were inhibited in infected cells, in turn explaining the appearance of chlorotic stripes of BSMV-infected barley leaves. Our results show that BSMV
infection can be detected at a very early stage of leaf development.