The effect of irradiance on the protein synthetic machinery of Vicia faba L. leaves

Abstract An increase in irradiance from 10 to 125 W/m 2 resulted in the activation of RNA polymerase I and recruiting of monosomes into polysomes in the leaves of Vicia faba L. Leaf discs from plants grown under 10 W/m 2 synthesised protein in vivo at a higher rate than discs from plants grown under 125 W/m 2 , especially when calculated per dry weight basis. The translation activity of polysomes in the cell-free system was also significantly higher in the preparations from plants grown under 10 W/m 2 . A search for possible regulators of polysome translation activity resulted in the detection of two major non-ribosomal polypeptides with M r of about 42 and 55 kDa in the polysome preparations. The abundance of these polypeptides depended on the irradiance and leaf age. Preliminary immunoassays and phalloidin test indicate the presence of polymeric actin in the polysome preparations.