Glyphosine, a plant growth regulator, affects chloroplast membrane proteins

Abstract

Glyphosine ( N, N-bis(phosphonomethyl)glycine) is known to increase sucrose levels in sugarcane and to cause chlorosis in maize and other plants. It has been suggested (Crofts, S.M., Arntzen, C.J., Vanderhoef, L.N. and Zettinger, C.S. (1974) Biochim. Biophys. Acta 335, 211–217) that its primary mode of action is to inhibit the synthesis of plastid rRNA. Growth of Lemna gibba L. G-3 on 5 · 10 −4M glyphosine causes the plants to produce fronds lacking chlorophyll. The plastids in these white fronds contain only a few internal membrane structures, some of which are stacked. Sodium dodecyl sulfate polyacrylamide gel electrophoresis shows an accumulation of substantial amounts of both the large and small subunits of ribulosebisphosphate carboxylase by the white fronds. The membrane fraction from these fronds contains only traces of the light-harvesting chlorophyll a b apoprotein in comparison to control plants. In vivo labeling and immunoprecipitation show that the large subunit of ribulose-bisphosphate carboxylase is actively synthesized by the white fronds. However, labeling of the chlorophyll a b apoprotein and a 32000 dalton protein in the membrane fraction is extremely low compared to control plants. We conclude that in Lemna, glyphosine differentially affects the synthesis and/or processing of soluble proteins and some membrane chloroplast proteins, and could be useful in understanding the biogenesis of chloroplast membranes.