Multiple effects of antibiotics on chloroplast and nuclear gene expression

Antibiotics are widely used to monitor signalling cascades within a plant cell, for example between the nucleus and chloroplasts, and to study the function of the photosynthetic machinery. In the present study, we attempted to test various antibiotics with respect to their expected modes of function and also to monitor their possible side effects on metabolic processes in mature leaves of pea (Pisum sativum L.). Streptomycin, despite its reported prokaryotic nature, prevented translation not only in the chloroplast, but also in the cytosol. Application of puromycin, an inhibitor of protein synthesis in both the pro- and eukaryotes, resulted in severe photoinhibition of photosystem II upon illumination, yet had no effect on plastid translation, thus implying a severe side effect on plastid metabolism. Prokaryotic-type translation inhibitors lincomycin, spectinomycin and erythromycin blocked translation in the chloroplast without any direct effects on cytoplasmic protein synthesis. More detailed studies with lincomycin, however, revealed a strong modulation of the expression of nuclear-encoded genes by slowing down the transcription rate of photosynthesis-related Lhcb and RbcS genes, and furthermore, lincomycin clearly decreased the phosphorylation level of the LHCII proteins.