Nitrogen Control of Chloroplast Development and Differentiation: Technical Progress Report.

摘要

This project concerns the role of nitrogen availability in regulation of photosynthetic gene expression in the nuclear and chloroplast compartments. These studies exploit a continuous culture system wherein Chlamydomonas reinhardtii is maintained at a steady-state of nitrogen-limited growth. Nitrogen deficiency leads to alteration of light-harvesting capabilities, augmentation of chlororespiratory electron transport flow by thylakoid membranes and redirection of photosynthetic carbon metabolism toward the accumulation of storage carbohydrates. Recovery from nitrogen-deficiency with accompanying changes in gene expression rapidly follows provision of ammonium to the cells. Previously, we found that expression of nuclear genes encoding apoproteins of light-harvesting complexes and, to a lesser extent, the small subunit of ribulose 1,5-bisphosphate carboxylase/oxygenase, are strongly regulated at the level of mRNA accumulation. Chloroplast activities are also strongly influenced by nitrogen availability but the effect is primarily due to restrictions of the translation of some, but not all, organellar mRNAs. No qualitative or quantitative effects on chloroplast (or mitochondrial) transcripts have been detected in northern analyses performed to date nor is there an appreciable effect of nitrogen limitation on the abundance of organellar DNA. 4 figs., 1 tab.