The Effects of Chlorophyll Photooxidation on Nuclear-Encoded Plastid Ribosomal Protein Mrnas in Norflurazon-Treated Pea Seedlings

Abstract

The development of functional chloroplasts from etioplasts or proplastids requires the expression of both nuclear and plastid genomes. Transcripts from genes located in the nucleus that encode proteins destined for the plastid are translated on cytosolic 80S ribosomes. To localize these proteins to the plastid these polypeptides contain an amino terminal transit sequence. The proteins are transported into the plastid where they are processed to their mature size through loss of their transit sequences. Messenger RNAs derived from plastid DNA are translated in the plastid compartment on 70S ribosomes. To form functional complexes, many of the plastid-encoded proteins associate with nuclear-encoded proteins and often all of these proteins accumulate in a coordinate manner. For example, the plastid ribosome is composed of equal numbers of approximately 55 different proteins, one-third of which are encoded in the plastid itself and the remaining two-thirds are encoded in the nucleus. The mechanisms responsible for the coordinate expression of genes located in different compartments are unknown.