Abstract
The expression of ribulose-bisphosphate carboxylase protein (Rubisco) was examined in relation to that of the mRNAs for SSU and LSU subunits in photomixotrophic cell suspensions from tobacco submitted to greening or allowed to acclimatize to different irradiances. A mutant devoid of holoenzyme but possessing both messengers was analyzed for comparison. The Rubisco protein was absent in dark grown cells but mRNAs for both subunits were detectable in wild type cells. Light induced an immediate increase in the relative content of SSU and LSU RNAs but Rubisco-protein synthesis lagged for 3 days. The same light-dependent increase of Rubisco mRNAs was observed in the Rubisco deficient mutant. Wild type cells adapted to low light doubled their Rubisco protein content when irradiance during growth was multiplied by 10. SSU mRNA varied in the same proportion whereas LSU mRNA hardly increased. These light responses were influenced by cell cycle phases in the suspension culture which induced massive changes in total RNA and introduced transient alteration of photosynthetic apparatus. The results are discussed in relation to responses in leaf tissue.
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