Changes in Rubisco and Rubisco activase gene expression and polypeptide content in Pinus halepensis M. subjected to ozone and drought

The regulation of ribulose-1,5-biphosphate carboxlase/oxygenase (Rubisco) and Rubisco activase was followed for 3 months in an experiment studying the effects of ozone and water stress on Aleppo pine. Rubisco activity was shown to be reduced by 30% in the presence of ozone, whereas no significant effect of water stress was noticed. The effect of combined stresses on Rubisco activity was similar to the effect of ozone. The changes in protein quantity of Rubisco large subunit (LSU) and Rubisco activase (RCA), compared with control plants, were similar to that of the Rubisco activity. Using homologous probes obtained by reverse transcription (RT)-polymerase chain reaction (PCR), rbcL and rca transcript quantities were quantified during the course of the experiment. RbcL and rca mRNA quantities decreased in ozone and after drought. Changes in rbcL transcript quantity in needles subjected to the combination of ozone and drought were similar to the ones detected when drought was applied alone. On the contrary, the pattern of rca changes under the combination of the two stresses was similar to that of ozone applied alone. A positive correlation existed between the effects of ozone on Rubisco activase and Rubisco LSU protein quantities, which was not so obvious by comparing transcript quantities. This could suggest a potential post-transcriptional coordinated regulation of the two proteins under stress-imposed conditions.