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) a nd Rubisco activase was followed for 3 months in an experiment studying the effects of ozone and water stress on Aleppo pine. Rubisco activity was sho wn to be reduced by 30% in the presence of ozone, whereas no significant ef fect of water stress was noticed. The effect of combined stresses on Rubisc o activity was similar to the effect of ozone. The changes in protein quant ity of Rubisco large subunit (LSU) and Rubisco activase (RCA), compared wit h control plants, were similar to that of the Rubisco activity. Using homol ogous probes obtained by reverse transcription (RT)-polymerase chain reacti on (PCR), rbcL and rca transcript quantities were quantified during the cou rse 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 und er the combination of the two stresses was similar to that of ozone applied alone. A positive correlation existed between the effects of ozone on Rubi sco activase and Rubisco LSU protein quantities, which was not so obvious b y comparing transcript quantities. This could suggest a potential post-tran scriptional coordinated regulation of the two proteins under stress-imposed conditions.