Effects of elevated carbon dioxide on gas exchange and photochemical and nonphotochemical quenching at low temperature in tobacco plants varying in Rubisco activity.

Elevated (700 micromol mol-1) and ambient (350 micromol mol-1) CO2 effects on total ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity, photosynthesis (A), and photoinhibition during 6 d at low temperature were measured on wild type (WT), and rbcS antisense DNA mutants (T3) of tobacco (Nicotiana tabacum L.) with 60% of WT total Rubisco activity. Prior to the low temperature treatment, A and quantum yield of PSII photochemistry in the light adapted state (phiPSII) were significantly lower in T3 compared to WT at each CO2 level. At this time, total nonphotochemical quenching (NPQTotal) levels were near maximal (0.75-0.85) in T3 compared to WT (0.39-0.50). A was stimulated by 107% in T3 and 25% in WT at elevated compared to ambient CO2. Pre-treatment acclimation to elevated CO2 occurred in WT resulting in lower Rubisco activity per unit leaf area and reduced stimulation of A. At low temperature, A of WT was similar at elevated and ambient CO2 while stimulation of A by elevated CO2 in T3 was reduced. In addition, at low temperature we measured significantly lower photochemical quenching at elevated CO2 compared to ambient CO2 in both genotypes. NPQTotal was similar (0.80-0.85) among all treatments. However, a larger proportion of NPQTotal was composed of qI,d, the damage subcomponent of the more slowly relaxing NPQ component, qI, in both genotypes at elevated compared to ambient CO2. Greater qI,d, at elevated CO2 during and after the low temperature treatment was not related to pre-treatment differences in total Rubisco activity.