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 μmol mol⁻¹) and ambient (350 μmol 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 (Rodermel et al. (1988) Cell 55: 673–681). Prior to the low temperature treatment, A and quantum yield of PSII photochemistry in the light adapted state (φ_PSII) were significantly lower in T3 compared to WT at each CO₂ level. At this time, total nonphotochemical quenching (NPQ_Total) 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. NPQ_Total was similar (0.80–0.85) among all treatments. However, a larger proportion of NPQ_Total was composed of q_I,d, the damage subcomponent of the more slowly relaxing NPQ component, q_I, in both genotypes at elevated compared to ambient CO₂. Greater q_I,d, at elevated CO₂ during and after the low temperature treatment was not related to pre-treatment differences in total Rubisco activity.