Ribulose 1, 5-bisphosphate Carboxylase/ Oxygenase Activities in Leaves of Greenhouse Roses

An enzyme assay was developed to measure the initial and Mg2+−CO2 activated forms of Ribulose 1,5-bisphosphate Carboxylase/Oxygenase (Rubisco) in rose leaves. The assay was verified by co-extraction of the leaflets with partially purified spinach Rubisco and through correlation with net photosynthetic rates of individual leaflets (r2=0.7324). Changes in activities were measured as a function of depth of leaves in the canopy for two cultivars of greenhouse hybrid tea roses. Initial Rubisco activity declined with increasing canopy depth for both cultivars. The activated form of the enzyme, however, remained constant with canopy depth for cv. Red Success; but increased with canopy depth, then declined after mid-canopy in the cv. Royalty. Rubisco activities were also measured in the cv. Red Success grown in CO2 enriched environments (100 mm3 dm−3) at three humidity levels. The activities were not significantly affected by humidity treatment. However, there was a trend for plants grown at lower humidity to have higher activated activities.