Oxygen and Carbon Dioxide Effects on the Pool Size of Some Photosynthetic and Photorespiratory Intermediates in Soybean (Glycine max [L.] Merr.)

Open Access
Publisher Website
Google Scholar
Abstract
The levels of ribulose 1,5-bisphosphate (RuBP), 3-phosphoglyceric acid (PGA), glycolate, glycine, and serine were measured in soybean leaflets during photosynthesis in atmospheres ranging from 1 to 60% O2 and from 0 to 500 microliters per liter CO2. The RuBP level remained constant as CO2 concentration was decreased in atmospheres containing 20 or 60% O2, but increased as CO2 concentration was decreased in atmospheres containing 1% O2. PGA levels decreased at CO2 concentrations near or below the CO2 compensation point under all O2 concentrations. The glycolate pool at 300 microliters per liter CO2 increased slightly with increasing O2 concentration, but remained nearly constant at very low CO2. The serine pool showed no measurable change over the range of CO2 or O2 concentrations tested. The glycine pool did not change significantly with varying CO2 concentration but increased linearly with increasing O2 concentration. Measured RuBP levels indicate an RuBP concentration less than the estimated concentration of RuBP carboxylase/oxygenase active sites. The constant RuBP pool size in 20% O2, however, indicates that RuBP level does not limit photosynthesis or photorespiration any more at 50 microliters per liter CO2 than at 450 microliters per liter.