Noninvasive Measurement of Internal Oxygen Concentration of Field-Grown Soybean Nodules

(...) a noninvasive method (based on spectrophotometry of leghemglobin) was used to measure O 2 concentration within intact, attached nodules of soybean [Glycine max (L.) Merr.]. A detopping (shoot removal) treatment, which interrupted phloem supply to nodules, resulted in lower internal O 2 concentration relative to controls suggesting that nodule respiration was directly limited by O 2 rather than carbohydrate. When the gas stream around a nodule was switched from pure N 2 to pure O 2 , internal O 2 concentration increased more rapidly in control nodules than in nodules attached to detopped plants (...)