Action of Respiratory Catalysts and Inhibitors on Oxygen Consumption by Nitella

Abstract

The material used consisted of young, actively growing coenocytic cells of Nitella clavata collected from a large outdoor pool. The growing tips of several dozen stems were cut off and kept in a large beaker of pond water in the dark for 24 hours prior to use. These clusters of cells were from 2 to 10 mm. in diameter.

The manometric technique, originally described by Barcroft and Haldane, and subsequently employed extensively by Warburg, was used for measuring oxygen consumption. The material was immersed in pond water. Five per cent KOH was used in the inset to absorb CO₂, and the vessels containing the green plants were wrapped in an opaque black cloth to exclude light. Oxygen consumption was measured as a rate, Qo₂, in cmm. per hour per gram wet weight.

The effects of NaCN and methylene blue, singly and combined, were studied, purely relative results being obtained when the agents were used separately. When methylene blue was added after the cyanide, all values were corrected for the percentage change of a control run at the same time. In every case the normal Qo₂ was established for the second hour of a 2-hour run. In the case of cyanide the vessels were then disconnected and 0.4 cc. of the proper NaCN concentration was added, and the Qo₂ of the second hour thereafter determined. When methylene blue was used alone the dye was poured into the plant environment from the side-arm after the normal Qo₂ had been established. When methylene blue was used in combination with NaCN, the percentage inhibition was first determined with cyanide alone, the methylene blue then added and the Qo₂ determined for the second hour thereafter, in conformance with the standard procedure. All inhibition and acceleration were expressed as percentage deviation from the normal as first established in each case.