Measurement of nematode respiration with the biological oxygen monitor.

Cartesian Diver (1) and manometric (2) techniques have frequently been used to measure the respiration rates of nematodes. However, the sensitivity and ease of operation of the polarographic oxygen-sensing equipment currently available offers a technique of great future value to plant nema-tologists. Our recent experience with the YSI Model 53 Biological Oxygen Monitor (Yellow Springs Instrument Co., Yellow Springs, Ohio 45387) has shown it is quite satisfactory for measuring the respiration rates of a Caenorhabditis sp. and ApheIenchus avenae Bastian. Oxygen consumption was 100 monitored with as few as 5000 nematodes per cuvette. It was, however, necessary to ~ 90 modify the stirring system; the pertinent in-80-formation is presented here to aid workers-~ who may wish to measure nematode respira-o tion using this type of equipment. "~ 70-The magnetic stirrers provided (1.9 cm E diameter discs) with the biological oxygen 0~ 60-monitor, fit quite closely to the sides of the 7-cuvene (2 cm i.d.) and caused a homogeniz-o 50-ing action on whole nematodes. In experi-m ments with 5000 of either nematode sus-~ 40 pended in 3 ml of water in a cuvette about-80% of the nematodes were damaged after ~ 30 40 minutes of stirring (see Fig. 1). The re-suiting decrease in respiration was directly 20-related to the mechanical killing of the nematodes. Thus, while the stirrer supplied 10 with the oxygen monitor is satisfactory for studies with mitochondria it is not satisfactory for work with whole nematodes. The problem of stirrer damage to the nematodes was overcome by using a smaller stirrer of the type supplied with the Radio-meter, model 25, pH meter (Radiometer, Copenhagen, Denmark). This stirrer is a round, teflon-coated magnetized disc, 1 cm in diameter. In an experiment similar to that described above there was practically no damage to either Caenorhabditis sp. or A. avenae over a period of 80 minutes. The