Some Effect of Ascorbic Acid and Metal-Complexing Agents on the Respiration of Barley Roots.

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Abstract
The respiratory rates of root segments from barley seedlings (Hordeum vulgare) of different ages are reported. Ascorbate not only increased the O2 uptake but also inhibited the CO2 production. Both effects were transitory and disappeared after the increased rate of O2 uptake accounted for the oxidative equivalent of the ascorbate added. The respiration inhibited by ascorbate, as measured by lowered CO2 production, was about equal in magnitude to the cyanide inhibited portion of oxygen uptake. Maximal inhibitions by 8-hydroxy-quinoline and phenylthiourea were about the same as the degree of cyanide inhibition. Sodium diethyldithiocarbamate inhibited respiration about half as effectively as the above reagents. Malonate inhibition of roots pretreated with diethyldithiocarbamate was low or absent in comparison with controls. The apparent ascorbic acid oxidase of root segments in vivo was about one-fourth the ascorbic acid oxidase activity which could be found in root homogenates. Diethyldithiocarbamate inhibited the apparent ascorbic acid oxidase to about 95% while 8-hydro-xyquinoline and phenylthiourea were less inhibitory. Both cytochrome oxidase and ascorbic acid oxidase in amounts sufficient to account for the respiration of untreated roots could be isolated from segments treated with diethyldithiocarbamate.