Terminal oxidases and growth in plant tissues. I. The terminal oxidase mediating growth of Avena coleoptile and Pisum stem sections

Abstract

Listen

Translate article

1. 1. The effects of oxygen pressure, carbon monoxide, cyanide, and several copper-enzyme poisons on the elongation of isolated sections of Pisum stems and Avena coleoptiles were studied in an effort to characterize the terminal oxidase mediating this growth process. 2. 2. Growth of Pisum sections is independent of the partial pressure of oxygen between 5 and 220% of an atmosphere, whereas the growth of Avena sections is markedly inhibited when the oxygen pressure falls below 10% of an atmosphere. 3. 3. Prolonged exposure to moderate positive pressures of nitrogen superimposed upon 1 atm. of air has little effect on growth. 4. 4. Twenty-four-hour exposure to positive pressures of carbon monoxide superimposed upon 1 atm. of air markedly inhibits the growth of the isolated sections. A 5:1 ratio of carbon monoxide to oxygen causes 70% inhibition of elongation of Avena and 50% inhibition of Pisum; at a 20:1 ratio the corresponding values are 86% and approximately 99%. Upon return to air, the sections grow rapidly and are able in large measure to “catch up” to the controls. 5. 5. The carbon monoxide inhibition of growth is essentially completely reversed by light at all carbon monoxide to oxygen ratios. 6. 6. Growth may also be inhibited by cyanide, but is insensitive to copper-enzyme poisons. 7. 7. It is concluded that the enzyme inhibited by carbon monoxide is cytochrome oxidase, and that the growth of Avena and Pisum sections is mediated entirely by this enzyme.