Interactions Between Oxygen Concentration and Climacteric Onset of Ethylene Evolution

The most significant action of low oxygen on the senescence of detached plant organs is the retardation of the onset of the climacteric rise in ethylene evolution. We have observed that this aspect of low oxygen is saturable, in that for oxygen to delay the climacteric rise in ethylene evolution in apples and carnation flowers its concentration must be reduced below about 6.078 kPa. In cut carnation flowers, 4.5% oxygen delays the accumulation in mRNA of both ACC-oxidase and -synthase by about 6–7 days beyond that found in air samples. In contrast, low oxygen enhances the activity of alcohol dehydrogenase (ADH). In flowers kept under 1.52 kPa O2 there is no accumulation of ACC-synthase or -oxidase transcripts for 17 days, the duration of the experiment. The data thus indicate that there is a mechanism that responds to low oxygen by retarding the synthesis of enzymes associated with normal senescence while at the same time enhancing the synthesis of anoxic proteins, yet without inducing anaerobic fermentation. Preliminary results indicate that a heme-containing protein may be involved in the “sensing” of the concentration of oxygen.