PHYSIOLOGIA PLANTARUM 81: 295-300. Copenhagen 1991 Oxygen concentration and ethylene production in roots and leaves of wheat: short term reaction in air after anoxic and hypoxic treatments Pietro Tonutti and Angelo Ramina Tonutti. P. and Ramina, A. 1991. Oxygen concentration and ethylene production in roots and leaves of wheat: short term reaction in air after anoxic and hypoxic treatments. - Physiol. Plant. 81: 295-3(X). Seven-day old wheat seedlings (Triticum aestivum L. cv. MEC) were incubated in small jars, fluxed with gas mixtures of nitrogen-oxygen (oxygen concentrations 0, 0.3. 1,2.5, 10%) for up to 48 h. Effects of anoxia and hypoxia on ethylene evolution and ethylene-forming enzyme (EFE) activity were determined 1 h after the plants had been transferred to air. respectively. 1-aminocyclopropane-l-carboxylic acid (ACC) content was measured immediately after treatments. Results showed that the ethylene production is differently affected hy oxygen deprivation in roots and leaves. The effects are more closely related to ACC accumulation than to the EFE activity. In leaves, ethylene evolution is almost unaffected by oxygen concentrations above ca 1%. Key words - 1-aminocyclopropane-l-carboxylic acid, ethyiene biosynthesis, ethylene- forming enzyme, oxygen, Triticum aestivum, wheat. P. Tonutti and A. Ramina (corresponding author), Inst. of Pomology, Univ. of Padova. via Gradenigo 6. 1-35131 Padova. Itaiy. Introduction In the ethylene biosynthetic pathway the conversion of 1-aminocyclopropane-l-carboxylic acid (ACC) to ethy- lene is oxygen-dependent (Adams and Yang 1979) but the mechanism by which ethylene formation is inhibited by anaerobiosis is unknown. Some information is avail- able on the effects of decreasing oxygen concentrations on the ethylene production by roots. In natural condi- tions, flooding of the root system leads to oxygen deple- tion and, under anoxia, ethylene formation by roots is reduced or blocked (Bradford et al. 1978, Drew et al. 1979, Jackson et al. 1978). In hypoxia, roots of barley (Jackson et al. 1984) and maize (Jackson 1982) in- creased ethylene biosynthesis even though the en- haticed ethylene concentration detected in the tissue could depend on the lower diffusivity of the hormone in Received 13 August, 1990; revised 4 December, 1990 Phvsli>l. Ptanl.SI. IVJl water than in air (Jackson 1985). As far as aerial parts are concerned, it is well known that, when soii is flooded, a stimulation of ACC formation occurs in the roots of tomato plants and the precursor is transported in the transpiration stream to the shoots where it is converted to ethylene (Bradford et al. 1980, 1982). Lit- tle is known on the effects of low oxygen concentrations on ACC formation directly in the shoots and on the activity of the ethylene-forming enzyme (EFE). These aspects are investigated in the present paper. Abbreviations - ACC, 1-aminocyclopropane-carhoxylic acid; AOA, aminooxyacetic acid; EFE, ethylene-forming enzyme; OC, oxygen concentration. 295