Antagonism Between Malate and Ethylene in the Regulation ofAvena sativaColeoptile Elongation

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Abstract
Etiolated Avena sativa L. coleoptile sections were used to determine the influence of C2H4 on in vivo and in vitro rates of CO2 fixation, and to measure the influence of various permutations of C2H4, CO2, and malate on growth. Whereas 1 mM malate or 320 μ I-1 CO2 stimulated growth by approximately 100 per cent, inhibition of growth by 10-8 μ I-1 C2H4 was substantial only in the presence of malate or CO2 The increase in growth rate in response to these two agents was eliminated by the simultaneous application of C2H4. The in vivo rate of dark [14C]bicarbonate fixation and in vitro enzymic assays of fixation were not measurably inhibited by C2H4. These results are discussed in the light of evidence which indicates that CO2-stimulated growth is mediated by dark fixation. The data do not support the view that C2H4 inhibition of growth results from an inhibition of fixation, but suggests that C2H4 may inhibit some step in the process by which malate stimulates growth.