Induction of coleoptile elongation by carbon dioxide

The ability of CO(2) to induce elongation of Avena sativa coleoptile segments was examined with the use of a high resolution growth-recording device. CO(2)-saturated water causes an 8- to 16-fold promotion in the rate of elongation within 1 minute. This elongation is insensitive to a variety of metabolic inhibitors that suppress auxin-induced elongation, and the CO(2) effect cannot be prevented by pretreatment with these inhibitors. Buffers of pH 3 to 4 also stimulate elongation quickly, and it seems that at least a major part of the action of CO(2) depends upon its ability to reduce pH. The rate of elongation of auxin-promoted segments can be further enhanced by treatment with CO(2) but not vice versa.The response to CO(2) can be inhibited by mannitol at osmotic concentrations that inhibit normal growth, by calcium, and by brief pretreatment with heavy water (D(2)O). The elongation rate that results from CO(2) treatment is sensitive to temperature, but the induction by CO(2) itself appears to be almost temperature-independent.Elongation following treatment with CO(2) may be a physical flow phenomenon, essentially independent of immediate biochemical participation, which occurs when wall polymer interactions that normally restrict strain in the cell wall are weakened or broken by CO(2) in a manner that in effect substitutes for the role of metabolism in normal auxin-inducible cell enlargement.