Light Stimulation of Ethylene Release from Leaves of Gomphrena globosa L

The effect of light and CO(2) on both the endogenous and 1-aminocyclopropane-1-carboxylic acid (ACC)-dependent ethylene evolution from metabolically active detached leaves and leaf discs of Gomphrena globosa L. is reported. Treatment with varying concentrations of ACC did not appear to inhibit photosynthesis, respiration, or stomatal behavior. In all treatments, more ethylene was released into a closed flask from ACC-treated tissue, but the pattern of ethylene release with respect to light/dark/CO(2) treatments was the same.Leaf tissue in the light with a source of CO(2) sufficient to maintain photosynthesis always generates 3 to 4 times more ethylene than tissue in the dark. Conversely, the lowest rate of ethylene release occurs when leaf tissue is illuminated and photosynthetic activity depletes the CO(2) to the compensation point. Ethylene release in the dark is also stimulated by CO(2) either added to the flask as bicarbonate or generated by dark respiration. Ethylene release increases dramatically and in parallel with photosynthesis at increasing light intensities in this C(4) plant. Ethylene release appears dependent on CO(2) both in the light and in the dark. Therefore, it is suggested that the important factor regulating the evolution of ethylene gas from leaves of Gomphrena may be CO(2) metabolism rather than light per se.