Light-induced Ethylene Production in Sorghum

Abstract

Ethylene production was induced in sections of dark-grown Sorghum vulgare L. seedlings by treatment with light in the blue and far red regions of the light spectrum. The action spectrum closely resembled the previously reported spectra for high irradiance response; thus, light-induced ethylene production is probably a high irradiance response with phytochrome as the initial photoreceptor.Ethylene production in plant tissue may be regulated by light. Two modes of regulation are frequently encountered.In one, ethylene production is decreased by light exposure and is associated with low irradiance, short induction time, and the fully reversible phytochrome system. In the second, ethylene production is increased after light exposure and appears not to be mediated through the low irradiance, reversible phytochrome receptor.Ethylene production measured by Goeschl et al. (7) in etiolated pea seedlings decreased after exposure to red light. Far red irradiation immediately following the red light treatment reversed the effect of red light and gave ethylene production identical with that produced by far red alone. Red light has also been shown to reduce the rate of ethylene production in bean hooks (12) and rice coleoptiles (10).An increase in the rate of ethylene production following light exposure has been observed in lettuce seeds (2), cranberries (4), sorghum seedlings (5), rose tissue cultures (14), and oat seedlings (15). In each case, light approximately doubled the rate of ethylene production. However, the particular wavelengths of light that are active in inducing ethylene production by plant tissue are unknown. Earlier work (2) has shown that light-induced ethylene production in lettuce seeds was not caused by red or far red light. The purpose of these experiments was to determine the effectiveness of selected wavelengths of light for inducing ethylene production in plant tissue.MATERIALS AND METHODS Tissue sections from 4-day-old seedlings of Sorghum vulgare L. cv. E55 and E57 were used. The seedlings were grown in the dark on agar in 125-ml Erlenmeyer flasks at 28 + 1 C as previously described (5 measurements of ethylene production, 10-mm sections were cut just proximal to the first node from the seedling tissue under a green safelight (fluorescent lamp with acrylic and cellophane filters) (3) that produced no detectable effect on ethylene production even after extended, continuous exposure.After cutting, the sections were left on moist paper for 4 hr for dissipation of wound ethylene. The sections of tissue were then mixed, and a random selection of 10 sections for each sample was sealed with a rubber vaccine cap in a 20-ml vaccine bottle containing 2 ml of sterile 1.5% agar along one side.Irradiation treatments were done in an interference filter monochromator system modified for 1 500-w incandescent sources after Withrow (16) and utilizing Baird Atomic and Bausch and Lomb blocked interference filters with maximum half band width of ± 15 nm. The action spectrum was done in two sections (345-450 nm an...

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