Abstract

Dark-grown barley seedlings were treated with levulinic acid and exposed to different light-dark regimes. Light-induced ALA formation was dependent on wave length and total energy. With tungsten light (400–700 nm) about 18 Joules·m−2 and with monochromatic light (650 nm) 250 Joules·m−2 were required for maximum ALA accumulation. A light flash of 1 sec was sufficient using tungsten light (22.6 watts·m−2) to interrupt the dark period and give maximum ALA induction. Although measurable ALA was found in dark-grown barley 1 hr after the interruption of the dark period, at least 5 hr of dark incubation were necessary for maximum ALA accumulation.

The light action spectrum for ALA induction was similar to those exhibited by photomorphogenesis with the major peak at 650 nm. Only small amounts of ALA were induced in the far-red region. Far-red light had a reverse potentiation effect on ALA and chlorophyll formation in dark-grown barley.

A classical phytochrome reaction involving ALA induction was not found. However, far-red light largely cancelled out the light-induction of ALA if it preceded the red or white light treatment and was followed by a dark period.

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