PHYTOCHROME CONVERSION AS AN IN SITU ASSAY FOR EFFECTIVE LIGHT GRADIENTS IN ETIOLATED SEEDLINGS OF Zea mays

Abstract— In situ photochemical conversion and measurement of phytochrome can be used as a non-intrusive assay for axial light conduction along etiolated plant tissues of Zea maysL. A computerized single beam spectrophotometer was used to measure phytochrome conversion just below the coleoptilar node following irradiation of the plant shoot with 632 nm light at various distances from the measurement point. Photochemical conversion decreased log-linearly with increasing distance between the irradiation and measurement points. The distance over which the light was attenuated by 50% was 1.80 mm for mesocotyl, 1.60 mm for coleoptile plus primary leaf, and 1.15 mm for primary leaf alone (coleoptile removed). These results verify the photochemical significance of axially conducted light and thereby provide supporting evidence that such light conduction is important for photomorphogenesis.