The Effect of Light and Phytochrome on 1-Aminocyclopropane-1-Carboxylic Acid Metabolism in Etiolated Wheat Seedling Leaves

Abstract

ABSTRACITWhile light-grown wheat leaves produced ethylene at a low rate of <0.1 nanomoles per gram per hour and contained 1-aminocyclopropane-1-carboxylic acid (ACC) at low levels of <2.5 nanomoles per gram, etiolated wheat leaves produced ethylene at a rate of 2 nanomoles per gram per hour and accumulated concentrations of ACC at levels of 40 nanomoles per gram. Upon illumination of 8-day-old etiolated wheat seedlings with white light, the ethylene production rate increased initially, due to the activation of ethylene-forming activity, but subsequently declined to a low level (0.1 nanomoles per gram per hour) at the end of the 6-hour illumination. This light-induced decline in ethylene production rate resulted from a decline (more than 35 nanomoles per gram) in ACC level, which was accompanied by a corresponding increase in 1-malonylamino)cyclopropane-l-carboxylic acid content. These data indicate that illumination promoted ACC malonylation, resulting in reduced ACC level and consequently reduced ethylene production. However, light did not cause any significant increase in the extractable ACC-malonyltransferase activity. A number of reports have shown that light regulated ethylene production which in turn modified plant growth (4,5,9,18,19 m-2 s-'), red light or far-red light. The red and far-red light sources were from a projector equipped with a 650 nm and 730 nm filter, respectively. For the red light treatment, tubes were exposed to red light with intensity of 12 ,uE m-2 s-' for 5 min; for far-red treatment, tubes were exposed to far-red light with intensity of0.85 uE m-2 s-' for 10 min. Tubes were returned to darkness for the subsequent measurements.Determination of Ethylene Production. Leaf segments in tube were flushed with air and sealed with a rubber serum cap after each sampling. At indicated time intervals, 1 ml gas samples were drawn from the tubes and injected into a gas chromatograph equipped with an alumina column and a FID detector at 90°C.Determination of ACC and MACC. Samples were extracted twice with 5 ml of 80% ethanol at 55°C for 10 min. The ethanol extract was evaporated under vacuum at the same temperature. The residue was dissolved in 2 ml water and the pigment was removed by the addition of 0.5 ml chloroform. ACC content in 0.2 ml aliquots of the aqueous solutions was determined according to the method of Lizada and Yang (14). The quantitation of MACC in the extract was carried out first by passing 0.2 ml extract through a Dowex 50 (H+-form) resin column with 0.5 ml bed volume to removed ACC. The effluent solution containing MACC was hydrolyzed in 2 N HCl for 3 h as described previously (13). Following neuralization with NaOH, the resulting hydrolysate was assayed for ACC content, which was taken as the amount of MACC in the extract.

Effect of light quality on ethylene formation in leaf and petal discs of Begonia � hiemalis Fotsch cv. Schwabenland Red

“…In addition, all experiments showed that 0 .5,umol m-2 s -1 PFD of far-red light stimulated the ethylene production by 60-90% . These data strongly support earlier reports [10,11,12] on inhibitory effects of light on ACC conversion to ethylene . The data also confirmed previous proposals concerning the regulatory role of phytochrome [6,8,13] .…”

Cytokinin, Acting through Ethylene, Restores Gravitropism to Arabidopsis Seedlings Grown under Red Light

“…Continuous white light decreases ethylene levels in oat leaves (Gepstein and Thimann, 1980). Light may decrease ethylene levels by promoting ACC malonylation, and there is evidence from red light / far-red light photoreversibility that phytochrome is the photoreceptor (Jiao et al, 1987). In Arabidopsis seedlings, on the other hand, growth in (white) light strongly increased ethylene levels, as compared with dark-grown seedlings (Guzman and Ecker, 1990).…”

ACC synthase and its cognate E3 ligase are inversely regulated by light

“…To test this, we examined the effect of light on ETO1/EOL proteins as light has a substantial effect on ethylene biosynthesis in various plant species, including Arabidopsis. [21][22][23] Light treatment of 3-day-old etiolated seedlings caused an increase in the level of myc-ACS5 protein within 2 h (Fig. 2A).…”