Regulation of enzymes involved in anthocyanin biosynthesis in carrot cell cultures in response to treatment with ultraviolet light and fungal elicitors

Abstract

The accumulation of anthocyanins in cell cultures of Daucus carota L. and the enzymes involved in their biosynthesis were investigated under growth in the dark, continuous irradiation with UV light, incubation with elicitors from Pythium aphanidermatum, and elicitor treatment of UV-irradiated cells. Upon UV irradiation, anthocyanin accumulation was strongly enhanced, and the enzymes of the phenylpropanoid and flavonoid pathways, including the "late" enzymes cyanidin galactosyltransferase, cyanidin galactoside xylosyltransferase, cyanidin triglycoside sinapoyltransferase and sinapic acid glucosyltransferase, all showed transient increases in their activities. The time courses of the enzyme activities exhibited successive maxima with an ordered sequence corresponding to their position in the biosynthetic pathway, suggesting a coordinated induction of the entire set of enzymes. The key enzymes phenylalanine ammonia-lyase and chalcone synthase are regulated on a transcriptional level. Incubation of dark-grown carrot cells with fungal elicitors led to a rapid and transient induction of phenylalanine ammonia-lyase corresponding to the formation of 4-hydroxybenzoic acid, but the amount of anthocyanin did not increase and there was no enhancement of any of the enzyme activities which are part of the anthocyanin pathway, including the enzymes catalyzing glycosylation and acylation reactions. Treatment with UV light and elicitors resulted in a rapid induction of the phenylpropanoid pathway, whereas the inducing effect of UV light on the anthocyanin content, on chalcone synthase and on the enzymes catalyzing the final steps of anthocyanin biosynthesis was suppressed. These results indicate a coordinated regulation of the enzymes involved in anthocyanin biosynthesis, an independent inducibility of the phenylpropanoid pathway, and a hierarchy of the different effectors, as shown by the dominating role of the elicitor-signal over the UV stimulus.

Suppression of Powdery Mildew (Podosphaera pannosa) in Greenhouse Roses by Brief Exposure to Supplemental UV-B radiation

“…However, brief exposure of roses to UV-B daily for 1 week followed by inoculation did not affect Podosphaera pannosa development, indicating that the treatment effect was directly upon the exposed pathogen. Flavonoids and phenolic compounds have been reported to act as phytoalexins or antifungal compounds (24,27), increasing the plant resistance to fungal diseases (13,29). In our experiments, there were slight increases in flavonoids (flavonol and anthocyanin) but, at the lowest UV-B exposure time and level (1 h at 0,1 W m"^), there was no significant increase in these compounds, although these UV-B treatment levels effectively suppressed development of powdery mildew.…”

Anthocyanin, antioxidant activity and stress-induced gene expression in high CO2-treated table grapes stored at low temperature

“…3B). PAL was one of the first plant ''defense genes'' identified, and both PAL mRNA levels and PAL activity could be induced by a wide array of environmental cues, such as pathogen attack, low temperatures, UV irradiation, mechanical wounding, and light (Lawton and Lamb, 1987;Gläbgen et al, 1998;Kamo et al, 2000;Sanchez-Ballesta et al, 2000). PAL expression and activity may therefore be considered a good marker to investigate the process whereby high CO 2 levels effectively control the grape decay.…”

In vitro effect of UV-C irradiation on Guignardia citricarpa and on postharvest control of citrus black spot

“…The doses beyond the threshold of those required for the best level of Penicillium digitatum control in grapefruits resulted in high infection and peel blemishes (Droby et al, 1993). The occurrence of brown lesions on postharvest products is suggested to be due to the accumulation of phenolic compounds that are known to be induced by UV-C (Glaβgen et al, 1998;Erkan et al, 2001). In our experiment, low UV-C doses did not cause discoloration in 'Valência' orange peel.…”