UV-B radiation alters interactions between photosynthesis and secondary metabolism in variegated Plectranthus coleoides

Abstract

This study is based on the results obtained from the experiments conducted within two Short Term Science Missions (STSMs) in the Research Unit Environmental Simulation, Helmholtz Zentrum München during 2011 and 2012. Our aim was to investigate the effects of realistic UV-B doses on photosynthesis and secondary metabolism in variegated leaves. Variegated Plectranthus coleoides plants were exposed to UV-B radiation (0.90 W m-2) under two photosynthetic active radiation (PAR) intensities (LL: 395 and HL: 1350 μmol m-2 s-1) for nine days in the sun simulators at the Helmholtz Zentrum München. In the green leaf portions, UV-B radiation stimulated photosynthetic rates in P. coleoides at both PAR intensities and doubled the size of plastoglobuli whereas the contents of photosynthetic pigments were slightly increased at HL. The concentrations of phenylpropanoids, catechins and hydroxybenzoic acids, were preferentially accumulated in green leaf portions, independently on radiation regimes. A hallmark of UV-B induced changes in plant metabolism, the induction of flavonoid pathway, was evidenced in P. coleoides by accumulation of apigenin and cyanidin glycosides in the whole leaf at both background PARs. UV-B induced accumulation of apigenin and cyanidin glycosides was more pronounced in the white leaf portions, compared to green one. Moreover, we observed differential response of H2O2 scavenging system to high PAR and UV-B in relation to tissue type. Alteration of linear electron flow, provoked by acclimation to UV-B at HL was associated with decreased ascorbate redox state and APX activity. In summary, UV-B radiation stimulated CO2 assimilation and increased fixed carbon flow into photosynthetic pigments, phenylpropanoids and flavonoids/anthocyanins which might be important for photoprotection of photosynthetic machinery under high light intensity.Abstracts of the Final Netwotk Meeting of COST Action FA0906 UV4growth - Bled, Slovenia, 30 March - 2 April 2014