Different intra-organ antioxidant defence strategies towards UV-B irradiation

Marija Vidovic visited Dr. Jana Barbro Winkler in Germany (31 days in April 2011)

Different intra-organ antioxidant defence strategies towards UV-B irradiation in white and green leaf parts of himeric geranium.

The aim of this STSM was to study the effect of realistic environmental UVB and high light intensities on photosynthesis and stomatal conductance and on antioxidative system and secondary leaf metabolism of variegated pelargonium (Pelargonium zonale variegata) and Swedish ivy (Plectranthus coleoides variegatus). The exposure of plants in the sun simulators at Helmholtz Zentrum Munich played important role in this study because of their unique combination of lamps which allows simulation of sun irradiance for the both spectral quality and spectral quantity, enabling experimental set up which can corresponds real environmental conditions. The focus of our work was to monitor photosynthetic parameters, by changing only UVB irradiation, while the other conditions were constant and ecologically relevant, and to take samples for further biochemical analysis of antioxidative enzymes and metabolites.

The results obtained after gas exchange and fluorescence measurements showed that UVB itself did not influence the quantum yield of photosynthesis, neither in P. zonale neither in P. coleoides. Another aspect of UVB effect was monitored through the change in the leaf colour of both plant species, due to anthocyanins accumulation. In the case of P. coleoides, it was induced by the UVB itself, while the leaves of P. zonale developed red color under the high light intensity(Fig.1.). This result points to the significance of anthocyanins accumulation, but also to their distribution, as change in colour in P. coleoideswas present in the white part, and in P. zonale in green part of the leaves.

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Figure 1. The effect of the treatment on the leaf color. In the first two columns UVB treated plants are shown, and in the 3rd and 4th are control plants. A) P. coleoides; B) P. zonale. Arrows point leaves with the most expressive change of color.

Having in mind all the results obtained, our further work will be focused on investigating changes in the activities of the enzymes of antioxidative system and phenolics biosynthesis, especially anthocyanins from the samples collected in two performed experiments.

Although my visit to EUS was short, I have managed to improve my knowledge not only about photosynthesis, but also about designing experimental conditions. I have learned to use instruments for photosynthesis monitoring and it was my first experience in the physiological experiment. As such research approach is fundamental for the screening of primary plant metabolism it will be a foundation for my PhD thesis, along with studying antioxidative and phenolics metabolism under high light and UVB intensities.