I started my research career at the unit of Molecular Plant Biology at the University of Turku (Finland). Both my master’s thesis and PhD research dealt with the mechanism(s) by which light irreversible damages photosystem II. For that I needed to quantify production of reactive oxygen species, especially of singlet oxygen. In addition to photoinhibition, I directly measured the redox state of the plastoquinone pool, to understand it´s regulation under different light conditions. After completing the PhD, I worked a bit as a post-doctoral researcher in Turku, concentrating on autumn senescence. Now I am working as a post-doc in the university of Aveiro, Portugal. I continue to work with trees; I aim understand why autumn colors exist and how photosynthesis functions in a senescing leaf. In addition, together with the Marine Photophysiology & Phycotechnology lab I am investigating photoinhibition and photoprotection in macroalgae.
35
Why senescing autumn leaves synthetize red anthocyanins?
H. MATTILA, M. RANTALA, E. TYYSTJÄRVI
University of Aveiro, ECOMARE, Porto de Pesca Costeira do Porto de Aveiro, 3830-565 Gafanha da Nazaré, Ílhavo, Portugal
During autumn senescence, chlorophylls and other macromolecules are degraded while anthocyanins can be synthetized. As to why leaves accumulate red pigments, no consensus exists.
We compared green, red and yellow leaf sections of senescing Norway maple and found no significant differences in Photosystem II (PSII) photoinhibition between red and yellow sections. However, a Norway maple variety (Faassen’s black) resisted photoinhibition, presumably due to its high anthocyanin content. Individual Norway maple leaves were followed from late summer until abscission; red pigments mainly accumulated during last phases of senescence. In contrast, Faassen’s black contains anthocyanins already prior senescence. Thus, differences in amount and timing of anthocyanin synthesis can explain the different photoinhibition results.
Red Norway maple showed stress symptoms (low PSII activity, high non-photochemical quenching and carotenoid content). We suggest that the primary function of anthocyanin synthesis is not photoprotection but to dispose of carbohydrates, allowing light reactions to produce energy for nutrient translocation. Despite decreased photoinhibition, also Faassen’s black exhibited the above-mentioned stress symptoms. Degradation of photosynthetic complexes, studied by native gel electrophoresis, was also more “chaotic” in Faassen’s black.
Senescing leaves showed weak recovery from photoinhibition, which will be studied in individual cells and chloroplasts with a PAM fluorescence microscope.