A1 Refereed original research article in a scientific journal
Singlet oxygen, flavonols and photoinhibition in green and senescing silver birch leaves
Authors: Mattila Heta, Sotoudehnia Pooneh, Kuuslampi Telma, Stracke Ralf, Mishra Kumud B., Tyystjärvi Esa
Publisher: SPRINGER HEIDELBERG
Publication year: 2021
Journal: Trees - Structure and Function
Journal name in source: TREES-STRUCTURE AND FUNCTION
Journal acronym: TREES-STRUCT FUNCT
Number of pages: 16
ISSN: 0931-1890
eISSN: 1432-2285
DOI: https://doi.org/10.1007/s00468-021-02114-x
Web address : https://link.springer.com/article/10.1007/s00468-021-02114-x
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/53660280
During autumn senescence, deciduous trees degrade chlorophyll and may
synthesize flavonols. We measured photosynthetic parameters, epidermal
flavonols, singlet oxygen production in vivo and photoinhibition of the
photosystems (PSII and PSI) from green and senescing silver birch (Betula pendula) leaves. Chlorophyll a fluorescence and P700
absorbance measurements showed that the amounts of both photosystems
decreased throughout autumn senescence, but the remaining PSII units
stayed functional until ~ 90% of leaf chlorophyll was degraded. An
increase in the chlorophyll a to b ratio, a decrease
in > 700 nm absorbance and a blue shift of the PSI fluorescence peak
at 77 K suggest that light-harvesting complex I was first degraded
during senescence, followed by light-harvesting complex II and finally
the photosystems. Senescing leaves produced more singlet oxygen than
green leaves, possibly because low light absorption by senescing leaves
allows high flux of incident light per photosystem. Senescing leaves
also induced less non-photochemical quenching, which may contribute to
increased singlet oxygen production. Faster photoinhibition of both
photosystems in senescing than in green leaves, under high light, was
most probably caused by low absorption of light and rapid singlet oxygen
production. However, senescing leaves maintained the capacity to
recover from photoinhibition of PSII. Amounts of epidermal flavonols and
singlet oxygen correlated neither in green nor in senescing leaves of
silver birch. Moreover, Arabidopsis thaliana mutants, incapable
of synthesizing flavonols, were not more susceptible to photoinhibition
of PSII or PSI than wild type plants; screening of chlorophyll
absorption by flavonols was, however, small in A. thaliana. These results suggest that flavonols do not protect against photoinhibition or singlet oxygen production in chloroplasts.
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