Biology subjects

Holzwarth, A. R.

Publications and source records attributed to Holzwarth, A. R..

3 recordsLinked to original sources

bioRxiv2025

Spillover is the dominant non-photochemical quenching mechanism in angiosperms

Non-photochemical quenching (NPQ) is an important photoprotective process in plants, but all molecular details of the process(es) involved are yet not understood. We have used advanced spectroscopic techniques (including simultaneous time- and spectrally-resolved room-temperature chlorophyll fluorescence analysis and spectro-kinetic deconvolution) to analyse the processes in Arabidopsis, hybrid aspen and Scots pine plants. We used four well-characterized Arabidopsis lines (npq1, npq2, npq4 and L17) affected in NPQ, together with hybrid aspen lines with corresponding modifications that we generated. The data are described best by a model for NPQ induction with up to five fluorescence components representing distinct biochemical entities. A dominant fluorescing species at the end of NPQ induction was identified as functionally detached and quenched LHCII but most importantly we believe that one represents a "PSII-PSI (Photosystem II-Photosystem I) complex" where direct energy transfer between PSII and PSI (spillover) take place. This provides strong quenching in all three plant species. We suggest a new integrated model for NPQ in higher plants where spillover is a major element and suggest roles for PsbS and zeaxanthin. Moreover, we discuss the link between NPQ and thylakoid rearrangements as thylakoid destacking facilitates direct contact between PSII and PSI; a prerequisite for spillover.

plant biology↗

bioRxiv2022

The dynamics of non-photochemical quenching and cyclic electron transport in A.thaliana exposed to harmonically oscillating light

In natural environments, plants are exposed to rapidly changing light. Maintaining photosynthetic efficiency while avoiding photodamage requires equally rapid regulation of photoprotective mechanisms. We asked what the operation frequency range of regulation is in which plants can efficiently respond to varying light. Chlorophyll fluorescence, P700, plastocyanin, and ferredoxin responses of wild-type Arabidopsis thaliana were measured in oscillating light of various frequencies. We also investigated the npq1 mutant lacking violaxanthin de-epoxidase, the npq4 mutant lacking PsbS-protein, and the mutants crr2-2, and pgrl1ab impaired in different pathways of the cyclic electron transport. The fastest was the PsbS-regulation responding to oscillation periods longer than 10s. Processes involving violaxanthin de-epoxidase dampened changes of chlorophyll fluorescence in oscillation periods of 2min or longer. Knocking out the PGRL1-PGR5 pathway strongly reduced variations of all monitored parameters, probably due to congestion in the electron transport. Incapacitating the NDH-like pathway only slightly changed the photosynthetic dynamics. Our observations are consistent with the assumption that non-photochemical quenching in slow light oscillations involves violaxanthin de-epoxidase to produce, presumably, a stationary, non-oscillating level of zeaxanthin. We interpret the observed dynamics of Photosystem I components as being formed in slow light oscillations partially by thylakoid remodeling that modulates the redox rates.

plant biology↗

bioRxiv2020

Direct energy transfer from photosystem II to photosystem I is the major regulator of winter sustainability of Scots pine

Evergreen conifers in boreal forests can survive extremely cold (freezing) temperatures during the long dark winter and fully recover during the summer. A phenomenon called sustained quenching putatively provides photoprotection and enables their survival, but its precise molecular and physiological mechanisms are not understood. To unveil them, we have analyzed the seasonal adaptation of the photosynthetic machinery of Scots pine (Pinus sylvestris) trees by monitoring multi-year changes in weather, chlorophyll fluorescence, chloroplast ultrastructure, and changes in pigment-protein composition. Recorded Photosystem II and Photosystem I performance parameters indicate that highly dynamic structural and functional seasonal rearrangements of the photosynthetic apparatus occur. Although several mechanisms might contribute to sustained quenching of winter/early spring pine needles, time-resolved fluorescence analysis shows that extreme down-regulation of photosystem II activity along with direct energy transfer from photosystem II to photosystem I plays a major role. This mechanism is enabled by extensive thylakoid destacking allowing for mixing of PSII with PSI complexes. These two linked phenomena play crucial roles in winter acclimation and protection. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=125 SRC="FIGDIR/small/144170v1_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@b9d757org.highwire.dtl.DTLVardef@e8ba28org.highwire.dtl.DTLVardef@115c5b2org.highwire.dtl.DTLVardef@6634f5_HPS_FORMAT_FIGEXP M_FIG C_FIG

plant biology↗