Biology subjects

Tikkanen, M.

Publications and source records attributed to Tikkanen, M..

3 recordsLinked to original sources

bioRxiv2024

Sustained non-photochemical quenching and regulation of PSII repair cycle during combined low temperature and high light stress in lettuce

In nature, light and other environmental conditions are constantly changing, requiring plants to have several overlapping regulatory mechanisms to keep light reactions and metabolism in balance. Here, we show that high light (HL) induces a much stronger down-regulation of light reactions when lettuce plants are exposed to 1500 {micro}mol photons m-2 s-1 for 4 h at 13{degrees}C (low temperature, LT) compared to 23{degrees}C (growth temperature, GT). GT/HL treatment induced non-photochemical quenching (NPQ), which relaxed during 1 h recovery in darkness. In contrast, LT/HL treatment induced an exceptionally high NPQ that only partially relaxed during 1 h in darkness at GT. Such a high sustained NPQ (sNPQ) cannot be explained by canonical NPQ mechanism(s). Instead, sNPQ was associated with partial disassembly of PSII-LHCII complexes and a transient increase in phosphorylation of the minor antenna proteins LHCB4.1/LHCB4.2. This coincided with increased expression of the light-harvesting-like proteins SEP2 and ELIP1.2, the PSII assembly proteins HCF173 and LPA3, and accumulation of the pre-D1 protein. These results lead us to propose that LHCB4.1/LHCB4.2 phosphorylation- dependent disassembly of PSII-LHCII supercomplexes allows SEP2 to bind to CP47 and hypothetically quenches the inner PSII core antenna, while free CP43 released during PSII repair is proposed to be protected by LPA3.

plant biology↗

bioRxiv2020

Efficient cooperation of chloroplasts and mitochondria enhances ATP and sucrose production

Efficient photosynthesis requires a balance of ATP and NADPH production/consumption in chloroplasts and the exportation of reducing equivalents from chloroplasts is important for balancing stromal ATP/NADPH ratio. Here we showed that the overexpression of purple acid phosphatase 2 on the outer membranes of chloroplasts and mitochondria can streamline the production and consumption of reducing equivalents in these two organelles, respectively. A higher capacity of consumption of reducing equivalents in mitochondria can indirectly help chloroplasts to balance the ATP/NADPH ratio in stroma and recycle NADP+, the electron acceptors of the linear electron flow. A higher rate of ATP and NADPH production from the linear electron flow, a higher capacity of carbon fixation by the Calvin-Benson-Bassham cycle and a greater consumption of NADH in mitochondria, enhance photosynthesis in the chloroplasts, ATP production in the mitochondria, sucrose synthesis in the cytosol, and eventually boosting plant growth and seed yields in the overexpression lines.

plant biology↗

bioRxiv2018

Regulation of chloroplast NADH dehydrogenase-like complex by NADPH-dependent thioredoxin system

Linear electron transport in the thylakoid membrane drives both photosynthetic NADPH and ATP production, while cyclic electron flow (CEF) around photosystem I only promotes the translocation of protons from stroma to thylakoid lumen. The chloroplast NADH-dehydrogenase-like complex (NDH) participates in one CEF route transferring electrons from ferredoxin back to the plastoquinone pool with concomitant proton pumping to the lumen. CEF has been proposed to balance the ratio of ATP/NADPH production and to control the redox poise particularly in fluctuating light conditions, but the mechanisms regulating the NDH complex remain unknown. We have investigated potential regulation of the CEF pathways by the chloroplast NADPH-thioredoxin reductase (NTRC) in vivo by using an Arabidopsis knockout line of NTRC as well as lines overexpressing NTRC. Here we present biochemical and biophysical evidence showing that NTRC activates the NDH-dependent CEF and regulates the generation of proton motive force, thylakoid conductivity to protons and redox balance between the thylakoid electron transfer chain and the stroma during changes in light conditions. Further, protein-protein interaction assays suggest a putative thioredoxin-target site in close proximity to the ferredoxin binding domain of NDH, thus providing a plausible mechanism for regulation of the NDH ferredoxin:plastoquinone oxidoreductase activity by NTRC.\n\nOne sentence summaryChloroplast thioredoxins regulate photosynthetic cyclic electron flow that balances the activities of light and carbon fixation reactions and improves plant fitness under fluctuating light conditions.

plant biology↗