Biology subjects

Rintamaki, E.

Publications and source records attributed to Rintamaki, E..

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↗

bioRxiv2019

Increased expression of mitochondrial dysfunction stimulon genes affects chloroplast redox status and photosynthetic electron transfer in Arabidopsis

Mitochondrial retrograde signals control expression of nuclear mitochondrial dysfunction stimulon (MDS) genes. Although MDS gene products mostly affect mitochondrial functions, they also influence production of reactive oxygen species (ROS) and redox status of chloroplasts. To study this inter-organellar interaction, we analysed the response of the Arabidopsis MDS-overexpressor mutant rcd1 to methyl viologen (MV), which catalyses electron transfer from Photosystem I (PSI) to molecular oxygen, generating ROS in Mehlers reaction. The response of plants to MV was investigated by imaging chlorophyll fluorescence in aerobic and hypoxic environments, and by membrane inlet mass spectrometry. Hypoxic treatment abolished the effect of MV on photosynthetic electron transfer in rcd1, but not in wild type. A similar reaction to hypoxia was observed in other MDS-activating lines and treatments. This suggests that MDS gene products contribute to oxygen depletion at the PSI electron-acceptor side. In unstressed growth conditions this MDS-related effect is likely masked by endogenous oxygen evolution and gas exchange with the atmosphere. In rcd1, altered Mehlers reaction coincided with more reduced state of the chloroplast NADPH-thioredoxin oxidoreductase C (NTRC) and its targets, suggesting that NTRC performs feedback control of photosynthesis. This regulation may represent a novel mechanism whereby mitochondrial retrograde signalling affects chloroplast functions.

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↗