Thylakoid Ultrastructure Research Articles

Barley Cultivar Sarab 1 Has a Characteristic Region on the Thylakoid Membrane That Protects Photosystem I under Iron-Deficient Conditions.

The barley cultivar Sarab 1 (SRB1) can continue photosynthesis despite its low Fe acquisition potential via roots and dramatically reduced amounts of photosystem I (PSI) reaction-center proteins under Fe-deficient conditions. We compared the characteristics of photosynthetic electron transfer (ET), thylakoid ultrastructure, and Fe and protein distribution on thylakoid membranes among barley cultivars. The Fe-deficient SRB1 had a large proportion of functional PSI proteins by avoiding P700 over-reduction. An analysis of the thylakoid ultrastructure clarified that SRB1 had a larger proportion of non-appressed thylakoid membranes than those in another Fe-tolerant cultivar, Ehimehadaka-1 (EHM1). Separating thylakoids by differential centrifugation further revealed that the Fe-deficient SRB1 had increased amounts of low/light-density thylakoids with increased Fe and light-harvesting complex II (LHCII) than did EHM1. LHCII with uncommon localization probably prevents excessive ET from PSII leading to elevated NPQ and lower PSI photodamage in SRB1 than in EHM1, as supported by increased Y(NPQ) and Y(ND) in the Fe-deficient SRB1. Unlike this strategy, EHM1 may preferentially supply Fe cofactors to PSI, thereby exploiting more surplus reaction center proteins than SRB1 under Fe-deficient conditions. In summary, SRB1 and EHM1 support PSI through different mechanisms during Fe deficiency, suggesting that barley species have multiple strategies for acclimating photosynthetic apparatus to Fe deficiency.

State transition is quiet around pyrenoid and LHCII phosphorylation is not essential for thylakoid deformation in Chlamydomonas 137c

Photosynthetic organisms have developed a regulation mechanism called state transition (ST) to rapidly adjust the excitation balance between the two photosystems by light-harvesting complex II (LHCII) movement. Though many researchers have assumed coupling of the dynamic transformations of the thylakoid membrane with ST, evidence of that remains elusive. To clarify the above-mentioned coupling in a model organism Chlamydomonas, here we used two advanced microscope techniques, the excitation-spectral microscope (ESM) developed recently by us and the superresolution imaging based on structured-illumination microscopy (SIM). The ESM observation revealed ST-dependent spectral changes upon repeated ST inductions. Surprisingly, it clarified a less significant ST occurrence in the region surrounding the pyrenoid, which is a subcellular compartment specialized for the carbon-fixation reaction, than that in the other domains. Further, we found a species dependence of this phenomenon: 137c strain showed the significant intracellular inhomogeneity of ST occurrence, whereas 4A+ strain hardly did. On the other hand, the SIM observation resolved partially irreversible fine thylakoid transformations caused by the ST-inducing illumination. This fine, irreversible thylakoid transformation was also observed in the STT7 kinase-lacking mutant. This result revealed that the fine thylakoid transformation is not induced solely by the LHCII phosphorylation, suggesting the highly susceptible nature of the thylakoid ultrastructure to the photosynthetic light reactions.

Loss of 2-Cys-Prx affects cellular ultrastructure, disturbs redox poise and impairs photosynthesis in cyanobacteria.

In a striking similarity to plant chloroplasts, the cyanobacterium Anabaena displays very low catalase activity, but expresses several peroxiredoxins (Prxs), including the typical 2-Cys-Prx (annotated as Alr4641), that detoxify H2 O2 . Due to the presence of multiple Prxs, the precise contribution of Alr4641 to the oxidative stress response of Anabaena is not well-defined. To unambiguously assess its in vivo function, the Alr4641 protein was knocked down using the CRISPRi approach in Anabaena PCC 7120. The knockdown strain (An-KD4641), which showed over 85% decrease in the content of Alr4641, was viable, but grew slower than the control strain (An-dCas9). An-KD4641 showed elevated levels of reactive oxygen speciesand the expression of several redox-responsive genes was analogous to that of An-dCas9 subjected to oxidative stress. The knockdown strain displayed reduced filament size, altered thylakoid ultrastructure, a marked drop in the ratio of phycocyanin to chlorophyll a and decreased photosynthetic parameters compared to An-dCas9. In comparison to the control strain, exposure to H2 O2 had a more severe effect on the photosynthetic parameters or survival of An-KD4641. Thus, in the absence of adequate catalase activity, 2-Cys-Prx appears to be the principal Prx responsible for maintaining redox homoeostasis in diverse photosynthetic systems ranging from chloroplasts to cyanobacteria.

Porphyrosiphon annulatus sp. nov. (Oscillatoriales, Cyanobacteria) isolated on moist soil in Suwon, Republic of Korea

Porphyrosiphon annulatus sp. nov. belonging to Microcoleaceae, Oscillatoriales was collected from the moist soil under the rock in the Gwanggyo Mountain of Suwon City, Gyeonggi Province, Korea and cultured. Using the raw and cultured samples of the collected strains, we observed their morphological features through LM and TEM. Furthermore, their 16S rRNA gene and 16S–23S rRNA intergenic transcribed spacer (ITS) sequences were determined to be used phylogenetic analyses. We affirmed that thick sheath of the cells possessed transversely annular and longitudinal lamellations. The ultrastructure of thylakoids was a radial arrangement, which corresponds with a characteristic of the Microcoleaceae. In addition, P. annulatus displays the most similar morphology with type species P. notarisii; however, it differently holds the transversely annular lamellations with a shorter cell length and relatively dense trichome. Our 16S rRNA gene phylogeny showed that P. annulatus formed a clade with P. notarisii, and their DNA similarity was calculated to be 96.2%. The family Microcoleaceae was found to be paraphyletic with a distinct linage of the genus Porphyrosiphon. The ITS sequence of P. annulatus was unique in length and nucleotide composition, with different secondary structures of D1–D1ʹ and Box-B helices compared to those of close relatives. Overall, morphology and genetic traits of the Korean Porphyrosiphon suggest that P. annulatus should be considered to be a novel species.

Thylakoid attachment to the plasma membrane in Synechocystis sp. PCC 6803 requires the AncM protein.

Thylakoids are the highly specialized internal membrane systems that harbor the photosynthetic electron transport machinery in cyanobacteria and in chloroplasts. In Synechocystis sp. PCC 6803, thylakoid membranes (TMs) are arranged in peripheral sheets that occasionally converge on the plasma membrane (PM) to form thylakoid convergence membranes (TCMs). TCMs connect several thylakoid sheets and form local contact sites called thylapses between the two membrane systems, at which the early steps of photosystem II (PSII) assembly occur. The protein CurT is one of the main drivers of TCM formation known so far. Here, we identify, by whole-genome sequencing of a curT- suppressor strain, the protein anchor of convergence membranes (AncM) as a factor required for the attachment of thylakoids to the PM at thylapses. An ancM- mutant is shown to have a photosynthetic phenotype characterized by reductions in oxygen-evolution rate, PSII accumulation, and PS assembly. Moreover, the ancM- strain exhibits an altered thylakoid ultrastructure with additional sheets and TCMs detached from the PM. By combining biochemical studies with fluorescence and correlative light-electron microscopy-based approaches, we show that AncM is an integral membrane protein located in biogenic TCMs that form thylapses. These data suggest an antagonistic function of AncM and CurT in shaping TM ultrastructure.

Saturation of thylakoid-associated fatty acids facilitates bioenergetic coupling in a marine diatom allowing for thermal acclimation.

In a rapidly warming world, we ask, "What limits the potential of marine diatoms to acclimate to elevated temperatures?," a group of ecologically successful unicellular eukaryotic photoautotrophs that evolved in a cooler ocean and are critical to marine food webs. To this end, we examined thermal tolerance mechanisms related to photosynthesis in the sequenced and transformable model diatom Phaeodactylum tricornutum. Data from transmission electron microscopy (TEM) and fatty acid methyl ester-gas chromatography mass spectrometry (FAME-GCMS) suggest that saturating thylakoid-associated fatty acids allowed rapid (on the order of hours) thermal tolerance up to 28.5°C. Beyond this critical temperature, thylakoid ultrastructure became severely perturbed. Biophysical analyses revealed that electrochemical leakage through the thylakoid membranes was extremely sensitive to elevated temperature (Q10 of 3.5). Data suggest that the loss of the proton motive force (pmf) occurred even when heat-labile photosystem II (PSII) was functioning, and saturation of thylakoid-associated fatty acids was active. Indeed, growth was inhibited when leakage of pmf through thylakoid membranes was insufficiently compensated by proton input from PSII. Our findings provide a mechanistic understanding of the importance of rapid saturation of thylakoid-associated fatty acids for ultrastructure maintenance and a generation of pmf at elevated temperatures. To the extent these experimental results apply, the ability of diatoms to generate a pmf may be a sensitive parameter for thermal sensitivity diagnosis in phytoplankton.

Measuring the dynamic response of the thylakoid architecture in plant leaves by electron microscopy.

The performance of the photosynthesis machinery in plants, including light harvesting, electron transport, and protein repair, is controlled by structural changes in the thylakoid membrane system inside the chloroplasts. In particular, the structure of the stacked grana area of thylakoid membranes is highly dynamic, changing in response to different environmental cues such as light intensity. For example, the aqueous thylakoid lumen enclosed by thylakoid membranes in grana has been documented to swell in the presence of light. However, light‐induced alteration of the stromal gap in the stacked grana (partition gap) and of the unstacked stroma lamellae has not been well characterized. Light‐induced changes in the entire thylakoid membrane system, including the lumen in both stacked and unstacked domains as well as the partition gap, are presented here, and the functional implications are discussed. This structural analysis was made possible by development of a robust semi‐automated image analysis method combined with optimized plant tissue fixation techniques for transmission electron microscopy generating quantitative structural results for the analysis of thylakoid ultrastructure.Significance StatementA methodical pipeline ranging from optimized leaf tissue preparation for electron microscopy to quantitative image analysis was established. This methodical development was employed to study details of light‐induced changes in the plant thylakoid ultrastructure. It was found that the lumen of the entire thylakoid system (stacked and unstacked domains) undergoes light‐induced swelling, whereas adjacent membranes on the stroma side in stacked grana thylakoid approach each other.

PSB33 protein sustains photosystem II in plant chloroplasts under UV-A light.

Plants can quickly and dynamically respond to spectral and intensity variations of the incident light. These responses include activation of developmental processes, morphological changes, and photosynthetic acclimation that ensure optimal energy conversion and minimal photoinhibition. Plant adaptation and acclimation to environmental changes have been extensively studied, but many details surrounding these processes remain elusive. The photosystem II (PSII)-associated protein PSB33 plays a fundamental role in sustaining PSII as well as in the regulation of the light antenna in fluctuating light. We investigated how PSB33 knock-out Arabidopsis plants perform under different light qualities. psb33 plants displayed a reduction of 88% of total fresh weight compared to wild type plants when cultivated at the boundary of UV-A and blue light. The sensitivity towards UV-A light was associated with a lower abundance of PSII proteins, which reduces psb33 plants' capacity for photosynthesis. The UV-A phenotype was found to be linked to altered phytohormone status and changed thylakoid ultrastructure. Our results collectively show that PSB33 is involved in a UV-A light-mediated mechanism to maintain a functional PSII pool in the chloroplast.

Characterization of a novel allele of bc12/gdd1 indicates a differential leaf color function for BC12/GDD1 in Indica and Japonica backgrounds

Leaf color is directly associated with plant photosynthesis. Here, we have isolated and identified a spontaneous rice mutant named yd1 that has yellowish leaves and dwarf stature. Map-based cloning reveals that YD1 encodes a previously reported kinesin protein from the kinesin-4 subfamily, BC12/GDD1. Arginine-328 is replaced by leucine in yd1, BC12328Leu. YD1 is mainly expressed in leaves and is involved in chlorophyll (Chl) synthesis. The yd1 mutant had less Chl and a reduced and disordered thylakoid ultrastructure. In yd1 plants, Chl biosynthesis and photosynthesis associated gene expression was decreased and Chl degradation gene expression was increased, thereby leading to a reduced photosynthesis rate and grain yield. In this study we reveal that the novel BC12328Leu allele of BC12 modulated plant leaf color in yd1 plants, which has not been previously reported in studies of BC12/GDD1/MTD1/SRG1. Gene knockout results indicated that YD1 regulates leaf color in the indica rice background, but not in the japonica rice background. Our study provides new insights into molecular regulation of rice growth by BC12/GDD1 in different genetic backgrounds.

Composition, phosphorylation and dynamic organization of photosynthetic protein complexes in plant thylakoid membrane

The photosystems (PS), catalyzing the photosynthetic reactions of higher plants, are unevenly distributed in the thylakoid membrane: PSII, together with its light harvesting complex (LHC)II, is enriched in the appressed grana stacks, while PSI–LHCI resides in the non-appressed stroma thylakoids, which wind around the grana stacks. The two photosystems interact in a third membrane domain, the grana margins, which connect the grana and stroma thylakoids and allow the loosely bound LHCII to serve as an additional antenna for PSI. The light harvesting is balanced by reversible phosphorylation of LHCII proteins. Nevertheless, light energy also damages PSII and the repair process is regulated by reversible phosphorylation of PSII core proteins. Here, we discuss the detailed composition and organization of PSII–LHCII and PSI–LHCI (super)complexes in the thylakoid membrane of angiosperm chloroplasts and address the role of thylakoid protein phosphorylation in dynamics of the entire protein complex network of the photosynthetic membrane. Finally, we scrutinize the phosphorylation-dependent dynamics of the protein complexes in context of thylakoid ultrastructure and present a model on the reorganization of the entire thylakoid network in response to changes in thylakoid protein phosphorylation.

Biochemical properties and ultrastructure of mesophyll and bundle sheath thylakoids from maize (Zea mays) chloroplasts.

A characteristic feature of C4 plants is the differentiation of the photosynthetic leaf tissues into two distinct cell types: mesophyll (M) and bundle sheath (BS) cells. We have investigated several biochemical parameters, including pigment composition, polypeptide patterns, fluorescence at 77K, the activity of photosystems and ultrastructure of mesophyll and bundle sheath chloroplasts of maize (Zea mays L.) plants. It is shown that the BS chloroplasts have ~2-fold higher chlorophyll a/b ratio than M chloroplasts, 6.15 and 3.12 respectively. The PSI apoprotein (68 kDa) was more abundant in BS than in M thylakoids. Polypeptides belonging to PSII core antenna, are in similar amounts in both types of membranes, but the 45kDa band is more intensive in M thylakoids. Polypeptides in the region of 28-24 kDa of the light-harvesting complex of PSII (LHCII) are also present in both types of chloroplasts, though their amounts are reduced in BS thylakoids. The chlorophyll fluorescence emission spectra in M cells showed the presence of three bands at 686, 695 and 735 nm characteristics of LHCII, PSII core and PSI complexes, respectively. However, in the fluorescence spectrum of agranal plastids, there are almost traces of the band at 695 nm, which belongs to the PSII core complex. The research results revealed that the photochemical activity of PSII in BS chloroplasts is ~5 times less than in the chloroplasts of M cells. The highest PSI activity was found in maize BS chloroplasts.

Physiological characterization and thylakoid ultrastructure analysis in super high-yield hybrid rice leaves under drought stress

Rice serves for more than a third of the world's population. However, drought stress (DS) affects its growth and yield. In order to understand plant drought adaptability, we explored the physiological and thylakoid ultrastructural alteration in super high-yield hybrid rice Liangyoupeijiu (LYPJ) under DS. Results showed that DS altered the thylakoid ultrastructure; twisted and fractured stroma thylakoids and more starch granules in chloroplast of LYPJ were present. Also, DS lowered chlorophyll and carotenoid contents in LYPJ after 7 d. DS reduced the proportion of unsaturated fatty acids in thylakoid membranes and increased the content of linoleic and abscisic acids (ABA) and osmotic substances such as calcium and potassium in LYPJ. Based on these results, we concluded that although DS severely affected normal growth, plants employed various strategies, such as changing their membrane lipid fluidity, increasing endogenous ABA and osmotic substance contents and stabilizing the grana thylakoids, in order to adapt to drought stress.

Plastoglobular protein 18 is involved in chloroplast function and thylakoid formation.

Plastoglobules are lipoprotein particles that are found in different types of plastids. They contain a very specific and specialized set of lipids and proteins. Plastoglobules are highly dynamic in size and shape, and are therefore thought to participate in adaptation processes during either abiotic or biotic stresses or transitions between developmental stages. They are suggested to function in thylakoid biogenesis, isoprenoid metabolism, and chlorophyll degradation. While several plastoglobular proteins contain identifiable domains, others provide no structural clues to their function. In this study, we investigate the role of plastoglobular protein 18 (PG18), which is conserved from cyanobacteria to higher plants. Analysis of a PG18 loss-of-function mutant in Arabidopsis thaliana demonstrated that PG18 plays an important role in thylakoid formation; the loss of PG18 results in impaired accumulation, assembly, and function of thylakoid membrane complexes. Interestingly, the mutant accumulated less chlorophyll and carotenoids, whereas xanthophyll cycle pigments were increased. Accumulation of photosynthetic complexes is similarly affected in both a Synechocystis and an Arabidopsis PG18 mutant. However, the ultrastructure of cyanobacterial thylakoids is not compromised by the lack of PG18, probably due to its less complex architecture.

Regulation of Oxygenic Photosynthesis during Trophic Transitions in the Green Alga Chromochloris zofingiensis.

Light and nutrients are critical regulators of photosynthesis and metabolism in plants and algae. Many algae have the metabolic flexibility to grow photoautotrophically, heterotrophically, or mixotrophically. Here, we describe reversible Glc-dependent repression/activation of oxygenic photosynthesis in the unicellular green alga Chromochloris zofingiensis. We observed rapid and reversible changes in photosynthesis, in the photosynthetic apparatus, in thylakoid ultrastructure, and in energy stores including lipids and starch. Following Glc addition in the light, C. zofingiensis shuts off photosynthesis within days and accumulates large amounts of commercially relevant bioproducts, including triacylglycerols and the high-value nutraceutical ketocarotenoid astaxanthin, while increasing culture biomass. RNA sequencing reveals reversible changes in the transcriptome that form the basis of this metabolic regulation. Functional enrichment analyses show that Glc represses photosynthetic pathways while ketocarotenoid biosynthesis and heterotrophic carbon metabolism are upregulated. Because sugars play fundamental regulatory roles in gene expression, physiology, metabolism, and growth in both plants and animals, we have developed a simple algal model system to investigate conserved eukaryotic sugar responses as well as mechanisms of thylakoid breakdown and biogenesis in chloroplasts. Understanding regulation of photosynthesis and metabolism in algae could enable bioengineering to reroute metabolism toward beneficial bioproducts for energy, food, pharmaceuticals, and human health.

Thylakoid membrane unstacking increases LHCII thermal stability and lipid phase fluidity.

Thylakoids are highly protein-enriched membranes that harbor a number of multicomponent photosynthetic complexes. Similarly to other biological membranes the protein constituents are heterogeneously distributed laterally in the plane of the membrane, however the specific segregation into stacked (grana patches) and unstacked (stroma lamellae) membrane layers is a unique feature of the thylakoid. Both the lateral and the vertical arrangements of the integral membrane proteins within the three-dimensional thylakoid ultrastructure are thought to have important physiological function. In this work we explore the role of membrane stacking for the thermal stability of the photosynthetic complexes in thylakoid membranes. By means of circular dichroism and differential scanning calorimetry we demonstrate that the thermal stability of the monomeric and trimeric forms of the major light harvesting complex of photosystem II (LHCII) increases upon unstacking. This effect was suggested to be due to the detachment of LHCII from photosystem II and consequent attachment to photosystem I subunits and/or the fluidization of the lipid matrix upon unstacking. The changes in the physical properties of the protein and lipid membrane components upon unstacking result in strongly reduced photosystem II excitation energy utilization.

Overexpression of thioredoxin m in tobacco chloroplasts inhibits the protein kinase STN7 and alters photosynthetic performance.

The activity of the protein kinase STN7, involved in phosphorylation of the light-harvesting complex II (LHCII) proteins, has been reported as being co-operatively regulated by the redox state of the plastoquinone pool and the ferredoxin-thioredoxin (Trx) system. The present study aims to investigate the role of plastid Trxs in STN7 regulation and their impact on photosynthesis. For this purpose, tobacco plants overexpressing Trx f or m from the plastid genome were characterized, demonstrating that only Trx m overexpression was associated with a complete loss of LHCII phosphorylation that did not correlate with decreased STN7 levels. The absence of phosphorylation in Trx m-overexpressing plants impeded migration of LHCII from PSII to PSI, with the concomitant loss of PSI-LHCII complex formation. Consequently, the thylakoid ultrastructure was altered, showing reduced grana stacking. Moreover, the electron transport rate was negatively affected, showing an impact on energy-demanding processes such as the Rubisco maximum carboxylation capacity and ribulose 1,5-bisphosphate regeneration rate values, which caused a strong depletion in net photosynthetic rates. Finally, tobacco plants overexpressing a Trx m mutant lacking the reactive redox site showed equivalent physiological performance to the wild type, indicating that the overexpressed Trx m deactivates STN7 in a redox-dependent way.

Functional Role of Fibrillin5 in Acclimation to Photooxidative Stress.

The functional role of a lipid-associated soluble protein, fibrillin5 (FBN5), was determined with the Arabidopsis thaliana homozygous fbn5-knockout mutant line (SALK_064597) that carries a T-DNA insertion within the FBN5 gene. The fbn5 mutant remained alive, displaying a slow growth and a severe dwarf phenotype. The mutant grown even under growth light conditions at 80 µmol m-2 s-1 showed a drastic decrease in electron transfer activities around PSII, with little change in electron transfer activities around PSI, a phenomenon which was exaggerated under high light stress. The accumulation of plastoquinone-9 (PQ-9) was suppressed in the mutant, and >90% of the PQ-9 pool was reduced under growth light conditions. Non-photochemical quenching (NPQ) in the mutant functioned less efficiently, resulting from little contribution by energy-dependent quenching (qE). The ultrastructure of thylakoids in the mutant revealed that their grana were unstacked and transformed into loose and disordered structures. Light-harvesting complex (LHC)-containing large photosystem complexes and photosystem core complexes in the mutant were less abundant than those in wild-type plants. These results suggest that the lack of FBN5 causes a decrease in PQ-9 and imbalance of the redox state of PQ-9, resulting in misconducting both short-term and long-term control of the input of light energy to photosynthetic reaction centers. Furthermore, in the fbn5 mutant, the expression of genes involved in jasmonic acid biosynthesis was suppressed to ≤10% of that in the wild type under both growth-light and high-light conditions, suggesting that FBN5 functions as a transmitter of 1O2 in the stroma.

Overexpression of the protein disulfide isomerase AtCYO1 in chloroplasts slows dark-induced senescence in Arabidopsis

BackgroundChlorophyll breakdown is the most obvious sign of leaf senescence. The chlorophyll catabolism pathway and the associated proteins/genes have been identified in considerable detail by genetic approaches combined with stay-green phenotyping. Arabidopsis CYO1 (AtCYO1), a protein disulfide reductase/isomerase localized in the thylakoid membrane, is hypothesized to assemble the photosystem by interacting with cysteine residues of the subunits.ResultsIn this study, we report that ectopic overexpression of AtCYO1 in leaves induces a stay-green phenotype during darkness, where oxidative conditions favor catabolism. In AtCYO1ox leaves, Fv/Fm and both chlorophyll a and chlorophyll b content remained high during dark-induced senescence. The thylakoid ultrastructure was preserved for a longer time in AtCYO1ox leaves than in wild type leaves. AtCYO1ox leaves maintained thylakoid chlorophyll-binding proteins associated with both PSII (D1, D2, CP43, CP47, LHCB2, and Cyt f) and PSI (PSA-A/B), as well as stromal proteins (Rubisco and ferredoxin-NADP+ reductase). AtCYO1ox did not affect senescence-inducible gene expression for chlorophyll catabolism or accumulation of chlorophyll catabolites.ConclusionsOur results suggest that ectopic overexpression of AtCYO1 had a negative impact on the initiation of chlorophyll degradation and proteolysis within chloroplasts. Our findings cast new light on the redox regulation of protein disulfide bonds for the maintenance of functional chloroplasts.

Fine-Tuning of Photosynthesis Requires CURVATURE THYLAKOID1-Mediated Thylakoid Plasticity.

The thylakoid membrane system of higher plant chloroplasts consists of interconnected subdomains of appressed and nonappressed membrane bilayers, known as grana and stroma lamellae, respectively. CURVATURE THYLAKOID1 (CURT1) protein complexes mediate the shape of grana stacks in a dosage-dependent manner and facilitate membrane curvature at the grana margins, the interface between grana and stroma lamellae. Although grana stacks are highly conserved among land plants, the functional relevance of grana stacking remains unclear. Here, we show that inhibiting CURT1-mediated alteration of thylakoid ultrastructure in Arabidopsis (Arabidopsis thaliana) reduces photosynthetic efficiency and plant fitness under adverse, controlled, and natural light conditions. Plants that lack CURT1 show less adjustment of grana diameter, which compromises regulatory mechanisms like the photosystem II repair cycle and state transitions. Interestingly, CURT1A suffices to induce thylakoid membrane curvature in planta and thylakoid hyperbending in plants overexpressing CURT1A. We suggest that CURT1 oligomerization is regulated at the posttranslational level in a light-dependent fashion and that CURT1-mediated thylakoid plasticity plays an important role in fine-tuning photosynthesis and plant fitness during challenging growth conditions.

Salinity reduces 2,4-D efficacy in Echinochloa crusgalli by affecting redox balance, nutrient acquisition, and hormonal regulation.

Distinct salinity levels have been reported to enhance plants tolerance to different types of stresses. The aim of this research is to assess the interaction of saline stress and the use of 2,4-D as a means of controlling the growth of Echinochloa crusgalli. The resultant effect of such interaction is vital for a sustainable approach of weed management and food production. The results showed that 2,4-D alone treatment reduces the chlorophyll contents, photosynthetic capacity, enhanced MDA, electrolyte leakage, and ROS production (H2O2, O2·-) and inhibited the activities of ROS scavenging enzymes. Further analysis of the ultrastructure of chloroplasts indicated that 2,4-D induced severe damage to the ultrastructure of chloroplasts and thylakoids. Severe saline stress (8dSm-1) followed by mild saline stress treatments (4dSm-1) also reduced the E. crusgalli growth, but had the least impact as compared to the 2,4-D alone treatment. Surprisingly, under combined treatments (salinity + 2,4-D), the phytotoxic effect of 2,4-D was reduced on saline-stressed E. crusgalli plants, especially under mild saline + 2,4-D treatment. This stimulated growth of E. crusgalli is related to the higher activities of enzymatic and non-enzymatic antioxidants and dynamic regulation of IAA, ABA under mild saline + 2,4-D treatment. This shows that 2,4-D efficacy was affected by salinity in a stress intensity-dependent manner, which may result in the need for greater herbicide application rates, additional application times, or more weed control operations required for controlling salt-affected weed.