Prolonged Darkness Research Articles

Light niche construction: Motility of sediment-inhabiting diatoms determines the experienced light environment

Diatoms are an extraordinarily diverse, evolutionarily successful, and ecologically important group of single-cell algae. Diatoms of the group of the pennates are particularly important in estuarine sedimentary habitats, where they form highly productive microphytobenthos communities that cover extensive areas of intertidal flats. The pennates are capable of directed motility, an evolutionary and unique trait amongst diatoms, which has long been hypothesized to confer a critical adaptive advantage, by enabling these cells to vertically migrate within the photic zone of the sediment and behaviorally regulate light exposure. This study investigated the role of diatom motility on the active regulation of light exposure by developing a model to quantitatively characterize and compare the experienced light environment of individual cells of two life forms of pennate diatoms that inhabit intertidal estuarine sediments: epipelic species, motile cells dominant in fine sediments, and epipsammic species, non-motile or slowly motile cells, that colonize coarser sediments. The conceptual framework of the model was based on the identification and parameterization of the main controlling factors of the light regime perceived by cells inhabiting the two types of sedimentary environments: (i) solar irradiance incident at the sediment surface, determined by the superimposition of the tidal cycle on the day-night cycle; (ii) light attenuation within the sediment; (iii) sediment mixing by tidal currents or bioturbation, repositioning the cells in the sediment column; (iv) cell velocity, as a function of light intensity and of the photoacclimation state of the cells that determines their photosynthetic light preferences. The model was run for realistic scenarios based on published ecological, photophysiological and cellular motility data (light attenuation, mixing depth, photosynthesis light-response curves, cell velocity), simulating (i) the variation in the vertical position of a diatom cell due to vertical migration and (ii) the irradiance level to which it is exposed at each moment. The results confirm the hypothesis that epipelic and epipsammic diatoms experience a significantly different light environment. Vertical migration enables motile species to experience a much less variable light regime, with increased mean daily light doses received. In contrast, non-motile species experience a much more unstable light environment, including the frequent exposure to supersaturating light levels and to periods of prolonged darkness. These results have important ecological significance, as they support the adaptive value of light-driven motility as a form of optimizing photosynthesis and growth, and they identify vertical migration as a niche-construction activity, allowing motile diatoms to regulate the light environment they experience through habitat selection.

Pentosan polysulfate maculopathy: a brief primer for general practitioners, ophthalmologists, optometrists and urologists.

Pentosan polysulfate maculopathy: a brief primer for general practitioners, ophthalmologists, optometrists and urologists.

Melatonin and vitamin D, two sides of the same coin, better to land on its edge to improve multiple sclerosis

Previous studies revealed a latitudinal gradient of multiple sclerosis (MS) prevalence, increasing by moving from the equator to the poles. The duration and quality of an individual’s exposure to sunlight vary with latitude. Skin exposure to sunlight activates vitamin D synthesis, while light absence, as perceived by the eyes, activates melatonin synthesis in the pineal gland. Vitamin D or melatonin deficiency/insufficiency or overdose can occur at any latitude due to specific lifestyles and diets. Moving away from the equator, especially beyond 37°, decreases vitamin D while raising melatonin. Furthermore, melatonin synthesis increases in cold habitats like northern countries. Since melatonin's beneficial role was shown in MS, it is expected that northern countries whose individuals have higher endogenous melatonin should show a lower MS prevalence; however, these are ranked with the highest scores. In addition, countries like the United States and Canada have uncontrolled over-the-counter usage. In high latitudes, vitamin D deficiency and a higher MS prevalence persist even though vitamin D is typically compensated for by supplementation and not sunlight. Recently, we found that prolonged darkness increased MS melatonin levels, mimicking the long-term increase in northern countries. This caused a reduction in cortisol and increased infiltration, inflammation, and demyelination, which were all rescued by constant light therapy. In this review, we explain melatonin and vitamin D's possible roles in MS prevalence. The possible causes in northern countries are then discussed. Finally, we suggest strategies to treat MS by manipulating vitamin D and melatonin, preferably with sunlight or darkness, not supplements.

Optical coherence tomography in healthy human subjects in the setting of prolonged dark adaptation

Human studies have established that short periods of dark adaptation can induce outer retinal thinning and various band intensity changes that can be detected with Optical Coherence Tomography (OCT). Similar findings were observed in mice, including a positive correlation between the degree of outer retinal changes and dark adaptation duration. We decided to assess potential retinal structural changes following prolonged dark adaptation in humans. 40 healthy subjects without any ocular diseases participated in this study. For each subject, one eye was covered for dark adaptation for four hours, and the other eye was left uncovered as a control. Before and after the dark adaptation period, both eyes were assessed with OCT. Using the Heidelberg Spectralis system, basic statistical functions, and qualitative and quantitative analysis, we were able to compare retinal layer thicknesses and band intensities between covered (dark adapted) versus uncovered (control) eyes. Prolonged dark adaptation did not induce any significant thickness, volume, or intensity changes in the outer retina or in the inner or overall retina. These observations thus alter our current understanding of the mechanisms underlying dark adaptation’s neuroprotective effects in preventing blindness and require further study.

ВЛИЯНИЕ МЕЛАТОНИНА НА ДИНАМИКУ МАССЫ ТЕЛА И УРОВЕНЬ БЕЛКА КЛОТО В КРОВИ У ЖИВОТНЫХС ПРЕЖДЕВРЕМЕННЫМ СТАРЕНИЕМ, ВЫЗВАННЫМТЕМНОВОЙ ДЕПРИВАЦИЕЙ

On the model of premature aging induced by 30-day dark deprivation (light-dark cycle 24/0 h, artificial illumination 300 Lux), the effect of exogenous melatonin (0.3 mg/kg, 14 days after the cancellation of dark deprivation, intragastric dailyin 2 % starch mucus) on the dynamics of body weight and the level of Klotho protein in the blood was studied in outbred white male rats of 4 months of age. It has been shown that prolonged dark deprivation is accompanied by a statistically significantdecrease in the content of the Klotho protein in the blood serum, which is a marker of premature aging. Metabolic disorders associated with a statistically significant decrease in the level of melatonin and Klotho protein in the blood were expressedin fluctuations in the dynamics and rate of body weight gain in animals. At the same time, exogenous melatonin had a protective effect on the condition of animals –it contributed to an increase in the content of Klotho protein in the blood serum and restoredthe level of melatonin to the values of the negative control indicator.

Interactive effects of temperature and irradiance including spectral light quality on the photosynthesis of a brown alga Saccharina japonica (Laminariales) from Hokkaido, Japan

The interactive effects of temperature and irradiance including spectral light quality on the photosynthesis of a brown alga, Saccharina japonica (var. japonica, Laminariales) from Hokkaido, Japan were examined using a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. Assessment of maximum quantum yields (in darkness) and effective quantum yields (at 50 μmol photons m−2 s−1) at nine temperatures (4–36 °C, four increments) during 3-d culture indicated a temperature threshold at 24 °C, with early decline of maximum quantum yields at such temperature, which could probably be due to exhaustion of carbohydrate reserves by respiration in prolonged darkness. Unlike maximum quantum yields that was relatively stable through 4–20 °C, effective quantum yields under 50 μmol photons m−2 s−1 gradually declined at low temperatures, revealing light sensitivity under chilling temperatures. Chronic 6-h exposures under 200 (low) and 1000 (high) μmol photons m−2 s−1 at 4, 16, and 24 °C generated a significant decline in effective quantum yields at 4 °C under both irradiances; however, only treatments under low irradiance fully recovered after a subsequent 12-h dim light treatment. Moreover, post-dim light acclimation effective quantum yields of treatments at 16 and 24 °C under high irradiance returned to initial levels, suggesting accelerated photoinhibition at low temperature. Photosynthesis–irradiance responses at 16 °C under blue (450 nm), green (525 nm), red (660 nm), and white light (metal halide lamp) showed that the maximum photosynthetic output occurred under blue and white lights. The photoinhibitory sensitivity to chilling-light stress and the enhanced photosynthesis under blue light of S. japonica presented additional evidence of their physiological adaptation to cold-temperate subtidal waters.

Out of water in the dark: Plasticity in visual structures and function in an amphibious fish

Many fishes encounter periods of prolonged darkness within their lifetime, yet the consequences for the visual system are poorly understood. We used an amphibious fish (Kryptolebias marmoratus) that occupies dark terrestrial environments during seasonal droughts to test whether exposure to prolonged darkness diminishes visual performance owing to reduced optic tectum (OT) size and/or neurogenesis. We performed a 3-week acclimation with a 2 2 factorial design, in which fish were either acclimated to a 12 h:12 h or 0 h:24 h light:dark photoperiod in water or in air. We found that water-exposed fish had poorer visual acuity when acclimated to the dark, while air-acclimated fish had poorer visual acuity regardless of photoperiod. The ability of K. marmoratus to capture aerial prey from water followed a similar trend, suggesting that good vision is important for hunting effectively. Changes in visual acuity did not result from changes in OT size, but air-acclimated fish had 37% fewer proliferating cells in the OT than water-acclimated fish. AsK. marmoratus are unable to eat on land, reducing cell proliferation in the OT may serve as a mechanism to reduce maintenance costs associated with the visual system. Overall, we suggest that prolonged darkness and air exposure can impair vision in K. marmoratus, and that changes in visual performance may be mediated, in part, by OT neurogenesis. More broadly, we show that plastic changes to the visual system of fishes can have potential consequences for organismal performance and fitness.

STN7 Kinase Is Essential for Arabidopsis thaliana Fitness under Prolonged Darkness but Not under Dark-Chilling Conditions.

Reversible phosphorylation of photosystem II light harvesting complexes (LHCII) is a well-established protective mechanism enabling efficient response to changing light conditions. However, changes in LHCII phosphorylation were also observed in response to abiotic stress regardless of photoperiod. This study aimed to investigate the impact of dark-chilling on LHCII phosphorylation pattern in chilling-tolerant Arabidopsis thaliana and to check whether the disturbed LHCII phosphorylation process will impact the response of Arabidopsis to the dark-chilling conditions. We analyzed the pattern of LHCII phosphorylation, the organization of chlorophyll–protein complexes, and the level of chilling tolerance by combining biochemical and spectroscopy techniques under dark-chilling and dark conditions in Arabidopsis mutants with disrupted LHCII phosphorylation. Our results show that during dark-chilling, LHCII phosphorylation decreased in all examined plant lines and that no significant differences in dark-chilling response were registered in tested lines. Interestingly, after 24 h of darkness, a high increase in LHCII phosphorylation was observed, co-occurring with a significant FV/FM parameter decrease. The highest drop of FV/FM was detected in the stn7-1 line–mutant, where the LHCII is not phosphorylated, due to the lack of STN7 kinase. Our results imply that STN7 kinase activity is important for mitigating the adverse effects of prolonged darkness.

Response of benthic dinoflagellates Amphidinium carterae and Bysmatrum gregarium to salinity changes and prolonged darkness: elucidation through laboratory experiments

Response of benthic dinoflagellates Amphidinium carterae and Bysmatrum gregarium to salinity changes and prolonged darkness: elucidation through laboratory experiments

ACA pumps maintain leaf excitability during herbivore onslaught

Recurrent damage by lepidopteran folivores triggers repeated leaf-to-leaf electrical signaling. We found that the ability to propagate electrical signals-called slow wave potentials-was unexpectedly robust and was maintained in plants that had experienced severe damage. We sought genes that maintain tissue excitability during group insect attack. When Arabidopsis thaliana P-Type II Ca2+-ATPase mutants were mechanically wounded, all mutants tested displayed leaf-to-leaf electrical signals. However, when the auto-inhibited Ca2+-ATPase double-mutant aca10 aca12 was attacked by Spodoptera littoralis caterpillars, electrical signaling failed catastrophically, and the insects consumed these plants rapidly. The attacked double mutant displayed petiole base deformation and chlorosis, which spread acropetally into laminas and led to senescence. A phloem-feeding aphid recapitulated these effects, implicating the vasculature in electrical signaling failure. Consistent with this, ACA10 expressed in phloem companion cells in an aca10 aca12 background rescued electrical signaling and defense during protracted S.littoralis attack. When expressed in xylem contact cells, ACA10 partially rescued these phenotypes. Extending our analyses, we found that prolonged darkness also caused wound-response electrical signaling failure in aca10 aca12 mutants. Our results lead to a model in which the plant vasculature acts as a capacitor that discharges temporarily when leaves are subjected to energy-depleting stresses. Under these conditions, ACA10 and ACA12 function allows the restoration of vein cell membrane potentials. In the absence of these gene functions, vascular cell excitability can no longer be restored efficiently. Additionally, this work demonstrates that non-invasive electrophysiology is a powerful tool for probing early events underlying senescence.

Murals as Social Criticism: Movements of Resistance and Urban Liberation Against the Authoritarian of Regimes

The Economist Intelligence Unit's report (EIU) shows that the democracy index score in Indonesia has decreased in the last 5 years, and that number could decrease even more when the state makes society an object of conflict in which public criticism is threatened and silenced. There is an unfavorable relationship between power and society in the state process. Art in the concept of urban society is understood as a medium of awareness and liberation. Public awareness will give birth to a critical culture in identifying injustice and how to change it. Muralism is a form of criticism movement due to the disappointment and dissatisfaction of the Indonesian people towards the performance of the State and the power of authoritarianism in the midst of social, health and economic crises due to the Covid-19 pandemic. This thought movement was carried out through mural writing on the walls as a form of intellectual resistance to the authoritarian style of power and its policies which were far from the expectations of the people. This study uses a qualitative method with a phenomenological approach. The results of the study show that the freedom of expression carried out by urban communities through mural writing, graffiti, satire is always responded to by repressive actions by the authorities, ranging from arrests, silencing, deletion of murals, hacking social media, doxing, verbative intimidation, and other forms of threats. This condition turned into a curse for the style of authoritarianism. Currently, various vices and crimes of power are starting to be revealed, such as corruption, pandemics becoming business projects, tax smuggling by state officials, acts of violence, human rights violations, sexual harassment by state officials and others. This became a prolonged dark spot and became the basis of community resistance to make fundamental changes to the condition of the State.

Fiddler crab electroretinograms reveal vast circadian shifts in visual sensitivity and temporal summation in dim light.

ABSTRACTMany animals with compound eyes undergo major optical changes to adjust visual sensitivity from day to night, often under control of a circadian clock. In fiddler crabs, this presents most conspicuously in the huge volume increase of photopigment-packed rhabdoms and the widening of crystalline cone apertures at night. These changes are hypothesised to adjust the light flux to the photoreceptors and to alter optical sensitivity as the eye moves between light- and dark-adapted states. Here, we compared optical sensitivity in fiddler crab (Gelasimus dampieri) eyes during daytime and night via three electroretinogram (ERG) experiments performed on light- and dark-adapted crabs. (1) Light intensity required to elicit a threshold ERG response varied over six orders of magnitude, allowing more sensitive vision for discriminating small contrasts in dim light after dusk. During daytime, the eyes remained relatively insensitive, which would allow effective vision on bright mudflats, even after prolonged dark adaptation. (2) Flicker fusion frequency (FFF) experiments indicated that temporal summation is employed in dim light to increase light-gathering integration times and enhance visual sensitivity during both night and day. (3) ERG responses to flickering lights during 60 min of dark adaptation increased at a faster rate and to a greater extent after sunset compared with daytime. However, even brief, dim and intermittent light exposure strongly disrupted dark-adaptation processes. Together, these findings demonstrate effective light adaptation to optimise vision over the large range of light intensities that these animals experience.

The Fucoxanthin Chlorophyll a/c-Binding Protein in Tisochrysis lutea: Influence of Nitrogen and Light on Fucoxanthin and Chlorophyll a/c-Binding Protein Gene Expression and Fucoxanthin Synthesis

We observed differences in lhc classification in Chromista. We proposed a classification of the lhcf family with two groups specific to haptophytes, one specific to diatoms, and one specific to seaweeds. Identification and characterization of the Fucoxanthin and Chlorophyll a/c-binding Protein (FCP) of the haptophyte microalgae Tisochrysis lutea were performed by similarity analysis. The FCP family contains 52 lhc genes in T. lutea. FCP pigment binding site candidates were characterized on Lhcf protein monomers of T. lutea, which possesses at least nine chlorophylls and five fucoxanthin molecules, on average, per monomer. The expression of T. lutea lhc genes was assessed during turbidostat and chemostat experiments, one with constant light (CL) and changing nitrogen phases, the second with a 12 h:12 h sinusoidal photoperiod and changing nitrogen phases. RNA-seq analysis revealed a dynamic decrease in the expression of lhc genes with nitrogen depletion. We observed that T. lutea lhcx2 was only expressed at night, suggesting that its role is to protect \\cells from return of light after prolonged darkness exposure.

The possible fates of Fragilariopsis cylindrus (polar diatom) cells exposed to prolonged darkness.

At high latitudes, the polar night poses a great challenge to photosynthetic organisms that must survive up to six months without light. Numerous studies have already shed light on the physiological changes involved in the acclimation of microalgae to prolonged darkness and subsequent re-illumination. However, these studies have never considered inter-individual variability because they have mainly been conducted with bulk measurements. On the other hand, such long periods are likely to impact within-population selection processes. In this study, we hypothesized that distinct subpopulations with specific traits may emerge during acclimation of a population of diatoms to darkness. We addressed this hypothesis using flow cytometry (FCM), which allow to individually characterize large numbers of cells. The ecologically dominant polar pennate diatom Fragilariopsis cylindrus was subjected to three dark acclimation (DA) experiments of one, three, and five months duration, during which all cultures showed signs of recovery once light became available again. Our results suggest that darkness survival of F. cylindrus relies on reduction of metabolic activity and consumption of carbon reserves. In addition, FCM allowed us to record three different causes of death, each shared by significant numbers of individuals. The first rendered cells were unable to survive the stress caused by the return to light, probably due to a lack of sufficient photoprotective defenses. The other two were observed in two subpopulations of cells whose physiological state deviated from the original population. The data suggest that starvation and failure to maintain dormancy were the cause of cell mortality in these two subpopulations.

Survival and recovery of planktonic organisms in prolonged darkness and their implications on ballast water management

Understanding the population dynamics of transported organisms in the ship's ballast tanks during shipping operations and their ability to survive and colonize in the receiving environment (destination) can aid in developing effective ballast water treatment and management strategies. In the present study a natural plankton pool harvested from a tropical coast was used to study their survival in prolonged darkness and their regrowth potential upon re-illumination in laboratory conditions. In darkness, phytoplankton density and chlorophyll-a biomass decreased with increase in nutrient levels attributing to cell lysis. However, when subjected to vital staining using SYTOX® green, about 60% of phytoplankton survived in the dark tanks. Upon re-illumination after 36 days of incubation in darkness, >80% of recovered phytoplankton were pennate diatoms. On the other hand, zooplankton failed to survive/recover during the experiments when incubated in the dark. Less than 30% of the live zooplankton stained using Neutral Red in the dark tanks failed to recover during experiments. The data obtained clearly shows that prolonged dark incubation may promote the growth of opportunistic organisms and may alter their invasive potential through time and cause serious negative impacts to the receiving environment when transported by ballast water.

A Warmer Arctic Compromises Winter Survival of Habitat-Forming Seaweeds

Continuous winter darkness at a latitude of 79°N was simulated in cultures of four species of Arctic seaweeds at 3 and 8°C. The laminarians Saccharina latissima and Alaria esculenta, and the rhodophytes Phycodrys rubens and Ptilota gunneri were monitored for 4 months in total darkness and after 1 week following light return in early spring, under controlled laboratory conditions. Biomass loss during darkness was enhanced by the high temperature in all species. At 8°C, the two laminarians were unable to resume growth upon re-illumination. Alaria esculenta showed new blade production by the end of the dark period, but only at 3°C. In all species, the photosynthetic ability was sustained, not suspended, during the whole dark period. P. rubens exhibited lower photosynthetic potential at 8°C than at 3°C during the darkness period, but it was able to recover its O2 evolving potential upon re-illumination, as P. gunneri and S. latissima did, but the latter only at 3°C. The reactivation of photosynthesis seemed to involve photosystem II over photosystem I, as 7 d of photoperiod after the prolonged darkness was not enough to fully recover the PAM-related photosynthetic parameters. Only small changes were recorded in the internal chemical composition (total C, total N, carbohydrates, proteins, and lipids), but species-specific differences were observed. Unlike subarctic areas with an operating photoperiod along the year, a warmer polar night might pose a limit to the ability of multi-year seaweeds to occupy the new ice-free illuminated areas of the Arctic coasts, so that newcomers will potentially be restricted to the spring-summer season.

The extent of involvement of ouabain, hippocampal expression of Na+/K+-ATPase, and corticosterone/melatonin receptors ratio in modifying stress-induced behavior differs according to the stressor in context.

The aim of this study was to assess the effect of two types of stressors, regarding the extent of involvement of ouabain (OUA), hippocampal sodium/potassium ATPase (NKA) expression, and the hippocampal corticosterone receptors (CR)/melatonin receptors (MR) expression ratio, on the behavioral and cardiovascular responses and on the hippocampal cornu ammonis zone 3 (CA3) and dentate gyrus (DG). Thirty adult male Wistar albino rats aged 7-8 months were exposed to either chronic immobilization or a disturbed dark/light cycle and treated with either ouabain or vehicle. In the immobilized group, in the absence of hippocampal corticosterone (CORT) changes, rats were non-responsive to stress, despite experiencing increased pulse rate, downregulated hippocampal sodium/potassium pump, and enhanced hippocampal CR/MR expression ratio. Prolonged darkness precipitated a reduced upright attack posture, with elevated CORT against hippocampal MR downregulation. Both immobilization and, to a lesser extent, prolonged darkness stress resulted in histopathological and ultrastructural neurodegenerative changes in the hippocampus. OUA administration did not change the behavioral resilience in restrained rats, despite persistence of the underlying biochemical derangements, added to decreased CORT. On the contrary, with exposure to short photoperiods, OUA reverted the behavior towards a combative reduction of inactivity, with unvaried CR/MR and CORT, while ameliorating hippocampal neuro-regeneration, with co-existing NKA and MR repressions. Therefore, the extent of OUA, hippocampal NKA expression, and CR/MR expression, and subsequent behavioral and cardiac responses and hippocampal histopathology, differ according to the type of stressor, whether immobilization or prolonged darkness.

Phytochrome B Conveys Low Ambient Temperature Cues to the Ethylene-Mediated Leaf Senescence in Arabidopsis.

Leaf senescence is an active developmental process that is tightly regulated through extensive transcriptional and metabolic reprogramming events, which underlie controlled degradation and relocation of nutrients from aged or metabolically inactive leaves to young organs. The onset of leaf senescence is coordinately modulated by intrinsic aging programs and environmental conditions, such as prolonged darkness and temperature extremes. Seedlings growing under light deprivation, as often experienced in severe shading or night darkening, exhibit an accelerated senescing process, which is mediated by a complex signaling network that includes sugar starvation responses and light signaling events via the phytochrome B (phyB)-PHYTOCHROME-INTERACTING FACTOR (PIF) signaling routes. Notably, recent studies indicate that nonstressful ambient temperatures profoundly influence the onset and progression of leaf senescence in darkness, presumably mediated by the phyB-PIF4 signaling pathways. However, it is not fully understood how temperature signals regulate leaf senescence at the molecular level. Here, we demonstrated that low ambient temperatures repress the nuclear export of phyB and the nuclear phyB suppresses the transcriptional activation activity of ethylene signaling mediator ETHYLENE INSENSITIVE3 (EIN3), thus delaying leaf senescence. Accordingly, leaf senescence was insensitive to low ambient temperatures in transgenic plants overexpressing a constitutively nuclear phyB form, as observed in ein3 eil1 mutants. In contrast, leaf senescence was significantly promoted in phyB-deficient mutants under identical temperature conditions. Our data indicate that phyB coordinately integrates light and temperature cues into the EIN3-mediated ethylene signaling pathway that regulates leaf senescence under light deprivation, which would enhance plant fitness under fluctuating natural environments.

Pharmacological Correction of Long-Term Effects of Acute Severe Poisoning with Sodium Thiopental under Chronic Light Desynchronosis

We experimentally studied the possibility of using a peptide extract from the pituitary gland of a reindeer (Rangifer tarandus) to correct the functional state of the body under the combined effect of acute severe poisoning with sodium thiopental in rats, at a dose of LD50 under long-term light desynchronosis. The research was conducted using the statistical method of two-factor analysis of variance. It was found that, under constant light, a peptide extract from the pituitary gland of a reindeer affects such parameters as diene conjugates concentration, the activity of glutathione-S-transferase and glucose-6-phosphate dehydrogenase. Under prolonged darkness, the extract under study affected the activity of glutathione-S-transferase, glutathione peroxidase and glucose-6-phosphate dehydrogenase.

The versatility of plant organic acid metabolism in leaves is underpinned by mitochondrial malate-citrate exchange.

Malate and citrate underpin the characteristic flexibility of central plant metabolism by linking mitochondrial respiratory metabolism with cytosolic biosynthetic pathways. However, the identity of mitochondrial carrier proteins that influence both processes has remained elusive. Here we show by a systems approach that DICARBOXYLATE CARRIER 2 (DIC2) facilitates mitochondrial malate–citrate exchange in vivo in Arabidopsis thaliana. DIC2 knockout (dic2-1) retards growth of vegetative tissues. In vitro and in organello analyses demonstrate that DIC2 preferentially imports malate against citrate export, which is consistent with altered malate and citrate utilization in response to prolonged darkness of dic2-1 plants or a sudden shift to darkness of dic2-1 leaves. Furthermore, isotopic glucose tracing reveals a reduced flux towards citrate in dic2-1, which results in a metabolic diversion towards amino acid synthesis. These observations reveal the physiological function of DIC2 in mediating the flow of malate and citrate between the mitochondrial matrix and other cell compartments.