High CO2 Treatment Research Articles

Ocean acidification may alleviate the toxicity of zinc to the macroalga, Ulva lactuca

We investigated the toxic effects of different zinc (Zn) concentrations (natural seawater, 25 μg/L, and 100 μg/L) under two CO2 concentrations (410 ppmv, and 1000 ppmv) on Ulva lactuca. A significant decrease in the relative growth rate of U. lactuca was observed with an increase in Zn concentration under the low CO2 treatment condition, and we observed a notable decrease at 100 μg/L Zn under the high CO2 treatment condition. Moreover, the net photosynthetic rate increased when thalli were cultured under 25 and 100 μg/L Zn under the high CO2 treatment condition. The concentrations of chlorophyll a and b were significantly increased under 100 μg/L Zn and the high CO2 treatment conditions. Malondialdehyde content decreased under high CO2 treatment conditions, compared with the low CO2 treatment conditions, regardless of the Zn concentration. These findings suggest that ocean acidification may alleviate the toxic effects of Zn pollution on U. lactuca.

Physiological and Proteomic Responses of the Tetraploid Robinia pseudoacacia L. to High CO2 Levels.

The increase in atmospheric CO2 concentration is a significant factor in triggering global warming. CO2 is essential for plant photosynthesis, but excessive CO2 can negatively impact photosynthesis and its associated physiological and biochemical processes. The tetraploid Robinia pseudoacacia L., a superior and improved variety, exhibits high tolerance to abiotic stress. In this study, we investigated the physiological and proteomic response mechanisms of the tetraploid R. pseudoacacia under high CO2 treatment. The results of our physiological and biochemical analyses revealed that a 5% high concentration of CO2 hindered the growth and development of the tetraploid R. pseudoacacia and caused severe damage to the leaves. Additionally, it significantly reduced photosynthetic parameters such as Pn, Gs, Tr, and Ci, as well as respiration. The levels of chlorophyll (Chl a and b) and the fluorescent parameters of chlorophyll (Fm, Fv/Fm, qP, and ETR) also significantly decreased. Conversely, the levels of ROS (H2O2 and O2·-) were significantly increased, while the activities of antioxidant enzymes (SOD, CAT, GR, and APX) were significantly decreased. Furthermore, high CO2 induced stomatal closure by promoting the accumulation of ROS and NO in guard cells. Through a proteomic analysis, we identified a total of 1652 DAPs after high CO2 treatment. GO functional annotation revealed that these DAPs were mainly associated with redox activity, catalytic activity, and ion binding. KEGG analysis showed an enrichment of DAPs in metabolic pathways, secondary metabolite biosynthesis, amino acid biosynthesis, and photosynthetic pathways. Overall, our study provides valuable insights into the adaptation mechanisms of the tetraploid R. pseudoacacia to high CO2.

The combined effects of ocean warming and ocean acidification on Pacific cod (Gadus macrocephalus) early life stages

The eastern North Pacific is simultaneously experiencing ocean warming (OW) and ocean acidification (OA), which may negatively affect fish early life stages. Pacific cod (Gadus macrocephalus) is an economically and ecologically important species with demonstrated sensitivity to OW and OA, but their combined impacts are unknown. Through a ~ 9-week experiment, Pacific cod embryos and larvae were reared at one of six combinations of three temperatures (3, 6, 10 °C) and two CO2 levels (ambient: ~ 360 μatm; high: ~ 1560 μatm) in a factorial design. Both embryonic and larval mortality were highest at the warmest temperature. Embryonic daily mortality rates were lower under elevated CO2 and there was no effect of CO2 level on larval daily mortality rates. Growth rates of young larvae (0 to 11 days post-hatch) were faster at warmer temperatures and at high CO2 levels, but growth during the 11–28 days post-hatch interval increased by temperature alone. The condition of larvae decreased with age, but less markedly under high CO2 levels. However, at 6 °C, fish incubated in ambient CO2 remained in higher condition than fish in the high CO2 treatment throughout the experiment. Overall, temperature had the greater influence on Pacific cod early life stages across each measurement endpoint, while CO2 effects were more modest and inconsistent. Subtle developmental differences in larval Pacific cod could be magnified later in life and important in the context of recruitment. These results show the complexity of stage- and trait-specific responses to and value of investigating the combined effects of co-occurring climatic stressors.

The appendicularian Oikopleura dioica can enhance carbon export in a high CO2 ocean.

Gelatinous zooplankton are increasingly recognized to play a key role in the ocean's biological carbon pump. Appendicularians, a class of pelagic tunicates, are among the most abundant gelatinous plankton in the ocean, but it is an open question how their contribution to carbon export might change in the future. Here, we conducted an experiment with large volume insitu mesocosms (~55-60 m3 and 21 m depth) to investigate how ocean acidification (OA) extreme events affect food web structure and carbon export in a natural plankton community, particularly focusing on the keystone species Oikopleura dioica, a globally abundant appendicularian. We found a profound influence of O. dioica on vertical carbon fluxes, particularly during a short but intense bloom period in the high CO2 treatment, during which carbon export was 42%-64% higher than under ambient conditions. This elevated flux was mostly driven by an almost twofold increase in O. dioica biomass under high CO2 . This rapid population increase was linked to enhanced fecundity (+20%) that likely resulted from physiological benefits of low pH conditions. The resulting competitive advantage of O. dioica resulted in enhanced grazing on phytoplankton and transfer of this consumed biomass into sinking particles. Using a simple carbon flux model for O. dioica, we estimate that high CO2 doubled the carbon flux of discarded mucous houses and fecal pellets, accounting for up to 39% of total carbon export from the ecosystem during the bloom. Considering the wide geographic distribution of O. dioica, our findings suggest that appendicularians may become an increasingly important vector of carbon export with ongoing OA.

Browning inhibition in fresh-cut Chinese water chestnut under high pressure CO2 treatment: Regulation of reactive oxygen species and membrane lipid metabolism.

Fresh-cut Chinese water chestnut (CWC) was treated with high pressure CO2 (HPCD) to inhibit the browning reactions, and the underlying mechanism was investigated in this study. Results showed that HPCD at 2MPa pressure significantly inhibited lipoxygenase activity and enhanced superoxide dismutase activity, leading to decreased malondialdehyde and H2O2 contents in surface tissue. Moreover, HPCD could reduce total phenols/flavonoids content of surface tissue. Compare with control, homoeriodictyol, hesperetin, and isorhamnetin contents of 2MPa HPCD-treated samples on day 10 were reduced by 95.72%, 94.31%, and 94.02%, respectively. Furthermore, HPCD treatment enhanced antioxidant enzyme activities, and improved the O2- scavenging ability and reducing power of inner tissue. In conclusion, by regulating ROS and membrane lipid metabolism, HPCD treatment with appropriate pressure could retard the biosynthesis of flavonoids and enzymatic oxidation of phenolic compounds in surface tissue, and enhance antioxidant activity of inner tissue, thereby, delaying the quality deterioration of fresh-cut CWC.

Transcriptome combined with long non-coding RNA analysis reveals the potential molecular mechanism of high-CO2 treatment in delaying postharvest strawberry fruit ripening and senescence

Strawberry fruit is susceptible to postharvest spoilage with a short shelf-life, and high-CO2 treatment is an effective method to maintain the postharvest storage quality of fruit and vegetables. The aim of this study is to investigate the molecular mechanisms of high-CO2 treatment delaying the ripening and senescence of strawberry fruit after harvest. The results of this study showed that high-CO2 treatment delayed the softening and anthocyanin accumulation of strawberry fruit during storage. Transcriptome combined with long non-coding RNA (lncRNA) analysis revealed that ripening and senescence-related genes involved in abscisic acid (ABA) metabolism, cell wall degradation and anthocyanin accumulation could be regulated as potential targets by lncRNAs. Under high-CO2 treatment conditions, the expression levels of a large number of lncRNAs were altered, thereby affecting the expression patterns of downstream ripening and senescence-related target genes and resulting in the delay of fruit ripening and senescence. This study provides new insights into the molecular mechanisms of strawberry fruit ripening and senescence and high-CO2 treatment applied to postharvest preservation of strawberry fruit from the lncRNA-mRNA perspective.

Characterization of the TcCYPE2 Gene and Its Role in Regulating Trehalose Metabolism in Response to High CO2 Stress

Cytochrome P450 monooxygenase (CYP) is one of the three detoxification metabolic enzymes in insects, and is involved in the metabolism and transformation of endogenous substances as well as the activation and degradation of exogenous compounds. This study aims to reveal the molecular mechanism of CYP9E2 in Tribolium castaneum in adapting to high-CO2 stress. By predicting the sequence function of CYP9E2, analyzing the temporal and spatial expression profile of TcCYP9E2, and using RNAi to silence TcCYP9E2 combined with a high-CO2 stress treatment, we measured the carbohydrate content, trehalase activity, and gene expression levels in trehalose metabolism of T. castaneum. A bioinformatics analysis showed that the predicted molecular weight of the protein encoded by TcCYP9E2 is 60.15, the theoretical isoelectric point is 8.63, there is no signal peptide, and the protein is hydrophilic. An evolutionary tree analysis showed that TcCYP9E2 belongs to the CYP6 family and belongs to the CYP3 group; and the spatiotemporal expression profile results showed that TcCYP9E2 was highly expressed in the larvae midgut 48 h after injection of dsCYP9E2, with survival rates decreasing with the increase in CO2 concentration. Under the condition of 75% CO2, the contents of glycogen, glucose, ATP, and membrane-bound trehalase decreased significantly after the injection of dsCYP9E2. The expression of TRE-1, TRE-2, and GP in trehalose metabolism and energy pathways was significantly downregulated.

Tissue-specific modulation of functional stress responsive proteins and organic osmolytes by a single or dual short-term high CO2 treatment during long-term cold storage Autumn Royal table grapes

Plant cell response to damage from environmental stressors that cause dehydration involves stress-related proteins and osmotically active compounds whose constitutive levels increase in association with the tolerance response mechanism. In table grape postharvest scope, the application of a second 3 d 20 kPa CO2 treatment significantly reduced the incidence and severity of long-term cold postharvest storage disorders in Autumn Royal cv. counteracting ultrastructural cell damage and restraining intracellular and membrane oxidative stress. In this sense, it may be of relevance to postharvest quality to know how this dual short-term high CO2 treatment modulates the cell stress responsive defense strategies, and whether these are tissue-dependent and timing-regulated. In this work, we studied the differential profile of protective osmolytes proline, glycine betaine, γ-aminobutyric acid and trehalose in the berry tissues. Likewise, we assessed the temporal and spatial expression and accumulation patterns of the thaumatin-like protein (VviTL1, VviOsmo) and dehydrin (VviDHN1a, VviDHN4, VviDHN2, VviDHN2D) isoforms in the whole berry tissues and rachis of cv. Autumn Royal table grapes during long-term cold storage period and evaluated the profile-shift by CO2 treatments. Their subcellular localization in the pericarp tissues was also determined by immunocytochemical transmission electron microscopy (TEM). The results showed that the cold-drought defense strategies activated by the short-term high CO2 are dose-dependent, tissue-specific and transcriptionally timing-regulated during long-term postharvest cold storage period in table grapes. The results also showed that the more short-term high CO2 treatment is applied to Autumn Royal grapes, the more microstructural evidence there is of enhanced tolerance to storage disorders in terms of thicker and denser cell wall that could contribute to restrain swelling, dehydration and osmotic stress.

Combined effects of ocean deoxygenation, acidification, and phosphorus limitation on green tide macroalga, Ulva prolifera

Ocean deoxygenation, acidification, and decreased phosphorus availability are predicted to increase in coastal ecosystems under future climate change. However, little is known regarding the combined effects of such environmental variables on the green tide macroalga Ulva prolifera. Here, we provide quantitative and mechanistic understanding of the acclimation mechanisms of U. prolifera to ocean deoxygenation, acidification, and phosphorus limitation under both laboratory and semi-natural (mesocosms) conditions. We found that there were significant interactions between these global environmental conditions on algal physiological performance. Although algal growth rate and photosynthesis reduced when the nitrogen-to‑phosphorus (N/P) ratio increased from 16:1 to 35:1 under ambient CO2 and O2 condition, they remained constant with further increasing N/P ratios of 105:1, 350:1, and 1050:1. However, the increasing alkaline phosphatase activities at high N/P ratios suggests that U. prolifera could use organic P to support its growth under phosphorus limitation. Deoxygenation had no effect on specific growth rate (SGR) but decreased photosynthesis under low N/P ratios of 16:1, 35:1, and 105:1, with reduced activities of several enzymes involved in N assimilation pathway being observed. Elevated CO2 promoted algal growth and alleviated the negative effect of deoxygenation on algal photosynthesis. The patterns of responses to high CO2 and low O2 treatments in in situ experiments were generally consistent with those observed in laboratory experiments. Our results generally found that the strong physiological acclimation capacity to elevated CO2, low O2, and high N/P could contribute to its large-scale blooming in coastal ecosystem.

Metabolomics Approach to Reveal the Effects of Ocean Acidification on the Toxicity of Harmful Microalgae: A Review of the Literature

Climate change has been associated with intensified harmful algal blooms (HABs). Some harmful microalgae produce toxins that accumulate in food webs, adversely affecting the environment, public health and economy. Ocean acidification (OA) is a major consequence of high anthropogenic CO2 emissions. The carbon chemistry and pH of aquatic ecosystems have been significantly altered as a result. The impacts of climate change on the metabolisms of microalgae, especially toxin biosynthesis, remain largely unknown. This hinders the optimization of HAB mitigation for changed climate conditions. To bridge this knowledge gap, previous studies on the effects of ocean acidification on toxin biosynthesis in microalgae were reviewed. There was no solid conclusion for the toxicity change of saxitoxin-producing dinoflagellates from the genus Alexandrium after high CO2 treatment. Increased domoic acid content was observed in the diatom Pseudo-nitzschia. The brevetoxin content of Karenia brevis remained largely unchanged. The underlying regulatory mechanisms that account for the different toxicity levels observed have not been elucidated. Metabolic flux analysis is useful for investigating the carbon allocations of toxic microalgae under OA and revealing related metabolic pathways for toxin biosynthesis. Gaining knowledge of the responses of microalgae in high CO2 conditions will allow the better risk assessment of HABs in the future.

Loss of peroxisomal NAD kinase 3 (NADK3) affects photorespiration metabolism in Arabidopsis

Nicotinamide adenine dinucleotides (NAD+ and NADP+) are electron mediators involved in various metabolic pathways. NADP(H) are produced by NAD kinase (NADK) through the phosphorylation of NAD(H). The Arabidopsis NADK3 (AtNADK3) is reported to preferentially phosphorylate NADH to NADPH and is localized in the peroxisome. To elucidate the biological function of AtNADK3 in Arabidopsis, we compared metabolites of nadk1, nadk2 and nadk3 Arabidopsis T-DNA inserted mutants. Metabolome analysis revealed that glycine and serine, which are intermediate metabolites of photorespiration, both increased in the nadk3 mutants. Plants grown for 6 weeks under short-day conditions showed increased NAD(H), indicating a decrease in the phosphorylation ratio in the NAD(P)(H) equilibrium. Furthermore, high CO2 (0.15%) treatment induced a decrease in glycine and serine in nadk3 mutants. The nadk3 showed a significant decrease in post-illumination CO2 burst, suggesting that the photorespiratory flux was disrupted in the nadk3 mutant. In addition, an increase in CO2 compensation points and a decrease in CO2 assimilation rate were observed in the nadk3 mutants. These results indicate that the lack of AtNADK3 causes a disruption in the intracellular metabolism, such as in amino acid synthesis and photorespiration.

Balance dysfunction in large yellow croaker in response to ocean acidification

Large yellow croaker (Larimichthys crocea) is a coastal-dwelling soniferous, commercially important fish species that is sensitive to sound. An understanding of how ocean acidification might affect its auditory system is therefore important for its long-term viability and management as a fisheries resource. We tested the effects of ocean acidification with four CO2 treatments (440 ppm (control), 1000 ppm, 1800 ppm, and 3000 ppm) on the inner ear system of this species. After exposure to acidified water for 50 d, the impacts on the perimeter and mass of the sagitta, asteriscus, and lapillus otoliths were determined. In the acidified water treatments, the shape of sagittal otoliths became more irregular, and the surface became rougher. Similar sound frequency ranges triggered startle responses of fish in all treatments. In the highest CO2 treatment (3000 ppm CO2), significant asymmetry of the left and right lapillus perimeter and weight was apparent. Moreover, in the higher CO2 treatments (1800 ppm and 3000 ppm CO2), the fish were unable to maintain a balanced dorsal-up posture and tilted to one side. This result suggested that the balance functions of the inner ear might be affected by ocean acidification, which may threaten large yellow croaker individuals and populations. The molecular response to acidification was analyzed by RNA-Seq. The differentially expressed genes (DEGs) between right and left sensory epithelia of the utricle in each CO2 treatment group were identified. In higher CO2 concentration groups, nervous system function and regulation of bone mineralization pathways were enriched with DEGs. The comparative transcriptome analyses provide valuable molecular information about how the inner ear system responds to an acidified environment.

CO2 modified atmosphere packaging: stress condition or treatment to preserve fruit and vegetable quality?

In addition to the adoption of proper temperature and relative humidity, the selection of an atmosphere surrounding packaged fresh produce with reduced O2 and/or increased CO2 is one of the most widely used and useful tools to prolong the shelf-life of horticultural crops. However, as O2 and/or CO2 values that might cause injury are strictly related to the commodity, they should be optimized for each product. Here three study cases are reported about the application of modified atmospheres (MA), with different CO2 concentrations (0-40 kPa), to table grapes (cv. Italia) and sweet cherries (cv. Ferrovia) and, as short-term treatment (48 h at 0 °C), to fresh-cut artichokes (cv. Violet de Provence). In each trial, the effect of high CO2 treatment on quality parameters was observed during cold storage. Concerning table grape “Italia”, our results show that low CO2 (up to 10kPa) MA preserved the quality and sensory parameters of the fruit, whereas high CO2 (> 20 kPa) caused a fermentative metabolism. As for sweet cherries 'Ferrovia', 20 kPa CO2 MA helped to maintain the quality traits during storage. On the other hand, this fruit proved to be sensitive to CO2 accumulation (over 20kPa) in hypoxic conditions, since it caused an increase in respiration rate and the biosynthesis of volatile fermentative metabolites. Finally, for fresh-cut artichokes, a short-term CO2 treatment, up to 10kPa, reduced respiration rate and browning index, preserving the volatile profile, while high CO2 (40 kPa) may have caused fermentative metabolism. In conclusion, the application of a MA enriched in CO2 has been shown to have different effects on the quality parameters of the three products, in agreement with the fact that CO2 sensibility depends on each specific fruit or vegetable under study.

A story of resilience: Arctic diatom Chaetoceros gelidus exhibited high physiological plasticity to changing CO2 and light levels.

Arctic phytoplankton are experiencing multifaceted stresses due to climate warming, ocean acidification, retreating sea ice, and associated changes in light availability, and that may have large ecological consequences. Multiple stressor studies on Arctic phytoplankton, particularly on the bloom-forming species, may help understand their fitness in response to future climate change, however, such studies are scarce. In the present study, a laboratory experiment was conducted on the bloom-forming Arctic diatom Chaetoceros gelidus (earlier C. socialis) under variable CO2 (240 and 900 µatm) and light (50 and 100 µmol photons m-2 s-1) levels. The growth response was documented using the pre-acclimatized culture at 2°C in a closed batch system over 12 days until the dissolved inorganic nitrogen was depleted. Particulate organic carbon and nitrogen (POC and PON), pigments, cell density, and the maximum quantum yield of photosystem II (Fv/Fm) were measured on day 4 (D4), 6 (D6), 10 (D10), and 12 (D12). The overall growth response suggested that C. gelidus maintained a steady-state carboxylation rate with subsequent conversion to macromolecules as reflected in the per-cell POC contents under variable CO2 and light levels. A substantial amount of POC buildup at the low CO2 level (comparable to the high CO2 treatment) indicated the possibility of existing carbon dioxide concentration mechanisms (CCMs) that needs further investigation. Pigment signatures revealed a high level of adaptability to variable irradiance in this species without any major CO2 effect. PON contents per cell increased initially but decreased irrespective of CO2 levels when nitrogen was limited (D6 onward) possibly to recycle intracellular nitrogen resources resulting in enhanced C: N ratios. On D12 the decreased dissolved organic nitrogen levels could be attributed to consumption under nitrogen starvation. Such physiological plasticity could make C. gelidus "ecologically resilient" in the future Arctic.

Climate Stressors on Growth, Yield, and Functional Biochemistry of two Brassica Species, Kale and Mustard.

Due to climate change, the attainment of global food security is facing serious challenges in meeting the growing food demand. Abiotic stresses are the foremost limiting factors for agricultural productivity. However, not much information is available on the effect of multiple abiotic stresses on the morphological and biochemical aspects of kale and mustard. Therefore, an experiment was designed to study the effects of UV-B radiation, CO2 concentration, and high temperature on the growth, yield, and biochemistry of two Brassica species, namely B. oleracea L. var. acephala Winterbor F1 (hybrid kale) and B. juncea var. Green wave O.G. (mustard greens), which were grown under optimal nutrients and soil moisture conditions in soil–plant–atmosphere–research (SPAR) units. Two levels of UV-B radiation (0 and 10 kJ m−2 d−1), two concentrations of CO2 (420 and 720 ppm), and two different temperature treatments (25/17 °C and 35/27 °C) were imposed 12 days after sowing (DAS). Several morphological and biochemical parameters were measured at harvest (40 DAS) in both species. All the traits declined considerably under individual and multi-stress conditions in both species except under elevated CO2 levels, which had a positive impact. Marketable fresh weight decreased by 64% and 58% in kale and mustard plants, respectively, growing under UV-B treatment. A slight increase in the chlorophyll content was observed in both species under the UV-B treatment alone and in combination with high temperature and elevated CO2. Understanding the impacts of high temperature, CO2, and UV-B radiation treatments on leafy vegetables, such as kale and mustard, can help to improve existing varieties to enhance resilience towards environmental stresses while simultaneously improving yield, morphology, and biochemistry in plants.

Changes in Volatile Compounds in Short-Term High CO2-Treated 'Seolhyang' Strawberry (Fragaria × ananassa) Fruit during Cold Storage.

‘Seolhyang’ strawberry is harvested before it is fully ripened and treated with CO2 to extend the shelf-life. However, the volatile changes in the ‘Seolhyang’ strawberry after short-term CO2 treatment have not been investigated, although the volatile profile is an important quality attribute. Herein, we investigated the effect of short-term high CO2 treatment on the changes in the composition of volatile compounds in ‘Seolhyang’ strawberries at two ripening stages (i.e., half-red and bright-red) during cold storage using headspace solid-phase microextraction and gas chromatography-mass spectrometry. Furthermore, the effect of CO2 treatment on fruit quality with respect to the aroma was investigated. A total of 30 volatile compounds were identified. Storage increased the volatile compound concentrations, and the total concentration of volatiles in the CO2-treated strawberries was lower than that of the untreated strawberries during storage. The production of some characteristic strawberry volatiles (e.g., 4-methoxy-2,5-dimethyl-3(2H)-furanone) was inhibited in CO2-treated strawberries. However, CO2 treatment helped maintain the concentrations of hexanal and 2-hexenal, which are responsible for the fresh odor in strawberries. Interestingly, CO2 treatment suppressed the production of off-odor volatiles, acetaldehyde, and hexanoic acid during strawberry storage. Thus, short-term CO2 treatment may help maintain the fresh aroma of strawberries during cold storage.

Mechanism of HIF1-α-mediated regulation of Tribolium castaneum metabolism under high CO2 concentration elucidated

HIF1-α is an inducer that plays an important role in the regulation of hypoxia stress in insects in the way of regulating the corresponding enzyme activity which depends on the oxygen concentration through the hydroxylation of proline residues. In this study, we silenced HIF1-α expression in the model insect Tribolium castaneum under a hypoxic environment to explore its role in regulating metabolism in T. castaneum. We found that ATP and NAD + contents decreased significantly after HIF1-α interference at normoxic conditions, while activity of the soluble trehalase increased. The expression of TRE1-2, TRE1-3, TRE2, and TPS genes in the trehalose metabolism pathway were highly enhanced which are compared with normoxic conditions. Meanwhile, the expression of InR2 was significantly up-regulated, both of which play an important role in metabolism. We speculate that the enhancement of the insulin metabolic pathway may lead to enhanced glycolysis. We propose that the HIF1-α gene effectively regulates metabolism for T. castaneum to adapt to high CO2 concentrations in the environment. Our results provide a solid theoretical basis for controlling stored-grain pests incidence using high CO2 treatment.

Root-Zone CO2 Concentration Affects Partitioning and Assimilation of Carbon in Oriental Melon Seedlings.

Root-zone CO2 is essential for plant growth and metabolism. However, the partitioning and assimilation processes of CO2 absorbed by roots remain unclear in various parts of the oriental melon. We investigated the time at which root-zone CO2 enters the oriental melon root system, and its distribution in different parts of the plant, using 13C stable isotopic tracer experiments, as well as the effects of high root-zone CO2 on leaf carbon assimilation-related enzyme activities and gene expressions under 0.2%, 0.5% and 1% root-zone CO2 concentrations. The results showed that oriental melon roots could absorb CO2 and transport it quickly to the stems and leaves. The distribution of 13C in roots, stems and leaves increased with an increase in the labeled root-zone CO2 concentration, and the δ13C values in roots, stems and leaves increased initially, and then decreased with an increase in feeding time, reaching a peak at 24 h after 13C isotope labeling. The total accumulation of 13C in plants under the 0.5% and 1% 13CO2 concentrations was lower than that in the 0.2% 13CO2 treatment. However, the distributional proportion of 13C in leaves under 0.5% and 1% 13CO2 was significantly higher than that under the 0.2% CO2 concentration. Photosynthetic carbon assimilation-related enzyme activities and gene expressions in the leaves of oriental melon seedlings were inhibited after 9 days of high root-zone CO2 treatment. According to these results, oriental melon plants’ carbon distribution was affected by long-term high root-zone CO2, and reduced the carbon assimilation ability of the leaves. These findings provide a basis for the further quantification of the contribution of root-zone CO2 to plant communities in natural field conditions.

Dof Transcription Factors Are Involved in High CO2 Induced Persimmon Fruit Deastringency

High CO2 treatment is a widely used deastringency technology that causes the accumulation of acetaldehyde which precipitates the astringent soluble tannins from persimmon fruit, making them more attractive to consumers. The identification of DkADH1 and DkPDC2 (the key genes for acetaldehyde accumulation) and their regulators (e.g., ERFs), has significantly advanced our understanding of the fruit deastringency mechanism, but other TFs are also involved in the high CO2 response. Here, 32 DkDofs genes were identified from ‘Gongcheng-shuishi’ persimmon, with nine of them shown to differentially respond to high CO2 treatment. Dual luciferase assay indicated that DkDof3 and DkDof6 could repress the promoters of DkADH1 and DkPDC2, respectively. EMSA assay showed that DkDof3 and DkDof6 physically interacted with probes containing T/AAAAG elements from the DkADH1 promoter, whereas they failed to recognize similar elements from the DkPDC2 promoter. The expression of DkDof3 and DkDof6 was also found to be repressed in different persimmon cultivars in response to high CO2 treatment. It is proposed that DkDof3 and DkDof6 were involved in fruit deastringency by regulating the expression of DkADH1 and DkPDC2 in different persimmon cultivars.

Postharvest High-CO2 Treatments on the Quality of Soft Fruit Berries: An Integrated Transcriptomic, Proteomic, and Metabolomic Approach.

Soft fruits are appreciated for their taste qualities and for being a source of health-promoting compounds. However, their postharvest is affected by their high respiratory rates and susceptibility to fungal decay. Our aim here is to provide a perspective on the application of short-term high-CO2 treatments at a low temperature to maintain the postharvest quality of soft fruits. This work also suggests using a multi-omics approach to better understand the role of the cell wall and phenolic compounds in maintaining quality. Finally, the contribution of high-throughput transcriptomic technologies to understand the mechanisms modulated by the short-term gaseous treatments is also highlighted.