Biochemical insights into proline metabolism and its contribution to the endurant cell wall structure under metal stress.

The cell wall serves as the primary barrier against the entry of heavy metal ions into cells. However, excessive accumulation of heavy metals within plants can lead to alterations in the spatial structure and physical properties of the cell wall, thereby affecting the capacity of plants to capture heavy metals. Proline (Pro) is involved in the synthesis of the cell wall, modulating the stability and integrity of its structure. Extensins, core proteins that maintain the cell wall structure, are proline/hydroxyproline-rich glycoproteins that contain the characteristic sequence Ser-[Pro]3-5. They act as intermediates in the regulation of biological processes such as cell wall synthesis, assembly, and signal transduction, typically forming a network structure of cell wall proteins through cross-linking with pectin. This network is essential for the self-assembly expansion of the plant cell wall and plays an indispensable role in cell wall stress signal transduction through its interaction with intracellular signalling molecules. However, the mechanisms by which Pro affects the synthesis of cell wall structural proteins, cell wall assembly, and the sensing of cell wall stress under heavy metal stress remain unclear. This review, from the perspectives of biochemistry and molecular biology, comprehensively elaborates on the impact of Pro and Pro-rich proteins on the structure and function of the cell wall. These findings emphasize the mechanism by which Pro enhances the ability of the cell wall to capture heavy metals, providing new research ideas for the use of genetic engineering to manipulate cell wall synthesis and repair, thereby reducing the phytotoxicity of heavy metals.

Elucidating the intricacies of the H2S signaling pathway in gasotransmitters: Highlighting the regulation of plant thiocyanate detoxification pathways.

In recent decades, there has been increasing interest in elucidating the role of sulfur-containing compounds in plant metabolism, particularly emphasizing their function as signaling molecules. Among these, thiocyanate (SCN-), a compound imbued with sulfur and nitrogen, has emerged as a significant environmental contaminant frequently detected in irrigation water. This compound is known for its potential to adversely impact plant growth and agricultural yield. Although adopting exogenous SCN- as a nitrogen source in plant cells has been the subject of thorough investigation, the fate of sulfur resulting from the assimilation of exogenous SCN- has not been fully explored. There is burgeoning curiosity in probing the fate of SCN- within plant systems, especially considering the possible generation of the gaseous signaling molecule, hydrogen sulfide (H2S) during the metabolism of SCN-. Notably, the endogenous synthesis of H2S occurs predominantly within chloroplasts, the cytosol, and mitochondria. In contrast, the production of H2S following the assimilation of exogenous SCN- is explicitly confined to chloroplasts and mitochondria. This phenomenon indicates complex interplay and communication among various subcellular organelles, influencing signal transduction and other vital physiological processes. This review, augmented by a small-scale experimental study, endeavors to provide insights into the functional characteristics of H2S signaling in plants subjected to SCN--stress. Furthermore, a comparative analysis of the occurrence and trajectory of endogenous H2S and H2S derived from SCN--assimilation within plant organisms was performed, providing a focused lens for a comprehensive examination of the multifaceted roles of H2S in rice plants. By delving into these dimensions, our objective is to enhance the understanding of the regulatory mechanisms employed by the gasotransmitter H2S in plant adaptations and responses to SCN--stress, yielding invaluable insights into strategies for plant resilience and adaptive capabilities.

Proline-mediated modulation on DNA repair pathway in rice seedlings under chromium stress by integrating gene chip and co-expression network analysis.

Chromium (Cr) stress can cause oxidative burst to plants. Application of exogenous proline (Pro) is one of the most effective approaches to improve the tolerance of plants to Cr stress. In this study, we integrated the data of gene chip with co-expression network analysis to identify the key pathways involved in the DNA repair processes in rice seedlings under Cr(VI) stress. Based on KEGG pathway analysis, 158 genes identified are activated in five different types of DNA repair pathways, namely base excision repair (BER, 20 genes), mismatch repair (MMR, 30 genes), nonhomologous end joining (NHEJ, 8 genes), nucleotide excision repair (NER, 56 genes) and homologous recombination (HR, 44 genes). Co-expression network analysis showed that genes activated in DNA repair pathways were categorized into six different modules, wherein Module 1 (45.36%), Module 2 (27.84%) and Module 3 (19.59%) carried more weight than others. Integrating the data of gene chip and co-expression network analysis indicated that coordinated actions of HR and NER pathways are mainly associated with DNA repair processes in Cr(VI)-treated rice seedlings supplied with exogenous Pro. OsCSB, OsXPG, OsBRIP1, OsRAD51C, OsRAD51A2, OsRPA, OsTOPBP1C, OsTOP3, and OsXRCC3 activated in the HR pathway had a stronger impact on repairing DNA damage induced by Cr(VI) stress in rice seedlings supplied with exogenous Pro, while OsXPB1, OsTTDA2, OsTFIIH1, OsXPC, OsRAD23, OsDSS1, and OsRPA located at the NER pathway showed more contribution to repairing DNA damage than others.

Tracing the pollution and human risks of potentially toxic elements in agricultural area nearby the cyanide baths from an active private gold mine in Hainan Province, China.

Mining activities are well-known sources of potentially toxic elements (PTEs) pollution, which often jeopardize the biosphere, pedosphere, and hydrosphere. However, the soil and groundwater pollution caused by active private mining activities has long been neglected. This study investigated the occurrence of PTEs and cyanide (CN) in agricultural soils, mine tailings, and groundwater nearby the cyanide baths from a private gold mine in Hainan Province, southern China. Results indicated that concentrations of Pb, As, Cd, Hg, and CN in different soil depths and mine tailings were up to ten thousand mg/kg, and relatively higher content of As and Pb was detected in groundwater. The chemical forms of Cd, Pb, As, and Hg varied greatly in different soil depths; over 80% of Cd distributed in the water-soluble fraction, suggesting its higher mobility in soils, while approximately 60-90% of Pb, As, and Hg distributed in other chemical fractions, indicating relatively lower mobility in soils. The pollution indices also revealed the serious pollution and deterioration of site quality in this area. Human risk assessments also reflected a high non-carcinogenic/carcinogenic health risk in this area. The framework of integrated management strategies for private metal mines was proposed to mitigate PTEs pollution and reduce health risks.

Estimating the synergistic and antagonistic effects of dual antibiotics on plants through root elongation test.

Antibiotics are recently recognized as a group of emerging environmental contaminants that are frequently detected in various environmental matrixes. Relative root elongation (RRE) test is a rapid and effective strategy to evaluate the water/soil quality and the toxic effects of environmental contaminants on plants. In the present study, we examine the toxicity effect of ciprofloxacin (CIP), norfloxacin (NOR), and tetracycline (TET) to pakchoi individually and in combinations. Both independent action (IA) and concentration addition (CA) models are used for toxicity assessment. Results showed that the EC50 values of CIP, NOR, and TET are 193.59, 60.81, and 40.37 µM, respectively. Combinations of TET + CIP and TET + NOR caused more inhibitory effects on root elongation than those of CIP + NOR. Toxic Unit (TU) and Synergistic Ratio (SR) analysis showed that the relatively lower (higher) EC values are observed in the combinations with lower (higher) antibiotic concentrations, suggesting an effect of low-dose synergism and high-dose antagonism. The reliability of the simulation results from IA and CA models to predict that combined toxicity is highly dependent upon the results from the analysis of TU or SR.

A modelling study of a buffer zone in abating heavy metal contamination from a gold mine of Hainan Province in nearby agricultural area.

The establishment of new buffer zone in the mine areas lacks the basis of theoretical model. As a case study, this study presents the partition model of new buffer zone in a small-scale mine area located in the remote mountainous region of Hainan province, China. The investigation carried out by integration of geostatistical interpolation maps using unmanned aerial vehicle has revealed that As, Cd, Pb, Zn, and Hg are mainly distributed near the tailing ponds and the dressing plant, while Cr and Cu are prominent near the agricultural area. The partition model of buffer zone was established in accordance to the transport velocity of the liquid phase heavy metal in soil. The boundary line of buffer zone is integrated by comparing the 'predicted' heavy metal concentrations with the 'measured' heavy metal concentrations. Principal component analysis (PCA) and the variations of heavy metal concentrations with elevation, slope, and distance were performed to further evaluate the reliability of the predicted buffer zone, indicating that the new buffer zone has a significant effect on minimizing transport of heavy metals from the mining area into the agricultural land. This study is suggestive to provide risk control and sustainable development strategy for the ecosystem protection in mine areas.

Nucleoside diphosphate kinase B-activated intermediate conductance potassium channels are critical for neointima formation in mouse carotid arteries.

OBJECTIVE: Vascular smooth muscle cells (VSMC) proliferation is a hallmark of atherosclerosis and vascular restenosis. The intermediate conductance Ca(2+)-activated K(+) (SK4) channel is required for pathological VSMC proliferation. In T lymphocytes, nucleoside diphosphate kinase B (NDPKB) has been implicated in SK4 channel activation. We thus investigated the role of NDPKB in the regulation of SK4 currents (ISK4) in proliferating VSMC and neointima formation. APPROACH AND RESULTS: Function and expression of SK4 channels in VSMC from injured mouse carotid arteries were assessed by patch-clamping and real-time polymerase chain reaction. ISK4 was detectable in VSMC from injured but not from uninjured arteries correlating with the occurrence of the proliferative phenotype. Direct application of NDPKB to the membrane of inside-out patches increased ISK4, whereas NDPKB did not alter currents in VSMC obtained from injured vessels of SK4-deficient mice. The NDPKB-induced increase in ISK4 was prevented by protein histidine phosphatase 1, but not an inactive protein histidine phosphatase 1 mutant indicating that ISK4 is regulated via histidine phosphorylation in proliferating VSMC; moreover, genetic NDPKB ablation reduced ISK4 by 50% suggesting a constitutive activation of ISK4 in proliferating VSMC. In line, neointima formation after wire injury of the carotid artery was substantially reduced in mice deficient in SK4 channels or NDPKB. CONCLUSIONS: NDPKB to SK4 signaling is required for neointima formation. Constitutive activation of SK4 by NDPKB in proliferating VSMC suggests that targeting this interaction via, for example, activation of protein histidine phosphatase 1 may provide clinically meaningful effects in vasculoproliferative diseases such as atherosclerosis and post angioplasty restenosis.

Phytotoxicity and Transport of Gallium (Ga) in Rice Seedlings for 2-Day of Exposure.

Hydroponic experiments were conducted with rice seedlings to investigate the accumulation and phytotoxicity of gallium nitrate. A linear decrease in relative growth rate, transpiration rate and water use efficiency was observed in rice seedlings with increasing Ga concentrations. However, inhibition of these selected parameters was noted different at different Ga treatments. Relative growth rate was more sensitive towards Ga treatments. Phyto-transport of Ga was apparent, but recovery of Ga in different parts of rice seedlings varied significantly: roots were dominant site for Ga accumulation. The total accumulation rates of Ga were positively correlated to Ga concentrations. Results indicated that the addition of Ga did not cause deleterious effects on plant physiological functions over a 2-day exposure period. Large amounts of Ga were removed from the hydroponic solution through rice seedlings. Accumulation of Ga in plant tissues resulted in growth inhibition of rice seedlings.

SOS! Hydrogen Sulfide Enhances the Flavonoid Early Warning System in Rice Plants to Cope with Thiocyanate Pollution.

The presence of thiocyanate (SCN-) in irrigation water has adverse effects on both plant growth and crop output. Hydrogen sulfide (H2S) is an important gaseous signaling molecule that can alleviate SCN- stress. Flavonoids are secondary compounds produced by plants and are ubiquitous in the plant kingdom. They play important roles in several physiological and biochemical processes. To investigate the effect of exogenous H2S on the growth of early rice plants under SCN- stress, we carried out a hydroponic experiment focusing on the interaction of exogenous H2S with flavonoids. In this study, a hydroponic experiment was performed to investigate the behavior of SCN- when subjected to varying effective doses (EC20: 24.0 mg/L; EC50: 96.0 mg/L; and EC75: 300.0 mg/L). The findings indicated that the relative growth rate (RGR) of the plants treated with H2S + SCN- was greater than that of the plants treated with SCN- alone. Higher amounts of flavonoids were detected in the shoots than in the roots, with more variability in the shoots. The early warning level results showed that most of the flavonoids were present at levels I and II, while quercetin was present at level IV. Genetic expression variation factor (GEVF) analyses revealed an increase in the quantity of "promoter genes" with increasing SCN- concentration in both rice tissues. Furthermore, administering external H2S while exposing rice tissues to SCN- resulted in a considerable decrease in the levels of reactive oxygen species. This study provides novel insights into the regulation of flavonoid levels in rice plants by exogenous H2S, facilitating enhanced resistance to SCN- stress and promoting sustainable agriculture.

Unraveling the enigma of NPP variation in Chinese vegetation ecosystems: The interplay of climate change and land use change.

Global carbon emissions have exacerbated the greenhouse effect, exerting a profound impact on ecosystems worldwide. Gaining an understanding of the fluctuations in vegetation net primary productivity (NPP) is pivotal in the assessment of environmental quality, estimation of carbon source/sink potential, and facilitation of ecological restoration. Employing MODIS and meteorological data, we conducted a comprehensive analysis of NPP evolution in Chinese vegetation ecosystems (VESs), employing Theil-Sen median trend analysis and the Mann-Kendall test. Furthermore, utilizing scenario-based analysis, we quantitatively determined the respective contributions of climate change and land use change to NPP variations across various scales. The overall NPP exhibited a discernible upward trend from 2000 to 2020, with a growth rate of 5.83 gC·m-2·year-1. Forestland ecosystem (FES) displayed the highest rate of increase (9.40 gC·m-2·year-1), followed by cropland ecosystem (CES) (4.00 gC·m-2·year-1) and grassland ecosystem (GES) (3.40 gC·m-2·year-1). Geographically, NPP exhibited a spatial pattern characterized by elevated values in the southeast and diminished values in the northwest. In addition, climate change had elevated 76.39 % of CES NPP, 90.62 % of FES NPP, and 71.78 % of GES NPP. At the national level, climate change accounted for 83.14 % of the NPP changes, while land use change contributed 14.14 %. Notably, climate change emerged as the primary driving force behind NPP variations across all VEGs, with land use change exerting the most pronounced influence on CES. At the grid scale (2 km × 2 km), land use change played a substantial role in all VEGs, contributing 60.01 % in CES, 54.20 % in FES, and 55.61 % in GES of the NPP variations.

Transcriptome reveals the crucial role of exogenous hydrogen sulfide in alleviation of thiocyanate (SCN-) toxicity in rice seedlings.

Application of exogenous hydrogen sulfide (H2S) is a novel strategy for alleviation of the adverse effects caused by abiotic stresses. However, little is known about H2S-mediated global molecular response of rice seedlings to thiocyanate (SCN-) exposure. Herein, a hydroponic experiment was carried out to investigate the crucial role of exogenous H2S in alleviation of SCN- toxicity generated at different effective concentrations (EC20: 24.0 mg SCN/L, EC50: 96.0 mg SCN/L, and EC75: 300.0 mg SCN/L) in rice seedlings through transcriptome analysis. The results showed that the total numbers of differentially expressed genes (DEGs, upregulated genes/downregulated genes) in rice roots were 755/313, 1114/3303, and 2184/7427, while they were 427/292, 2134/526, and 2378/890 in rice shoots at EC20, EC50, and EC75 of SCN-, respectively. When exogenous H2S was supplied to rice seedlings exposed to SCN-, the total number of DEGs (upregulated genes/downregulated genes) in rice roots was 1158/316, 1943/2959, and 1737/5392, while it was 2067/937, 2689/683, and 3492/1062 in rice shoots at EC20, EC50, and EC75 of SCN-, respectively. Upregulated DEGs in shoots were positively correlated with SCN- concentration in the presence of exogenous H2S, suggesting its crucial role in regulating the phytotoxicity of SCN-. Gene function and pathway enrichment analyses showed that exogenous H2S triggered "secondary metabolite synthesis," "metabolic pathways," and "signal transduction mechanisms" in rice seedlings corresponding to different effective concentrations of SCN- exposure.

Evaluating the significance of amino acids (AAs) in cyanide-treated rice plants under different nitrogen fertilization using the relative importance index of AA.

The biosynthesis of amino acids (AAs) in plants is affected by different nitrogen (N) sources. The effects of exogenous cyanide (KCN) on the concentrations and profiles of AAs in rice seedlings were carried out in the presence of nitrate (+NO3-)/ammonium (+NH4+) or N deficiency (-N). Targeted metabolomics analysis indicated that the highest accumulation of AAs in CN--treated rice seedlings was detected in the "CN-+NH4+" treatments than in other treatments, wherein the doses of exogenous KCN did not significantly affect the total amount of AAs in rice seedlings at the same N fertilized condition. The total content of AAs in rice shoots under "CN-+NH4+" treatments was higher than other treatments, while the total content of AAs in rice roots under "CN-+NO3-" treatments was higher than other treatments. Also, the profiles of 21 AAs in CN--treated rice seedlings showed tissue-specific under different N fertilization. The relative importance index (RII) of AA was used to evaluate the importance of AAs in CN--treated rice seedlings under different N fertilization. The common AAs with higher RII values were compared between three different treatments of KCN (e.g., 0, 1, and 2 mg CN/L). Under "CN-+(-N)" treatments, Ala, Asp, Glu, Val, and Gly (Ala, Gly, Val, and Lys) were the common AAs in rice roots (shoots). Under "CN-+NO3-" treatments, Ala, Glu, Asp, Ser, and Thr (Asp, Ala, Thr, Ser, and Asn) were the common AAs with higher RII values in rice roots (shoots) between all CN- treatments. Under "CN-+NH4+" treatments, Asp, Gln, Asn, and Ala (Asp, Glu, and Thr) were the common AAs with higher RII values in rice roots (shoots) between all CN- treatments. These results suggested that using the RII to describe the change and fluctuation of AAs in rice plants may reflect the different N utilization strategies in response to exogenous CN- exposure.

Regulation of enzymatic and non-enzymatic antioxidants in rice seedlings against chromium stress through sodium hydrosulfide and sodium nitroprusside.

Hydrogen sulfide (H2S) and nitric oxide (NO) play a well-organized protective mechanism in coping with oxidative stress induced by toxic metals. However, the comparative effects of H2S and NO on enzymatic and non-enzymatic antioxidants in plants under Cr(III) stress have not been defined. In this study, we mathematically evaluate the importance of sodium hydrosulfide (NaHS) and sodium nitroprusside (SNP) on these two antioxidant systems in rice seedlings under Cr(III) stress. The results displayed that the optimal dose of NaHS and SNP was 100 µM and 75 µM, respectively, in rice tissues under Cr(III) stress, judging by the reactive oxygen species (ROS) levels in rice tissues. When rice seedlings were exposed to Cr(III) at concentrations of 3.57, 7.24, 26.52 mg Cr/l, Cr-induced ROS accumulation had a significant (p < 0.05) effect on the lipid peroxidation of cell membrane in rice tissues, and decreased the response of SOD, CAT, Pro, GSH, and AsA in rice tissues. Application of exogenous NaHS and SNP effectively (p < 0.05) alleviated the toxic effects of Cr(III) in rice seedlings by activating different antioxidants. A novel physiological response model suggested that the regulatory effect of NaHS and SNP on non-enzymatic antioxidants was stronger than that of enzymatic antioxidants. Moreover, NaHS-mediated response intensity of both enzymatic and non-enzymatic antioxidants was greater than that of SNP, suggesting the importance of utilizing NaHS over SNP as antioxidant regulators during detoxification of Cr(III) in rice seedlings.

Proline interacts with Ca2+-dependent signaling to enhance chromium tolerance in rice by manipulating nitrate reductase and sucrose phosphate synthase.

The entrance of chromium (Cr) into the agricultural system would exert a negative influence on the carbon/nitrogen metabolism (CNM) of plants. In this study, we investigated the role of exogenous proline-mediated Ca2+-dependent signaling in the regulation of CNM in rice subjected to Cr(VI) stress, with emphasis on the involvement of nitrate reductase (NR) and sucrose phosphate synthase (SPS). Results demonstrated that proline effectively mitigated the growth inhibition of rice imposed by Cr(VI) stress, which is achieved by a reduction in cytoplasmic Ca and Cr content and the activation of the downstream Ca2+-dependent signaling pathway. Additionally, proline displayed a positive effect in modulating the expression and activities of NR and SPS under Cr(VI) stress, which are attributed to the cross-regulation between calcium-dependent protein kinases (CDPKs) and 14-3-3 proteins (14-3-3s). Consequently, nitrogen use efficiency and sucrose content in rice under Cr(VI) + proline treatments were higher than Cr(VI) treatments. Gene expression variation factors underscored that the regulation of proline on NR is crucial to the Ca2+-dependent signaling pathway, initiated by the interaction between CDPKs and 14-3-3s in rice plants during Cr(VI) stress. These results reveal that proline interacts with Ca2+-dependent signaling pathways to enhance Cr tolerance in rice by regulating NR and SPS.

Spatial-temporal variations of proline and related amino acids reveal distinct nitrogenous utilization strategies in rice during detoxification of exogenous cyanide.

Cyanide (CN-) pollution in agricultural systems impairs amino acid metabolism in rice plants, hence decreasing their quality and yield. Meanwhile, little is known about the effects of CN- assimilation on the innate pool of proline (Pro) and its synthesis-related amino acids (Pro-AAs) in rice plants. In this study, a hydroponic experiment was carried out to investigate the effect of exogenous KCN on indigenous levels of Pro-AAs, i.e., Pro, glutamate (Glu), arginine (Arg), and ornithine (Orn) in rice seedlings fertilized with either nitrate (NO3-) or ammonium (NH4+) through the biochemical and RT-qPCR analysis. At the same KCN treatment concentration, the relative growth rate of NH4+-fed rice seedlings was considerably higher than that of NO3--fed rice seedlings, but the residual concentration of CN- in NH4+-fed rice tissues was lower than that of NO3--fed rice tissues. Based on the UPLC and stoichiometry molar ratio calculations, it is evident that the Glu pathway contributed significantly to Pro synthesis in rice under KCN + NO3- treatments; whereas the Orn pathway governed the synthesis of Pro in rice under KCN + NH4+ treatments. Moreover, transcriptional and bioinformatics analysis revealed that NH4+ fertilization resulted in spatial-temporal differences in the genetic response in rice tissue during detoxification of CN- compared with KCN + NO3- treatments. These findings suggested that the innate level of Pro serves as "a fishing float" to balance the flux between Pro and Pro-AAs in exogenous KCN-treated rice plants under different nitrogenous nutritional conditions.

Exogenous proline activated an integrated response of NER and HR pathways to reduce DNA damage in rice seedlings under chromium stress.

The DNA damage induced by hexavalent chromium [Cr(VI)] pollutant causes a genotoxic effect on rice seedlings. Hereby, we examined the effects of exogenous proline (Pro) on the alleviation of DNA damage in rice seedlings under different effective concentrations of Cr(VI). Our results revealed that Cr(VI) stress induced reactive oxygen species (ROS), i.e., H2O2 and O2·- accumulation in rice seedlings, repressed genes expression activated in the homologous recombination (HR) and nucleotide excision repair (NER) pathways, and caused DNA damage. Exogenous application of Pro increased Cr accumulation in rice roots, but decreased Cr accumulation in rice shoots, wherein Pro application decreased ROS accumulation in both tissues of rice seedlings. The comet assays suggested that exogenous application of Pro significantly alleviated the DNA damage in rice seedlings during Cr(VI) treatments, judged by the Olive tail moment and tail DNA. Transcriptional assays revealed that exogenous Pro upregulated the expression level of genes associated with the HR and NER pathways and triggered coordinated actions of both repairing pathways to modulate DNA lesion in rice plants during exposure to Cr(VI). Calculations from gene expression variation factors showed that regulative effect of exogenous application of Pro on DNA repair pathways was highly activated at 2.0 mg Cr/L. The current study revealed that Cr(VI) affect rice plants and exogenous Pro rescue these effects by the activation of HR and NER pathways.

Proline-mediated activation of glyoxalase II improve methylglyoxal detoxification in Oryza sativa L. under chromium injury: Clarification via vector analysis of enzymatic activities and gene expression.

Environmental factors affect plants in several ways including the excessive accumulation of methylglyoxal (MG), resulting in dysfunctions of many biological processes. Exogenous proline (Pro) application is one of the successful strategies to increase plant tolerance against various environmental stresses, including chromium (Cr). This study highlights the alleviation role of exogenous Pro on MG detoxification in rice plants induced by Cr(Vl) through modifying the expression of glyoxalase I (Gly I)- and glyoxalase II (Gly II)-related genes. The MG content in rice roots was significantly reduced by Pro application under Cr(VI) stress, however, there was little effect on the MG content in shoots. In this connection, the vector analysis was used to compare the involvement of Gly l and Gly II on MG detoxification in 'Cr(VI)' and 'Pro+Cr(VI)' treatments. Results exhibited that vector strength in rice roots increased with an increase in Cr concentrations, while there was a negligible difference in the shoots. The comparative analysis demonstrated that the vector strengths in roots under 'Pro+Cr(VI)' treatments were higher than 'Cr(VI)' treatments, suggesting that Pro improved Gly II activity more efficiently to reduce MG content in roots. Calculation of the gene expression variation factors (GEFs) indicated a positive effect of Pro application on the expression of Gly I and Gly ll-related genes, wherein a stronger impact was in roots than the shoots. Together, the vector analysis and gene expression data reveal that exogenous Pro chiefly improved Gly ll activity in rice roots which subsequently enhanced MG detoxification under Cr(VI) stress.

Merging the occurrence possibility into gene co-expression network deciphers the importance of exogenous 2-oxoglutarate in improving the growth of rice seedlings under thiocyanate stress.

Thiocyanate (SCN-) can find its way into cultivated fields, which might hamper the harmony in carbon and nitrogen metabolism (CNM) of plants, ebbing their quality and productivity. In the current study, we investigated the role of the exogenous application of 2-oxoglutarate (2-OG) in maintaining homeostasis of CNM in rice seedlings under SCN- stress. Results showed that SCN- exposure significantly repressed the gene expression and activities of CNM-related enzymes (e.g., phosphoenolpyruvate carboxylase, NADP-dependent isocitrate dehydrogenases, and isocitrate dehydrogenases) in rice seedlings, thereby reducing their relative growth rate (RGR). Exogenous application of 2-OG effectively mitigated the toxic effects of SCN- on rice seedlings, judged by the aforementioned parameters. The co-expression network analysis showed that genes activated in CNM pathways were categorized into four modules (Modules 1-4). In order to identify the key module activated in CNM in rice seedlings exposed to SCN-, the results from real-time quantitative PCR (RT-qPCR) tests were used to calculate the possibility of the occurrence of genes grouped in four different modules. Notably, Module 3 showed the highest occurrence probability, which is mainly related to N metabolism and 2-OG synthesis. We can conclude that exogenous application of 2-OG can modify the imbalance of CNM caused by SCN- exposure through regulating N metabolism and 2-OG synthesis in rice seedlings.

Individual and mutual effects of elevated carbon dioxide and temperature on salt and cadmium uptake and translocation by rice seedlings.

Plant kingdoms are facing increasingly harsh environmental challenges marked by the coexposure of salinity and pollution in the pedosphere and elevated CO2 and temperature in the atmosphere due to the rapid acceleration of industrialization and global climate change. In this study, we deployed a hydroponics-based experiment to explore the individual and mutual effects of different temperatures (low temperature, T1: 23°C; high temperature, T2: 27°C) and CO2 concentrations (ambient CO2: 360 ppm; medium CO2: 450 ppm; high CO2: 700 ppm) on the uptake and translocation of sodium chloride (NaCl, 0.0, 0.2, 0.6, and 1.1 g Na/L) and cadmium nitrate (Cd(NO3)2·4H2O, 0.0, 0.2, 1.8, and 5.4 mg Cd/L) by rice seedlings. The results indicated that Cd and Na exposure significantly (P< 0.05) inhibited plant growth, but T2 and medium/high CO2 alleviated the effects of Cd and Na on plant growth. Neither significant synergistic nor antagonistic effects of Cd and Na were observed, particularly not at T1 or high CO2. At increasing temperatures, relative growth rates increased despite higher concentrations of Cd and Na in both rice roots and shoots. Similarly, higher CO2 stimulated the growth rate but resulted in significantly lower concentrations of Na, while the Cd concentration was highest at medium CO2. Coexposure experiments suggested that the concentration of Cd in roots slightly declined with additional Na and more at T2. Overall, our preliminary study suggested that global climate change may alter the distribution of mineral and toxic elements in rice plants as well as the tolerance of the plants.

Transcriptional analysis of heavy metal P1B-ATPases (HMAs) elucidates competitive interaction in metal transport between cadmium and mineral elements in rice plants.

Cadmium (Cd) pollution has become a major threat to crop production and quality globally. The heavy metal P1B-ATPases (HMAs) play a crucial role in metal transport in plants. In the present study, we investigated the interaction in metal transport by HMAs between Cd and mineral elements in rice plants. Rice seedlings were treated with cadmium nitrate either in the nutrient solution ("Cd+M") or in the ultrapure water ("Cd-M"). Result showed that phytotoxicity of Cd to rice seedlings was evident from both Cd treatments, judged by relative growth rate (RGR), where more severe repression (p < 0.05) of RGR was observed in the "Cd-M" treatments than the "Cd+M" treatments. More Cd (p < 0.05) was accumulated in rice tissues from the "Cd-M" treatments than the "Cd+M" treatments, while there is a significant difference (p < 0.05) in distribution and translocation of mineral elements in rice tissues between the "Cd+M" and the "Cd-M" treatments. RT-qPCR analysis displayed that the expression patterns of HMAs related genes were quite different between "Cd+M" and "Cd-M" treatments, suggesting their different regulatory effects during the transport of Cd and mineral elements within rice plants. The competition in metal transport by HMAs mainly occurs between Cd and micro-elements of Zn and Cu in rice tissues during Cd exposure. Overall, this study provides new evidence to clarify the different translocation mechanisms of HMAs in metal transport between Cd and mineral elements in rice seedlings during Cd exposure.