H2 O2 mediates nitrate-induced iron chlorosis by regulating iron homeostasis in rice

IDD10-NAC079 transcription factor complex regulates sheath blight resistance by inhibiting ethylene signaling in rice

INTRODUCTION

Rhizoctonia solani Kühn is a pathogen causing rice sheath blight (ShB). Ammonium transporter 1 (AMT1) promotes resistance of rice to ShB by activating ethylene signaling. However, how AMT1 activates ethylene signaling remains unclear.

OBJECTIVE

In this study, the indeterminate domain 10 (IDD10)-NAC079 interaction model was used to investigate whether ethylene signaling is modulated downstream of ammonium signaling and modulates ammonium-mediated ShB resistance.

METHODS

RT-qPCR assay was used to identify the relative expression levels of nitrogen and ethylene related genes. Yeast two-hybrid assays, Bimolecular fluorescence complementation (BiFC) and Co-immunoprecipitation (Co-IP) assay were conducted to verify the IDD10-NAC079-calcineurin B-like interacting protein kinase 31 (CIPK31) transcriptional complex. Yeast one-hybrid assay, Chromatin immunoprecipitation (ChIP) assay, and Electrophoretic mobility shift assay (EMSA) were used to verify whether ETR2 was activated by IDD10 and NAC079. Ethylene quantification assay was used to verify ethylene content in IDD10 transgenic plants. Genetic analysis is used to detect the response of IDD10, NAC079 and CIPK31 to ShB infestation.

RESULTS

IDD10-NAC079 forms a transcription complex that activates ETR2 to inhibit the ethylene signaling pathway to negatively regulating ShB resistance. CIPK31 interacts and phosphorylates NAC079 to enhance its transcriptional activation activity. In addition, AMT1-mediated ammonium absorption and subsequent N assimilation inhibit the expression of IDD10 and CIPK31 to activate the ethylene signaling pathway, which positively regulates ShB resistance.

CONCLUSION

The study identified the link between ammonium and ethylene signaling and improved the understanding of the rice resistance mechanism.

Unveiling nitrogen preferences in indica rice: a classification study of cultivars in South China

Introduction

Do indica rice cultivars prefer ammonium or nitrate? Understanding this preference is key to optimizing nitrogen use efficiency in rice production. Ammonium and nitrate are crucial for plant nitrogen nutrition, as rice cultivars exhibit varying preferences. However, few studies have classified ammonium and nitrate preferences within indica cultivars.

Methods

For the first time, this study classifies indica rice cultivars based on their ammonium and nitrate preferences, revealing significant differences in biomass production under various nitrogen treatments. This study investigated the effects of ammonium-only nutrition (100:0), ammonium-nitrate mixed nutrition (75:25), and nitrate-only nutrition (0:100) on the maximum root length, shoot length, SPAD value, and biomass of 24 widely cultivated indica cultivars in South China.

Result

Compared to ammonium-only nutrition, a mixed ammonium-nitrate treatment significantly boosted root and shoot growth, while nitrate-only nutrition led to a decline in chlorophyll content. Compared with the 100:0 treatment, the maximum root length, shoot length, root dry weight, shoot dry weight, and total dry weight in the 75:25 treatment significantly increased by 29.85%, 4.11%, 7.65%, 1.71% and 3.03% (p < 0.01), respectively; and the SPAD value in the 0:100 treatment significantly decreased by 4.22% (p < 0.01).

Discussion

These results demonstrate distinct responses of rice cultivars to different nitrogen treatments. Through correlation, principal component, and cluster analyses, the rice cultivars were categorized into three types: ammonium-preferring type (APT), ammonium- and nitrate-preferring type (ANPT), and nitrate-preferring type (NPT). The APT, ANPT, and NPT showed the highest biomass in the 100:0, 75:25, and 0:100 treatments, respectively, with the biomass in the ANPT significantly exceeding that of the APT (p < 0.01). These insights provide a foundation for breeding high-yield indica rice, optimizing nitrogen fertilizer strategies, and improving nitrogen use efficiency in sustainable agriculture.

Aluminum alleviates iron deficiency chlorosis by interfering with phosphorus homeostasis in rice (Oryza sativa L.)

Rice (Oryza sativa L.) is a staple food for more than half of the human population. Rice plants are cultivated in several different environments, and face various abiotic stresses, including nutritional imbalance in soils. The ionome, the inorganic composition of an organism, is known to be tightly regulated, as changes in concentration of one element affect concentrations of others. Iron (Fe) is an essential element that is involved in redox reactions, nitrogen metabolism and chlorophyll synthesis. The hallmark of Fe deficiency in plants is leaf chlorosis, a phenotype known to be alleviated by deficiencies of other elements, such as phosphorus (P). Aluminum (Al) is abundant in soils and limits plant growth in acidic soils. Despite its well-established detrimental effects, Al has been proposed to have a positive effect on growth for some species, but little is known about this phenomenon. Here we aim to understand whether Al affects Fe homeostasis in rice. We found that Al alleviated Fe deficiency-induced chlorosis. +Al-Fe treatment decreased expression of Fe deficiency marker genes and partially recovered photosynthesis. We also observed that Al induced expression of a P deficiency marker gene, and addition of excess P to nutrient solution reversed effects of Al on chlorosis. Our data show that Al alleviates Fe deficiency-induced chlorosis, and suggests that this occurs indirectly by inducing P deficiency in leaves.

Direct determination of silicon overestimates the accumulation and translocation of SiO2 nanoparticles in rice seedlings

Silica nanoparticles (SiO2 NPs) have numerous applications in agriculture, but may also pose significant risks to plants. Nevertheless, their bioaccumulation, an important determinant of their risks, was often not accurately measured due to the lack of reliable methods. In this study, the accumulation in rice seedlings of SiO2 NPs of different sizes without and with a gold nanoparticle core (Au@SiO2 NPs) was examined. Potential interference from SiO2 NP dissolution was minimized by lowering the pH of the uptake medium, which did not result in any observable adverse bioeffects. Under this condition, the direct determination of Si showed the significant accumulation of SiO2 NPs in roots and shoots and a decrease in the accumulation of SiO2 NPs in shoots with increasing particle size. However, when accumulation was monitored using Au@SiO2 NPs, SiO2 NP accumulation was significantly higher when measured by direct Si determination than by Au determination, indicating that the former overestimates the accumulation of SiO2 NPs. Consequently, unlike direct Si determination, tracking the gold nanoparticle core revealed an increase in SiO2 NP accumulation in shoots with increasing particle size. Overall, accurate determination of SiO2 NP bioaccumulation is imperative for appropriate bioapplications and reliable biosafety assessments of these particles.

Interactions between arsenic and nitrogen regulate nitrogen availability and arsenic mobility in flooded paddy soils

In paddy soils, arsenic (As) stress influences nitrogen (N) transformation while application of N fertilizers during rice cropping affects As transformation. However, specific interactive effects between As and N in flooded paddy soils on As mobility and N availability were unclear. Here, we examined N and As dynamics in flooded paddy soils treated with four As levels (0, 30, 80 and 150 mg kg-1) and three urea additions (0, 4 and 8 mmol N kg-1). Arsenic contamination inhibited diazotrophs (nifH) and fungi but promoted AOA and denitrification genes (narG, nirK, nirS), decreasing dissolved organic N, NH4+-N and NO3--N. Besides, urea application stimulated As- and Fe-reducing bacteria (arrA and Geo) coupled with anammox. On Day 28, the addition of 8 mmol N kg-1 increased total As concentrations in solutions of soils treated with 30 and 80 mg As kg-1 by 2.4 and 1.8 times compared with the nil-N control. In contrast, at 150 mg As kg-1, it decreased the total As concentration in soil solution by 63 % through facilitating As(III) oxidation coupled with NO3--N reduction. These results indicate that As contamination decreases N availability, but urea application affects As mobility, depending on As contamination level.

Transcriptome and metabolome analyses reveal the mechanisms by which H2S improves energy and nitrogen metabolism in tall fescue under low-light stress

Hydrogen sulfide (H2S) functions as a signaling molecule affecting plant growth, development, and stress adaptation. Tall fescue (Festuca arundinacea Schreb.), a bioenergy crop, encounters significant challenges in agricultural production owing to low light by shading. However, the influence of H2S on tall fescue under low light stress (LLS) remains unclear. To examine the role of H2S in acclimation of tall fescue to low light, we conducted combined analyses of physiological traits, metabolomics, and transcriptomics. These results showed that H2S mitigated LLS-induced inhibition of photosynthesis and maintained normal chloroplast ultrastructure by boosting the expression of photosynthesis-related genes, including PsbQ, PsbR, PsaD, PsaK, and PetH, thereby enhancing the synthesis of carbohydrates (sucrose, starch). H2S upregulated the expression of key genes (PFK, PK, IDH, G6PD) connected to glycolysis, the tricarboxylic acid cycle, and the pentose phosphate pathway to promote carbon metabolism and ensure the supply of carbon skeletons and energy required for nitrogen metabolism. H2S application reverted the LLS-induced accumulation of nitrate nitrogen and the changes in the key nitrogen metabolism enzymes glutamate synthase (GOGAT, EC 1.4.1.13), nitrate reductase (NR, EC 1.6.6.1), glutamine synthetase (GS, EC 6.3.1.2), and glutamate dehydrogenase (GDH, EC 1.4.1.2), thus promoting amino acid decomposition to produce proteins involved in nitrogen assimilation and nitrogen use efficiency as well as specialized metabolism. Ultimately, H2S upregulated the C/N ratio of tall fescue, balanced its carbon and nitrogen metabolism, enhanced shade tolerance, and increased biomass. These results provided new insights into enhancing plant resilience under LLS.

Nitrate and ammonium, the yin and yang of nitrogen uptake: a time-course transcriptomic study in rice

Nitrogen is an essential nutrient for plants and a major determinant of plant growth and crop yield. Plants acquire nitrogen mainly in the form of nitrate and ammonium. Both nitrogen sources affect plant responses and signaling pathways in a different way, but these signaling pathways interact, complicating the study of nitrogen responses. Extensive transcriptome analyses and the construction of gene regulatory networks, mainly in response to nitrate, have significantly advanced our understanding of nitrogen signaling and responses in model plants and crops. In this study, we aimed to generate a more comprehensive gene regulatory network for the major crop, rice, by incorporating the interactions between ammonium and nitrate. To achieve this, we assessed transcriptome changes in rice roots and shoots over an extensive time course under single or combined applications of the two nitrogen sources. This dataset enabled us to construct a holistic co-expression network and identify potential key regulators of nitrogen responses. Next to known transcription factors, we identified multiple new candidates, including the transcription factors OsRLI and OsEIL1, which we demonstrated to induce the primary nitrate-responsive genes OsNRT1.1b and OsNIR1. Our network thus serves as a valuable resource to obtain novel insights in nitrogen signaling.

Straw return enhances grain yield and quality of three main crops: evidence from a meta-analysis

Straw return is regarded as a widely used field management strategy for improving soil health, but its comprehensive effect on crop grain yield and quality remains elusive. Herein, a meta-analysis containing 1822 pairs of observations from 78 studies was conducted to quantify the effect of straw return on grain yield and quality of three main crops (maize, rice, and wheat). On average, compared with no straw return, straw return significantly (p< 0.05) increased grain yield (+4.3%), protein content (+2.5%), total amino acids concentration (+1.2%), and grain phosphorus content (+3.6%), respectively. Meanwhile, straw return significantly (p< 0.05) decreased rice chalky grain rate (-14.4%), overall grain hardness (-1.9%), and water absorption of maize and wheat (-0.5%), respectively. Moreover, straw return effects on grain yield and quality traits were infected by cultivated crop types, straw return amounts, straw return methods, and straw return duration. Our findings illustrated that direct straw return increased three main crop grain yields and improved various quality traits among different agricultural production areas. Although improper straw return may increase plant disease risk and affect seed germination, our results suggest that full straw return with covered or plough mode is a more suitable way to enhance grain yield and quality. Our study also highlights that compared with direct straw return, straw burning or composting before application may also be beneficial to farmland productivity and sustainability, but comparative studies in this area are still lacking.

Mechanism for Fe(III) to decrease cadmium uptake of wheat plant: Rhizosphere passivation, competitive absorption and physiological regulation

The presence of dissolved Fe(III) and Fe(III)-containing minerals has been found to alleviate cadmium (Cd) accumulation in wheat plants grown in Cd-contaminated soils, but the specific mechanism remains elusive. In this work, hydroponic experiments were conducted to dissect the mechanism for dissolved Fe(III) (0-2000 μmol L-1) to decrease Cd uptake of wheat plants and study the influence of Fe(III) concentration and Cd(II) pollution level (0-20 μmol L-1) on the Cd uptake process. The results indicated that dissolved Fe(III) significantly decreased Cd uptake through rhizosphere passivation, competitive absorption, and physiological regulation. The formation of poorly crystalline Fe(III) oxides facilitated the adsorption and immobilization of Cd(II) on the rhizoplane (over 80.4 %). In wheat rhizosphere, the content of CaCl2-extractable Cd decreased by 52.7 % when Fe(III) concentration was controlled at 2000 μmol L-1, and the presence of Fe(III) may reduce the formation of Cd(II)-organic acid complexes (including malic acid and succinic acid secreted by wheat roots), which could be attributed to competitive reactions. Down-regulation of Cd uptake genes (TaNramp5-a and TaNramp5-b) and transport genes (TaHMA3-a, TaHMA3-b and TaHMA2), along with up-regulation of the Cd efflux gene TaPDR8-4A7A, contributed much to the reduction of Cd accumulation in wheat plants in the presence of Fe(III). The inhibitory effect of Fe(III) on Cd uptake and transport in wheat plants declined with increasing Cd(II) concentration, particularly at 20 μmol L-1. This work provides important implications for remediating Cd-contaminated farmland soil and ensuring the safe production of wheat by using dissolved Fe(III) and Fe(III)-containing minerals.

Quantitative evaluation and mechanism analysis of soil chemical factors affecting rice yield in saline-sodic paddy fields

Salinization and sodication have become an important abiotic stress affecting soil fertility and crop production in the western of the Songnen Plain in Northeast China. And rice cultivation is considered as one of the most effective biological methods to reclaim saline-sodic soils and ensure food security. However, it is difficult to select the optimal measures to regulate rice growth for increasing yield, because the independent and comprehensive influences of the soil limitation factors on rice yield are not quantitatively evaluated. In this study, the hierarchical partitioning (HP) and the structural equation model (SEM) were used to quantitatively evaluate the influences of salinization parameters, salt ion concentrations and soil nutrients to identify the dominant limitation factors and obstacle mechanism for rice yield. The results showed that soil pH was the key index in salinization parameters, [CO32- + HCO3-] was the key index in salt ion concentrations and available nitrogen (AN) was the key index in soil nutrients to impact rice yield, which independent influences reached 53.7 %, 45.4 % (negative) and 53.2 % (positive), respectively. Soil pH was determined by [CO32- + HCO3-], and the negative effect of alkali stress on rice yield mainly caused by [CO32- + HCO3-] was greater than that of salt stress mainly caused by [Na+] in saline-sodic paddy fields. Among the soil chemical factors, soil pH and AN were the most important explanatory variables of rice yield in saline-sodic paddy fields, which standardized total effects were - 0.32 and 0.40, respectively. Furthermore, the AN showed a more significant negative correlation with soil pH and a higher yield-increasing potential in severe saline-sodic soils (9 ≤ pH < 10) than that in moderate saline-sodic soils (8 ≤ pH < 9). Therefore, decreasing [CO32- + HCO3-] and increasing the content of AN are key to improve rice yield in saline-sodic paddy fields.

Mitigating nitrogen losses with almost no crop yield penalty during extremely wet years

Climate change-induced precipitation anomalies during extremely wet years (EWYs) result in substantial nitrogen losses to aquatic ecosystems (Nw). Still, the extent and drivers of these losses, and effective mitigation strategies have remained unclear. By integrating global datasets with well-established crop modeling and machine learning techniques, we reveal notable increases in Nw, ranging from 22 to 56%, during historical EWYs. These pulses are projected to amplify under the SSP126 (SSP370) scenario to 29 to 80% (61 to 120%) due to the projected increases in EWYs and higher nitrogen input. We identify the relative precipitation difference between two consecutive years (diffPr) as the primary driver of extreme Nw. This finding forms the basis of the CLimate Extreme Adaptive Nitrogen Strategy (CLEANS), which scales down nitrogen input adaptively to diffPr, leading to a substantial reduction in extreme Nw with nearly zero yield penalty. Our results have important implications for global environmental sustainability and while safeguarding food security.

Immobilization of zinc and cadmium by biochar-based sulfidated nanoscale zero-valent iron in a co-contaminated soil: Performance, mechanism, and microbial response

Mining and smelting of mineral resources causes excessive accumulation of potentially toxic metals (PTMs) in surrounding soils. Here, biochar-based sulfidated nanoscale zero-valent iron (SNZVI/BC) was designed via a one-step liquid phase reduction method to immobilize cadmium (Cd) and zinc (Zn) in a copolluted arable soil. A 60 d soil incubation experiment revealed that Cd and Zn immobilization efficiency by 6 % SNZVI/BC (25.2-26.2 %) was higher than those by individual SNZVI (13.9-18.0 %) or biochar (14.0-19.3 %) based on the changes in diethylene triamine pentaacetic acid (DTPA)-extractable PTM concentrations in soils, exhibiting a synergistic effect. Cd2+ or Zn2+ replaced isomorphously Fe2+ in amorphous ferrous sulfide, as revealed by XRD, XPS, and high-resolution TEM-EDS, forming metal sulfide precipitates and thus immobilizing PTMs. PTM immobilization was further enhanced by adsorption by biochar and oxidation products (Fe2O3 and Fe3O4) of SNZVI via precipitation and surface complexation. SNZVI/BC also increased the concentration of dissolved organic carbon and soil pH, thus stimulating the abundances of beneficial bacteria, i.e., Bacilli, Clostridia, and Desulfuromonadia. These functional bacteria further facilitated microbial Fe(III) reduction, production of ammonium and available potassium, and immobilization of PTMs in soils. The predicted function of the soil microbial community was improved after supplementation with SNZVI/BC. Overall, SNZVI/BC could be a promising functional material that not only immobilized PTMs but also enhanced available nutrients in cocontaminated soils.

Plant breeding for harmony between sustainable agriculture, the environment, and global food security: an era of genomics-assisted breeding

MAIN CONCLUSION

Genomics-assisted breeding represents a crucial frontier in enhancing the balance between sustainable agriculture, environmental preservation, and global food security. Its precision and efficiency hold the promise of developing resilient crops, reducing resource utilization, and safeguarding biodiversity, ultimately fostering a more sustainable and secure food production system. Agriculture has been seriously threatened over the last 40 years by climate changes that menace global nutrition and food security. Changes in environmental factors like drought, salt concentration, heavy rainfalls, and extremely low or high temperatures can have a detrimental effects on plant development, growth, and yield. Extreme poverty and increasing food demand necessitate the need to break the existing production barriers in several crops. The first decade of twenty-first century marks the rapid development in the discovery of new plant breeding technologies. In contrast, in the second decade, the focus turned to extracting information from massive genomic frameworks, speculating gene-to-phenotype associations, and producing resilient crops. In this review, we will encompass the causes, effects of abiotic stresses and how they can be addressed using plant breeding technologies. Both conventional and modern breeding technologies will be highlighted. Moreover, the challenges like the commercialization of biotechnological products faced by proponents and developers will also be accentuated. The crux of this review is to mention the available breeding technologies that can deliver crops with high nutrition and climate resilience for sustainable agriculture.

Microbial biogeochemical cycling reveals the sustainability of the rice-crayfish co-culture model

Aquaculture has great potential in nourishing the global growing population, while such staggering yields are coupled with environmental pollution. Rice-crayfish co-culture models (RCFP) have been widely adopted in China due to their eco-friendliness. However, little is known about RCFP's microbiome pattern, which hinders our understanding of its sustainability. This study has conducted metagenomic analysis across aquaculture models and habitats, which revealed aquaculture model-specific biogeochemical cycling pattern (e.g., nitrogen (N), sulfur (S), and carbon (C)): RCFP is advantageous in N-assimilation, N-contamination, and S-pollutants removal, while non-RCFP features N denitrification process and higher S metabolism ability, producing several hazardous pollutants in non-RCFP (e.g., nitric oxide, nitrogen monoxide, and sulfide). Moreover, RCFP has greater capacity for carbohydrate enzyme metabolism compared with non-RCFP in environmental habitats, but not in crayfish gut. Collectively, RCFP plays an indispensable role in balancing aquaculture productivity and environmental protection, which might be applied to the blue transformation of aquaculture.

Integrated transcriptomic analysis identifies coordinated responses to nitrogen and phosphate deficiency in rice

Nitrogen (N) and phosphorus (P) are two primary components of fertilizers for crop production. Coordinated acquisition and utilization of N and P are crucial for plants to achieve nutrient balance and optimal growth in a changing rhizospheric nutrient environment. However, little is known about how N and P signaling pathways are integrated. We performed transcriptomic analyses and physiological experiments to explore gene expression profiles and physiological homeostasis in the response of rice (Oryza sativa) to N and P deficiency. We revealed that N and P shortage inhibit rice growth and uptake of other nutrients. Gene Ontology (GO) analysis of differentially expressed genes (DEGs) suggested that N and Pi deficiency stimulate specific different physiological reactions and also some same physiological processes in rice. We established the transcriptional regulatory network between N and P signaling pathways based on all DEGs. We determined that the transcript levels of 763 core genes changed under both N or P starvation conditions. Among these core genes, we focused on the transcription factor gene NITRATE-INDUCIBLE, GARP-TYPE TRANSCRIPTIONAL REPRESSOR 1 (NIGT1) and show that its encoded protein is a positive regulator of P homeostasis and a negative regulator of N acquisition in rice. NIGT1 promoted Pi uptake but inhibited N absorption, induced the expression of Pi responsive genes PT2 and SPX1 and repressed the N responsive genes NLP1 and NRT2.1. These results provide new clues about the mechanisms underlying the interaction between plant N and P starvation responses.

Hydrogen sulfide and nitric oxide regulate the adaptation to iron deficiency through affecting Fe homeostasis and thiol redox modification in Glycine max seedlings

Iron (Fe) is a vital microelement required for the growth and development of plants. Hydrogen sulfide (H₂S) and nitric oxide (NO), as messenger molecules, participated in the regulation of plant physiological processes. Here, we studied the interaction effects of H₂S and NO on the adaptation to Fe deficiency in Glycine max L. Physiological, biochemical and molecular approaches were conducted to analyze the role of H₂S and NO in regulating the adaptation to Fe deficiency in soybean. We found that H₂S and NO had obvious rescuing function on the Fe deficiency-induced the plant growth inhibition, which was significantly correlated with the increase in Fe content in the leaves, stems, and roots of soybean. Meanwhile, H⁺-flux, ferric chelate reductase (FCR) activity, and root apoplast Fe content were significantly affected by H₂S and NO. Under Fe deficiency conditions NO and H₂S regulated the expression of genes related to Fe homeostasis. Moreover, photosynthesis (Pn) and photosystem II (PSII) efficiency were enhanced by H₂S and NO, and thiol redox modification was important for regulating the adaptation of Fe deficiency. The aforementioned affirmative influences caused by H₂S and NO were also totally reversed by cPTIO (a NO scavenger). Our results suggested that H₂S might act upstream of NO in response to Fe deficiency by affecting the Fe homeostasis enzyme activities and gene expression, and by promoting Fe accumulation in plant tissues as well as by enhancing thiol redox modification and photosynthesis in soybean plants.

Synergistic effects of nitrogen metabolites on auxin regulating plant growth and development

Nitrogen is one of the important nutrients required for plant growth and development. There is increasing evidences that almost all types of nitrogen metabolites affect, at least to some extent, auxin content and/or signaling in plants, which in turn affects seed germination, plant root elongation, gravitropism, leaf expansion and floral transition. This opinion focuses on the roles of nitrogen metabolites, NO 3 - , NH 4 + , tryptophan and NO and their synergistic effects with auxin on plant growth and development. Nitrate reductase (NR) converts nitrate into nitrite, and was roughly positive-correlated with the root auxin level, suggesting a crosstalk between nitrate signaling and auxin signaling. Abscisic Acid Responsive Element Binding Factor 3 (AFB3) and Tryptophan Aminotransferase of Arabidopsis 1 (TAA1) are also the key enzymes involved in nitrogen metabolite-regulated auxin biosynthesis. Recent advances in the crosstalk among NO 3 - , NH 4 + , tryptophan and NO in regulation to NR, AFB3 and TAA1 are also summarized.

Impact of Cadmium Stress on Growth and Physio-Biochemical Attributes of Eruca sativa Mill

Plants may experience adverse effects from Cadmium (Cd). As a result of its toxicity and mobility within the soil-plant continuum, it is attracting the attention of soil scientists and plant nutritionists. In this study, we subjected young Eruca sativa Mill. seedlings to different levels of Cd applications (0, 1.5, 6 and 30 µmol/L) via pot experiment to explore its morpho-physio-biochemical adaptations. Our results revealed a significant Cd accumulation in leaves at high Cd stress. It was also demonstrated that Cd stress inhibited photosynthetic rate and pigment levels, ascorbate peroxidase (APX), guaiacol peroxidase (GPX), catalase (CAT), and superoxide dismutase (SOD) enzyme activities, and increased malondialdehyde (MDA) levels. Conversely, the concentration of total ascorbate (TAS) increased at all levels of Cd application, whereas that of ascorbic acid (ASA), and dehydroascorbate (DHA) increased at 1.5 (non-significant), 6, 30 and 6 µmol/L (significant), though their concentrations decreased non-significantly at 30 µmol/L application. In conclusion, Cd-subjected E. sativa seedlings diverted much energy from growth towards the synthesis of anti-oxidant metabolites and osmolytes. However, they did not seem to have protected the E. sativa seedlings from Cd-induced oxidative stress, causing a decrease in osmotic adjustment, and an increase in oxidative damage, which resulted in a reduction in photosynthesis and growth. Accordingly, we recommend that the cultivation of E. sativa should be avoided on soil with Cd contamination.

Genome-wide identification of apple PPI genes and a functional analysis of the response of MxPPI1 to Fe deficiency stress

Iron (Fe) deficiency affects plant growth and development. The proton pump interactor (PPI) in plants responds to multiple abiotic stresses, although it has not been well characterized under Fe deficiency stress. In this study, we systematically identified and analyzed the PPI gene family in apple. Three PPI candidate genes were found, and they contained 318-1349 amino acids and 3-7 introns. Under Fe deficiency stress, we analyzed the expression of all the PPI genes in roots of apple rootstock Malus xiaojinensis. Expression of the gene MD11G1247800, designated PPI1, is obviously induced by Fe deficiency treatment in M. xiaojinensis. We first cloned MxPPI1 from M. xiaojinensis and determined its subcellular localization, which indicated that it is localized in the cell membrane and nucleus in tobacco. We found that the level of expression of the MxPPI1 protein increased significantly under Fe deficiency stress in apple calli. Moreover, overexpressing MxPPI1 in apple calli enhanced the activities of ferric chelate reductase and H⁺-ATPase, H⁺ secretion, MxHA2 gene expression and total Fe content when compared with the wild type calli. We further found that MxPPI1 interacted with MxHA2 using bimolecular fluorescence complementation and luciferase complementation assays. Overall, we demonstrated that MxPPI1 interacts with MxHA2 to enhance the activity of H⁺-ATPase to regulate Fe absorption in M. xiaojinensis.

Flooding-induced rhizosphere Clostridium assemblage prevents root-to-shoot cadmium translocation in rice by promoting the formation of root apoplastic barriers

Water managements are the most effective agricultural practices for restraining cadmium (Cd) uptake and translocation in rice, which closely correlated with rhizosphere assembly of beneficial microbiome. However, the role of the assemblage of specific microbiota in controlling root-to-shoot Cd translocation in rice remains scarcely clear. The aim of this study was to ascertain how water managements shaped rhizosphere microbiome and mediated root-to-shoot Cd translocation. To disentangle the acting mechanisms of water managements, we performed an experiment monitoring Cd uptake and transport in rice and changes in soil microbial communities in response to continuously flooding and moistening irrigation. Continuously flooding changed rhizosphere microbial communities, leading to the increased abundance of anaerobic bacteria such as Clostridium populations. Weighted gene co-expression network analysis (WGCNA) showed that a dominant OTU163, corresponding to Clostridium sp. CSP1, exhibited a strong negative correlation with root-to-shoot Cd translocation. An integrated analysis of transcriptome and metabolome further indicated that the Clostridium-secreted butyric acid was involved in the regulation of phenylpropanoid pathway in rice roots. The formation of endodermal suberized barriers and lignified xylems was remarkably enhanced in the Clostridium-treated roots, which led to more Cd retained in root cell wall and less Cd in the xylem sap. Collectively, our results indicate that the development of root apoplastic barriers can be orchestrated by beneficial Clostridium strains that are assembled by host plants grown under flooding regime, thereby inhibiting root-to-shoot Cd translocation.

Ethylene positively regulates Cd tolerance via reactive oxygen species scavenging and apoplastic transport barrier formation in rice

Ethylene regulates plant root growth and resistance to environment stress. However, the role and mechanism of ethylene signaling in response to Cd stress in rice remains unclear. Here, we revealed that ethylene signaling plays a positive role in the resistance of rice to Cd toxicity. Blocking the ethylene signal facilitated root elongation under normal conditions, but resulted in severe oxidative damage and inhibition of root growth under Cd stress. Conversely, ethylene signal enhancement by EIN2 overexpression caused root bending, similar to the response of roots to Cd stress, and displayed higher Cd tolerance than the wildtype (WT) plants. Comparative transcriptome analysis indicated EIN2-mediated upregulation of genes involved in flavonoid biosynthesis and peroxidase activity under Cd stress. The synthesis of phenolic acids and flavonoids were positively regulated by ethylene. Thus, the ein2 (ethylene insensitive 2) mutants displayed lower ROS scavenging capacity than the WT. Moreover, a significant increase in Cd accumulation and relatively increased apoplastic flow were observed in the root apex of the ein2 mutant compared with the WT plants. Overall, EIN2-mediated Cd resistance in rice is mediated by the upregulation of flavonoid biosynthesis and peroxidase activity to induce ROS scavenging, and apoplastic transport barrier formation reduces Cd uptake.

Combined amendment improves soil health and Brown rice quality in paddy soils moderately and highly Co-contaminated with Cd and As

In situ remediation technology applied aims to not only decrease cadmium (Cd) and arsenic (As) uptake by rice but also improve soil health and rice quality in contaminated paddy soils. Here the effects of a combined amendment, consisting of limestone, iron powder, silicon fertilizer, and calcium-magnesium-phosphate fertilizer, with three application rates (0, 450, and 900 g m^-2) on soil health, rice root system, and brown rice quality were compared in moderately versus highly Cd and As co-contaminated paddy fields. After the amendment application, soil pH, cation exchange capacity, four kinds of soil enzyme activities increased (sucrase, urease, acid phosphatase, and catalase), and concentrations of leached Cd/As decreased, as measured by the DTPA (diethylene triamine pentaacetic acid) and TCLP (toxicity characteristic leaching procedure). Changes in the above soil indicators promoted soil health. In both fields, the dithionite-citrate-bicarbonate (DCB)-Fe and DCB-Mn concentration in iron plaque increased and root length became longer. Changes in the above root system indicators reduced the root system's absorption of Cd and As but increased that of nutrients. Under 900 g m^-2 treatment, the Cd concentration in brown rice of two sites decreased by 55.8% and 28.9%, likewise inorganic As (iAs) decreased by 50.0% and 21.1%, whereas essential amino acids increased by 20.4% and 20.0%, respectively. Furthermore, the Cd and iAs concentrations in brown rice were <0.2 mg kg^-1 (maximum contaminant level of Cd and iAs in the Chinese National Food Safety Standards GB2762-2017 for brown rice) under the 900 g m^-2 in the moderately contaminated field. These results suggest the combined amendment can improve soil health and brown rice quality in the moderately and highly Cd- and As-co-contaminated paddy soils, offering potential eco-friendly and efficient remediation material for applications in such polluted paddy soils.

Shade Avoidance 3 Mediates Crosstalk Between Shade and Nitrogen in Arabidopsis Leaf Development

After nitrogen treatments, plant leaves become narrower and thicker, and the chlorophyll content increases. However, the molecular mechanisms behind these regulations remain unknown. Here, we found that the changes in leaf width and thickness were largely compromised in the shade avoidance 3 (sav3) mutant. The SAV3 gene encodes an amino-transferase in the auxin biosynthesis pathway. Thus, the crosstalk between shade and nitrogen in Arabidopsis leaf development was investigated. Both hypocotyl elongation and leaf expansion promoted by the shade treatment were reduced by the high-N treatment; high-N-induced leaf narrowing and thickening were reduced by the shade treatment; and all of these developmental changes were largely compromised in the sav3 mutant. Shade treatment promoted SAV3 expression, while high-N treatment repressed SAV3 expression, which then increased or decreased auxin accumulation in cotyledons/leaves, respectively. SAV3 also regulates chlorophyll accumulation and nitrogen assimilation and thus may function as a master switch responsive to multiple environmental stimuli.

Transcriptome Differences in Response Mechanisms to Low-Nitrogen Stress in Two Wheat Varieties

Nitrogen plays a crucial role in wheat growth and development. Here, we analyzed the tolerance of wheat strains XM26 and LM23 to low-nitrogen stress using a chlorate sensitivity experiment. Subsequently, we performed transcriptome analyses of both varieties exposed to low-nitrogen (LN) and normal (CK) treatments. Compared with those under CK treatment, 3534 differentially expressed genes (DEGs) were detected in XM26 in roots and shoots under LN treatment (p < 0.05, and |log2FC| > 1). A total of 3584 DEGs were detected in LM23. A total of 3306 DEGs, including 863 DEGs in roots and 2443 DEGs in shoots, were specifically expressed in XM26 or showed huge differences between XM26 and LM23 (log2FC ratio > 3). These were selected for gene ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses. The calcium-mediated plant–pathogen interaction, MAPK signaling, and phosphatidylinositol signaling pathways were enriched in XM26 but not in LM23. We also verified the expression of important genes involved in these pathways in the two varieties using qRT-PCR. A total of 156 transcription factors were identified among the DEGs, and their expression patterns were different between the two varieties. Our findings suggest that calcium-related pathways play different roles in the two varieties, eliciting different tolerances to low-nitrogen stress.

Two NPF transporters mediate iron long-distance transport and homeostasis in Arabidopsis

Iron (Fe) transport and reallocation are essential to Fe homeostasis in plants, but it is unclear how Fe homeostasis is regulated, especially under stress. Here we report that NPF5.9 and its close homolog NPF5.8 redundantly regulate Fe transport and reallocation in Arabidopsis. NPF5.9 is highly upregulated in response to Fe deficiency. NPF5.9 expresses preferentially in vasculature tissues and localizes to the trans-Golgi network, and NPF5.8 showed a similar expression pattern. Long-distance Fe transport and allocation into aerial parts was significantly increased in NPF5.9-overexpressing lines. In the double mutant npf5.8 npf5.9, Fe loading in aerial parts and plant growth were decreased, which were partially rescued by Fe supplementation. Further analysis showed that expression of PYE, the negative regulator for Fe homeostasis, and its downstream target NAS4 were significantly altered in the double mutant. NPF5.9 and NPF5.8 were shown to also mediate nitrate uptake and transport, although nitrate and Fe application did not reciprocally affect each other. Our findings uncovered the novel function of NPF5.9 and NPF5.8 in long-distance Fe transport and homeostasis, and further indicated that they possibly mediate nitrate transport and Fe homeostasis independently in Arabidopsis.

Inhibition of nitric oxide production under alkaline conditions regulates iron homeostasis in rice

Rice is one of the most susceptible plants to iron (Fe) deficiency under neutral and alkaline conditions. Alkaline stress induces H₂ O₂ production and increases the deposition of Fe on the root surface, which causes leaf chlorosis and Fe deficiency in rice. Gene chip and qRT-PCR analysis indicated that the expression of the nitrate reductase (NR) genes were downregulated by alkaline treatment, which resulted in significantly decreased nitrate activity and nitric oxide (NO) production in the epidermis and stele, where H₂ O₂ accumulated. In contrast, treatment with sodium nitroprusside (SNP), a NO donor, strongly alleviated alkaline-induced Fe deficiency by limiting Fe plaque formation. Increasing the NO signal significantly reduced the accumulation of H₂ O₂ and the lignin barrier but enhanced phenolic acid secretion in the root epidermis and stele under alkaline conditions. The secreted phenolic acid effectively mobilized the apoplast Fe and increased Fe uptake in roots, thereby alleviating the Fe-deficiency response and downregulating the expressions of Fe-uptake genes under alkaline conditions. In conclusion, alkaline stress inhibits NR activity and NO production in the roots of rice, which play vital roles in the mobilization of the apoplast Fe by regulation of H₂ O₂ and phenolic acid concentrations.

Effects of cadmium stress on growth and physiological characteristics of sassafras seedlings

The effects of cadmium stress on the growth and physiological characteristics of Sassafras tzumu Hemsl. were studied in pot experiments. Five Cd levels were tested [CT(Control Treatment) : 0 mg/kg, Cd5: 5 mg/kg, Cd20: 20 mg/kg, Cd50: 50 mg/kg, and Cd100: 100 mg/kg]. The growth and physiological characteristics of the sassafras seedlings in each level were measured. The results showed that soil Cd had negative influences on sassafras growth and reduced the net growth of plant height and the biomass of leaf, branch and root. Significant reductions were recorded in root biomass by 18.18%(Cd5), 27.35%(Cd20), 27.57%(Cd50) and 28.95%(Cd100). The contents of hydrogen peroxide decreased first then increased while malondialdehyde showed the opposite trend with increasing cadmium concentration. Decreases were found in hydrogen peroxide contents by 10.96%(Cd5), 11.82%(Cd20) and 7.02%(Cd50); increases were found in malondialdehyde contents by 15.47%(Cd5), 16.07%(Cd20) and 7.85%(Cd50), indicating that cadmium stress had a certain effect on the peroxidation of the inner cell membranes in the seedlings that resulted in damage to the cell membrane structure. Superoxide dismutase activity decreased among treatments by 17.05%(Cd5), 10,68%(Cd20), 20.85%(Cd50) and 8.91%(Cd100), while peroxidase activity increased steadily with increasing cadmium concentration; these results suggest that peroxidase is likely the main protective enzyme involved in the reactive oxygen removal system in sassafras seedlings. Upward trends were observed in proline content by 90.76%(Cd5), 74.36%(Cd20), 99.73%(Cd50) and 126.01%(Cd100). The increase in proline content with increasing cadmium concentration indicated that cadmium stress induced proline synthesis to resist osmotic stress in the seedlings. Compared to that in CT, the soluble sugar content declined under the different treatments by 32.84%(Cd5), 5.85%(Cd20), 25.55%(Cd50) and 38.69%(Cd100). Increases were observed in the soluble protein content by 2.34%(Cd5), 21.36%(Cd20), 53.15%(Cd50) and 24.22%(Cd100). At different levels of cadmium stress, the chlorophyll content in the seedlings first increased and then decreased, and it was higher in the Cd5 and Cd20 treatments than that in the CT treatment. These results reflected that cadmium had photosynthesis-promoting effects at low concentrations and photosynthesis-suppressing effects at high concentrations. The photosynthetic gas exchange parameters and photosynthetic light-response parameters showed downward trends with increasing cadmium concentration compared with those in CT; these results reflected the negative effects of cadmium stress on photosynthesis in sassafras seedlings.

How intercropping and mixed systems reduce cadmium concentration in rice grains and improve grain yields

Ecological theories can be applied to improve agricultural sustainability. In our study, a core hypothesis behind this claim is that "selfish behaviour" of rice cultivars results in "aversion" to a toxic substance in a multi-cropping system. We studied Changliangyou 772, a low-cadmium rice cultivar, cultivated with 11 different rice cultivars in intercropping and mixed systems. Rice cultivars with medium grain yield, ranging from 25 to 45 g plant^-1, had distinctly higher yields in mixtures. Rice varieties with lower grain cadmium concentrations in monocultures had greater reductions in grain cadmium in the mixtures. In the intercropping systems, the yields of Changliangyou 772 were positively correlated with those of the neighbouring rice cultivars, while the grain cadmium showed a negative correlation with the grain cadmium of intercrops in the monocultures. The neighbouring cultivars with low grain cadmium concentrations in the intercropping showed higher cadmium concentrations in the monocultures. The intercropping and mixtures reduced the grain cadmium in two ways: 1) they increased the soil pH, resulting in lower cadmium bioavailability; and 2) they enhanced the iron plaque (Ip). However, a high Ip or cadmium concentration that was too high in the Ip weakened the Ip to block cadmium uptake by the roots.

Water management increased rhizosphere redox potential and decreased Cd uptake in a low-Cd rice cultivar but decreased redox potential and increased Cd uptake in a high-Cd rice cultivar under intercropping

Excessive Cd in crop grains is toxic to humans. We conducted a field experiment to investigate the effects of intercropping on rice yield and grain Cd content as well as a pot experiment to compare the rhizosphere redox potentials of low-Cd 'Zhuliangyou 189' and the neighboring high-Cd 'Changxianggu' that mediated Cd uptake in a flooded or a ridge-furrow system. In the field experiment, Cd removal from contaminated soil in intercropping was 1.44 times higher than that in monoculture of Zhuliangyou 189. In both Zhuliangyou 189 and Changxianggu, intercropping improved the grain yield and decreased grain Cd content. In the pot experiment, Fe plaque amount was strongly and positively correlated with bulk soil Fe(II) content, root H₂O₂ concentration, and Fe(II)-oxidizing ability of root bacteria but negatively correlated with Fe(II)-oxidizing ability of bulk soil bacteria and root Cd content. In Zhuliangyou 189, intercropping increased root H₂O₂ concentration, rhizosphere redox potential, iron plaque amount but decreased Cd bioavailability, Fe(II)-oxidizing ability of bulk soil bacteria, and organ Cd content. In the flooded system, Zhuliangyou 189 showed higher bulk soil Fe(II) content than Changxianggu. In the ridge-furrow system, ridges decreased the Fe(II)-oxidizing ability of root and bulk soil bacteria, thereby decreasing Fe plaque amount and increasing organ Cd content of rice. In both monoculture and intercropping systems, rice cultivars planted on ridges showed higher Cd bioavailability and lower bulk boil Fe(II) content than those planted in furrows.

Direct and Bicarbonate-Induced Iron Deficiency Differently Affect Iron Translocation in Kiwifruit Roots

Bicarbonate-induced iron (Fe) deficiency (+Bic) is frequently observed in kiwifruit orchards, but more research attention has been paid to direct Fe deficiency (-Fe) in plants, including kiwifruit. Here we compared the differences of kiwifruit plants between -Fe and +Bic in: (1) the traits of ⁵⁷Fe uptake and translocation within plants, (2) Fe forms in roots, and (3) some acidic ions and metabolites in roots. The concentration of ⁵⁷Fe derived from nutrient solution (⁵⁷Fedfs) in roots was less reduced in +Bic than -Fe treatment, despite similar decrease in shoots of both treatments. +Bic treatment increased ⁵⁷Fedfs distribution in fine roots but decreased it in new leaves and stem, thereby displaying the inhibition of ⁵⁷Fedfs translocation from roots to shoots and from fine roots to xylem of coarse roots. Moreover, +Bic imposition induced the accumulation of water-soluble Fe and apoplastic Fe in roots. However, the opposite was observed in -Fe-treated plants. Additionally, the cell wall Fe and hemicellulose Fe in roots were less reduced by +Bic than -Fe treatment. +Bic treatment also triggered the reduction in H⁺ extrusion and the accumulation of NH₄⁺, succinic acid, and some amino acids in roots. These results suggest that, contrary to -Fe, +Bic treatment inhibits Fe translocation to shoots by accumulating water-soluble and apoplastic Fe and slowing down the release of hemicellulose Fe in the cell wall in kiwifruit roots, which may be related to the decreased H⁺ extrusion and the imbalance between C and N metabolisms.

Effects of carbide slag, lodestone and biochar on the immobilization, plant uptake and translocation of As and Cd in a contaminated paddy soil

The contamination of arsenic (As) and cadmium (Cd) in paddy soils is widely reported and these two metals are difficult to be co-remediated due to the contrasting chemical behaviors. This poses a challenge to simultaneously decrease their availability in soil and accumulation in rice via immobilization by amendments, especially in in-situ fields. This study compared the effects of carbide slag, lodestone and biochar on the bioavailability of As and Cd in soil and their accumulation in rice tissues and root Fe-Mn plaque at tillering and mature stages in a paddy field. The addition of three amendments significantly limited the mobilization of As and Cd in soil and decreased their accumulations in brown rice by 30-52% and 9-21%, respectively. Carbide slag was most whereas lodestone least effective in As and Cd immobilization in the tested contaminated soils. Community Bureau of Reference (BCR) sequential extraction analysis showed that the amendments changed the forms of As and Cd to less-available. Activated functional groups of the amendments (e.g. -OH, C-O, OC-O, OH^- and CO₃^2-) sequestered metals by precipitation, adsorption, ion exchange or electrostatic attributes contributed greatly to the As and Cd immobilization in soil. Furthermore, the amendments promoted the formation of Fe-Mn plaque in rice roots, which further limited the mobility of As and Cd in soil and prevented their transport from soil to rice roots. The application of carbide slag and biochar but not lodestone increased rice yield compared to the unamended control, indicating their applicability in situ remediation. Our study gives a strong reference to select immobilizing amendments for food safe production in co-contaminated paddy soils.

Transcriptomic comparison reveals modifications in gene expression, photosynthesis, and cell wall in woody plant as responses to external pH changes

Soil acidification is one of the crucial global environmental problems, affecting sustainable land use, crop yield, and ecosystem stability. Previous research reported the tolerance of crops to acid soil stress. However, the molecular response of woody plant to acid conditions remains largely unclear. Rhododendron L. is a widely distributed woody plant genus and prefers to grow in acidic soils. Herein, weighted gene coexpression network analysis was performed on R. protistum var. giganteum seedlings subjected to five pH treatments (3.5, 4.5, 5.5, 6.0, 7.0), and their ecophysiological characteristics were determined for the identification of their molecular responses to acidic environments. Through pairwise comparison, 855 differentially expressed genes (DEGs) associated with photosynthesis, cell wall, and phenylpropanoid metabolism were identified. Most of the DEGs related to photosynthesis and cell wall were up-regulated after pH 4.5 treatment. Results implied that the species improves its photosynthetic abilities and changes its cell wall characteristics to adapt to acidic conditions. Weighted gene co-expression network analyses showed that most of the hub genes were annotated to the biosynthetic pathways of ribosomal proteins and photosynthesis. Expression pattern analysis showed that genes encoding subunit ribosomal proteins decreased at pH 7.0 treatment, suggesting that pH 7.0 treatment led to cell injury in the seedlings. The species regulates protein synthesis in response to high pH stress (pH 7.0). The present study revealed the molecular response mechanism of woody plant R. protistum var. giganteum to acid environments. These findings can be useful in enriching current knowledge of how woody species adapt to soil acidification under global environmental changes.

Ethylene Response Factors MbERF4 and MbERF72 Suppress Iron Uptake in Woody Apple Plants by Modulating Rhizosphere pH

Iron (Fe) deficiency limits the yield of fruit trees. When subjected to Fe deficiency, H+ secretion increases in the rhizosphere of dicotyledonous plants and pH decreases. This leads to the acidification of the soil and promotes Fe3+ to Fe2+ conversion, which plants can better uptake. This study investigated the relationship between two inhibitory transcription factors (ethylene response factors MbERF4 and MbERF72) and the H+-ATPase gene MbHA2. Two species of apple woody plants were studied: the Fe-inefficient Malus baccata and the Fe-efficient Malus xiaojinensis. Yeast one-hybrid and electrophoretic mobility shift assays showed that both MbERF4 and MbERF72 bind to the GCC cassette (AGCCGCC) of the MbHA2 promoter. Moreover, yeast two-hybrid and bimolecular fluorescence complementation assays showed that MbERF4 interacts with MbERF72. Furthermore, β-glucuronidase and luciferase reporter assays showed that the MbERF4- and MbERF72-induced repression of MbHA2 expression is synergistic. Virus-induced gene silencing of MbERF4 or MbERF72 increased MbHA2 expression, and thus lowered the rhizosphere pH in M. baccata. Consequently, the high expressions of MbERF4 and MbERF72 induced by Fe deficiency contributed to the Fe sensitivity of M. baccata. Moreover, the low expressions of MxERF4 and MxERF72 contributed to the Fe-deficiency tolerance of M. xiaojinensis via different binding conditions to the HA2 promoter. In summary, this study identified the relationship of two inhibitory transcription factors with the H+-ATPase gene and proposed a model in which ERF4 and ERF72 affect the rhizosphere pH in response to Fe deficiency.

A Comparative Assessment of Measures of Leaf Nitrogen in Rice Using Two Leaf-Clip Meters

Accurate estimation and monitoring of crop nitrogen can assist in timely diagnosis and facilitate necessary technical support for fertilizer management. Four experiments, involving three cultivars and six nitrogen (N) treatments, were conducted in southeast China to compare the two leaf-clip meters (Dualex 4 Scientific+, Force-A, Orasy, France; Soil and Plant Analyzer Development (SPAD) meter, Minolta Camera Co., Osaka, Japan) for their ability to measure nitrogen nutrient-related indicators. The results indicated that Chl had a better monitoring accuracy for chlorophyll in per unit leaf area as compared to SPAD value, and there was no saturation to appear under high leaf chlorophyll concentration status. Flavonoids (Flav) presented the advantage of early diagnosis of rice N nutrition status (about one day as compared to SPAD value). As a reliable N nutrient diagnosis indicator, it also improved the estimation accuracy compared with the classical SPAD-based method. The other Dualex value also obtained good monitoring results. Flav was positively correlated with N deficiency, and with higher R2 in panicle initiation and booting stages with low RMSE, respectively; whereas SPAD value was negatively correlated with nitrogen deficiency. Therefore, the Flav-based nitrogen application model was found to provide an early rice nitrogen fertilizer application approach, especially in the panicle initiation and booting stages.

Comparison of Cd subcellular distribution and Cd detoxification between low/high Cd-accumulative rice cultivars and sea rice

Salt-tolerant rice cultivar (sea rice) is a research hotspot worldwide due to its high yield in high salinity soil. However, knowledge regarding the cadmium (Cd) effects on the growth of sea rice is limited. To determine the short-term and long-term impact of Cd stress, relatively low/high Cd-accumulative rice cultivars and sea rice were grown to compare their growth responses to Cd stress over time. The results showed that sea rice presented the highest Cd concentrations in the root, stem, and leaves under 32-days of Cd stress. Cd stress shortened and thickened the rice root, and decreased the proportion of root diameters in the 0-0.2 mm range. Cd stress remarkably increased the Cd and Fe concentration in dithionite-citrate-bicarbonate (DCB) extracts, and the DCB-Cd and DCB-Fe concentrations were the highest in sea rice. The subcellular distribution of Cd in the rice roots indicated that Cd accumulated the most in the soluble fraction and cell wall. The contents of pectin and hemicellulose 2 in the root cell wall of the low-Cd accumulative rice variety CL755 were higher than those in MXZ and sea rice. Collectively, this work provides a general understanding of the Cd effects on sea rice growth and indicates that sea rice has a relatively high Cd accumulation compared with the other two rice cultivars. However, the specifically-related mechanism remains to be further studied.

Assessment of Subcellular ROS and NO Metabolism in Higher Plants: Multifunctional Signaling Molecules

Reactive oxygen species (ROS) and nitric oxide (NO) are produced in all aerobic life forms under both physiological and adverse conditions. Unregulated ROS/NO generation causes nitro-oxidative damage, which has a detrimental impact on the function of essential macromolecules. ROS/NO production is also involved in signaling processes as secondary messengers in plant cells under physiological conditions. ROS/NO generation takes place in different subcellular compartments including chloroplasts, mitochondria, peroxisomes, vacuoles, and a diverse range of plant membranes. This compartmentalization has been identified as an additional cellular strategy for regulating these molecules. This assessment of subcellular ROS/NO metabolisms includes the following processes: ROS/NO generation in different plant cell sites; ROS interactions with other signaling molecules, such as mitogen-activated protein kinases (MAPKs), phosphatase, calcium (Ca²⁺), and activator proteins; redox-sensitive genes regulated by the iron-responsive element/iron regulatory protein (IRE-IRP) system and iron regulatory transporter 1(IRT1); and ROS/NO crosstalk during signal transduction. All these processes highlight the complex relationship between ROS and NO metabolism which needs to be evaluated from a broad perspective.

Metabolic reprogramming in nodules, roots, and leaves of symbiotic soybean in response to iron deficiency

To elucidate the mechanism of adaptation of leguminous plants to iron (Fe)-deficient environment, comprehensive analyses of soybean (Glycine max) plants (sampled at anthesis) were conducted under Fe-sufficient control and Fe-deficient treatment using metabolomic and physiological approach. Our results show that soybeans grown under Fe-deficient conditions showed lower nitrogen (N) fixation efficiency; however, ureides increased in different tissues, indicating potential N-feedback inhibition. N assimilation was inhibited as observed in the repressed amino acids biosynthesis and reduced proteins in roots and nodules. In Fe-deficient leaves, many amino acids increased, accompanied by the reduction of malate, fumarate, succinate, and α-ketoglutarate, which implies the N reprogramming was stimulated by the anaplerotic pathway. Accordingly, many organic acids increased in roots and nodules; however, enzymes involved in the related metabolic pathway (e.g., Krebs cycle) showed opposite activity between roots and nodules, indicative of different mechanisms. Sugars increased or maintained at constant level in different tissues under Fe deficiency, which probably relates to oxidative stress, cell wall damage, and feedback regulation. Increased ascorbate, nicotinate, raffinose, galactinol, and proline in different tissues possibly helped resist the oxidative stress induced by Fe deficiency. Overall, Fe deficiency induced the coordinated metabolic reprogramming in different tissues of symbiotic soybean plants.

Hydrogen peroxide alleviates P starvation in rice by facilitating P remobilization from the root cell wall

Phosphorus (P) deficiency limits rice production. Increasing the remobilization of P stored in the root cell wall is an efficient way to alleviate P starvation in rice. In the current study, we found that the addition of 50 μM H₂O₂ significantly increased soluble P content in rice. H₂O₂ stimulated pectin biosynthesis and increased pectin methylesterase (PME) activity, thus stimulating the release of P from the cell wall in roots. H₂O₂ also regulates internal P homeostasis by increasing the expression of P transporter genes OsPT2, OsPT6, and OsPT8 at different treatment times. In addition, the H₂O₂ treatment increased the expression of nitrate reductase (NR) genes OsNIA1 and OsNIA2 and the activity of NR, then increased the accumulation of nitric oxide (NO) in the rice root. The application of the NO donor sodium nitroprusside (SNP) and the H₂O₂ scavenger 4-hydroxy-TEMPO significantly increased soluble P content by increasing pectin levels and PME activity to enhance the remobilization of P from the cell wall. However, the addition of NO scavenger 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) with and without H₂O₂ had the opposite effect, suggesting that NO functions downstream of H₂O₂ to increase the remobilization of cell wall P in rice.

Characteristics of Free Amino Acids (the Quality Chemical Components of Tea) under Spatial Heterogeneity of Different Nitrogen Forms in Tea (Camellia sinensis) Plants

Nitrogen (N) forms are closely related to tea quality, however, little is known about the characteristics of quality chemical components in tea under the spatial heterogeneity of different N forms. In this study, a split-root system, high performance liquid chromatography (HPLC), and root analysis system (WinRHIZO) were used to investigate free amino acids (FAAs) and root length of tea plants under the spatial heterogeneity of different N forms. Uniform. (U.) ammonium (NH₄⁺) (both compartments had NH₄⁺), U. nitrate (NO₃⁻) (both compartments had NO₃⁻), Split. (Sp.) NH₄⁺ (one of the compartments had NH₄⁺), and Sp. NO₃⁻ (the other compartment had NO₃⁻) were performed. The ranking of total FAAs in leaves were as follows: U. NH₄⁺ > Sp. NH₄⁺/Sp. NO₃⁻ > U. NO₃⁻. The FAA characteristics of Sp. NH₄⁺/Sp. NO₃⁻ were more similar to those of U. NO₃⁻. The contents of the important FAAs (aspartic acid, glutamic acid, and theanine) that determine the quality of tea, increased significantly in U. NH₄⁺. The total root length in U. NH₄⁺ was higher than that in the other treatments. More serious root browning was found in U. NO₃⁻. In conclusion, NH₄⁺ improved the accumulations of FAAs in tea leaves, which might be attributed to the root development.