Rice Organs Research Articles

Molecular Characteristics and Expression Patterns of Carotenoid Cleavage Oxygenase Family Genes in Rice (Oryza sativa L.)

Carotenoid cleavage oxygenases (CCOs) cleave carotenoid molecules to produce bioactive products that influence the synthesis of hormones such as abscisic acid (ABA) and strigolactones (SL), which regulate plant growth, development, and stress adaptation. Here, to explore the molecular characteristics of all members of the OsCCO family in rice, fourteen OsCCO family genes were identified in the genome-wide study. The results revealed that the OsCCO family included one OsNCED and four OsCCD subfamilies. The OsCCO family was phylogenetically close to members of the maize ZmCCO family and the Sorghum SbCCO family. A collinearity relationship was observed between OsNCED3 and OsNCED5 in rice, as well as OsCCD7 and OsNCED5 between rice and Arabidopsis, Sorghum, and maize. OsCCD4a and OsCCD7 were the key members in the protein interaction network of the OsCCO family, which was involved in the catabolic processes of carotenoids and terpenoid compounds. miRNAs targeting OsCCO family members were mostly involved in the abiotic stress response, and RNA-seq data further confirmed the molecular properties of OsCCO family genes in response to abiotic stress and hormone induction. qRT-PCR analysis showed the differential expression patterns of OsCCO members across various rice organs. Notably, OsCCD1 showed relatively high expression levels in all organs except for ripening seeds and endosperm. OsNCED2a, OsNCED3, OsCCD1, OsCCD4a, OsCCD7, OsCCD8a, and OsCCD8e were potentially involved in plant growth and differentiation. Meanwhile, OsNCED2a, OsNCED2b, OsNCED5, OsCCD8b, and OsCCD8d were associated with reproductive organ development, flowering, and seed formation. OsNCED3, OsCCD4b, OsCCD4c, OsCCD8b, and OsCCD8c were related to assimilate transport and seed maturation. These findings provide a theoretical basis for further functional analysis of the OsCCO family.

Dynamics of Fe, Mn, and potentially harmful elements under reducing conditions in iron ore tailings after dam collapse in the Doce River basin-Brazil: flooded and non-flooded rice cultivations.

Potentially harmful element (PHE) bioavailability is important to environmental contamination and must be checked under several soil conditions. This study aimed to assess Fe, Mn, and PHE uptake by rice (Oryza sativa) grown on flooded and non-flooded Fe tailings collected from the Doce River basin after its collapse in Brazil. After 65days of sowing, shoots and roots were harvested to determine PHE concentrations. The mean concentrations of Mn in shoots and Fe in the roots of rice grown on the flooded tailings were 2140mgkg-1 and 15,219mgkg-1, respectively. Mn was extensively translocated from roots to shoots (translocation factor (TF) = 2). Conversely, Fe accumulated in roots (TF = 0.015) and caused morphological damage to this rice organ. The application of macro and micronutrients lessened Fe toxicity in the roots of rice cultivated on the flooded tailings. The flooding of tailings influenced more Fe accumulation than Mn accumulation by rice plants. The PHE Ag, As, Cd, Ni, Hg, Pb, and Sb exhibited low total concentrations (maximum of 9mgkg-1 for Ni and a minimum of 0.2mgkg-1 for Cd, Hg, and Sb), and it was not observed an increase in their availability under tailings flooding conditions.

Gibberellins Regulate Expression of Cyclins to Control Leaf Width in Rice

Leaves are the nutritive organs of rice. Leaf shape influences rice photosynthesis, subsequently impacting yield. Gibberellins, GAs, are important hormones, but the way in which GAs regulate leaf width is largely unknown. This study focuses on the d18 mutant with broader leaves due to defective GA biosynthesis. Statistical analysis indicates broader leaves in the d18 mutant compared to the wild-type group. An examination of leaf cell morphology shows a higher count of secondary vascular bundles in d18 than in the wild-type group. RNA-seq analysis demonstrates significantly higher expression of CYCB (CYCLIN B) and H4 (HISTONE H4) in d18 compared to wild type. In summary, the leaf width of d18 may due to a higher activity of cell division at leaf margin.

Molecular Mechanisms of MADS-box Genes in Regulating Floral Organ Development in Rice

As one of the most important food crops in China and worldwide, the morphological development of floral organs in rice is crucial, directly affecting its yield and quality. The MADS-box gene family significantly influences the development of floral organs in rice (Oryza sativa L.). This paper reviews the ABCDE model of floral organ development and provides an overview of recent advancements in research on MADS-box genes that influence the characteristics of floral organs in rice.

Chilling at grain filling stage reduced rice grain protein content: An experimental and modeling study

Climate change has increased the trend in the intensity of global extreme weather events, including chilling. Nitrogen is one of the most essential nutrients for rice growth and development. Chilling will limit the uptake and translocation of nitrogen and the formation of grain protein in rice plants. The experiment conducted in the climate chamber with chilling stress applied at the grain filling stage revealed different effects on protein concentration in aboveground organs and caused asymmetry in grain protein contents (GPC) and grain protein yield (GPY). Chilling stress applied during the grain filling stage reduced the accumulation rate of rice grain protein by inhibiting the nitrogen uptake and the translocation from vegetative organs to grains, which resulted in a 35 % decrease in grain nitrogen accumulation and a 92 % increase in vegetative organs during grain filling. Consequently, the average nitrogen harvest index is reduced by 12 %. Nitrogen accumulation was severely affected when cooling degree days (CDD) ≥ 70 °C days. As the chilling intensity increased, the decrease of GPY was more significant than that of GPC. Moreover, we improved the grain temperature-nitrogen uptake function under chilling stress based on the relationship between CDD and the reduction in rice grains. By comparing the improved function and the modules in the existing crop model using the datasets from open field and artificial control experiments, we demonstrated that the current research on quantifying rice nitrogen uptake at extreme temperature stress needed further improvement. The effects of environmental stress on grain nitrogen accumulation are complex. Future studies should pay more attention to the ability of extreme temperature stress to affect nitrogen accumulation in various rice organs.

Citric Acid Inhibits Cd Absorption and Transportation by Improving the Antagonism of Essential Elements in Rice Organs.

Excessive cadmium (Cd) in rice is a global environmental problem. Therefore, reducing Cd content in rice is of great significance for ensuring food security and human health. A field experiment was conducted to study the effects of foliar application of citric acid (CA) on Cd absorption and transportation in rice under high Cd-contaminated soils (2.04 mg·kg-1). This study revealed that there was a negative correlation between Cd content in vegetative organs and CA content, and that foliar spraying of CA (1 mM and 5 mM) significantly increased CA content and reduced Cd content in vegetative organs. The Cd reduction effect of 5 mM CA was better than that of 1 mM, and 5 mM CA reduced Cd content in grains and spikes by 52% and 37%, respectively. CA significantly increased Mn content in vegetative organs and increased Ca/Mn ratios in spikes, flag leaves, and roots. CA significantly reduced soluble Cd content in vegetative organs and promoted the transformation of Cd into insoluble Cd, thus inhibiting the transport of Cd from vegetative organs to grains. The foliar field application of 1 mM and 5 mM CA could inhibit Cd absorption and transportation by reducing Cd bioactivity and increasing the antagonistic of essential elements in rice vegetative organs. These results provide technical support and a theoretical basis for solving the problem of excessive Cd in rice.

Difference in responsiveness of expressions of starch synthesis-related genes to CRCT among rice cultivars

ABSTRACT CO2-Responsive CCT Protein (CRCT) is a transcription factor regulating the expression of starch synthesis-related genes in the vegetative organs of rice. Among six rice cultivars (Nipponbare, Koshihikari, Habataki, Takanari, Momiroman, Leafstar), the expression of CRCT was highly correlated with the starch content of leaf sheath in Nipponbare, but not in Koshihikari, Takanari and Momiroman during plant development. Meanwhile, the expressions of starch synthesis-related genes such as ADP-glucose pyrophosphorylase large subunit 1 was correlated with CRCT expression in Nipponbare, Momiroman, and Leafstar, but the correlations were ambiguous in Koshihikari, Habataki, and Takanari. In addition, the slopes of its regression lines in Nipponbare were larger than those cultivars. These results suggest that the influence of CRCT on starch synthesis varies among these cultivars. Additionally, the similar cultivar differences were observed when these gene expressions were analyzed after sucrose treatment in leaf blade. Some mutations in the promoter regions of the starch synthesis-related genes were identified among these cultivars. There were cultivars in which the presence of mutations correlated with decreased expression of starch synthesis genes in response to CRCT. Thus, these mutations can partially explain the responsiveness of the starch synthesis-related genes to CRCT, and difference in starch content of vegetative organs among rice cultivars.

Influence of Nitrogen Applications during Grain-Filling Stage on Rice (Oryza sativa L.) Yield and Grain Quality under High Temperature

High temperature frequently occurs during rice’s early grain-filling period in the south of China, negatively affecting rice yield and quality and posing a major threat to local rice production. This experiment researched the influence of 3.5 °C warming during the first 20 grain-filling days on rice yield and quality and emphatically investigated the effects of the low-broadcast nitrogen fertilizer application level (LBN), high-broadcast nitrogen fertilizer application level (HBN) and foliar nitrogen fertilizer application (FN) at heading on the rice organ temperature, leaf photosynthesis, chlorophyll fluorescence, yield and grain quality, pasting and thermal properties under high temperature in 2020 and 2022, with a widely planted japonica rice variety, “Wuyunjing31”, in order to explore the practical mitigation measures for reducing the adverse impact of high temperature on rice productivity. The results showed that high temperatures during grain filling increased the rice plant temperature, damaged the chlorophyll fluorescence system and decreased the net photosynthesis rate. This led to a decline in the seed-setting rate and grain weight, resulting in a 7.0% and 13.9% yield loss in 2020 and 2022, respectively. In addition, high temperature caused a decline in the head rice rate and an increase in chalk occurrence and pasting temperature, thereby deteriorating rice grain quality. Under high temperatures, HBN enhanced the rice yield by 3.6% and 13.0% in 2020 and 2022, respectively, while FN enhanced the rice yield by 11.5% in 2022. The increase in yield was linked to the increased seed-setting rate and 1000-grain weight. LBN did not significantly affect the rice yield under high temperatures. The positive effects of nitrogen fertilizer measures on rice yield were associated with their role in lowering plant temperature and protection against the damage to the chlorophyll fluorescence system. All three nitrogen application measures generally improved rice milling quality and appearance quality under high temperature, with HBN generally showing the greatest impact. Under high temperature, LBN and FN tended to make the texture of cooked rice softer due to the decreased consistency, retrogradation enthalpy and retrogradation percentage, and this was closely associated with the decline in amylose content. In summary, nitrogen supplementation at the heading could efficiently mitigate the adverse impact of high temperature during the early grain-filling period on rice yield and quality.

Foliar spraying of Zn/Si affects Cd accumulation in paddy grains by regulating the remobilization and transport of Cd in vegetative organs

The reduction of cadmium (Cd) accumulation in rice grains through biofortification of essential nutrients like zinc (Zn) and silicon (Si) is an area of study that has gained significant attention. However, there is limited understanding of the mechanism of Zn/Si interaction on Cd accumulation and remobilization in rice plants. This work used a pot experiment to examine the effects of Zn and Si applied singly or in combination on the physiological metabolism of Cd in different rice organs under Cd stress. The results revealed that: Zn/Si application led to a significant decrease in root Cd concentration and reduce the value of Tf Soil-Root in filling stage. The content of phytochelatin (PCs, particularly PC2) and glutathione (GSH) in roots, top and basal nodes were increased with Zn/Si treatment application. Furthermore, Zn/Si treatment promoted the distribution of Cd in cell wall during Cd stress. These findings suggest that Zn/Si application facilitates the compartmentalization of Cd within subcellular structures and enhances PCs production in vegetative organs, thereby reducing Cd remobilization. Zn/Si treatment upregulated the metabolism of amino acid components involved in osmotic regulation, secondary metabolite synthesis, and plant chelating peptide synthesis in vegetative organs. Additionally, it significantly decreased the accumulation of Cd in globulin, albumin, and glutelin, resulting in an average reduction of 50.87% in Cd concentration in milled rice. These results indicate that Zn/Si nutrition plays a crucial role in mitigating heavy metal stress and improving the nutritional quality of rice by regulating protein composition and coordinating amino acid metabolism balance.

Predicting Cd accumulation in rice and identifying nonlinear effects of soil nutrient elements based on machine learning methods

The spatial mismatch of Cd content in soil and rice causes difficulties in environmental management for paddy soil. To investigate the influence of soil environment on the accumulation of Cd in rice grain, we conducted a paired field sampling in the middle of the Xiangjiang River basin, examining the relationships between soil properties, soil nutrient elements, Cd content, plant uptake factor (PUFCd), and translocation factors in different rice organs (root, shoot, and grain). The total soil Cd (CdT) and available Cd (CdA) contents and PUFCd showed large spatial variability with ranges of 0.31–6.19 mg/kg, 0.03–3.07 mg/kg, and 0.02–3.51, respectively. Soil pH, CdT, CdA, and the contents of soil nutrient elements (Mg, Mn, Ca, P, Si, and B) were linearly correlated with grain Cd content (Cdg) and PUFCd. The decision tree analysis identified nonlinear effects of Si, Zn and Fe on rice Cd accumulation, which suggested that low Si and high Zn led to high Cdg, and low Si and Fe caused high PUFCd. Using the soil nutrient elements as predictor variables, random forest models successfully predicted the Cdg and PUFCd and performed better than multiple linear regressions. It suggested the impacts of soil nutrient elements on rice Cd accumulation should receive more attention.

ANALISIS KANDUNGAN LOGAM BERAT Pb, Cu, Cd, Cr PADA TANAMAN PADI DAN JAGUNG YANG SISTEM PENGAIRANNYA BERASAL DARI SUNGAI BADUNG

This research aims at identifying the content of heavy metals, namely Pb, Cu, Cd, and Cr in the rice and corn cultivated on the agricultural land of Subak Kerdung, Pemogan Village, South Denpasar District. Rice and corn plants are suspected of having indications of heavy metals due to pollution of the downstream Badung River, which is used as irrigation in Subak Kerdung agricultural land. The analysis of heavy metal contents is conducted on the rice and corn plant organs samples, including roots, stems, leaves, and seeds. The test results show that the organs of rice and corn plants detect the contents of heavy metals Pb, Cu, Cd, and Cr which exceed quality standards. According to the results of analysis tests on organs of the rice plant, the content of heavy metal Pb is detected 21.95 mg/kg; heavy metal Cu 170.42 mg/kg; heavy metals Cd 0.35 mg/kg; and heavy metal Cr 7.03 mg/kg. Meanwhile, the results of analysis test on organs of the corn plant detect the content of heavy metal Pb 16.96 mg/kg; heavy metal Cu 58.16 mg/kg; heavy metal Cd 2.5 mg/kg; and heavy metal Cr 3.16 mg/kg. Therefore, it can be concluded that the content of heavy metals Pb, Cu, Cd, and Cr is more detected in the roots of rice and corn plants, also partially translocated to their stems, leaves, and seeds.
 Keywords: heavy metals; rice plants; corn plants; Badung rivers

The Purple leaf (Pl) Alleles, Plw and Pli, Regulate Leaf Color Development Independently from the Pb Gene of Purple pericarp (Prp) in Rice

Color development in various rice organs results from the complementary expression of genes involved in anthocyanin biosynthesis. The Purple pericarp (Prp) trait and the Purple leaf (Pl) trait both display epistasis, relying on the complement of the Pb and Pp genes for pericarp coloration and the Pl and Pp genes for leaf coloration, respectively. However, there is still genetic uncertainty in identifying the genes responsible for the various color expressions and intensities of rice grain pericarp and leaves. In this study, we characterized the inheritance patterns of color development and the mode of anthocyanin pigments in rice by crossing two parental mutant lines. YUM051, exhibiting dark purple leaves (Plw) and purple pericarp (Prp), was crossed with YUM144, which displayed light purple leaves (Pli) and a white pericarp (prp). The F1 plants exhibited dark purple leaves with purple pericarps, indicating the dominant nature of the purple leaf (Pl) and purple pericarp (Prp) traits. The rice Prp traits display a complementary interaction, reflected in a 9:7 ratio of purple to white pericarp. However, the Prp trait followed Mendelian segregation with a 3:1 ratio of purple to white pericarp in this cross, indicating homozygous dominant Pp alleles in both parental plants. Meanwhile, the segregation of the purple leaf color in the F2 generation of this cross followed complementary inheritance, exhibiting a 9:7 segregation ratio between purple leaves and greenish leaves with purple leaf margins. Moreover, the co-segregation of Prp and Pl traits in the cross between YUM051 (Plw) and YUM144 (Pli) plants did not adhere to the Mendelian 9:3:3:1 independent assortment ratio, confirming that the Pl gene and Pb gene are linked on the same chromosome. Cyanidin-3-O-glucoside (C3G) was detected in the leaves of all progeny resulting from the Plw and Pli cross. However, C3G was exclusively identified in the seeds of offspring carrying the dominant Pb gene. Therefore, the Plw and Pli alleles are Pl genes responsible for purple leaf color, while the Pb gene is responsible for purple pericarp color in rice; these genes function independently of each other.

Combining vegetation, color, and texture indices with hyperspectral parameters using machine-learning methods to estimate nitrogen concentration in rice stems and leaves

Context or problemNitrogen is one of the important elements of crops, which plays a decisive role in crop growth and development and the formation of yields. Monitoring of rice organ-scale nitrogen concentration based on the unmanned aerial vehicle (UAV) images is of great significance for rice field management and yield prediction. Objective or research questionPrevious studies have focused on the use of traditional statistical methods and chlorophyll-related vegetation indices to construct plant nitrogen concentration, with models lacking generalizability. MethodsIn this study, rice field trials of two varieties (NJ9108, YD6) and nitrogen fertilizer treatments (N0-N3: 0, 105, 210 and 315 kg/ha) were conducted for 3 years with manual sampling and UAV digital and hyperspectral images during key fertility periods. Based on the data of the whole growth periods and combined with vegetation indices (VIs), color indices (CIs), hyperspectral parameters (HPs), texture indices (TIs) and machine-learning algorithms, monitoring models of nitrogen concentration at the organ scale of rice were constructed and used to estimate the N content of multiple organs (leaf and stem) of rice at different periods. Field experiments were used to collect the multi-organ nitrogen concentration of rice and the remote sensing (RS) data of UAV during the critical growth period of the two years (2021, 2022), and machine-learning algorithms were used to construct the estimation models. ResultsThe results showed that VIs had good correlations with leaf nitrogen concentration (LNC), stem nitrogen concentration (SNC) and plant nitrogen concentration (PNC), with correlation coefficients (r) of 0.86, 0.74 and 0.81, respectively. Machine learning estimation models combining multiple types of RS indices were more accurate than single parameter models constructed by traditional statistical methods, with the LNC optimal model (R2 = 0.8, RMSE = 3.83 mg/g), the SNC optimal model (R2 = 0.7, RMSE = 2.43 mg/g) and the PNC optimal model (R2 = 0.7, RMSE = 3.19 mg/g). Validated using data from 2020, the machine-learning models were far more accurate than traditional methods. ConclusionsThese results show that the use of multi-source remote sensing data based on machine-learning algorithms can effectively estimate the nitrogen concentration of organs in rice. ImplicationsThis study provides an accurate, stable and universal method for estimating rice nitrogen concentration in rice organs, which can be used as a reference for estimating rice nitrogen concentration in large fields using UAV RS technology.

Performance evaluation of the ORYZA_V3 model for rice growth and organ nitrogen content

AbstractThe ORYZA version 3 (ORYZA_V3) model is commonly used for simulating paddy rice (Oryza sativa L.) growth. However, few studies have investigated the performance of the ORYZA_V3 model for predicting in‐season crop growth variables, especially for the nitrogen (N) translocation process among paddy rice organs in the whole growing season, that is, from sowing to harvest stages. This study examines the prediction accuracy of seven paddy rice growth variables based on one cropping season of field experiment. The results show that (1) the ORYZA_V3 model generates accurate prediction of paddy rice leaf area index, above‐ground biomass, and yield, where root mean square errors (RMSEs) are 0.98–1.11 ha/ha, 2360.5–3028.7 kg/ha, and 492.9–515.2 kg/ha, respectively, coefficient of determination (R2) ranges from 0.76 to 1.00, and index of agreement (D‐index) ranges from 0.50 to 0.98. (2) The prediction accuracy of paddy rice leaf and stem N contents is acceptable, where RMSE ranges from 0.0017 to 0.0041 kg/kg, R2 ranges from 0.82 to 0.96, and D‐index ranges from 0.93 to 0.98. (3) The ORYZA_V3 model cannot generate accurate prediction of rice root and panicle N contents, where RMSE ranges from 0.0007 to 0.0022 kg/kg, R2 ranges from 0.01 to 0.20, and D‐index ranges from 0.17 to 0.65. The structural uncertainty in the N translocation module may be a major reason for the unacceptable crop model prediction. This study demonstrated the substantial potential of the ORYZA_V3 model for simulating and understanding paddy rice growth and organ N translocation.

OsGSTU34, a Bz2-like anthocyanin-related glutathione transferase transporter, is essential for rice (Oryza sativa L.) organs coloration

Anthocyanins are a flavonoid compound known as one of the most important chromogenic substances. They play several functions, including health promotion and sustaining plants during adverse conditions. They are synthesized at the endoplasmic reticulum and sequestered in the vacuole. In this work, we generated knock-out lines of OsGSTU34, a glutathione transporter's tau gene family, with no transgene line and off-target through CRISPR/Cas9 mutagenesis and highlighted the loss of pigmentation in rice flowers, leaves, stems, shoots, and caryopsis. The anthocyanin quantification in the wild-type BLWT and mutant line BLG34-8 caryopsis showed that cyanidin-3-O-glucoside (C3G) and peonidin-3-O-glucoside (P3G) were almost undetectable in the mutant line. A tandem mass tag (TMT) labeling proteomic analysis was conducted to elucidate the proteomic changes in the BLWT and BLG34-8. The result revealed that 1175 proteins were altered, including 408 that were down-regulated and 767 that were upregulated. The accumulation of the OsGSTU34-related protein (Q8L576), along with several anthocyanin-related proteins, was down-regulated. The enrichment analysis showed that the down-regulated proteins were enriched in different pathways, among which the phenylpropanoid biosynthesis pathway, flavonoid biosynthesis metabolites, and anthocyanin biosynthesis pathway. Protein interaction network prediction revealed that glutathione-S-transferase (Q8L576) was connected to the proteins involved in the flavonoid and anthocyanin biosynthesis pathways, such as flavanone 3-dioxygenase 1 (Q7XM21), leucoanthocyanidin dioxygenase 1 (Q93VC3), 4-coumarate-CoA ligase 2 (Q42982), phenylalanine ammonia-lyase (P14717), chalcone synthase 1 (Q2R3A1), and 4-coumarate-CoA ligase 5 (Q6ZAC1). However, the expression of the most important anthocyanin biosynthesis gene was not altered, suggesting that only the transport mechanism was affected. Our findings highlight new insight into the anthocyanin pigmentation in black rice and provide new perspectives for future research.

The effects of earthworm inoculation on cadmium-contaminated rice field in Southern China: a pot experiment and a field test.

Currently, the effects of earthworm inoculation on cadmium-contaminated rice field remain unclear. In this study, four treatments were tested, including rice monoculture (CK), earthworm inoculation with low density (L, 30 g/m2), middle density (M, 60 g/m2), and high density (H, 90 g/m2). The pot and field experiment were conducted in Hunan Province, China. In the pot experiment, the H treatment significantly decreased the available cadmium concentration in 0 ~ 20 cm soil by 5.21% ~ 16.51%, and the M treatment significantly decreased in 0 ~ 10 cm soil by 7.29% ~ 8.96%. The H treatment significantly decreased the total cadmium concentration in 0 ~ 5 cm soil by 10.36%. Moreover, the earthworm inoculation treatments significantly reduced cadmium accumulation in rice organs. In the field experiment, the M and H treatment decreased the available cadmium concentration in 0 ~ 20 cm soil by 14.05% ~ 47.52% and the H treatment decreased the total cadmium concentration in 0 ~ 20 cm soil by 0.78% ~ 5.75% although there was no significant difference. Furthermore, the earthworm inoculation treatments significantly decreased cadmium accumulation in part of rice organs. In conclusion, this study recommends that earthworm inoculation is an effective method of controlling cadmium contamination for rice production.

Variation Characteristics and Expression State of Nitrogen and Phosphorus Metering Ratio of Rice in Black Soil under Film Mulching and Irrigation Methods

In order to investigate the effects of film mulching and water-saving methods on soil inorganic nitrogen, nitrogen content of rice organs, nitrogen-phosphorus metering ratio, and nutrient limitation during rice yield formation, two water-saving irrigation methods and black biodegradable film mulching were adopted. The effects of water-saving film mulching on NH4+-N and NO3−-N in 0 to 60 cm soil, nitrogen accumulation and ratio, and nitrogen-phosphorus metering ratio in rice organs were analyzed. The nitrogen-phosphorus-limiting state of rice growth under water-saving film mulching was determined. The results showed that water-saving and film mulching methods could weaken the leaching of NH4+-N and NO3−-N and enhance the nitrogen uptake of rice. The water-saving method of mulching could reduce the metering ratio of nitrogen and phosphorus in rice organs. The panicle maturity process had been in a state of nitrogen limitation, and the effect was gradually enhanced. The nitrogen and phosphorus metering ratio of panicles was positively correlated with NH4+-N accumulation in the 0 to 60 cm soil layer and nitrogen accumulation of rice organs, and negatively correlated with soil NO3−-N accumulation under film mulching and water-saving methods. The correlation between stems and leaves’ nitrogen and phosphorus metering ratios and influencing factors was basically opposite to that of panicles’ nitrogen and phosphorus metering ratio. This study can provide a reference for the formulation of a fertilization system under film mulching in the black soil region of northeast China.

Production of phytolith and PhytOC and distribution of extractable Si Pools in aerobic rice as influenced by different Si sources.

Phytoliths are composed of 66 to 91% SiO2 and 1 to 6% organic carbon (C) known as phytolith occluded carbon (PhytOC). PhytOC is critical for long-term C storage in the agroecosystem. A field experiment was carried out to investigate the effect of three different sources of exogenous Si, i.e., diatomaceous earth (DE), silicic acid (SA) and rice husk biochar (RHB) on 1) plant phytolith, C content in phytolith and PhytOC content in different rice organs; 2) relationship between plant phytolith, C content in phytolith, PhytOC content, and soil properties (soil physicochemical properties and readily soluble silicon pools). Different Si sources produced significantly higher phytolith, PhytOC content, and readily soluble Si pools (CCSi, AASi, and ASi) than the control (RDF), with treatment receiving 4t RHB ha-1 outperforming the other treatments. Phytolith and PhytOC production were found to be significantly correlated to soil organic carbon (OC), available nitrogen (N) and potassium (K), 0.01 M CaCl2 extractable Si (CCSi) and amorphous Si (ASi) content in the soil. Redundancy analysis showed that treatments receiving 4t RHB ha-1 have a stronger relationship with the CCSi and ASi which majorly contributed to the higher phytolith and PhytOC production. Thus, practices such as Si fertilizers and RHB application have a high potential for phytolith production and PhytOC sequestration, a critical mechanism of the global biogeochemical C sink.

Biochar-mediated Cd accumulation in rice grains through altering chemical forms, subcellular distribution, and physiological characteristics

Biochar can change the availability and morphology of soil Cd. However, the influence of biochar on Cd chemical form and subcellular fraction in rice is poorly understood, particularly under different irrigation methods. A pot experiment of biochar application combined with two irrigation methods (continuous flooding and intermittent irrigation, CF and II) was conducted. The Cd accumulation, chemical form and subcellular fraction in rice organs and the associated physiological responses were examined. Biochar significantly reduced soil available Cd (30.85–47.26% and 32.35–52.35%) under CF and II but increased the Cd content (30.4–63.88% and 13.03–18.59%) in brown rice. Additionally, the Cd content in shoots/grains under II was higher than that under CF. Biochar elevated the Cd soluble fraction in roots while lowered the cell wall fraction under both irrigation methods, whereas the opposite result was observed in leaves. Biochar increased water-, ethanol-, and NaCl-extractable Cd in roots meanwhile increased ethanol-extractable Cd in leaves under both irrigation methods. Moreover, the total amount of water-, ethanol-, and NaCl-extractable Cd in rice roots was higher under II than under CF. Related hormones and antioxidant enzymes may also be involved in biochar-mediated Cd accumulation in rice grains. Thus, changes in Cd chemical form and subcellular fraction in the root and leaf are the main mechanisms of biochar-induced rice grains Cd accumulation.Graphical

Effects of knockout of CO2-responsive CCT protein, a regulator of starch synthesis on physiological characteristics of rice

ABSTRACT CO2-Responsive CCT Protein (CRCT) is suggested to be a positive regulator of starch synthesis-related genes in the vegetative organs of rice. To investigate the physiological function of CRCT, we produced CRCT knockout lines by CRISPR/Cas9 system. CRCT knockout tended to slightly reduce photosynthetic performance and had some adverse effects on growth parameters such as tiller number and straw dry weight. The starch content in the leaf sheath of CRCT knockout lines was significantly lower than that of wild-type. qRT-PCR and RNA-seq analysis showed that sucrose treatment induced the expression of CRCT, which, in turn, induced many starch synthesis-related genes in wild-type, whereas this induction did not occur in CRCT knockout lines. In conclusion, our results suggest that sugar induction of starch synthesis-related genes is almost fully dependent on CRCT, making it a necessary factor for normal photosynthesis and growth of rice.