Vermicompost Supply Enhances Fragrant-Rice Yield by Improving Soil Fertility and Eukaryotic Microbial Community Composition under Environmental Stress Conditions.

Heavy-metal contamination in agricultural soil, particularly of cadmium (Cd), poses serious threats to soil biodiversity, rice production, and food safety. Soil microbes improve soil fertility by regulating soil organic matter production, plant nutrient accumulation, and pollutant transformation. Addressing the impact of Cd toxicity on soil fungal community composition, soil health, and rice yield is urgently required for sustainable rice production. Vermicompost (VC) is an organic fertilizer that alleviates the toxic effects of Cd on soil microbial biodiversity and functionality and improves crop productivity sustainably. In the present study, we examined the effects of different doses of VC (i.e., 0, 3, and 6 tons ha-1) and levels of Cd stress (i.e., 0 and 25 mg Cd kg-1) on soil biochemical attributes, soil fungal community composition, and fragrant-rice grain yield. The results showed that the Cd toxicity significantly reduced soil fertility, eukaryotic microbial community composition and rice grain yield. However, the VC addition alleviated the Cd toxicity and significantly improved the soil fungal community; additionally, it enhanced the relative abundance of Ascomycota, Chlorophyta, Ciliophora, Basidiomycota, and Glomeromycta in Cd-contaminated soils. Moreover, the VC addition enhanced the soil's chemical attributes, including soil pH, soil organic carbon (SOC), available nitrogen (AN), total nitrogen (TN), and microbial biomass C and N, compared to non-VC treated soil under Cd toxicity conditions. Similarly, the VC application significantly increased rice grain yield and decreased the Cd uptake in rice. One possible explanation for the reduced Cd uptake in plants is that VC amendments influence the soil's biological properties, which ultimately reduces soil Cd bioavailability and subsequently influences the Cd uptake and accumulation in rice plants. RDA analysis determined that the leading fungal species were highly related to soil environmental attributes and microbial biomass C and N production. However, the relative abundance levels of Ascomycota, Basidiomycota, and Glomeromycta were strongly associated with soil environmental variables. Thus, the outcomes of this study reveal that the use of VC in Cd-contaminated soils could be useful for sustainable rice production and safe utilization of Cd-polluted soil.

Multi-walled carbon nanotubes affect yield, antioxidant response, and rhizosphere microbial community of scented rice under combined cadmium-lead (Cd-Pb) stress.

Rice production is threatened by heavy metal stress. The use of multi-walled carbon nanotubes (MWCNTs) in agriculture has been reported in previous studies. We aimed to quantify the impact of MWCNTs on the growth and physiological characteristics of scented rice under cadmium (Cd) and lead (Pb) stresses. Therefore, a pot experiment was conducted, two scented rice varieties Yuxiangyouzhan and Xiangyaxiangzhan were used as materials grown under different concentrations of MWCNTs (0, 100, and 300 mg kg-1 recorded as CK, CNPs100, and CNPs300, respectively). The yield, antioxidant response, and rhizosphere microbial community of scented rice were studied. The results showed that compared with the CK treatment, the CNPs100 and CNPs300 treatments increased leaf dry weight by 17.95%-56.22% at the heading stage, and the H2O2 content in leaves decreased significantly by 36.64%-42.27% at the maturity stage. Under CNPs100 treatment, the grain yield of two scented rice varieties increased significantly by 17.54% and 27.40%, respectively. The MWCNTs regulated the distribution of the Cd and Pb in different plant tissues. The content of Cd (0.11-0.20 mg kg-1) and Pb (0.01-0.04 mg kg-1) in grain were at a safety level (<0.2 mg kg-1). Moreover, MWCNTs increased soil microbial community abundance and altered community composition structure under Cd-Pb stress, which in turn improved agronomic traits and quality of scented rice. Overall, this study suggested that the application of MWCNTs regulates the growth, yield, physiological response, and soil microbial community, the genotypes response effect of scented rice to MWCNTs is needed further studied.

Substation of vermicompost mitigates Cd toxicity, improves rice yields and restores bacterial community in a Cd-contaminated soil in Southern China.

Cadmium (Cd) contamination in agricultural soil is a global concern for soil health and food sustainability because it can cause Cd accumulation in cereal grains. An in-situ stabilizing technology (using organic amendments) has been widely used for Cd remediation in arable lands. Therefore, the current study examined the influence of vermicompost (VC) on soil biochemical traits, bacterial community diversity and composition, Cd uptake and accumulation in rice plants and grain yield in a Cd-contaminated soil during the late growing season in 2022. Different doses of VC (i.e., V1 = 0 t ha-1, V2 = 3 t ha-1 and V3 = 6 t ha-1) and two concentrations of Cd (i.e., Cd1 = 0 and Cd2 = 50 mg Cd Kg-1 were used. We performed high-throughput sequencing of 16S ribosomal RNA gene amplicons to characterize soil bacterial communities. The addition of VC considerably affected the diversity and composition of the soil bacterial community; and increased the relative abundance of phyla Chloroflexi, Proteobacteria, Acidobacteriota, Plantomycetota, Gemmatimonadota, Patescibacteria and Firmicute. In addition, VC application, particularly High VC treatment, exhibited the highest bacterial diversity and richness (i.e., Simpson, Shannon, ACE, and Chao 1 indexes) of all treatments. Similarly, the VC application increased the soil chemical traits, including soil pH, soil organic carbon (SOC), available nitrogen (AN), total nitrogen (TN), total potassium (TK), total phosphorous (TP) and enzyme activities (i.e., acid phosphatase, catalase, urease and invertase) compared to non-VC treated soil under Cd stress. The average increase in SOC, TN, AN, TK and TP were 5.75%, 41.15%, 18.51%, 12.31%, 25.45% and 29.67%, respectively, in the High VC treatment (Pos-Cd + VC3) compared with Cd stressed soil. Redundancy analysis revealed that the leading bacterial phyla were associated with SOC, AN, TN, TP and pH, although the relative abundance of Firmicutes, Proteobacteria, Bacteroidata, and Acidobacteria on a phylum basis and Actinobacteria, Gammaproteobacteria and Myxococcia on a class basis, were highly correlated with soil environmental factors. Moreover, the VC application counteracted the adverse effects of Cd on plants and significantly reduced the Cd uptake and accumulation in rice organs, such as roots, stem + leaves and grain under Cd stress conditions. Similarly, applying VC significantly increased the fragrant rice grain yield and yield traits under Cd toxicity. The correlation analysis showed that the increased soil quantities traits were crucial in obtaining high rice grain yield. Generally, the findings of this research demonstrate that the application of VC in paddy fields could be useful for growers in Southern China by sustainably enhancing soil functionality and crop production.

Nitric oxide confers cadmium tolerance in fragrant rice by modulating physio-biochemical processes, yield attributes, and grain quality traits.

Cadmium (Cd) stress causes serious disruptions in plant metabolism, physio-biochemical processes, crop yield, and quality characters. Nitric oxide (NO) improves the quality features and nutritional contents of fruit plants. However, how NO confers Cd toxicity in fragrant rice plants, is sparse. Hence, the present study investigated the effects of 50 µM NO donor sodium nitroprusside (SNP) on physio-biochemical processes, plant growth attributes, grain yield, and quality traits of fragrant rice under Cd stress (100 mg kg-1 soil). The results revealed that Cd stress diminished rice plant growth, impaired photosynthetic apparatus and antioxidant defense system, and deteriorated the grain quality traits. However, foliar application of SNP mitigated Cd stress by improving plant growth and gas exchange attributes. Higher electrolyte leakage (EL) was accompanied with elevated levels of malondialdehyde (MDA) and hydrogen peroxide (H2O2) under Cd stress; however, exogenous application of SNP reduced them. The activities and relative expression levels of enzymatic antioxidants; superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) and non-enzymatic antioxidants, glutathione (GSH) contents were reduced by Cd stress, while SNP application regulated their activity and transcript abundances. SNP application improved fragrant rice grain yield and 2-acetyl-1-pyrroline content by 57.68 % and 75.54 % respectively, which is concomitant with higher biomass accumulation, photosynthetic efficiency, photosynthetic pigment contents, and an improved antioxidant defense system. Collectively, our results concluded that SNP application regulated the fragrant rice plant physio-biochemical processes, yield traits and grain quality characters under Cd-affected soil.

Optimization of liquid fertilizer management improves grain yield, biomass accumulation, and nutrient uptake of late-season indica fragrant rice.

BACKGROUND: The use of liquid fertilizer is an effective measure to increase rice yield and nitrogen use efficiency. There has been a lack of information regarding the effects on the grain yield, biomass accumulation, and nutrient uptake in late-season indica fragrant rice of split fertilizer application and of nitrogen management in liquid fertilizer application. RESULTS: A 2-year field experiment was carried out during 2019 and 2020 with two fragrant rice cultivars grown under differing fertilizer management treatments. Results showed that the fertilization treatments affected the grain yield, yield components, biomass accumulation, and nutrient accumulation significantly. The mean nitrogen recovery efficiency with liquid fertilizer management was greater than in a control treatment corresponding to a practice commonly used by farmers (H2). The effects of nitrogen metabolism enzymes in the leaves of both rice cultivars were stronger with liquid fertilizer treatments than with H2. Grain yield was positively associated with the effective panicle number, spikelets per panicle, dry matter accumulation, N and K accumulation, and the nitrogen metabolism enzymes. CONCLUSIONS: Optimized liquid fertilizer management increases biomass accumulation, nitrogen utilization efficiency, and nitrogen metabolism. It stabilizes yields and increases the economic benefits of late-season indica fragrant rice. © 2023 Society of Chemical Industry.

Foliar spray of La2O3 nanoparticles regulates the growth, antioxidant parameters, and nitrogen metabolism of fragrant rice seedlings in wet and dry nurseries.

Nanoparticles (NPs) have been widely used in agriculture, and lanthanum oxide nanoparticles (La2O3) NPs can regulate plant growth. La2O3 NPs treatment was hypothesized to affect the accumulation and distribution of substances in rice seedlings under wet and dry nursery conditions. The objective of the present study was to ascertain the effects of La2O3 NPs foliar spray on the morphology and physiology of fragrant rice seedlings under wet and dry nursery conditions. Seedlings of two fragrant rice cultivars, namely 'Xiangyaxiangzhan' and 'Yuxiangyouzhan,' were grown under wet and dry nursery conditions with La2O3 NPs treatments at three concentrations (CK, La2O3 NPs 0 mg L-1; T1, La2O3 NPs 20 mg L-1; and T2, La2O3 NPs 40 mg L-1). The results showed that the seedling-raising method was significantly associated with La2O3 NPs application (P < 0.05), affecting the leaf area of both cultivars. Changes in plant morphological parameters, such as dry weight and root-shoot ratio, were the reasons for the differences in cultivars in response to La2O3 NPs application. Changes were also observed in the plant morphological and physiological parameters of leaf area, specific leaf area, chlorophyll contents, antioxidant properties, and activities of nitrogen metabolism enzymes. The relationship between morphological and physiological processes in fragrant rice was investigated to test the hypothesis. In both wet and dry nursery methods, the T2 concentration of La2O3 NPs was beneficial for rice seedlings and significantly increased their leaf area due to changes in morphological and physiological parameters. Therefore, the results of this study provide a theoretical basis for expanding the research on La2O3 NPs application in rice, as well as relevant references for strengthening rice seedlings in the nursery, which has a positive effect on the grain yield improvement in fragrant rice.

Exogenous TiO2 Nanoparticles Alleviate Cd Toxicity by Reducing Cd Uptake and Regulating Plant Physiological Activity and Antioxidant Defense Systems in Rice (Oryza sativa L.).

Cadmium (Cd) is a potentially hazardous element with significant biological toxicity, negatively affecting plant growth and physio-biochemical metabolism. Thus, it is necessary to examine practical and eco-friendly approaches to reduce Cd toxicity. Titanium dioxide nanoparticles (TiO2-NPs) are growth regulators that help in nutrient uptake and improve plant defense systems against abiotic and biological stress. A pot experiment was performed in the late rice-growing season (July-November) 2022 to explore the role of TiO2-NPs in relieving Cd toxicity on leaf physiological activity, biochemical attributes, and plant antioxidant defense systems of two different fragrant rice cultivars, i.e., Xiangyaxiangzhan (XGZ) and Meixiangzhan-2 (MXZ-2). Both cultivars were cultivated under normal and Cd-stress conditions. Different doses of TiO2-NPs with and without Cd-stress conditions were studied. The treatment combinations were: Cd-, 0 mg/kg CdCl2·2.5 H2O; Cd+, 50 mg/kg CdCl2·2.5 H2O; Cd + NP1, 50 mg/kg Cd + 50 TiO2-NPs mg/L; Cd + NP2, 50 mg/kg Cd + 100 TiO2-NPs mg/L; Cd + NP3, 50 mg/kg Cd + 200 TiO2-NPs mg/L; Cd + NP4, 50 mg/kg Cd + 400 TiO2-NPs mg/L. Our results showed that the Cd stress significantly (p < 0.05) decreased leaf photosynthetic efficiency, stomatal traits, antioxidant enzyme activities, and the expression of their encoding genes and protein content. Moreover, Cd toxicity destabilized plant metabolism owing to greater accretion of hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels at vegetative and reproductive stages. However, TiO2-NPs application improved leaf photosynthetic efficacy, stomatal traits, and protein and antioxidant enzyme activities under Cd toxicity. Application of TiO2-NPs decreased the uptake and accumulation of Cd in plants and levels of H2O2 and MDA, thereby helping to relieve Cd-induced peroxidation damage of leaf membrane lipids by enhancing the activities of different enzymes like ascorbate peroxidase (APX), catalase (CAT), peroxidase (POS), and superoxide dismutase (SOD). Average increases in SOD, APX, CAT, and POS activities of 120.5 and 110.4%, 116.2 and 123.4%, 41.4 and 43.8%, and 36.6 and 34.2% in MXZ-2 and XGZ, respectively, were noted in Cd + NP3 treatment across the growth stages as compared with Cd-stressed plants without NPs. Moreover, the correlation analysis revealed that the leaf net photosynthetic rate is strongly associated with leaf proline and soluble protein content, suggesting that a higher net photosynthetic rate results in higher leaf proline and soluble protein content. Of the treatments, the Cd + NP3 (50 mg/kg Cd + 200 mg/L TiO2-NPs) performed the best for both fragrant rice cultivars under Cd toxicity. Our results showed that TiO2-NPs strengthened rice metabolism through an enhanced antioxidant defense system across the growth stages, thereby improving plant physiological activity and biochemical characteristics under Cd toxicity.

Biosynthesis of 2-Acetyl-1-pyrroline in Fragrant Rice: Recent Insights into Agro-management, Environmental Factors, and Functional Genomics.

Rice is a staple food for more than half of the world's population, and rice fragrance is a key quality attribute which is highly desired by consumers and attracts premium prices in the international market. There are around 200 volatile compounds involved in rice fragrance, but 2-acetyl-1-pyrroline (2-AP) has been considered a master regulator of aroma in fragrant rice. Consequently, efforts were made to increase the 2-AP contents in the grain by managing agronomical practices or by using modern functional genomic tools, which successfully converted nonfragrant cultivars to fragrant rice. Furthermore, environmental factors were also reported to influence the 2-AP contents. However, a comprehensive analysis of 2-AP biosynthesis in response to agro-management practices, environmental factors, and the application of functional genomic tools for fragrant rice production was missing. In this Review, we summarize how micro/macronutrients, cultivation practices, amino acid precursors, growth regulators, and environmental factors, such as drought, salinity, light, and temperature, influence the 2-AP biosynthesis to modulate the aroma of fragrant rice. Furthermore, we also summarized the successful conversion of nonfragrant rice cultivars to fragrant rice using modern gene editing tools, such as RNAi, TALENS, and CRISPR-Cas9. Finally, we discussed and highlighted the future perspective and challenges related to the aroma of fragrant rice.

Alternate wetting and drying modulated physio-biochemical attributes, grain yield, quality, and aroma volatile in fragrant rice.

Alternate wetting and drying (AWD) has been recognized as a water-saving technology in rice production systems; however, pre- and post-flowering AWD could induce changes in yield, quality and aroma biosynthesis in fragrant rice. In the present study, two fragrant rice cultivars (Guixiangzhan and Nongxiang-18) were subjected to AWD till soil water potential reached -25 to -30 kPa during vegetative stage (VS), reproductive stage (RS), and both stages (VS + RS). The AWD did not affect net photosynthesis and gas exchange significantly, while malondialdehyde (MDA), H2 O2 and electrolyte leakage (EL) were higher than in control plants. The AWD treatments variably affected soluble sugars, proline and protein accumulation as well as the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), and reduced glutathione (GSH) contents. Moreover, filled grain percentage and 1000-grain weight in AWD treatments were found to be statistically similar (p > 0.05) to control, except grains panicle-1 under AWD-VS + RS that was reduced by 11% and 14% for Guixiangzhan and Nongxiang-18, respectively. On average, yield and related attributes in Guixiangzhan remained higher than in Nongxiang-18. In addition, the grain aroma volatile (2-acetyl-1-pyrroline, 2-AP) content increased by 8.79%, 14.45%, and 6.87% and 7.95%, 14.02%, and 5.04% under AWD-VS, AWD-RS, and AWD-VS + RS treatments, for Guixiangzhan and Nongxiang-18, respectively. Overall, AWD treatments, either at VS or RS, could promote rice aroma in terms of accumulation of 2AP, which might be linked with enhanced endogenous proline contents (a precursor for 2AP biosynthesis) without any severe consequences on rice yield and quality.

Post-transcriptional regulation of 2-acetyl-1-pyrroline (2-AP) biosynthesis pathway, silicon, and heavy metal transporters in response to Zn in fragrant rice.

Fragrant rice (Oryza sativa L.) has a high economic and nutritional value, and the application of micronutrients regulates 2-acetyl-1-pyrroline (2-AP) production, which is responsible for aroma in fragrant rice. Alternative splicing (AS) is an important post-transcriptional regulatory mechanism to generate transcript variability and proteome diversity in plants. However, no systematic investigation of AS events in response to micronutrients (Zn) has been performed in fragrant rice. Furthermore, the post-transcriptional regulation of genes involved in 2-AP biosynthesis is also not known. In this study, a comprehensive analysis of AS events under two gradients of Zn treatment in two different fragrant rice cultivars (Meixiangzhan-2 and Xiangyaxiangzhan) was performed based on RNA-seq analysis. A total of 386 and 598 significant AS events were found in Meixiangzhan-2 treated with low and high doses of Zn, respectively. In Xiangyaxiangzhan, a total of 449 and 598 significant AS events were found in low and high doses of Zn, respectively. Go analysis indicated that these genes were highly enriched in physiological processes, metabolism, and cellular processes in both cultivars. However, genotype and dose-dependent AS events were also detected in both cultivars. By comparing differential AS (DAS) events with differentially expressed genes (DEGs), we found a weak overlap among DAS and DEGs in both fragrant rice cultivars indicating that only a few genes are post-transcriptionally regulated in response to Zn treatment. We further report that Zn differentially regulates the expression of 2-AP biosynthesis-related genes in both cultivars and Zn treatment altered the editing frequency of single nucleotide polymorphism (SNPs) in the genes involved in 2-AP biosynthesis. Finally, we showed that epigenetic modifications associated with active gene transcription are generally enriched over 2-AP biosynthesis-related genes. Similar to the 2-AP pathway, we found that heavy metal transporters (genes related to silicon, iron, Zn and other metal transport) are also regulated at transcriptional and post-transcriptional levels in response to Zn in fragrant rice. Taken together, our results provide evidence of the post-transcriptional gene regulation in fragrant rice in response to Zn treatment and highlight that the 2-AP biosynthesis pathway and heavy metal transporters may also be regulated through epigenetic modifications. These findings will serve as a cornerstone for further investigation to understand the molecular mechanisms of 2-AP biosynthesis and regulation of heavy metal transporters in fragrant rice.

Exogenous Gamma-Aminobutyric Acid Application Induced Modulations in the Performance of Aromatic Rice Under Lead Toxicity.

Gamma-aminobutyric acid (GABA) is a non-protein amino acid and has a multi-functional role in abiotic stress tolerance. A pot experiment was conducted to assess the role of exogenous gamma-aminobutyric acid (GABA) application to modulate the growth, yield, and related physio-biochemical mechanisms in two aromatic rice cultivars, that is, Guixiangzhan (GXZ) and Nongxiang 18 (NX-18), under Pb toxic and normal conditions. The experimental treatments were comprised of Ck: without Pb and GABA (control), GABA: 1 mM GABA is applied under normal conditions (without Pb), Pb + GABA: 1 mM GABA is applied under Pb toxicity (800 mg kg-1 of soil), and Pb= only Pb (800 mg kg-1 of soil) is applied (no GABA). The required concentrations of GABA were applied as a foliar spray. Results revealed that Pb stress induced oxidative damage in terms of enhanced malondialdehyde (MDA), electrolyte leakage (EL), and H2O2 contents, while exogenous GABA application improved leaf chlorophyll, proline, protein and GABA contents, photosynthesis and gas exchange, and antioxidant defense under Pb toxicity in both rice cultivars. Moreover, glutamine synthetase (GS) and nitrate reductase (NR) activities were variably affected due to GABA application under Pb stress. The yield and related traits, that is, productive tillers/pot, grains/panicle, filled grain %, 1,000-grain weight, and grain yield were 13.64 and 10.29, 0.37% and 2.26%, 3.89 and 19.06%, 7.35 and 12.84%, and 17.92 and 40.56 lower under Pb treatment than Pb + GABA for GXZ and NX-18, respectively. Furthermore, exogenous GABA application in rice reduced Pb contents in shoot, leaves, panicle, and grains compared with Pb-exposed plants without GABA. Overall, GXZ performed better than NX-18 under Pb toxic conditions.

Water and Nitrogen Management at the Booting Stage Affects Yield, Grain Quality, Nutrient Uptake, and Use Efficiency of Fragrant Rice Under the Agro-Climatic Conditions of South China.

The present study was conducted to assess the effects of water and nitrogen applications at the booting stage on yield, grain quality, and nutrient use efficiencies in fragrant rice in the early (March-July) and late (July-November) seasons of 2013. The experiment was comprised of two fragrant rice cultivars, i.e., Nongxiang 18 and Basmati; three nitrogen levels, i.e., 0 kg N ha-1 (N0), 30 kg N ha-1 (N1), and 60 kg N ha-1 (N2); and three water levels, i.e., 2-4 cm water layer well-watered (W0), water with a soil water potential of -15 ± 5 kPa (W1), and water with a soil water potential of -25 ± 5 kPa (W2), which were randomized in a split-split plot design. Results showed that Basmati produced a higher grain yield than Nongxiang 18 (16.20 and 9.61% in the early and late season, respectively), whereas the W1 exhibited the maximum grain yield and harvest index. The moderate application of nitrogen (N1) at the booting stage resulted in higher grain yield, nevertheless, cultivar, water, and nitrogen revealed different trends for some of the grain quality attributes, i.e., brown rice rate, milled rice rate, head milled rice rate, protein content, and amylose content as well as nutrient uptake and use efficiencies in the double rice production system. Basmati had a higher nitrogen harvest index (NHI; 18.28-20.23%) and P harvest index (PHI; 3.95-12.42%) but lower physiological P use efficiency for biomass (PPUEB; 7.66-23.66%) and physiological K use efficiency for biomass (PKUEB; 2.53-7.10%) than Nongxiang 18 in both seasons. Furthermore, the grain number per panicle, biomass yield, grain P uptake, and the whole plant P uptake were significantly related to the grain yield of fragrant rice. In both seasons, the interaction of water and nitrogen (W × N) had a significant effect on panicle number, grain quality attributes, and N, P uptake of straw, as well as the physiological N, P use efficiency for grain and the physiological N, K use efficiency for biomass. Overall, results suggest that moderate nitrogen and irrigation input at the booting stage could be feasible to improve the productivity and quality of the double rice production system with improved nutrient use efficiency under the agro-climatic conditions of South China.

Transcriptional cascades in the regulation of 2-AP biosynthesis under Zn supply in fragrant rice.

Transcription factors (TFs) regulate gene expression to control certain genetic programs, such as growth and development, phytohormone regulation, and environmental stresses. 2-acetyl-1-pyrroline (2-AP) is the key element involved in aroma biosynthesis pathway, and the application of micronutrients can increase the 2-AP levels. However, little is known about the micronutrient-induced TFs involved in 2-AP biosynthesis. Here, we identify a number of TF families in two fragrant rice varieties, "Meixiangzhan-2" (M) and "Xiangyaxiangzhan" (X), in response to Zinc (Zn) application through transcriptomic analysis. A total of ~678 TFs were identified and grouped into 26 TF families, each of which was found to be involved in numerous signaling pathways. The WRKY TF family was found to be the most abundant, followed by bHLH and MYB. Furthermore, members of the WRKY, bHLH, MYB, ERF, HSF, MADS-box, NFY, and AP2 TF families were significantly upregulated and may be involved in the transcriptional regulation of aroma biosynthesis. In brief, this study enhances our understanding of the molecular mechanism of 2-AP biosynthesis and highlights the key TFs potentially involved in the production of aroma in fragrant rice.

Nitrogen modulates early growth and physio-biochemical attributes in fragrant rice grown under cadmium and multiwall carbon nanotubes stresses.

Nitrogen (N) modulates plant growth, but its impact on the early growth and physio-biochemical characteristics of rice under cadmium (Cd) and multiwall carbon nanotubes (MWCNTs) toxicity has received little attention. In this study, a hydroponic experiment was conducted on two fragrant rice cultivars, e.g., Xiangyaxiangzhan (XYXZ) and Yuxiangyouzhan (YXYZ), grown under two N levels (N and 1/4 N) and various Cd and MWCNTs treatments (CK: without CdCl2 or MWCNTs; Cd: 100 µmol L-1 CdCl2; MWCNTs: 100 mg L-1 MWCNTs; and Cd-MWCNTs: 100 µmol L-1 CdCl2 + 100 mg L-1 MWCNTs). Results showed that when compared to CK, the total dry weight of the Cd and MWCNTs treatments did not change under 1/4 N for both varieties, whereas Cd and Cd-MWCNTs treatments resulted in a significant reduction in total dry weight by 18.78-37.85% for XYXZ and the Cd-MWCNTs treatment resulted in a significant reduction in the total dry weight by 20.24% for YXYZ. The changes in total dry weight were linked to changes in the dry weight of the different parts of the plant. Besides, the antioxidant parameters and the enzymes involved in the nitrogen metabolism changed in different varieties and different plant parts under two N levels and various Cd and MWCNTs treatments. In addition, differences in total dry weight changes at the N levels and various Cd and MWCNTs treatments were identified between the two varieties, and the relations between total dry weight and other investigated parameters indicated that the modulation processes varied between varieties. Overall, N modulates the early growth and physio-biochemical attributes in fragrant rice seedlings under Cd, MWCNTs, and their combined toxicity.

Effect of Exogenous Melatonin Application on the Grain Yield and Antioxidant Capacity in Aromatic Rice under Combined Lead-Cadmium Stress.

This study aimed to determine the mechanism of exogenous melatonin application in alleviating the combined Pb and Cd (Pb-Cd) toxicity on aromatic rice (Oryza sativa L.). In this study, a pot experiment was conducted; two aromatic rice varieties, Yuxiangyouzhan and Xiangyaxiangzhan, were selected, and sprays using 50, 100, 200, and 400 µmol L-1 melatonin (denoted as S50, S100, S200, and S400) and irrigation using 100, 300, and 500 µmol L-1 melatonin (denoted as R100, R300, and R500) were also selected. The results showed that, under the S50, S100, and S200 treatments, the Pb content of aromatic rice grain decreased, and the grain yield increased significantly. Moreover, the application of exogenous melatonin significantly reduced the accumulation of H2O2 in rice leaves at maturity under Cd-Pb stress and reduced the MDA content in Xiangyaxiangzhan leaves. In addition, the microbial community structure changed significantly under S50 and R300 treatments. Some pathways, such as the synthesis of various amino acids and alanine, aspartate, and glutamate metabolism, were regulated by S50 treatment. Overall, melatonin application improved aromatic rice grain yield while reducing heavy metal accumulation by regulating the antioxidant capacity and metabolites in aromatic rice plants and altering the physicochemical properties and microbial community structures of the soil.

Zinc oxide nanoparticles and polyethylene microplastics affect the growth, physiological and biochemical attributes, and Zn accumulation of rice seedlings.

Metal nanoparticles and microplastics are becoming important pollutants in agricultural fields, but there are few studies on the interaction of zinc oxide nanoparticles (ZnONPs) and polyethylene (PE) microplastics with rice seedlings. The two rice cultivars Xiangyaxiangzhan and Yuxiangyouzhan were grown at three ZnONP levels (0 mg L-1, 50 mg L-1, and 500 mg L-1) and three PE levels (0 mg L-1, 250 mg L-1, and 500 mg L-1), and the growth, physiological attributes, and Zn uptake of rice seedlings were measured. Result showed that the ZnONPs and PE treatment effects on the investigated parameters differed between the cultivars, whilst Yuxiangyouzhan produced 6.98% higher in mean total dry biomass than Xiangyaxiangzhan. The mean total dry biomass in Xiangyaxiagnzhan and Yuxiangyouzhan changed by 10.22-30.85% and - 11.74-25.58% under ZnONPs, respectively. The PE treatments reduced growth parameters in Xiangyaxiangzhan, whilst the 250 mg L-1 PE treatment reduced the growth parameter of Yuxiangyouzhan. Besides, the ZnONP treatment had a stronger effect on rice seedling growth than the PE treatment. Furthermore, the ZnONPs modulated the physiological parameter in plant tissue of the two rice varieties. ZnONP treatment lead to the accumulation of Zn in plant tissue and the shoot Zn content was strongly related to shoot cellulose content. Overall, ZnONPs and PE treatments modulated the growth, physiological and biochemical attributes, and Zn uptake of rice seedlings, and the cultivars and dose effects could not be ignored.

Radiocesium distribution caused by tillage inversion affects the soil-to-crop transfer factor and translocation in agroecosystems.

This study reports the translocation of cesium-137 (137Cs) into deep soil layers, and the 137Cs transfer from soil to soybean in farmland under three tillage (no tillage, NT; rotary cultivation, RC; moldboard plow; MP) treatments and an undisturbed grassland (GL) at eight years after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident on 11 March 2011 in Japan. Tillage influences the 137Cs distribution in the 0-30 cm of soil; the distribution of 137Cs in the soil was uniform under RC and MP treatments, while in the grassland, most 137Cs was concentrated on the soil surface (0-2.5 cm). The center of vertical 137Cs radioactivity concentration (the thickness of the soil from surface which containing half of the 137Cs inventory) in GL was 5.5 cm, which was shallower than that in farmland (9.5 cm in NT, 13.6 cm in RC and 15.2 cm in MP). Hence, the total translocation distance of 137Cs 8 years after FDNPP accident showed the following trend: GL (2.4 cm) < NT (7.0 cm) < RC (10.0 cm) < MP (12.3 cm). Meanwhile, a significant positive correlation was observed between 137Cs radioactivity concentration and organic carbon and nitrogen content in the soil. However, the 137Cs radioactivity concentration in soybean grains was negatively correlated with the center of vertical 137Cs radioactivity concentration but positively correlated with the ratio of exchangeable 137Cs (ExCs) and K content in the soil. The ExCs/K and 137Cs distributions in the soil were combined into a statistical model to predict the 137Cs radioactivity concentration in soybean grain. The results revealed the magnitude of the impact of 137Cs distribution on the 137Cs transfer from soil to crop. The addition of the 137Cs distribution dramatically improved the accuracy of the prediction model of 137Cs radioactivity concentration in soybean.

Application of hydrogen-rich water modulates physio-biochemical functions and early growth of fragrant rice under Cd and Pb stress.

Application of hydrogen-rich water (HRW) could improve plant growth under stress conditions; however, its effects on early growth and related physiological functions of fragrant rice under cadmium (Cd) and lead (Pb) toxicity are unknown. The present study was composed of two HRW treatments, i.e., H0: without H2 and HRW: with 500ppb H2 gas, three treatments with two metals, i.e., M0: without heavy metal, Cd: 75 µmol l-1 of Cd, Pb: 750 µmol l-1 of Pb applied to two popular fragrant rice cultivars, i.e., Yuxiangyouzhan and Xiangyaxiangzhan. The growth and physio-biochemical attributes of fragrant rice at 5 and 10 days after treatment (DAT) were assessed. Results showed that HRW treatment promoted the growth of rice seedlings in terms of increased dry biomass of shoot, root, and the whole seedling at 10 DAT. Moreover, HRW also improved early growth of fragrant rice under Pb stress with substantial increase in fresh and dry weight of roots and the whole seedling at 5 and 10 DAT. Application of HRW slightly alleviated the root inhibition caused by Cd toxicity in rice seedlings at 10 DAT. In addition, antioxidant activities, i.e., catalase (CAT) and peroxidase (POD), were increased with HRW application at 10 DAT while decreased root Pb and Cd contents of both rice cultivars. Overall, HRW alleviated the inhibitory effects of Cd and Pb toxicity by regulating the antioxidant defense response in growing rice plants.

Ultrasonic seed treatment improved morpho-physiological and yield traits and reduced grain Cd concentrations in rice.

Rice cultivation under cadmium (Cd) contaminated soil often results in reduced growth with excess grain Cd concentrations. A pot experiment was conducted to assess the potential of ultrasonic seed treatment to alleviate Cd stress in rice. Seeds of two aromatic rice cultivars i.e., Xiangyaxiangzhan and Meixiangzhan 2 and two non-aromatic rice cultivars i.e., Huahang 31 and Guangyan 1 were exposed to ultrasonic waves for 1.5 min in 20-40 KHz mixing frequency. The experimental treatments were comprised of untreated seeds (U0) and ultrasonic treated seeds (U1) transplanted in un-contaminated soil (H0) and Cd-contaminated soil (H1). Results revealed that Cd contents and Cd accumulation in grain in U1 were 33.33-42.31% and 12.86-57.58% lower than U0 for fragrant rice cultivars under H1. Meanwhile, biomass production was higher in U1 than U0 under H0 and better yield was assessed in U1 for all cultivars under H1. The activity of peroxidase (POD) in flag leaves was increased by 8.28-115.65% for all cultivars while malondialdehyde (MDA) contents were significantly decreased in U1 compared with U0 under H0. Conclusively, ultrasonic treatment modulated Cd distribution and accumulation in different parts while improved physiological performance as well as yield and grain quality of rice under Cd contaminated conditions.

ZnO nanoparticle-based seed priming modulates early growth and enhances physio-biochemical and metabolic profiles of fragrant rice against cadmium toxicity.

BACKGROUND: Cadmium (Cd) is amongst the most toxic heavy metals that severely affects crop growth, whereas application of nanoparticles (NPs) to negate the toxic effects of heavy metals could be an effective management approach. In the present study, the seeds of two fragrant rice varieties i.e., Yuxiangyouzhan and Xiangyaxiangzhan under normal and Cd stress conditions i.e., 0 and 100 mg L- 1 applied with four levels of ZnO NPs i.e., 0, 25, 50, and 100 mg L- 1. RESULTS: Seed priming with ZnO NPs had no significant effect on the seed germination (p > 0.05) however, it substantially improved the seedling growth and other related physiological attributes under the Cd stress. The mean fresh weight of the shoot, and whole seedling was increased by 16.92-27.88% and by 16.92-27.88% after ZnO NPs application. The root fresh weight, root-shoot length was also substantially improved under ZnO NPs treatment. Moreover, application of ZnO NPs induced modulations in physiological and biochemical attributes e.g., the superoxide dismutase (SOD) activity in root and shoot, the peroxidase (POD) activity and metallothionein contents in root were increased under low levels of ZnO NPs. The α-amylase and total amylase activity were improved by ZnO NPs application under Cd Stress. Besides, modulation in Zn concentration and ZnO NPs uptake in the seedling were detected. The metabolomic analysis indicated that various pathways such as alanine, aspartate and glutamate metabolism, phenylpropanoid biosynthesis, and taurine and hypotaurine metabolism were possibly important for rice response to ZnO NPs and Cd. CONCLUSION: Overall, application of ZnO NPs substantially improved the early growth and related physio-biochemical attributes in rice. Our findings provide new insights regarding the effects of ZnO NPs on seed germination, and early growth of rice, and its potential applications in developing crop resilience against Cd contaminated soils.