Roots Of Rice Seedlings Research Articles

Transcriptome and Co-Expression Network Analysis Reveals the Molecular Mechanism of Rice Root Systems in Response to Low-Nitrogen Conditions.

Nitrogen is an important nutrient for plant growth and essential metabolic processes. Roots integrally obtain nutrients from soil and are closely related to the growth and development of plants. In this study, the morphological analysis of rice root tissues collected at different time points under low-nitrogen and normal nitrogen conditions demonstrated that, compared with normal nitrogen treatment, the root growth and nitrogen use efficiency (NUE) of rice under low-nitrogen treatment were significantly improved. To better understand the molecular mechanisms of the rice root system's response to low-nitrogen conditions, a comprehensive transcriptome analysis of rice seedling roots under low-nitrogen and control conditions was conducted in this study. As a result, 3171 differentially expressed genes (DEGs) were identified. Rice seedling roots enhance NUE and promote root development by regulating the genes related to nitrogen absorption and utilization, carbon metabolism, root growth and development, and phytohormones, thereby adapting to low-nitrogen conditions. A total of 25,377 genes were divided into 14 modules using weighted gene co-expression network analysis (WGCNA). Two modules were significantly associated with nitrogen absorption and utilization. A total of 8 core genes and 43 co-expression candidates related to nitrogen absorption and utilization were obtained in these two modules. Further studies on these genes will contribute to the understanding of low-nitrogen adaptation and nitrogen utilization mechanisms in rice.

Root cell wall remodeling: A way for exopolysaccharides to mitigate cadmium toxicity in rice seedling.

Exopolysaccharides (EPS) are macromolecules with environment beneficial properties. Currently, numerous studies focus on the absorption of heavy metals by EPS, but less attention has been paid to the effects of EPS on the plants. This study explored the effects of EPS from Lactobacillus plantarum LPC-1 on the structure and function of cell walls in rice seedling roots under cadmium (Cd) stress. The results showed that EPS could regulate the remodeling process of the cell walls of rice roots. EPS affects the synthesis efficiency and the content of the substances that made up the cell wall, and thus plays an essential role in limiting the uptake and transport of Cd in rice root. Furthermore, EPS could induce plant resistance to heavy metals by regulating the lignin biosynthesis pathway in rice roots. Finally, the cell wall remodeling induced by EPS likely contributes to plant stress responses by activating the reactive oxygen species (ROS) signaling.

Exogenous Melatonin Positively Regulates Rice Root Growth through Promoting the Antioxidant System and Mediating the Auxin Signaling under Root-Zone Hypoxia Stress

Root growth and development is an important indicator of root-zone hypoxia tolerance in rice. Melatonin has been suggested to function as a crucial regulator in modulating root growth and improving plant abiotic stress resistance. To explore the role and potential mechanism of melatonin in regulating the root growth under root-zone hypoxia stress, rice seedlings were treated with hypoxia (oxygen level at 0.9–2.1 mg·L−1), combined with or without a 20 μmol·L−1 melatonin pretreatment under a hydroponic condition. The results showed that the exogenous application of melatonin significantly alleviated the inhibition of the rice root growth that was induced by the hypoxia stress. The morphological–phenotypic analyses showed that after the melatonin pretreatment, the primary root length, lateral root length, and lateral root density increased by 11.6%, 8.2%, and 36.8%, respectively, under hypoxia stress. The physiological–biochemical analyses showed that the exogenous melatonin significantly increased the root activity and O2 influx in the root meristem zone under hypoxia stress to 1.5 times that observed in the hypoxia stress group. The melatonin pretreatment significantly improved the activity of superoxide dismutase (SOD) and decreased the accumulation of superoxide anions (O2•−) in the seedling roots, whereas it increased the content of hydrogen peroxide (H2O2) under hypoxia stress. The exogenous melatonin pretreatment significantly increased the content of indole-3-acetic acid (IAA) by 51.5% in the rice roots compared to the plants without melatonin pretreatment under hypoxia stress. Quantitative real-time PCR (qRT-PCR) analyses revealed that the melatonin pretreatment induced the expression of OsPIN1a~1d, OsPIN8, OsPIN9, OsAUX1, OsARF19, and OsGH3-2 in the rice seedling roots under aerated conditions, whereas it only obviously upregulated the expression of OsPIN1b, OsPIN2, and OsGH3-2 under hypoxia stress. These results indicate that melatonin positively regulates root growth and development under hypoxia stress, through improving the antioxidant system and directly or indirectly activating the auxin signaling pathway. This study demonstrates the important role of melatonin to modulate root growth under hypoxia stress, providing a new strategy for improving hypoxia tolerance.

Effects of Exogenous Chlorinated Amino Acetic Acid on Cadmium and Mineral Elements in Rice Seedlings.

To explore the effect of exogenous application of chlorinated amino acetic acid on cadmium (Cd) transport characteristics in rice seedlings, X24 and Z35 rice were taken as the research objects to carry out hydroponics experiments, and the changes of Cd content in rice seedlings, rice mineral elements and amino acid content in rice were analyzed. The results showed that exogenous application of 1.2 mmol·L-1 chlorinated amino acetic acid inhibited cadmium in shoots and roots of rice seedlings; Cd content in shoots and roots were reduced by up to 62.19% and 45.61%, respectively. The majority of cadmium was in the cell wall of shoots and roots; this decreased with the increase of the concentration of chlorinated acetic acid. In addition, the Mn content in shoots and Ca content in roots of rice seedlings increased significantly after the application of chlorinated amino acetic acid. The results of amino acid analysis showed that the contents of aspartic acid, glutamic acid and cystine in rice seedlings were increased. These results indicate that exogenous application of chlorinated amino acetic acid is beneficial to the synthesis of aspartic acid, glutamic acid and cysteine in rice seedlings, increases the content of Mn in shoots and Ca in roots of rice seedlings, and significantly alleviates cadmium stress in seedlings. This provides a theoretical basis for the development of an environmentally friendly Cd-lowering foliar fertilizer for rice.

Preparation of an Environmentally Friendly Rice Seed Coating Agent and Study of Its Mechanism of Action in Seedlings

Traditional rice seed coating agents (TRSCA) contain toxic components that pollute the environment and threaten human health. The use of safe, high-efficiency, and environmentally friendly seed coating agents is vital for environmental protection. We studied the production of a new, environmentally friendly rice seed coating agent and its mechanism at the seedling stage. We assess the difference in mechanism of action between the new seed coating agent and the representative TRSCAs on the market through laboratory and field experiments. Following the application of the new seed coating agent, bakanae disease was controlled at a rate of over 80.5% and insect pest feeding was controlled at a rate of 81%. More importantly, the LC50 value was 10 times higher than following TRSCA treatment. The coating agent can enhance the activity of plant protective enzymes (peroxidase [POD], catalase [CAT], and superoxide dismutase [SOD]) and the activity of rice seedling roots. The coating agent is antibacterial, disease preventative, deworming, safe, and environmentally protective, and results in the production of strong seedlings, suggesting it would be a good alternative to TRSCA. Our analysis found that the control effect of the seed coating on rice seedling disease was likely achieved by activating the plant protection enzymes (e.g., POD, CAT, and SOD). The effect of the coating agent on rice is likely achieved through increased root activity and the improvement of the rhizosphere micro-ecological system.

First report of Pythium aristosporum causing root rot on rice seedling in Taiwan.

Rice (Oryza sativa L.) is the principle staple crops in the World and its production can be severely damaged by Pythium species. Several Pythium species including P. afertile, P. arrhenomanes, P. dissotocum, P. elongatum, P. spinosum, have been recorded to cause rice seedling root rot in Taiwan (List of Plant Diseases in Taiwan edited by Tzean et al., 2019). During the survey of rice seedling diseases, we identified a new species of Pythium that causes seedling root rot on rice in commercial nursery trays in two nursery fields in 2019 in Taichung, Taiwan. Stunting and root rot symptom were found on the affected plants and up to 20% seedlings in a nursery tray showed similar symptoms. To isolate the pathogen, symptomatic roots were surface sterilized with 75% ethanol for 1 min and rinsed in sterile water. The margin of lesion was cut off, placed on 1.5% water agar and incubated at 28 ℃. After 24 h, the hyphal tips of a white colony growing from the diseased region were transferred to potato dextrose agar (PDA) medium. Koch's postulates were fulfilled by inoculating the germinated rice seeds with mycelia. Rice seeds of O. sativa var. Tainan11 (TN11) were treated with 75% ethanol and then 1.2% NaOCl for 15 min. The sterilized seeds were soaked in sterile water under dark condition for 3 days and the water was replaced every day. Five of the pre-germinated seeds with 2~5 mm embryonic shoot were placed in a sterile petri-dish and inoculated with 3-ml mycelial suspension (OD600 = 0.045) prepared by blending the mycelia of a 3-days PDA culture using an Oster 10 speed blender 6640 (Oster, USA). The seeds-mycelia were then covered with sterilized soil mixture of Akadama soil and rice husk (1:1, volume to volume) and incubated in a growth chamber at 28 ℃. Seven days post-inoculation, the inoculated seedlings showed stunting with short and necrotic roots (Fig. S1). The pathogen was reisolated from the diseased seedlings and identified with morphology and molecular methods. For morphological characterization, the pathogen was cultured on V8 agar to produce oogonia and zoospore (Chamswarng and Cook 1985). Globose oogonia with multiple antheridia (1-5 per oogonium), inflated filamentous sporangia, vesicle with abundant zoospores, main hypha with up to 6.57 μm wide and mature aplerotic oospores with diameter 24.35-30.81 μm (average= 27.22 μm; n=20) were observed (Fig. S1) that are similar to the descriptions for P. aristosporum (van der Plaats-Niterink 1981). Genomic DNA was extracted with CTAB method (Wang and White 1997) and the sequences of the internal transcribed spacer (ITS) region and gene region of β-tubulin (tub) and cytochrome c oxidase subunit II (cox II) were amplified with published primers (Villa et al., 2006). The obtained sequences were submitted to GenBank (accession nos: OL701302 (ITS), OL763269 (tub), and OL763270 (cox II); Fig. S2). Phylogenetic relationships between this Pythium pathogen and other 55 Pythium isolates, including the type species of P. aristosporum (ATCC11101), were conducted with the concatenated sequences of tub and cox II and analyzed by Bayesian interference (Fig. S3). Based on the tree built with tub and cox II sequences, this pathogen was identified as P. aristosporum that has not been reported in rice and other plants in Taiwan. It was observed in laboratory assays that this pathogen caused significant root-rot symptoms on several major rice varieties grown in Taiwan, including TN11, Tainung67 and Kaoshiung139. It may potentially cause severe crop loss in rice production, especially in nurseries. This identification provides important information on rice disease management.

Oxidative Damage in Roots of Rice (Oryza sativa L.) Seedlings Exposed to Microplastics or Combined with Cadmium

This study aimed to investigate the effect of 10-40mg L-1 polystyrene microplastics (PS-MPs), 0.05mg L-1 cadmium (Cd) and their combination on the growth and related physiological and toxicological responses in Oryza sativa L. seedling roots. Results showed that the fresh weight, dry weight and root lengths of treatments by PS-MPs, Cd single and combinative were all lower than the control, and opposite phenomenon appeared in production of superoxide radical (O2-.), malondialdehyde (MDA) and carbonylated protein. Superoxide dismutase (SOD) and guaiacol peroxidase (POD) activities induced by 10-40mg L-1 PS-MPs and combination with Cd were almost higher than those by Cd alone, expression of heat shock protein (HSP)70 and carbonylated protein slightly decreased. In compound exposure, 10-20mg L-1 PS-MPs alleviated Cd damage and promoted root growth by increasing SOD and POD activities, but 40mg L-1 PS-MPs accelerated the accumulation of Cd, MDA, and O2-., which was responsible for decreasing root biomass and the aggravating necrosis of root tip cells.

Seed priming using Moringa oleifera leaf decoction increases BPT 5204 rice yield

Abstract The present study screened different concentrations of Moringa oleifera (M. oleifera) leaf decoction (M. oleifera hot water extract-MWE) (100, 10, 1, and 0.1 g/L) to investigate their potential in increasing the yield of BPT 5204 rice variety. We aimed to analyze the effect of MWE on rice yield with different modes of treatment such as seed soaking, root treatment, and foliar spray. Rice seeds were soaked at different concentrations of MWE for 24 h before seeding. Plants grown from rice seeds soaked in 100 g/L MWE produced 6.6 tons/ha yield, whereas, roots of rice seedlings soaked for 4 h in varied MWE concentrations before transplantation and plants treated with 100 g/L MWE produced an yield of 6 tons/ha. In the last group, 45 day old rice plants were subjected to foliar spray with varying concentrations of MWE, where the foliar spray of rice plants with 100 g/L MWE showed a 6.5 tons/ha yield. As plants grown from rice seeds soaked in 100 g/L MWE produced a high yield, the leaves from these plants were analyzed to study the effect of MWE treatment on phenylalanine lyase and hydrogen peroxide (H2O2) and nitric oxide levels and genes involved in rice yield. The leaves of plants grown from rice seeds soaked in 100 g/L MWE showed increased H2O2 and SAM2 gene levels compared to control plants. This study reports the potential role of MWE as an environmentally safe, cost-effective and easy-to-use biostimulant for enhancing yield of rice.

Effects of Piper betle L. Extract and Allelochemical Eugenol on Rice and Associated Weeds Germination and Seedling Growth

Natural herbicide is considered as a sustainable approach for weed management in agriculture. Here, allelopathic activities of Piper betle L. extract (BE) and known allelochemical eugenol (EU) were studied against rice and associated weeds in terms of germination and seedling growth. Five plant species including a rice crop (Oryza sativa L.); a dicot weed, false daisy (Eclipta prostrata (L.) L.); and three monocot weeds, barnyard grass (Echinochloa crus-galli (L.) P. Beauv.), swollen fingergrass (Chloris barbata Sw.), and weedy rice (Oryza sativa f. spontanea Roshev.) were studied. The paper-based results demonstrated that BE and EU had inhibitory effects on seed germination and seedling growth. The IC50 values of BE and EU for seed germination were ranked from swollen fingergrass, to false daisy, barnyard grass, rice, and weedy rice, respectively. The ratio of root to shoot length of the seedlings indicated that the roots were more affected by the treatments than the shoots. In addition, the gel-based results showed the reduction of the rice seedling root system, especially on lateral root length and the numbers upon the treatments. Taken together, BE had an allelopathic activity similar to that of EU. Interestingly, the major paddy weed, barnyard grass, was more sensitive to BE than rice, underlining BE as a natural herbicide in rice agriculture.

Exopolysaccharides from Lactobacillus plantarum reduces cadmium uptake and mitigates cadmium toxicity in rice seedlings.

Exopolysaccharides (EPSs) can be used as effective exogenous substances to alleviate the toxic effect of cadmium (Cd) on rice and other crops, thus improving plant growth characteristics under stress conditions, and reducing the accumulation of Cd in grains, but the underlying mechanism is still unclear. In the present work, the effects of EPSs from Lactobacillus plantarum on the efficiency of Cd absorption and distribution in rice seedlings under Cd stress were investigated. The results revealed that growth of rice seedlings was severely inhibited by exposure to Cd, resulting in the decrease of plant height, leaf length and biomass. This inhibition phenomenon was alleviated by the addition of EPSs from L. plantarum LPC-1. The underlying mechanism might be that EPSs could facilitate the accumulation efficiency of Cd in rice roots and reduce the transportation rate of Cd from root to leaves, therefore decreasing the Cd content in leaves. Further research showed that Cd contents in the cell wall fraction of the rice seedling root were increased by the addition of EPSs, while the proportions of Cd in the cell organelle and cell soluble component were reduced. Application of EPSs promotes the proportion of pectate- and protein- integrated Cd in rice roots. While the content of water-soluble Cd, which is more toxic to plants, decreased continuously both in roots and leaves. Our study clearly confirmed the positive effects of EPSs on alleviating Cd toxicity and decreasing Cd translocation in rice above-ground parts. Furthermore, the subcellular distribution and chemical forms of Cd in different rice seedlings parts were also affected by the addition of EPSs, which might be an important potential mechanism for EPSs in respect of alleviating Cd toxicity for rice. These findings provided a foundation for the application of exogenous substances on improving the growth performance of crops under heavy metal stress.

Photoelectrochemical immunosensor for RNA methylation detection based on the enhanced photoactivity of Bi2S3 nanorods by g-C3N4 nanosheets

As an emerging analytical technology, photoelectrochemical (PEC) biosensor have attracted widespread attentions for detection of various targets. Herein, a simple, sensitive and selective PEC immunosensor was constructed for RNA methylation detection, where g-C3N4/Bi2S3 with improved photoelectric properties was used as the photoactive material, anti-m6A antibody was employed as target recognition molecule, and the target of m6A RNA was also adopted as photocurrent inhibitor. Under optimal experimental conditions, the immunosensor presented wide linear range from 0.1 − 50 nM and low detection limit of 0.025 nM (S/N = 3). The immunosensor also possessed high stability. Considering the growing threat of heavy metal and antibiotic pollution to food security, the applicability of the develop method was assessed by investigating the effect of Pb2+-antibiotics binary pollutants on RNA methylation level in the leaves and roots of rice seedlings.

OsABT Is Involved in Abscisic Acid Signaling Pathway and Salt Tolerance of Roots at the Rice Seedling Stage.

Rice is a staple cereal crop worldwide, and increasing its yields is vital to ensuring global food security. Salinity is a major factor that affects rice yield. Therefore, it is necessary to investigate salt tolerance mechanisms in rice. Proteins containing WD40 repeats play important roles in eukaryotic development and environmental adaptation. Here, we showed that overexpression of OsABT, a gene encoding a WD40-repeat protein, enhanced salt tolerance in rice seedlings by regulating root activity, relative conductivity, malondialdehyde and H2O2 content, and O2•− production rate. Root ion concentrations indicated that OsABT overexpression lines could maintain lower Na+ and higher K+/Na+ ratios and upregulated expression of salt-related genes OsSOS1 and OsHAK5 compared with the wild-type (WT) Nipponbare plants. Furthermore, Overexpression of OsABT decreased the abscisic acid (ABA) content, while downregulating the ABA synthesis genes OsNCED3 and OsNCED4 and upregulating the ABA catabolic gene OsABA8ox2. The yeast two-hybrid and bimolecular fluorescence complementation analyses showed that OsABT interacted with the ABA receptor proteins OsPYL4, OsPYL10, and PP2C phosphatase OsABIL2. A transcriptome analysis revealed that the differentially expressed genes between OsABT overexpression lines and WT plants were enriched in plant hormone signal transduction, including ABA signaling pathway under salt stress. Thus, OsABT can improve the salt tolerance in rice seedling roots by inhibiting reactive oxygen species accumulation, thereby regulating the intracellular Na+/K+ balance, ABA content, and ABA signaling pathway.

Effects of Exogenous Jasmonic Acid on Arsenic Accumulation and Response to Stress in Roots of Rice Seedlings

Arsenic (As) pollution has a toxic effect on crop growth, leading to reduced crop quality and yield. Therefore, it is urgent to explore safe and effective strategies to reduce its toxicity. In this experiment, hydroponics, fluorescent probe locating technology, differential centrifugation, and Fourier infrared spectroscopy (FTIR) analysis were used to research the effect of exogenous jasmonic acid (JA) on the accumulation and stress resistance of rice seedlings. The results showed that JA application reduced the As content in the roots and shoots of rice by 31.4% and 51.4%, respectively, and significantly reduced As content in the cell wall and soluble fractions of rice roots. JA changed the distribution ratio of As in the subcellular components. The distribution ratio of As in the cell wall increased by 16.4%, and the distribution ratio of soluble fractions decreased by 17.3%. JA enhanced the fixation of As by the cell wall and reduced the As content in the soluble fraction. Furthermore, JA increased the levels of SOD, CAT, GSH, and PEPC in root cells and reduced the contents of H2O2 and MDA, indicating that JA reduced lipid peroxidation damage, regulated carbon and nitrogen metabolism, and alleviated As toxicity. This research provides a new approach for the prevention and control of rice As pollution.

Temporal Dynamics of Endogenous Bacterial Composition in Rice Seeds During Maturation and Storage, and Spatial Dynamics of the Bacteria During Seedling Growth.

Seed endophytes are of interest because they are believed to affect seed quality, and ultimately, plant growth and fitness. A comprehensive understanding of the assembly of the seed microbiome during seed development and maturation, the fate of microbes during storage, and the migration of microbes during seedling growth are still lacking. In this study, to understand the assembly and fate of endogenous bacteria in rice seeds from the ripening stage to the storage and seedling stages, we employed culture-dependent and metagenomic analyses. Bacterial communities in rice seeds were composed of a few dominant taxa that were introduced at the milky and dough stages, and they persisted during seed maturation. The culturable bacterial population gradually increased during the ripening stage, whereas there was a gradual decrease during storage. Bacteria that persisted during storage proliferated after imbibition and were distributed and established in the shoots and roots of rice seedlings. The storage temperature influenced the abundance of bacteria, which consequently changed the bacterial composition in the shoots and roots of seedlings. Pantoea, Pseudomonas, and Allorhizobium were consistently abundant from seed development to the germination stage. Some endogenous bacterial strains significantly promoted the growth of Arabidopsis and rice plants. Overall, our results indicate that rice seeds are colonized by a few bacterial taxa during seed development, and their relative abundance fluctuates during storage and contributes significantly to the establishment of endophytes in the stems and roots of rice plants. The selected bacterial isolates can be used to improve the growth and health of rice plants. To the best of our knowledge, this is the first study to reveal the dynamics of bacterial populations during storage of rice seeds at different temperatures. The temporal dynamics of the bacterial community during seed storage provide clues for the manipulation of endogenous bacteria in rice plants.

Binderless board made from composted rice straw as substrate for rice seedlings

A binderless board was produced from mechanically dissociated compost straw via suction filtration. The binderless board was applied to replace the topsoil that is currently used predominantly as the substrate for rice seedlings in China. The binderless board showed the highest tensile strength when the rice straw had been composted for 20 days. The bulk density, aeration, and total porosity of the binderless board showed an increasing trend with composting time, due to the increased decomposition of rice straw. The examination of the growth parameters and root morphology of the rice seedlings showed that electrical conductivity (EC), pH, and nutrient content of the binderless board made from rice straw composted for 10 days were conducive to the growth of seedlings. Polyphenols inhibited rice seedling height and shoot weight and promoted the rice seedling stem diameter and root weight. Considering the quality loss, growth index, and the strength of the binderless board, 10 days of composting is the optimal condition. These results indicate that binderless board can replace top soil and peat when used as the substrate for rice seedling.

Identification and profiling of silicate-solubilizing bacteria for plant growth-promoting traits and rhizosphere competence

Excessive use of synthetic fertilizers may negatively affect overall soil health and the environment. There is a need to come up with alternative strategies to ensure competitive yields of crops and at the same time maintain soil ecological balance. The use of soil microorganisms as microbial inoculants in agriculture is considered an alternative approach to enhance crop growth. Soil is a good source of microorganisms that are capable of producing different beneficial enzymes such as silicase, phosphatase and other growth-promoting enzymes which are important in crop growth. Soil beneficial microorganisms such as silicate-solubilizing bacteria play an important role in solubilizing insoluble forms of silicates that are important in crop growth. This study was conducted to identify and profile silicate-solubilizing bacteria (SSB) in Louisiana soils and to document the colonization potential of SSB in rice (Oryza sativa) plants. Bacterial isolates were spot-inoculated on silica agar medium and incubated at 37 °C for 48 h. The clearing zone around colonies was measured and used to compute for solubilization index (SI), i.e., halo diameter (mm)/colony diameter (mm). Despite of the abundance of microorganisms found in these soils only 20 bacterial isolates are capable of solubilizing silicates; 16 were with low (SI < 2.0) and 4 with intermediate (2.00 < SI < 4.00) solubilization capacities. Further analysis also revealed that three of the isolates with intermediate silicate solubilization capacities also produced plant growth-promoting enzymes: phosphatase, 1-aminocyclopropane-1-carboxylic acid deaminase and indole-3-acetic acid enzyme. Based on the sequencing information and the phylogenetic tree, the putative SSB were identified into four genera: Aeromonas, Bacillus, Enterobacter and Pseudomonas. The fluorescent microscopy analysis revealed that the GFP-tagged SSB can colonize roots of young rice seedlings, a good indicator of SSB potential as seed treatment for scaling up its application in production field. Furthermore, information on the survival of SSB inoculates in different soil-plant systems in Louisiana and impact of management practices on SSB activity and population are needed to fully develop this bio-based approach to improve Si nutrition in soil and plants.

The NADPH oxidase OsRbohA increases salt tolerance by modulating K+ homeostasis in rice

Rice (Oryza sativa L.) is a staple cereal for more than two thirds of the world’s population. Soil salinity severely limits rice growth, development, and grain yield. It is desirable to elucidate the mechanism of rice’s salt-stress response. As the major source of H2O2, NADPH oxidase (Rboh) is believed to be involved in salt-stress tolerance. However, the function and mechanism of rice Rboh in salt stress response remain unclear. In this study, we found that the expression of OsRbohA was up-regulated by NaCl treatment in the shoots and roots of rice seedlings. Knockout of OsRbohA reduced the tolerance of rice to salt stress. Knockout of OsRbohA blocked NaCl-induced increases of NADPH activity and H2O2 content in roots. OsRbohA knockout inhibited root growth and disrupted K+ homeostasis by reducing the expression of K+ transporters and channel-associated genes (OsGORK, OsAKT1, OsHAK1, and OsHAK5) in roots under NaCl treatment. Under NaCl treatment, OsRbohA knockout also reduced subcellular K+ contents of the plasma membrane and soluble fraction. Overexpression of OsRbohA increased the expression of K+ transporters and channel-associated genes and reduced the loss of K+ ions in roots. These results indicate that OsRbohA-mediated H2O2 accumulation modulates K+ homeostasis, thereby increasing salt tolerance in rice.

Effects of Burkholderia sp. Y4 on Cadmium Damage and Uptake in Rice Seedlings

In order to investigate the effects of Burkholderia sp. Y4 on rice seedlings under cadmium (Cd) stress, seed germination and vermiculite culture experiments were conducted using low Cd-accumulation xiangzaoxian 24 (X24) and high Cd-accumulation Tyou 705 (T705) varieties. The effects of Burkholderia sp. Y4 on rice growth, oxidative damage caused by Cd, and Cd accumulation were studied. Additionally, the Cd2+ flux rates in the elongation zone of rice roots under Burkholderia sp. Y4 application were detected using non-invasive micro-test technology. Burkholderia sp. Y4 alleviated the inhibition effect of Cd on rice seed germination by 13.8%. After inoculation with Burkholderia sp. Y4 for 7 d, the length of rice roots and buds increased by 83.3% and 12.2%, and their dry weight increased by 56.8% and 12.5%, respectively; those in the 10 d Y4 inoculation group increased by 28.6% and 20.0% in length and by 113.2% and 46.0% in dry weight, respectively. Burkholderia sp. Y4 inoculation also alleviated rice oxidative stress damage caused by Cd. The application of strain Y4 significantly reduced the content of the oxidative damage product malondialdehyde (MDA) in the shoots and roots of rice seedlings by 21.5% and 16.9%, respectively. Under Burkholderia sp. Y4 inoculation, the significant changes in antioxidant enzyme SOD and CAT activities caused by Cd stress disappeared in rice roots; those in shoots also decreased from 176.9% and 74.8% to 53.3% and 21.5%, respectively. Conversely, Burkholderia sp. Y4 inhibited Cd uptake by rice seedlings with different genotypes, including the low Cd-accumulation variety X24 and high Cd-accumulation variety T705. The root application of strain Y4 significantly reduced Cd accumulation in the shoots and roots of rice seedlings by 79.2% and 62.7% in T705 and by 57.3% and 24.1% in X24, respectively. The Cd2+ flux rate of high Cd-accumulation variety T705 was significantly higher than that of low Cd-accumulation variety X24. Under Burkholderia sp. Y4 inoculation, the yellow membrane was formed on the root surface of rice seedlings, and the Cd2+ flux rate in the elongation zone of T705 and X24 roots decreased by 36.0% and 35.0% in 3-day-old seedlings, as well as by 44.6% and 24.9% in 10-day-old seedlings, respectively. In conclusion, Burkholderia sp. Y4 inoculation inhibited the toxic effects of Cd on rice seedling growth through alleviating oxidative stress and damage caused by Cd. Furthermore, the root application of Burkholderia sp. Y4 effectively decreased the Cd2+ flux rate in the elongation zone of roots to inhibit the Cd uptake and accumulation in roots and shoots of rice seedlings. This study provides theoretical basis and data support for the application of Burkholderia sp. Y4 as a Cd-reducing and growth-promoting agent for rice in contaminated farmland.

Application of RNA sequencing to understand the benefits of endophytes in the salt-alkaline resistance of rice seedlings

Endophytes significantly improve salt-alkaline resistance of rice seedlings and promote their growth, but the definite mechanisms remain largely unknown. This study aimed to understand the molecular players behind the endophytic benefits for rice seedlings under salt-alkaline stress. RNA sequencing (RNA-seq) was performed on the roots and shoots of rice seedling ( Oryza sativa L.) with/without endophytic infection under 10 mM Na 2 CO 3 -treatment. The differential expression genes (DEGs) resulting from endophytic infection were analyzed, and the functions of DEGs were annotated using gene ontology (GO) enrichment and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Results showed endophytic infection significantly promoted the growth of rice seedlings under salt-alkaline stress. Through RNA-seq, many genes were shown to be potentially involved in the endophytic benefits for rice seedlings. At one day of endophytic infection, RNA-seq identified 3469 DEGs in rice seedling roots and 572 DEGs in shoots, whereas five days of endophytic infection led to 297 and 257 DEGs in roots and shoots, respectively. According to the GO and KEGG annotation of DEGs, the growth-promotion processes correlating with the beneficial endophyte-rice interplay involve a multitude of molecular events, including biosynthesis, energy metabolism, enzyme activity, photosynthesis, ROS-scavenging system, and hormonal signaling, etc. Together, this work presents evidence of plant-microbe interaction that extends insights into the mechanisms underlying the endophyte-rice association. • The endophyte orchestrates phenotypic traits of rice seedlings under salt-alkaline stress. • The endophyte affects a multitude of gene expression in rice plant. • Endophytic benefit is a cumulative outcome of differential expression genes.

Biochar-based fertiliser enhances nutrient uptake and transport in rice seedlings

Biochar-based compound fertilisers (BCF) are gaining increasing attention as they are cost-effectiveness and improve soil fertility and crop yield. However, little is known about the mechanisms by which micron-size BCF particles enhance crop growth. In the present study, Wuyunjing7 rice seedlings were exposed to micron-size particles of wheat straw-based BCF (mBCF) diffused through a 25-μm nylon mesh. The control was fertilised with urea, diammonium phosphate, and potassium chloride to ensure that both treatments received comparables level of N, P, and K. The effects of mBCF on rice seedling growth were evaluated by determining the changes in nitrogen uptake and utilisation via nitrogen content measurements, short-term 15N-NH4+ influx assays, and analyses of transcript-level nutrient transporter gene expression. The shoot biomass of rice seedling treated with mBCF at the rate of 5 mg/ g soil was 33% greater than that for the control. Root and shoot 15N accumulation rates were 44% and 14% higher, respectively, in the mBCF-treated than the control. The mBCF-treated rice seedlings had higher phosphorus, potassium, and iron content than the control. Moreover, the treatments significantly differed in terms of their nutrient transporter gene expression levels. Spectroscopy and microscopy were used to visualise nutrient distributions across transverse root sections. There were relatively higher iron oxide nanoparticle and silicon-based compound concentrations in the roots of the mBCF-treated rice seedlings than in those of the control. The foregoing difference might account for the fact that the growth of the mBCF-treated rice was superior to that of the control. We demonstrated that the mBCF treatment created a more negative electrical potential at the root epidermal cell layer (~ − 160 mV) than the root surface. This potential difference may have been the driving force for mineral nutrient absorption.