Effects of Different Kinds of Exogenous Auxin on the Growth of Rice Roots under Cadmium Stress

[Objective] The aim was to study the effect of different kinds of exogenous auxin on the growth of rice roots under cadmium stress.[Method] Oryza sativa L.cv Zhonghua No.11 was used as experimental materials to detect the effect of different kinds of exogenous auxin on the growth of rice roots.[Result] The results showed that 0.1 mmol/L Cd treatment could not only increase primary,adventitious and lateral root length but also lateral root number,whereas the shoot growth was inhibited.When supplemented with different concentrations of NAA,IAA,IBA and 2,4-D,the growth of root system varied and similar change trend had been found.At the auxin concentration of 10^-9-10^-7 mol/L in particular 10^-8 mol/L,all four kinds of auxin promoted the elongation growth of primary and adventitious roots,but inhibition was observed when auxin was higher than 10^-7 mol/L.The decreased shoot growth caused by Cd could not be counteracted by supplementing with the four kinds of auxin.However,at the auxin concentration of 10^-9-10^-8 mol/L,NAA could improve rice growth under Cd stress condition.The formation and development of lateral roots on primary and adventitious roots was not only similar but also different after applying the same concentration of four auxins.[Conclusion] The addition of suitable amount of auxin under cadmium stress （such as 10^-9-10^-8 mol/L of NAA and so on） could ease the damage of cadmium on plants to a certain extent.

Enhancement of NH_4^+ Uptake by NO_3^- in Relation to Expression of Nitrate-Induced Genes in Rice (Oryza sativa) Roots

This study aimed to survey the expression of genes involved in rice N uptake and aasimilatory network and to understand the potential molecular mechanisms responsible for the NO3^-enhanced NH4^＋ uptake. By using quantitative real-time polymerase chain reaction （PCR）, the genes related to N nutrition, including ammonium transporters （AMTs） and ammonium assimilatory enzymes （GS and GOGAT）, were transcriptionally analyzed in rice plants grown in the absence and presence of NO4^- in the NH4^＋-containing medium. The results showed that NH4^＋ uptake by rice was enhanced by the NO3^- supply to the medium. At the same time and in parallel, the amount of transcripts of seven genes （OsAMT1;1, OsAMT1;2, OsAMT4;1, OsGLNP, OsGLU1, OsGLT1, and OsGLTP） was increased in rice roots, but the expression of two genes （OsGLN1;1 and OsGLN1;P） was decreased and that of OsAMT1;3 remained without change. Up- or downregulation of these genes involved in NH4^＋ uptake and assimilation correlated with the increase in NH4^＋ uptake in the presence of NO3^- in rice roots.

Comparative proteomic study and functional analysis of translationally controlled tumor protein in rice roots under Hg^(2+) stress

So far, very little is known about mercury stress-induced intercellular metabolic changes in rice roots at the proteome level. To investigate the response of rice roots to mercury stress, changes in protein expression in rice roots were analyzed using a comparative proteomics approach. Six-leaf stage rice seedlings were treated with 50 μmol/L HgC12 for 3 hr; 29 protein spots showed a significant changes in abundance under stress when compared with the Hg2＋-tolerant rice mutant and wild type （Zhonghua 11）. Furthermore, all these protein spots were identified by mass spectrometry to match 27 diverse protein species. The identified proteins were involved in several processes, including stress response, redox homeostasis, signal transduction, regulation and metabolism; some were found to be cellular structure proteins and a few were unknown. Among the up-regulated proteins, OsTCTP （translationally controlled tumor protein） was chosen to perform hetereologous expression in yeast which was presumed to participate in the Hg2~ tolerance of rice, providing evidence for its role in alleviating Hg2~ damage. Among the many tests, we found that OsTCTP-overexpressed yeast strains were more resistant to Hg2＋ than wild-type yeast. Thus, we propose that OsTCTP contributes to Hg2＋ resistance. Here we present, for the first time, the functional characterization of OsTCTP in connection with Hg2＋ stress in plants.

Effect of Glucose on Zinc-induced Growth of Root System in Rice

[Objective] This study was aimed at exploring the effect of glucose signal on the zinc-induced growth of root system using rice as the material.[Method] The variation of root system growth,active oxygen production and proton secretion of root systems treated with various concentrations of glucose,glucose ＋ Zn（NO3）2,mannitol and Zn（NO3）2 ＋ mannitol were analyzed in rice（Oryza sativa L.cv Zhonghua no.11）.[Result] The results showed that the concentrations of glucose had affected the shoot height,primary root length,amount and length of lateral roots on primary roots,adventitious root length and length of lateral roots on adventitious roots in varying degrees,but not the amount of adventitious roots and lateral roots on adventitious roots under Zn＋ and Zn-condition.Glucose of high concentrations induced the production of active oxygen,while lacking of glucose would lead to the decrease of proton secretion of root systems.However,there were significant differences in these indexes between under Zn＋ and under Zn-condition treated with the same concentrations of glucose.The effects of glucose and mannitol with the same concentration on the growth of root systems were significantly different,indicating that the variation was resulting from sugar signal but not the osmotic potential.[Conclusion] The glucose had played important roles in the growth of rice root system both under normal condition and under Zn＋ condition.

Regulation of ABA on Rice Root System Growth under Cadmium Stress

[Objective] The regulation of ABA on rice root system growth under Cd stress was studied.[Method] Taking rice Zhonghua No.11 as material,changes in rice root system growth were studied under the treatments of Cd,Cd ＋ ABA and Cd ＋ ABA inhibitor.[Result] Exogenous ABA could shorten the length of primary roots and adventitious roots of rice and could obviously inhibit the formation of lateral roots in primary roots and adventitious roots;ABA could obviously shorten the distance from root hair to root tip,but had little effect on the quantity of adventitious roots.[Conclusion] ABA takes part in the regulation in rice root system growth under Cd stress.

Regulation of Sucrose and Zinc on Root System Growth in Rice

[Objective] The aim was to study the relationship between urcrose, zinc and the root system growth in rice. [Method] Changes of root system growth, ROS generation and root system proton export ability were analyzed in rice （Oryza sativa L. cv Zhonghua No.11） treated with different concentrations of Zn （NO3）3 sucrose, com- bined sucrose and Zn （NO3）3 mannitol as well as mannitol plus Zn （NO3）2. [Result] The results showed that treatment with 1-3 mM Zn（NO3）2 resulted in significant increases in total root length /number and in accumulation of H202 and 02- but decreases in root system proton export ability. With the exception of shoot length, the length of primary, adventitious, and lateral roots, and the number of adventitious, and lateral roots on primary /adventitious roots were all influenced by different concentrations of sucrose. High concentrations of sucrose caused increases in H202 and O2-, starva- tion or high concentrations of sucrose reduced root system proton export ability after treating with or without Zn. However, at the same concentration of sucrose, different changes of these indicators were observed between Zn and non-Zn treatments. The regulation of root system growth induced by sucrose was marked different from that of mannitol at the same concentration of 5%, suggesting that these effects were caused by sugar signal but not by osmotic potential. [Conclusion] This study indicat- ed that both sucrose and Zn play important roles in the regulation of rice root system growth.

Effects of Superoxide Radical on Root System Growth and Auxin Distribution in Rice

[Objective] This study aimed to investigate the effect of superoxide radical on root system growth and auxin distribution in rice （Oryza sativa L. cv Zhonghua No.11）. [Method] With rice Zhonghua No.ll as the experimental material, the effects of DDC （SOD inhibitor） and Tiron （superoxide radical scavenger） on the root system growth, superoxide radical generation and root system auxin distribution in rice were analyzed. [Result] The growth and elongation of primary and adventitious roots were significantly promoted by DDC, while Tiron significantly inhibited the growth and elongation of shoots, primary roots and their lateral roots, and also suppressed the formation and growth of the adventitious roots as well as the elongation of their lateral roots. The superoxide radical was increased with the induction of DDC, while Tiron decreased the accumulation of superoxide radical. Increased accumulation of auxin in the vascular bundle and behind the elongation zone was observed in DDC- treated roots, while the treatment with Tiron resulted in a decrease of auxin in the same position. [Conclusion] This study indicated that the regulation of rice root sys- tem growth by superoxide radical was closely related with the accumulation and distribution of auxin.

MT 10 Mutant of Rice with Altered Lateral Root Initiation

Mutants with increased resistance to toxic anxin concentrations were first isolated in rice.The present report describes their isolation,genetics and physiological characterization.

Effect of Exogenous Ammonium on GlutamineSynthetase, Glutamate Synthase, and Glutamate Dehydrogenase in the Root of Rice Seedling

Root biomass of rice seedlings was increased at lower concentration of exogenous NH 4 + , but it was decreased at higher concentration of exogenous NH 4 + . The level of free NH 4 + in the roots was accumulated gradually with the increase of NH 4 + concentration in the nutrient solution. The content of the soluble proteins was essentially constant at higher NH 4 + . The activities of glutamine synthetase (GS), NADH-dependent glutamate synthase (NADH-GOGAT), and NADH-dependent glutamate dehydrogenase (NADH-GDH) were risen with exogenous NH 4 + concentration at the lower NH 4 + concentration range. But the activities of GS and NADH-GOGAT were declined, and the level of NADH-GDH activity was kept constant under higher NH 4 + concentration. The GS/GDH ratio suggested that NH 4 + was assimilated by GS-GOGAT cycle under lower NH 4 + concentration, but NADH-GDH was more important for NH 4 + assimilation and detoxifying NH 4 + to the tissue cells at the higher NH 4 + level. According to the growth and the activity changes of these ammonium-assimilating enzymes of rice seedling roots, 10. 0 μg/mL NH 4 + -N in nutrient solution was more suitable to the rice growth.

Suberin Biopolymer in Rice Root Exodermis Reinforces Preformed Barrier Against Meloidogyne graminicola Infection

Exploration of novel genetic resources against root-knot nematode(RKN)is necessary to strengthen the resistance breeding program in cultivated rice,and investigations on the role of genotype-specific root anatomy in conferring a structural barrier against nematode invasion are largely underexplored.Here,we reported a highly-resistant rice germplasm Phule Radha that conferred remarkably lower RKN parasitic fitness in terms of reduced penetration and delayed development and reproduction when compared with susceptible cultivar PB1121.Using histological and biochemical analyses,we demonstrated that an enhanced suberin deposition in the exodermal root tip tissue of Phule Radha compared to PB1121 can effectively form a penetrative barrier against RKN infection,and this preformed barrier in the control tissue did not necessarily alter to a greater extent when challenged with RKN stress.Using qRT-PCR analysis,we showed that a number of suberin biosynthesis genes were greatly expressed in the exodermis of Phule Radha compared to PB1121.In sum,the present study established the role of rice exodermal barrier system in defense against an important soil-borne pathogen.

OsABA8ox2, an ABA catabolic gene, suppresses root elongation of rice seedlings and contributes to drought response

In rice, OsABA8ox encodes abscisic acid(ABA) 8′-hydroxylase, which catalyzes the committed step of ABA catabolism. The contribution of ABA catabolism in root development remains unclear. We investigated the role of OsABA8ox2 in root growth and development and drought response. GUS staining results showed that OsABA8ox2 was expressed mainly in roots at seedling stage and was strongly expressed in the meristematic zone of the radicle. OsABA8ox2 expression in roots was markedly decreased after 0.5 h polyethylene glycol(PEG) treatment and increased after 0.5 h rehydration, implying that OsABA8ox2 is a drought-responsive gene.OsABA8ox2 knockout mediated by the CRISPR-Cas9 system increased drought-induced ABA and indole-3-acetic acid accumulation in roots, conferred increased ABA sensitivity, and promoted a more vertically oriented root system architecture(RSA) beneficial to drought tolerance.OsABA8ox2 overexpression suppressed root elongation and increased stomatal conductance and transpiration rate. Consequently, OsABA8ox2 knockout dramatically improved rice drought tolerance, whereas OsABA8ox2 overexpression seedlings were hypersensitive to drought stress,suggesting that OsABA8ox2 contributes to drought response in rice. Compared with wild type,functional leaves of OsABA8ox2 knockout seedlings showed higher ABA levels, whereas overexpression lines showed lower ABA levels, suggesting that OsABA8ox2, as an ABA catabolic gene, modulates ABA concentration through ABA catabolism. OsABA8ox2 and OsABA8ox3 were both localized in the endoplasmic reticulum. Together, these results indicate that OsABA8ox2 suppresses root elongation of rice seedlings, increases water transpiration, and contributes to drought response through ABA catabolism, and that OsABA8ox2 knockout dramatically improves rice drought tolerance. They highlight the key role of ABA catabolism mediated by OsABA8ox2 on root growth and development. OsABA8ox2, as a novel RSA gene, would be a potential genetic target for the improvement of rice drought tolerance.

Effects of CO_2 laser on chromosomal aberration in the root tip cells of rice

Seeds of japonica rice cv.Zhenuo 2 with twodifferent physiological states(dry seeds withwater content 13% and wet seeds soaked in thewater for 36 h)were irradiated by COlaser infour different power-densities and durations re-spectively.The treatment irradiated with 200GY ofCo γ-rays was considered as control.The flesh root tips were cut and fixed inCarnoy’s fluid for cytological examination.

Hydrogen Peroxide-Mediated Growth of the Root System Occurs via Auxin Signaling Modification and Variations in the Expression of Cell-Cycle Genes in Rice Seedlings Exposed to Cadmium Stress

The link between root growth, H2O2, auxin signaling, and the ceil cycle in cadmium （Cd）-stressed rice （Oryza sativa L. cv. Zhonghua No. 11） was analyzed in this study. Exposure to Cd induced a significant accumulation of Cd, but caused a decrease in zinc （Zn） content which resulted from the decreased expression of OsHMA9 and OsZIP. Analysis using a Cd-specific probe showed that Cd was mainly localized in the meristematic zone and vascular tissues. Formation and elongation of the root system were significantly promoted by 3-amino-l,2,4-triazole （AT）, but were markedly inhibited by N,N＇. dimethylthiourea （DMTU） under Cd stress. The effect of H2O2 on Cd-stressed root growth was further confirmed by examining a gain-of-function rice mutant （carrying catalasel and glutathione-S-transferase） in the presence or absence of diphenylene iodonium. DR5-GUS staining revealed close associations between H2O2 and the concentration and distribution of auxin. H2O2 affected the expression of key genes, including OsYUCCA, OsPIN, OsARF, and OslAA, in the auxin signaling pathway in Cd-treated plants. These results suggest that H2O2 functions upstream of the auxin signaling pathway. Furthermore, H2O2 modified the expression of cell-cycle genes in Cd-treated roots. The effects of H2O2 on root system growth are therefore linked to auxin signal modification and to variations in the expression of cell-cycle genes in Cd-stressed rice. A working model for the effects of H2O2 on Cd-stressed root system growth is thus proposed and discussed in this paper.

Root microbiota shift in rice correlates with resident time in the field and developmental stage

Land plants in natural soil form intimate relationships with the diverse root bacterial microbiota. A growing body of evidence shows that these microbes are important for plant growth and health. Root microbiota composition has been widely studied in several model plants and crops; however, little is known about how root microbiota vary throughout the plant's life cycle under field conditions. We performed longitudinal dense sampling in field trials to track the time-series shift of the root microbiota from two representative rice cultivars in two separate locations in China. We found that the rice root microbiota varied dramatically during the vegetative stages and stabilized from the beginning of the reproductive stage, after which the root microbiota underwent relatively minor changes until rice ripening. Notably, both rice genotype and geographical location influenced the patterns of root microbiota shift that occurred during plant growth. The relative abundance of Deltaproteobacteria in roots significantly increased overtime throughout the entire life cycle of rice, while that of Betaproteobacteria, Firmicutes, and Gammaproteobacteria decreased. By a machine learning approach, we identified biomarker taxa and established a model to correlate root microbiota with rice resident time in the field(e.g., Nitrospira accumulated from 5 weeks/tillering in field-grown rice). Our work provides insights into the process of rice root microbiota establishment.

Improving Nitrogen Use Efficiency in Rice through Enhancing Root Nitrate Uptake Mediated by a Nitrate Transporter, NRT1.1B

Nitrogen （N） is one of most important nutrients for crop production, which makes up 1%-5% of total plant dry matter （Marschner, 2012）. Due to the limited availability of N in soil, application of N fertilizers has been an important agronomic practice to increase crop yield. However, over-application of N fertilizers has caused pollution of N in soil, water and air. It was estimated that the nitrogen use efficiency （NUE, the total biomass or grain yield produced per unit of applied fertilizer N） in cereal crops is as low as 33% （Raun and Johnson, 1999）. Therefore, improving NUE together with reducing application of N fertilizers is an important issue for environment and sustainable production of crops. This is especially important for rice, which is a staple food for half population in the world.

Using diffusive gradients in thin films technique for in-situ measurement of labile phosphorus around Oryza sativa L. roots in flooded paddy soils

Behavior of phosphorus(P) in flooded rice soil is controlled by iron(Fe) redox cycling in root-zone. In this study, we applied a novel approach—the diffusive gradients in thin films(DGT) technique—for investigating the in-situ distribution of labile phosphorus(P) and Fe in close proximity to Asian rice(Oryza sativa L.) roots at submillimeter to millimeter spatial resolutions during the seedling and booting stages. We conducted a seven-year field experiment under rice-wheat rotation with different P fertilizer treatments. The results showed a significant and strong positive relationship of the average DGT-labile P concentration with soil Olsen P(R2= 0.77, P < 0.01) and with rice total P concentration(R^(2)= 0.62, P < 0.05). Furthermore, results on one-and two-dimensional changes of DGT-labile P indicated that fertilization only in the wheat season produced sufficient amounts of labile P in the flooded paddy soils, similar to when fertilizer was applied only in the rice season;dissolved P concentrations, however, were lower. A co-occurrence and significant positive correlation(P < 0.01) between DGT-labile P and Fe indicated Fe-coupled mobilization of P in flooded paddy soils. These results collectively indicated that the DGT technique provided information on in-situ distribution of labile P and its variability in close proximity to rice roots. This suggests that the DGT technique can improve our understanding of in-situ and high-resolution labile P processes in paddy soils and can provide useful information for optimizing P fertilization.

Nuclear translocation of OsMADS25 facilitated by OsNAR2.1 in reponse to nitrate signals promotes rice root growth by targeting OsMADS27 and OsARF7

Nitrate is an important nitrogen source and signaling molecule that regulates plant growth and development.Although several components of the nitrate signaling pathway have been identified,the detailed mechanisms are still unclear.Our previous results showed that OsMADS25 can regulate root development in response to nitrate signals,but the mechanism is still unknown.Here,we try to answer two key questions:how does OsMADS25 move from the cytoplasm to the nucleus,and what are the direct target genes activated by OsMADS25 to regulate root growth after it moves to the nucleus in response to nitrate?Our results demonstrated that OsMADS25 moves from the cytoplasm to the nucleus in the presence of nitrate in an OsNAR2.1-dependentmanner.Chromatin immunoprecipitation sequencing,chromatin immunoprecipitation qPCR,yeast one-hybrid,and luciferase experiments showed that OsMADS25 directly activates the expression of OsMADS27 and OsARF7,which are reported to be associated with root growth.Finally,OsMADS25-RNAi lines,the Osnar2.1 mutant,and OsMADS25-RNAi Osnar2.1 lines exhibited significantly reduced root growth compared with the wild type in response to nitrate supply,and expression of OsMADS27 and OsARF7 was significantly suppressed in these lines.Collectively,these results reveal a new mechanismby which OsMADS25 interacts with OsNAR2.1.This interaction is required for nuclear accumulation of OsMADS25,which promotes OsMADS27 and OsARF7 expression and root growth in a nitratedependent manner.

Nutrient Composition and Distance from Point Placement to the Plant Affect Rice Growth

Point placement of urea is an efficient technology to improve urea use efficiency in transplanted rice(Oryza sativa L.), but it is largely unknown how nutrient composition in the point placement and the distance from placement site to the plant influence rice root distribution and growth, nutrient uptake, and rice grain yield. A controlled greenhouse experiment was conducted using both N-and P-deficient soil with point placement of N only or N and P together(N + P) at a distance close to or far from the plant,in comparison to an N-spilt application and a no-N control. Both nutrient composition and distance significantly affected rice root growth. Compared with the N point placement, the N + P point placement led to smaller root length and mass densities, higher specific root length(SRL) around the placement site, smaller root system, higher straw mass and grain yield, and higher N and P uptake. The difference between the N + P and N point placements was greater when close to the plant than when far from the plant. It is suggested that higher SRL around the placement site is essential for improving nutrient uptake and rice grain yield, and simultaneous point placement of N and P has a synergistic effect on rice growth.

Visual Modeling of Rice Root Growth Based on B-Spline Curve

As a major food production crop in China,the growth and development of rice is an extremely complex systemic process,and the root system is the main organ for rice to obtain nutrients.Therefore,3D modeling and visualization of the rice root system can help to further understand its morphology,structure and function,and provide an aid for scientific cultivation of rice and improving rice yield for decision making.In this paper,a mathematical model of the rice root system is established based on the B spline curve combined with the L-system approach,using mathematical knowledge based on the 3D morphological characteristics of the real rice root system.The B-Spline Curve is chosen to simulate this,and the recursive definition of B-Spline Curve and its formula are used to realize the modeling of the rice root system curve.Based on the mathematical method of rice root system integration,the bending effect of rice root system at different periods and different growth positions is realized.Finally,the L-system combined with B-Spline Curve is used to construct a rice root system model and realize the rice root system visualization simulation.The simulated image is closer to the real rice root system image in terms of morphological structure and has a strong sense of realism.