Effects of Biostimulant NEAU10 on Growth of Rice Seedlings and Soil Physicochemical Parameters

The process of rice(Oryza sativa L.)seedling cultivation is often subjected to adverse environmental stress.Biostimulants regulate the robust growth of rice seedlings and play a crucial role in promoting the green and ecological development of agriculture.In this study,1.0 and 2.0 g•m^(-2) of the biostimulant were applied to soil in rice seedbeds.Growth indicators of rice,antioxidant enzyme activities and soil physicochemical characteristics were assessed at the 2.5-leaf and 4-leaf stages of rice.The results indicated that applying 2.0 g•m^(-2) of the biostimulant at both the 2.5-leaf and 4-leaf stages had the most significant promoting effect on rice growth.At the 2.5-leaf and 4-leaf stages,the number of fibrous roots increased by 23.43%and 22.25%,stem base width increased by 19.05%and 19.58%,above ground dry weight increased by 18.09%and 16.47%,root dry weight increased by 19.67%and 18.28%,leaf peroxidase(POD)activity increased by 34.44%and 42.94%,superoxide dismutase(SOD)activity increased by 37.24%and 56.79%,malondialdehyde(MDA)content decreased by 18.60%and 27.67%,and chlorophyll content increased significantly by 28.31%and 34.24%,respectively.At the 4-leaf stage of rice,urease,phosphatase and cellulase activities in the seedbed soil increased by 42.13%,25.96%and 33.59%,respectively,while soil alkaline nitrogen,available phosphorus and available potassium content decreased by 19.76%,19.02%and 17.88%,respectively.The application of biostimulants played a crucial role in promoting the growth of rice seedlings and enhancing soil nutrient absorption.

Effects of High Temperature Stress on Growth of Stress-Tolerant Rice Seedlings with Resistibility

Two heat-tolerant rice varieties, N5 and TQ, were chosen as test materi- als. Specifically, rice seedlings （leaf age at 2.1）, cultivated in room, were treated at 40 ℃ for 7 d and some indices were measured, including plant height, dry weight, leaf color, proline, malondialdehyde and conductivity. The results showed that high temperature advanced the growth of N5 seedlings, for example, plant height, root length and dry weight of ground parts all increased. However, high temperature prevented TQ seedlings growth, plant height in particular. Furthermore, high temper- ature treatment increased the content of chlorophyll of N5 and had none effects on PSII of N5, with little damages on membrane system. On the other hand, high temperature actually reduced PSII activity of TQ, and seriously damaged TQ mem- brane system. It is speculated that the differences of the two varieties lie on pro- duction or removing capacity of reactive oxide species.

Effect of external and internal phosphate status on arsenic toxicity and accumulation in rice seedlings

Phosphorus （P） deficiency is thought to exacerbate the arsenic （As） phytotoxicity in paddy rice. The experiments were conducted to investigate the effects of external phosphate supply on As accumulation in rice and its toxicity under phosphate deficiency conditions. Rice seedlings pretreated with a phosphorus deficient nutrient solution （-P） for 14 d accumulated more As than those pretreated with a normal phosphorus supply nutrient solution （＋P）. Rice protreated with -P showed As toxicity symptoms after being exposed to 50 μmol/L arsenate for 4 h, while ＋P rice did not show any toxicity symptoms. Arsenic toxicity symptoms can be alleviated by increasing external P concentrations. The arsenate uptake rate and accumulation corresponded with the As toxicity in rice plants. Arsenic concentrations in rice roots decreased with increasing external phosphate concentrations. The lowest As accumulation and the highest P accumulation were found when the external P concentration reached 100μmol/L. In short, P deficiency increased the sensitivity of rice to arsenate and increasing of external phosphate supply could alleviate As toxicity.

Protective Roles of Brassinolide on Rice Seedlings under High Temperature Stress

Two indica rice （Oryza sativa L.） materials, Xieqingzao B （sensitive to heat stress） and 082 （tolerant to heat stress） were used to study the role of brassinolide （BR） in protection of rice seedlings from heat stress. Young seedlings were subjected to high temperature （38℃/30℃） and sprayed with 0.005 mg/L of BR. Analysis was conducted on the contents of chlorophyll, protein and malondialdehyde （MDA）, the leakage of electrolyte, the activities of peroxidase （POD） and superoxide dismutase （SOD） and their isozymes expression levels in leaves. Under the high temperature treatment, application of BR significantly increased the contents of chlorophyll and protein, and the activities of POD and SOD, and reduced the content of MDA and the leakage of electrolyte in the leaves of the heat-sensitive material Xieqingzao B, whereas BR had less effect on those of the heat-tolerant material 082 relatively. The BR treatment enhanced the expression of POD isozymes in the leaves of both materials. Under the high temperature stress and BR treatment, the expression of four SOD isozymes reduced in 082, but the expression of two SOD isozymes increased in Xieqingzao B. This suggests that BR plays an important role in protection of rice seedlings from heat stress by enhancing the activities or expression level of protective enzymes in the leaves. The materials with various heat-tolerance might differ in the mechanism of response to heat stress with BR application.

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 Biochar with Organic Materials on Substratum for Raising Rice Seedlings

[Objective] With a rice variety ＂Long Rice 11＂ as a test cultivar,an experiment of raising rice seedlings with the new substrata prepared from biochar,and maize stalks,rice husks,organic fertilizer,turf,zeolite,fine river sand and arable layer soil by mixing according to certain volume proportions was caried out,in order to investigate the physical and chemical properties of different organic-material seedling-raising substrata and the effects of these substrata on seedling growth.[Method] The experiment raised seedlings in greenhouses and adopted randomized block arrangement.[Result] The substratum of biochar mixed with maize stalks and rice husks could increase the maximum water-holding capacity of the substratum,reduce the volume weight of the substratum and improve the buffering effect of the substratum.It also had great effects on the contents of alkali-hydrolyzale nitrogen and rapidly available potassium in the substratum,and could improve the root number and substantial degree of rice seedlings.[Conclusion] Biochar with maize stalks and rice husks（the treament HC） is the optimal substratum in this study.

Protein changes in rice seedlings during the enhancement of chilling resistance by different stress pretreatment

The changes of proteins in the rice (Oryzasativa L.) Tesanai 2 seedling under salt (NaCl,4 g/L), heat shock (42℃, 3h ), and cold(14℃, 3d ) pretreatments were compared toexplore the mechanism of the cross adaptationto different environmental stresses. The chill-ing resistance of rice seedling after 1℃, 150pmol·msPFD(photo flux density) for 2d was enhanced distinctly by salt, heat shock,

Effects of aluminum on NAD kinase activity in chloroplast fraction from leaves of rice seedlings

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Silencing of Os XDH reveals the role of purine metabolism in dark tolerance in rice seedlings

Xanthine dehydrogenase(XDH) is a crucial enzyme involved in purine metabolism. To evaluate the effect of XDH deficiency on rice growth during dark treatment, wild type(WT) Nipponbare(Oryza sativa L.) and two independent transgenic lines with severe RNAi suppression(xdh3 and xdh4) were used in the present experiment. Under normal growth conditions, chlorophyll levels and biomass were indistinguishable between WT and the two RNAi transgenic lines, but XDH enzyme activity and ureide levels were suppressed in XDH RNAi transgenic lines. When XDH RNAi transgenic lines were subjected to dark treatment, chlorophyll content and biomass were significantly decreased, while O~–· production rate and malonaldehyde(MDA) were significantly increased compared to WT. The spraying test of exogenous allantoin raised chlorophyll content and biomass and reduced O~–· production rate and MDA in WT and both transgenic lines, and it also simultaneously reduced differences between RNAi and WT plants caused by XDH deficiency in growth potential and anti-oxidative capacity under dark treatment. These results suggested that fully functional purine metabolism plays an important role in reducing the sensitivity of rice seedlings to dark stress.

A Study of the Factors that Affect Safe Full Heading of Machine-transplanted Rice Seedlings in the Temperate and Cool Rice-growing Areas

This paper studies the factors that affect the safe full heading of machine-transplanted rice seedlings in the temperate and cool ricegrowing areas,and explores the influence of machine-transplanted rice seedling varieties,seedling age,nitrogen fertilizer application rate and management on the safe full heading of machine-transplanted rice seedlings. Results show that for the mechanized production in the temperate and cool rice-growing areas,we should select the mid-early maturity cold-resistant varieties with growth period of not exceeding 180 d,control the seedling age to be 30- 35 d and total amount of pure nitrogen to be not more than 300 kg / ha,and moderately reduce the nitrogen fertilizer postponing ratio. Under this condition,we can achieve safe full heading of machine-transplanted rice seedlings and ensure the yield.

Effect of LaCl_3 on the chilling tolerance of rice seedlings

The rice variety Tesanai 2 is susceptible tochilling.Exposure of the seedlings grown at 28±1℃ and under a photo flux density(PFD)of30 μmol/m~2s to 1℃ and under a PFD of 150μmol/m~2s for 2 d caused a physiological disor-der called chilling injury which reduced the sur-vival rate to 50%.The experimental results in-

Calcium effect on the process of cold-hardening of rice seedlings

Low temperature is an important environmen-tal factor that limits the productivity and dis-tribution of plant. The ability to cold acclima-tion is a common adaptive response in plantsnative in temperate regions and results in en-hancing tolerance to chilling stress. In presentstudy the seedlings of Tesanai 2 were grown at28±1℃ and under a photo flux density (PFD)of 30μmol/m~2s for 8 d. The cold acclimationresponse is triggered by 14℃ under a PFD of75 μmol/m~2s for 3 d. Rice seedlings for cold-hardening were germinated from seeds treatedwith or without immersion in 30 mmol/L ofCaClsolution. Change of membrane systemprotection in leaves at various periods(viz:fol-lowing cold-hardening, chilling stress and onthe 3rd day of recovery), the ratio of survival

The technology of raising rice seedlings in dry nursery in China

A new technology of raising rice seedlings in dry nursery began to be adopted in early 1980’s inChina. It expanded in Northeast of the Country and spreaded from North to South in the followingyears. In 1995, it was listed as one of the national popularization project during the ’Ninth Five-Year-Plan’ by the Country Government. The total area was up to 9.3 million hm~2 in 1996 (cover-ing 80% paddy field in the northern parts of China). The expected popularized area will be up to15.3 million hm~2 in 2000 according to the Ministry of Agriculture, half of the total rice-growingarea in China.

Effect of exogenous salicylic acid on resistance of rice seedlings to blast

Salicylic acid(SA)is an endogenous regulatorymolecule for plant flowering and thermogene-sis,and has been reported as a signal moleculeof plant disease resistance in the plant-pathogen interaction.Exogenous SA is capableof inducing disease resistance in a wide range ofplants.This study was to evaluate the poten-tial for SA to induce resistance of rice seedlings

Effect of gradient magnetic field on physiochemistry functions of rice seedlings

Rice varieties Handao 2,Zhongbai 4,Han-jingzi,and Akihikari were treated with gradi-ent magnetic fileld to study the effect of gradi-ent field on rice.The magnetic field was madeup of 12 plots magnetic plates arranged in eachother south and north pole.The magneticstrength was 0-40 mT.Each four varieties wasput under the magnetic plate 15 cm away,andwent through the magnetic field with the speedof 20 cm/s.The same varieties without thetreatment were used as CK.Both of the seedswere soaked in water for 48 h in room temper-ature,and then sprouted on the porcelain platewith absorbed water paper.When the

Effect of seed soaked with urea solution on the cold tolerance of rice seedlings

In the Yangtze river aera,the first crop of indi-ca rice is sown in late Mar to early Apr andtransplanted in early May.Usually,seedlingsperish when abnormal low temperature of 6-10℃ lasted for 3 d or longer.The effect ofsocking seed with urea solution on increasingthe cold tolerance at the seedling stage was

Shade-induced stem elongation in rice seedlings:Implication of tissue-specific phytohormone regulation

Summary A better understanding of shade avoidance syndrome （SAS） is an urgent need because of its effect on energy reallocation. Leverage-related mechanism in crops is of potential economic interest for agricultural applications. Here we report the SAS phenotype at tissue level rice seedlings. Tissue-specific RNA-sequencing indicates auxin plays different roles between coleoptile and the first leaf. Phenotypes of wild type treated by gibberellin and brassinosteroid biosynthesis inhibitors and of related mutants suggest these two hormones positively regulate SAS. Our work reveals the diversity of hormone responses in different organs and different species in shade conditions.

Field experimental study on pullout forces of rice seedlings and barnyard grasses for mechanical weed control in paddy field

Pullout forces of rice seedling and barnyard grass were tested by universal testing machine controlled by WDW-5 type microcomputer to obtain the pullout forces of rice seedling and barnyard grass.The measured pullout force was used to improve the weeding rate and reduce the rice seedling damage rate caused by mechanical weeding device.According to the measured continuous curve of pullout forces of rice seeding and barnyard grasses in weeding period,the best range of force required to pull out barnyard grasses from soil with no injury and damage to rice seedlings was discussed.Reasons for the difference in the pulling force were analyzed.Results show that,with the increment of the number of single cell rice seedlings the pullout force increases.The pullout forces of single cell rice seedlings and barnyard grasses at first increased slowly reaching the maximum value followed by rapid drop and finally it remained steady.The minimum pullout forces recorded during rice seedlings at the first and the second weeding periods were 2.57 N and 9.70 N,respectively,while the minimum forces during the first and second weeding periods were recorded as 1.24 N and 7.51 N,respectively,for barnyard grasses.The results show that the pullout forces of weeding to rice seedlings and barnyard grasses should be within 1.24 N to 2.57 N and 7.51 N to 9.70 N respectively in the first and second weeding periods.

Effects of Bast Fiber Seedling Film on Quality and Root Respiration Enzyme Activities of Seedlings of Different Rice Varieties

This study was conducted to investigate the effects of bast fiber seedling film on rice seedling growth. In this study, indica cultivar ＇Xiangwanxian 13＇ and indica hybrid cuitivar ＇Y Liangyou 1＇ were used to investigate the changes of aboveground part growth and root respiration enzyme activities of rice seedlings af- ter the application of bast fiber seedling film. The results showed that, compared with the CK, the accumulation of shoot biomass, chlorophyll content, root bleeding intensity, soluble sugar content, and nitrate nitrogen content were significantly im- proved with the application of bast fiber seedling film. In addition, the activities of malate dehydrogenas （MDH） and alcohol dehydrogenas （ADH） were higher in rice seedling roots raised with bast fiber seedling film, while there was no significant change in lactate dehydrogenase （LDH） after the application of bast fiber seedling film. However, there were no significant differences in these indexes between the two cultivars. All the results indicated that the growth and development of rice seedlings could be improved with the application of bast fiber seedling film.

Single-cell transcriptome atlas of the leaf and root of rice seedlings

As a multicellular organism,rice flourishes relying on gene expression diversity among cells of various functions.However,cellular-resolution transcriptome features are yet to be fully recognized,let alone cell-specific transcriptional responses to environmental stimuli.In this study,we apply single-cell RNA sequencing to both shoot and root of rice seedlings growing in Kimura B nutrient solution or exposed to various abiotic stresses and characterize transcriptomes for a total of 237,431 individual cells.We identify 15 and 9 cell types in the leaf and root,respectively,and observe that common transcriptome features are often shared between leaves and roots in the same tissue layer,except for endodermis or epidermis.Abiotic stress stimuli alter gene expression largely in a cell type-specific manner,but for a given cell type,different stresses often trigger transcriptional regulation of roughly the same set of genes.Besides,we detect proportional changes in cell populations in response to abiotic stress and investigate the underlying molecular mechanisms through single-cell reconstruction of the developmental trajectory.Collectively,our study represents a benchmark-setting data resource of single-cell transcriptome atlas for rice seedlings and an illustration of exploiting such resources to drive discoveries in plant biology.