Wetting alternating with partial drying during grain filling increases lysine biosynthesis in inferior rice grain

Lysine content is a criterion of the nutritional quality of rice.Understanding the process of lysine biosynthesis in early-flowering superior grain(SG)and late-flowering inferior grain(IG)of rice would advance breeding and cultivation to improve nutritional quality.However,little information is available on differences in lysine anabolism between SG and IG and the underlying mechanism,and whether and how irrigation regimes affect lysine anabolism in these grains.A japonica rice cultivar was grown in the field and two irrigation regimes,continuous flooding(CF)and wetting alternating with partial drying(WAPD),were imposed from heading to the mature stage.Lysine content and activities of key enzymes of lysine biosynthesis,and levels of brassinosteroids(BRs)were lower in the IG than in the SG at the early grainfilling stage but higher at middle and late grain-filling stages.WAPD increased activities of these key enzymes,BR levels,and contents of lysine and total amino acids in IG,but not SG relative to CF.Application of 2,4-epibrassinolide to rice panicles in CF during early grain filling reproduced the effects of WAPD,but neither treatment altered the activities of enzymes responsible for lysine catabolism in either SG or IG.WAPD and elevated BR levels during grain filling increased lysine biosynthesis in IG.Improvement in lysine biosynthesis in rice should focus on IG.

Effect of irrigation regime on grain yield,water productivity,and methane emissions in dry direct-seeded rice grown in raised beds with wheat straw incorporation

Dry direct-seeded rice grown in raised beds is becoming an important practice in the wheat–rice rotation system in China.However,little information has been available on the effect of various irrigation regimes on grain yield,water productivity(WP),nitrogen use efficiency(NUE),and greenhouse gas emission in this practice.This study investigated the question using two rice cultivars in 2015 and 2016 grown in soil with wheat straw incorporated into it.Rice seeds were directly seeded into raised beds,which were maintained under aerobic conditions during the early seedling period.Three irrigation regimes:continuous flooding(CF),alternate wetting and drying(AWD),and furrow irrigation(FI),were applied from 4.5-leaf-stage to maturity.Compared with CF,both AWD and FI significantly increased grain yield,WP,and internal NUE,with greater increases under the FI regime.The two cultivars showed the same tendency in both years.Both AWD and FI markedly increased soil redox potential,root and shoot biomass,root oxidation activity,leaf photosynthetic NUE,and harvest index and markedly decreased global warming potential,owing to substantial reduction in seasonalThe results demonstrate that adoption of either AWD or FI could increase grain yield and resource-use efficiency and reduce environmental risks in dry direct-seeded rice grown on raised beds with wheat straw incorporation in the wheat–rice rotation system.

Inhibition of protein degradation increases the Bt protein concentration in Bt cotton

Bacillus thuringiensis(Bt)cotton production is challenged by two main problems,i.e.,the low concentration of Bt protein at the boll setting stage and the lowest insect resistance in bolls among all the cotton plant’s organs.Therefore,increasing the Bt protein concentration at the boll stage,especially in bolls,has become the main goal for increasing insect resistance in cotton.In this study,two protein degradation inhibitors(ethylene diamine tetra acetic acid(EDTA)and leupeptin)were sprayed on the bolls,subtending leaves,and whole cotton plants at the peak flowering stage of two Bt cultivars(medium maturation Sikang 1(SK1))and early maturation Zhongmian 425(ZM425)in 2019 and 2020.The Bt protein content and protein degradation metabolism were assessed.The results showed that the Bt protein concentrations were enhanced by 21.3 to 38.8%and 25.0 to 38.6%in the treated bolls of SK1 and ZM425 respectively,while they were decreased in the subtending leaves of these treated bolls.In the treated leaves,the Bt protein concentrations increased by 7.6 to 23.5%and 11.2 to 14.9%in SK1 and ZM425,respectively.The combined application of EDTA and leupeptin to the whole cotton plant increased the Bt protein concentrations in both bolls and subtending leaves.The Bt protein concentrations in bolls were higher,increasing by 22.5 to 31.0%and 19.6 to 32.5%for SK1 and ZM425,respectively.The organs treated with EDTA or/and leupeptin showed reduced free amino acid contents,protease and peptidase activities and significant enhancements in soluble protein contents.These results indicated that inhibiting protein degradation could improve the protein content,thus increasing the Bt protein concentrations in the bolls or/and leaves of cotton plants.Therefore,the increase in the Bt protein concentration without yield reduction suggested that these two protein degradation inhibitors may be applicable for improving insect resistance in cotton production.

Optimizing integrative cultivation management improves grain quality while increasing yield and nitrogen use efficiency in rice

A major challenge in rice(Oryza sativa L.)production is to cope with increasing grain yield and fertilizer use efficiency without compromising grain quality.This study was designed to determine if optimizing integrative cultivation management in rice could improve grain quality while increase yield and nitrogen use efficiency(NUE).An indica-japonica hybrid rice cultivar and a japonica rice cultivar were grown in the field,with five cultivation managements including no N application(0 N),local farmer's practice(LFP),and three optimizi ng in teg rati ve cultivati on managements,reducing N rate and increasi ng plant density(ND),ND+alternate wetting and moderate soil drying irrigation(NDW),and NDW+applying rapeseed cake fertilizer(NDWR).The results showed that the optimizi ng integrative cultivati on man ageme nts could not only in crease grain yield,but also enhance NUE compared to LFP.Compared to LFP,NDWR sign ifica ntly in creased brow n,milled,head milled rice rate,ratio of the kern el le ngth to breadth and breakdown value of starch,whereas decreased amylose content,gel consiste ncy,prolamin con tent,setback value,perce ntage of chalky kern els,and chalki ness.The three optimizing in tegrative cultivation managements increased con tents of total protei ns,albumin and glutelin,activities of the key enzymes involved in the sucrose-starch con version in grains,root oxidati on activity,and malic and succinic acid concentrations in root exudates during the grain-filling period.The results suggested that optimizing integrative cultivation managements could improve grain quality meanwhile increase grain yield and NUE by enhancing physiological activities of rice plants.

Detection and enumeration of wheat grains based on a deep learning method under various scenarios and scales

Grain number is crucial for analysis of yield components and assessment of effects of cultivation measures.The grain number per spike and thousand-grain weight can be measured by counting grains manually,but it is time-consuming,tedious and error-prone.Previous image processing algorithms cannot work well with different backgrounds and different sizes.This study used deep learning methods to resolve the limitations of traditional image processing algorithms.Wheat grain image datasets were collected in the scenarios of three varieties,six background and two image acquisition devices with different heights,angles and grain numbers,1748 images in total.All images were processed through color space conversion,image flipping and rotation.The grain was manually annotated,and the datasets were divided into training set,validation set and test set.We used the TensorFlow framework to construct the Faster Region-based Convolutional Neural Network Model.Using the transfer learning method,we optimized the wheat grain detection and enumeration model.The total loss of the model was less than 0.5 and the mean average precision was 0.91.Compared with previous grain counting algorithms,the grain counting error rate of this model was less than 3%and the running time was less than 2 s.The model can be effectively applied under a variety of backgrounds,image sizes,grain sizes,shooting angles,and shooting heights,as well as different levels of grain crowding.It constitutes an effective detection and enumeration tool for wheat grain.This study provides a reference for further grain testing and enumeration applications.

Evaluating the grassland net primary productivity of southern China from 2000 to 2011 using a new climate productivity model

Grassland is the important component of the terrestrial ecosystems. Estimating net primary productivity （NPP） of grassland ecosystem has been a central focus in global climate change researches. To simulate the grassland NPP in southern China, we built a new climate productivity model, and validated the model with the measured data from different years in the past. The results showed that there was a logarithmic correlation between the grassland NPP and the mean annual temperature, and there was a linear positive correlation between the grassland NPP and the annual precipitation in southern China. Al these results reached a very signiifcant level （P〈0.01）. There was a good correlation between the simulated and the measured NPP, withR2 of 0.8027, reaching the very signiifcant level. Meanwhile, both root mean square errors （RMSE） and relative root-mean-square errors （RRMSE） stayed at a relatively low level, showing that the simulation results of the model were reliable. The NPP values in the study area had a decreasing trend from east to west and from south to north, and the mean NPP was 471.62 g C m？2 from 2000 to 2011. Additionaly, there was a rising trend year by year for the mean annual NPP of southern grassland and the tilt rate of the mean annual NPP was 3.49 g C m？2 yr？1 in recent 12 years. The above results provided a new method for grassland NPP estimation in southern China.

Brassinosteroids mediate the effect of high temperature during anthesis on the pistil activity of photo-thermosensitive genetic male-sterile rice lines

Brassinosteroids(BRs)play critical roles in a wide range of plant developmental processes.However,it is unknown whether and how BRs mediate the effect of high temperature(HT)stress during anthesis on the pistil activity of photo-thermosensitive genetic male-sterile(PTSGMS)rice(Oryza sativa L.)lines.This study investigated the question.Three pot-grown PTSGMS rice lines were subjected to HT stress during anthesis.The contents of 24-epibrassinolide(24-EBL)and 28-homobrassinolide(28-HBL),the major forms of BR in rice plants,and levels of reactive oxygen species(ROS)or antioxidants(AOS),hydrogen peroxide(H2O2),1-aminocylopropane-1-carboxylic acid(ACC),ascorbic acid(AsA),and catalase activity in pistils,were determined.HT stress significantly reduced the contents of both 24-EBL and 28-EBL relative to those under normal temperatures,but the reduction varied by PTSGMS line.A line with higher BR contents under HT stress showed lower contents of ACC and H2O2,higher catalase activity and AsA content in pistils,and higher fertilization rate,seed-setting rate,and seed yield when the line was crossed with a restorer line,indicating that higher levels of BRs increase HT stress resistance.Applying 24-EBL,28-HBL or an inhibitor of BR biosynthesis confirmed the roles of BRs in response to HT stress.The results suggest that BRs mediate the effect of HT stress on pistil activity during anthesis and alleviate the harm of HT stress by increasing AOS and suppressing ROS generation.

Effects of high temperature during grain filling on physicochemical properties of waxy maize starch

Understanding the waxy maize starch physicochemical properties response to heat stress during grain filling could improve starch quality.The effects of heat stress during early（1-15 days after pollination,DAP） and late（16-30 DAP） grain filling stages on the starch physicochemical properties of four waxy maize varieties were evaluated.Crystallinity only increased in Suyunuo 5 after exposure to high temperature at late grain filling stage.The effects of heat stress on digestibility and swelling power were dependent on varieties and stages.Generally,swelling power was increased by heat stress at early grain development stage and digestibility was increased by high temperature at late grain filling stage,respectively.The results of correlation analysis indicated the starch with large granule size could swell well and easy digest.Peak,trough,final,and breakdown viscosities in response to heat stress were dependent on stages and varieties.In general,peak,trough and final viscosities were decreased and increased by heat stress at early grain formation and late grain filling stages,respectively;whereas the breakdown and setback viscosities were similar among the three treatments.Heat stress increased the gelatinization temperatures and retrogradation percentage.Gelatinization range decreased under heat stress at 1-15 DAP but remained constant under heat stress at 16-30 DAP in all varieties.The starch exposed to high temperature at 16-30 DAP presented higher digestibility and peak viscosity and lower retrogradation percentage than those at 1-15 DAP.Therefore,heat stress at early grain formation stage severely affects the physicochemical properties of starch.

RGB1 Regulates Rice Panicle Architecture and Grain Filling Through Monitoring Cytokinin Level in Inflorescence Meristem and Grain Abscisic Acid Level During Filling Stage

RGB1 regulated not only rice panicle architecture but also the grain filling process.Suppression of RGB1 expression resulted in a denser panicle and smaller grain size and weight,which was largely due to the lower endogenous cytokinin(CK)level caused by the increased expression of cytokinin oxidase genes in the inflorescence meristem.Suppression of RGB1 expression also significantly delayed the grain development and reduced the starch accumulation rate through reducing grain abscisic acid(ABA)accumulation during early filling stage.Exogenous ABA can partially rescue the detrimental effects of suppression of RGB1 expression on starch accumulation and grain weight.In conclusion,RGB1 regulated rice panicle architecture and grain filling through monitoring CK level in the inflorescence meristem and grain ABA level during filling stage.

Genome-Wide Association Studies Reveal New Genetic Targets for Five Panicle Traits of International Rice Varieties

Narrow genetic background is a key limiting factor in breeding stable high-yielding rice. The introduction and utilization of international rice core germplasm is an important way to increase the genetic diversity of domestic rice varieties. We conducted a genome-wide association study on 5 panicle traits of 315 rice accessions introduced from the international rice micro-core germplasm bank. Based on the tests from Yangzhou of China and Arkansas of American, environment exhibited a significant impacts on panicle length and primary branch number, while grain length, grain width and grain length/width ratio were insensitive to environment changes. We discovered a total of 7, 5, 10, 8 and 6 chromosomal regions or single nucleotide polymorphism marker loci that were significantly associated with primary branch number, panicle length, grain length, grain width and grain length/width ratio, respectively. Among them, eleven regions were associated with grain shape and one region associated with primary branch number, showing the good consistence in two different environments. Significant linear correlation was discovered between the average trait value and the number of favorable alleles carried by the varieties in all associated loci. Among the associated loci, varieties in aromatic and tropical japonica sub-groups possessed most favorable alleles, while those in temperate japonica sub-group contained the least. The domestic varieties mainly harbored unfavorable alleles in six of the associated loci being detected. On the contrary, 15 varieties from 11 different countries harbored more favorable alleles （as many as 30 or more） than the others. Remarkably, all these 15 varieties belonged to the tropical japonica sub-group. In conclusion, our study demonstrates that varieties in the tropical japonica sub-group had high potentials for breeding stable high-yielding rice. Based on this discovery, we proposed a new approach for improving the panicle traits of domestic rice by using tropical japonica varieties.

Enhancing boll protein synthesis and carbohydrate conversion by the application of exogenous amino acids at the peak flowering stage increased the boll Bt toxin concentration and lint yield in cotton

In Bacillus thuringenesis(Bt) transgenic cotton, the cotton boll has the lowest insecticidal protein content when compared to the other organs. The present study investigated the effects of amino acid spray application at the peak flowering stage on the cotton boll Bt toxin concentration and yield formation. Boll protein synthesis and carbohydrate conversion were also studied to reveal the fundamental mechanism. Three treatments(i.e., CK, the untreated control;LA1, five amino acids;LA2, 21 amino acids) were applied to two Bt cultivars of G. hirsutum(i.e., the hybrid Sikang 3 and the conventional Sikang 1) in the cotton-growing seasons during 2017 and 2018. Amino acid spray application at the peak flowering stage resulted in an increase of 5.2–16.4% in the boll Bt protein concentration and an increase of 5.5–11.3%in the seed cotton yield, but there was no difference between the two amino acid treatments. In addition, amino acid applications led to increases in the amino acid content, soluble protein content, glutamate pyruvate transaminase(GPT)activity, glutamate oxaloacetate transaminase(GOT) activity, glucose content, fructose content and soluble acid invertase(SAI) activity. This study also found that Bt protein content, enhanced boll number and the weight of opened bolls were closely related to carbon and nitrogen metabolism. The Bt protein content had significant linear positive correlations with amino acid and soluble protein contents. Enhanced boll number had significant linear positive correlations with the GPT and GOT activities from 15–25 days after flowering(DAF). The weight of opened bolls from 55–65 DAF had a significant linear positive correlation with the SAI activity. These results indicate that the enhancement of boll protein synthesis and carbohydrate conversion by amino acid application resulted in a simultaneous increase in the boll Bt protein concentration and cotton lint yield.

The effects of water and nitrogen on the roots and yield of upland and paddy rice

It is of great significance to study the root characteristics of rice to improve water and nitrogen(N) use efficiency and reduce environmental pollution. This study investigated whether root traits and architecture of rice influence grain yield, as well as water and N utilization efficiency. An experiment was conducted using the upland rice cultivar Zhonghan 3(a japonica cultivar) and paddy rice cultivar Huaidao 5(also a japonica cultivar) using three N levels, namely, 2 g urea/pot(low amount, LN), 3 g urea/pot(normal amount, NN), and 4 g urea/pot(high amount, HN), and three soil water potentials(SWPs, namely, well-watered(0 kPa), mildly dried(–20 kPa) and severely dried(–40 kPa). The results showed that with decreasing SWP, the percentage of upland rice roots increased in the 0–5 cm tillage layer, and decreased in the 5–10 and 10–20 cm tillage layers, whereas paddy rice roots showed the opposite trend. With increasing amounts of N, the yield of upland and paddy rice increased, and the percentage of root volume ratios of the two rice cultivars in the 0–5 and 5–10 cm tillage layers increased, whereas that in the 10–20 cm tillage layer decreased. The roots of upland rice are mainly distributed in the 10–20 cm tillage layer, whereas most paddy rice roots are in the 0–5 cm tillage layer. These results indicate that the combination of-20 kPa SWP and NN in upland rice and 0 kPa SWP and LN in paddy rice promotes the growth of the root system during the middle and late stages, which in turn may decrease the requirements for water and N fertilizer and increase rice yield.

Accumulation characteristic of protein bodies in different regions of wheat endosperm under drought stress

The structural characteristics of protein body accumulation in different endosperm regions of hard wheat cultivar （XM33） and soft wheat cultivar （NM13） under drought stress were investigated. Drought stress treatment was implemented from plant regreening to the caryopsis mature stage. Microscope images of endosperm cells were obtained using resin semi- thin slice technology to observe the distribution and relative area of protein body （PB）. Compared with NM13, relative PB area of XM33 was significantly higher in sub-aleurone endosperm region. The amount of accumulation, including the size and relative area of PB, in two wheat cultivars was higher in sub-aleurone region than that in central region at 18 days post anthesis （DPA）. Drought stress significantly enhanced the sizes and relative areas of PBs in the dorsal and abdominal endosperms in two wheat cultivars. Particularly for dorsal endosperm, drought stress enhanced the relative PB area at 18 DPA and NM13 （5.0% vs. 6.73%） showed less enhancement than XM33 （5.49% vs. 8.96%）. However, NM13 （9.58% vs. 12.02%） showed greater enhancement than XM33 （10.25% vs. 11.7%） at 28 DPA. The protein content in the dorsal and abdominal endosperms of the two wheat cultivars decreased at 12 DPA and then increased until 38 DPA. Drought stress significantly increased the protein contents in the two main regions. From 12 to 38 DPA, the amount of PB accumulation and the protein content were higher in XM33 than those in NM13. The results revealed that PB distribution varied in different endosperm tissues and that the amount of PB accumulation was remarkably augmented by drought stress.

A multivariate partial least squares approach to joint association analysis for multiple correlated traits

Many complex traits are highly correlated rather than independent. By taking the correlation structure of multiple traits into account, joint association analyses can achieve both higher statistical power and more accurate estimation. To develop a statistical approach to joint association analysis that includes allele detection and genetic effect estimation, we combined multivariate partial least squares regression with variable selection strategies and selected the optimal model using the Bayesian Information Criterion(BIC). We then performed extensive simulations under varying heritabilities and sample sizes to compare the performance achieved using our method with those obtained by single-trait multilocus methods. Joint association analysis has measurable advantages over single-trait methods, as it exhibits superior gene detection power, especially for pleiotropic genes. Sample size, heritability,polymorphic information content(PIC), and magnitude of gene effects influence the statistical power, accuracy and precision of effect estimation by the joint association analysis.

Identification of New Resistance Loci Against Sheath Blight Disease in Rice Through Genome-Wide Association Study

Sheath blight(SB) caused by the soil borne pathogen Rhizoctonia solani is one of the most serious global rice diseases. Breeding resistant cultivar is the most economical and effective strategy to control the disease. However, no rice varieties are completely resistant to SB, and only a few reliable quantitative trait loci(QTLs) linked with SB resistance have been identified to date. In this study, we conducted a genome-wide association study(GWAS) of SB resistance using 299 varieties from the rice diversity panel 1(RDP1) that were genotyped using 44 000 high-density single nucleotide polymorphism(SNP) markers. Through artificial inoculation, we found that only 36.5% of the tested varieties displayed resistance or moderate resistance to SB. In particular, the aromatic and aus sub-populations displayed higher SB resistance than the tropical japonica(TRJ), indica and temperate japonica sub-populations. Seven varieties showed similar resistance levels to the resistant control YSBR1. GWAS identified at least 11 SNP loci significantly associated with SB resistance in the three independent trials, leading to the identification of two reliable QTLs, qSB-3 and qSB-6, on chromosomes 3 and 6. Using favorable alleles or haplotypes of significantly associated SNP loci, we estimated that both QTLs had obvious effects on reducing SB disease severity and can be used for enhancing SB resistance, especially in improving SB resistance of TRJ sub-population rice varieties. These results provided important information and genetic materials for developing SB resistant varieties through breeding.

Nitrogen spraying affects seed Bt toxin concentration and yield in Bt cotton

Cotton bolls exhibit the lowest insecticidal efficacy among all organs of Bt cotton,which would ultimately affect the yield formation.The objective of this study was to investigate the effects of different urea concentrations on the seed Bt protein contents,seed cotton yield and the corresponding protein metabolism mechanism.The experiments were conducted during 2017–2018 cotton growing seasons.Two cultivars,Sikang 3(hybrid,SK3)and Sikang 1(conventional,SK1),were treated with six urea concentrations and their seed Bt protein contents were compared during boll formation period.The urea spray concentration had a significant effect on the seed Bt toxin content and seed cotton yield.Spraying of either 5 or 6%urea led to higher insecticidal protein contents and higher seed cotton yield for both cultivars.Moreover,the highest amino acid and soluble protein contents,as well as GPT and GOT activities,and lower protease and peptidase activities were observed at the 5 to 6%urea levels.Significant positive correlations between the seed Bt toxin and amino acid contents,and between the seed Bt toxin content and GPT activities were detected.The lower boll worm number and hazard boll rate were also observed with the 5 to 6%urea treatments,which may be the reason why nitrogen spraying increased the seed cotton yield.Therefore,our results suggested that the seed Bt toxin content and insect resistance were impacted markedly by external nitrogen application,and 5 to 6%urea had the greatest effect on insect resistance.

Architecture of stem and branch affects yield formation in short season cotton

The cotton direct seeding after wheat(rape) harvested is under trial and would be the future direction at the Yangtze River Valley region of China.The objective of this study was to quantify the effects of branch and stem architecture on cotton yield and identify the optimal cotton architecture to compensate the yield loss due to the reduction of individual production capacity under high planting density in the direst seeding after wheat harvested cropping system.The characteristics of the stem and branch architecture and the relationships between architecture of the stem and branch with yield formation were studied on eight short season cotton cultivars during 2015 and 2016 cotton growth seasons.Based on the two years results,three cultivars with different architectures of stem and branch were selected to investigate the effect of mepiquat chloride(MC) application on the architecture of the stem and branch,boll retention,and the yield in 2017.Significant differences were observed on plant height,all fruiting nodes to branches ratio(NBR) in the cotton plant,and the curvature of the fruiting branch(CFB) among the studied cultivars.There were three types of stem and fruiting branch structures: Zhong425 with stable and suitable plant height and NBR(about 90 cm and 2.5,respectively),high CFB(more than 10.0),and high boll retention speed and seed cotton yield;Siyang 822 with excessive plant height and NBR,low CFB,and low boll retention speed and seed cotton yield;and other studied cultivars with unstable structure of stem and branch,boll retention speed,and seed cotton yield across years.And MC application could promote the appropriate plant height and NBR and high CFB and thus resulted in high boll retention speed and the yield.The results suggested that the suitable plant height and NBR(about 90 cm and 2.5 respectively),and high CFB(more than 10.0),which was related to both genotype and cultural practice,could promote the higher boll retention speed and seed cotton yield.

Polyamines mediate the effect of post-anthesis soil drying on starch granule size distribution in wheat kernels

Polyamines(PAs) are important endogenous plant growth regulators responding to environmental stress and mediating many physiological processes including grain filling in cereals.This study investigated whether PAs mediate the effect of post-anthesis soil drying on starch granule size distribution,starch content,and weight of superior and inferior kernels of wheat(Triticum aestivum L.).Two wheat cultivars were grown in pots.Three treatments,well-watered(WW),moderate soil drying(MD) and severe soil drying(SD),were imposed from 9 days post-anthesis until maturity.PA levels in kernels and small,medium and large granules were measured.The results showed that superior kernels had much higher free spermidine(Spd) and free spermine(Spm) concentrations,larger volumes of medium starch granules,and smaller-sized large granules than did inferior kernels under all the treatments.Compared to WW,MD significantly increased the concentrations of free Spd and free Spm,activities of soluble starch synthase and granule-bound starch synthase,volume of medium granules,and starch content and kernel weight of inferior kernels,and decreased the size of large granules.SD produced the opposite effect.Application of Spd or Spm to spikes produced effects similar to those of MD,and application of an inhibitor of Spd and Spm synthesis produced effects similar to those of SD.These results suggest that PAs mediate the effect of post-anthesis soil drying on starch biosynthesis in wheat kernels by regulating key enzymes in starch synthesis and that elevated PA levels under MD increase the volume of medium granules and kernel weight of inferior kernels.

Effects of CO_2 enrichment and spikelet removal on rice quality under open-air field conditions

The increase of atmospheric carbon dioxide（CO_2） concentration adversely affect several quality traits of rice grains, but the biochemical mechanism remains unclear. The objectives of this study were to determine how changes in the source-sink relationship affected rice quality. Source-sink manipulation was achieved by free-air CO_2 enrichment from tillering to maturity and partial removal of spikelet at anthesis using a japonica rice cultivar Wuyunjing 23. Enrichment with CO_2 decreased the head rice percentage and protein concentration of milled rice, but increased the grain chalkiness. In contrast, spikelet removal resulted in a dramatic increase in the head rice percentage and protein concentration, and much less grain chalkiness. Neither CO_2 enrichment nor spikelet removal affected the starch content, but the distribution of starch granule size showed distinct treatment effects. O n average, spikelet removal decreased the percentage of starch granules of diameter 〉10 and 5–10 μm by 23.6 and 5.6%, respectively, and increased those with a diameter of 2–5 and 〈2 μm by 4.6 and 3.3%, respectively. In contrast, CO_2 elevation showed an opposite response： increasing the proportion of large starch granules（〉5 μm） and decreasing that of 〈5 μm. The starch pasting properties were affected by spikelet removal much more than by CO_2 elevation. These results indicated that the protein concentration and starch granule size played a role in chalkiness formation under these experimental conditions.

Roles of jasmonates and brassinosteroids in rice responses to high temperature stress——A review

High temperature (HT) stress has become one of the most detrimental stresses in crop production among constantly changing environmental factors.Exploiting approaches to enhance crop thermotolerance would have great significance in assuaging adverse effects of HT stress on crop growth and development.As jasmonates (JAs) and brassinosteroids (BRs) are novel phytohormones and play important roles in responses to biotic and abiotic stresses and in a wide range of plant developmental processes,this paper reviewed the roles and mechanisms of JAs and BRs in mitigating HT stress,with focus on rice (Oryza sativa L.) subjected to HT stress during anthesis.It is demonstrated that JAs alleviate spikelet-opening impairment and BRs ameliorate pistil fertilization ability under HT stress during anthesis of rice,although there are controversial observations.Activating the defense system,enhancing osmotic regulation,protecting photosynthesis,and interacting with other phytohormones,especially with ethylene and abscisic acid,are main physiological mechanisms by which JAs or BRs attenuate HT stress to plants.Elevating levels of JAs or BRs in plants could be considered as an important approach to enhance crop thermotolerance through breeding new varieties.Using JAs or BRs as chemical regulators and adopting proper water and nitrogen management practices could reduce the harm of HT stress to rice.Further research is needed to elucidate the roles of JAs and BRs in different plant tissues in responses to HT stress under different genetic backgrounds and environments,reveal the molecular mechanism underlying JAs and BRs mediating HT stress,understand the cross-talk between phytohormones in modulating HT stress,and establish integrated crop management to minimize the hazard of HT stress in rice production.