Effects of mepiquat chloride and plant population density on leaf photosynthesis and carbohydrate metabolism in upland cotton

Background Mepiquat chloride(MC)application and plant population density(PPD)increasing are required for modern cotton production.However,their interactive effects on leaf physiology and carbohydrate metabolism remain obscure.This study aimed to examine whether and how MC and PPD affect the leaf morpho-physiological characteristics,and thus final cotton yield.PPD of three levels(D1:2.25 plants·m^(-2),D2:4.5 plants·m^(-2),and D3:6.75 plants·m^(-2))and MC dosage of two levels(MC0:0 g·ha^(-2),MC1:82.5 g·ha^(-2))were combined to create six treatments.The dynamics of nonstructual carbohydrate concentration,carbon metabolism-related enzyme activity,and photosynthetic attributes in cotton leaves were examined during reproductive growth in 2019 and 2020.Results Among six treatments,the high PPD of 6.75 plants·m^(-2)combined with MC application(MC1D3)exhibited the greatest seed cotton yield and biological yield.The sucrose,hexose,starch,and total nonstructural carbohydrate(TNC)concentrations peaked at the first flowering(FF)stage and then declined to a minimum at the first boll opening(FBO)stage.Compared with other treatments,MC1D3 improved starch and TNC concentration by 5.4%~88.4%,7.8%~52.0% in 2019,and by 14.6%~55.9%,13.5%~39.7% in 2020 at the FF stage,respectively.Additionally,MC1D3 produced higher transformation rates of starch and TNC from the FF to FBO stages,indicating greater carbon production and utilization efficiency.MC1D3 displayed the maximal specific leaf weight(SLW)at the FBO stage,and the highest chlorophyll a(Chl a),Chl b,and Chl a+b concentration at the mid-late growth phase in both years.The Rubisco activity with MC1D3 was 2.6%~53.2% higher at the flowering and boll setting stages in both years,and 2.4%~52.7% higher at the FBO stage in 2020 than those in other treatments.These results provided a explanation of higher leaf senescence-resistant ability in MC1D3.Conclusion Increasing PPD coupled with MC application improves cotton yield by enhancing leaf carbohydrate production and utilization efficiency and delaying leaf senescence.

Mepiquat chloride priming confers the ability of cotton seed to tolerate salt by promoting ABA-operated GABA signaling control of the ascorbate–glutathione cycle

Background Ensuring that seeds germinate and emerge normally is a prerequisite for cotton production,esp.in areas with salinized soil.Priming with mepiquat chloride(MC)can promote seed germination and root growth under salt stress,but its mechanism has not been fully elucidated.In this study,physiological and biochemical experiments revealed that MC-priming promotes the tolerance of cotton seeds to salt stress by increasing the ability of antioxidant enzymes related to the ascorbate-glutathione(AsA-GSH)cycle to scavenge reactive oxygen species(ROS).Results Results revealed that treatment with inhibitors of abscisic acid(ABA)and γ-aminobutyric acid(GABA)biosynthesis reduced the positive effects of MC-priming.Similarly,MC-priming increased the contents of ABA and GABA under salt stress by stimulating the expression levels of GhNCED2 and GhGAD4 and the activity of calmodulin-binding(CML)glutamate decarboxylase(GAD).Further analysis showed that an inhibitor of ABA synthesis reduced the positive impacts of MC-priming on the content of GABA under salt stress,but the content of ABA was not affected by the GABA synthesis inhibitor.Furthermore,a multi-omics analysis revealed that MC-priming increased the abundance and phosphorylation levels of the proteins related to ABA signaling,CML,and Ca^(2+)channels/transporters in the MC-primed treatments,which resulted in increased oscillations in Ca^(2+)in the MC-primed cotton seeds under salt stress.Conclusion In summary,these results demonstrate that MC-mediated ABA signaling operates upstream of the GABA synthesis generated by GAD by activating the oscillations of Ca^(2+)and then enhancing activity of the AsA-GSH cycle,which ensures that cotton seeds are tolerant to salt stress.

Effects of plant density and mepiquat chloride application on cotton boll setting in wheat–cotton double cropping system

Sowing cotton directly after harvesting wheat in the Yangtze River Valley of China requires early mature of cotton without yield reduction.Boll-setting period synchronisation and more yield bolls distributed at the upper and middle canopy layers are also required for harvesting.The objective of this study is to quantify the individual and interaction effects of plant density and plant growth regulator mepiquat chloride(MC)on temporal and spatial distributions of yield bolls,as well as yield and yield components.During the 2013–2016 cotton growing seasons,the experiments were conducted on a shortseason cotton cultivar CRRI50 at Yangzhou University,China.Various combinations of plant density(12.0,13.5 and 15.0 plants m^(–2))and MC dose(180,270 and 360 g ha^(–1))were applied on cotton plants.The combination of 13.5 plants m^(–2)and 270 g ha^(–1)MC resulted in the greatest boll number per unit area,the highest daily boll setting number and more than 90%of bolls positioned within 45–80 cm above the ground.In conclusion,appropriate MC dose in combination of high plant density could synchronize boll-setting period and retain more bolls at the upper and middle canopy layers without yield reduction in the system of direct-seeded cotton after wheat harvest,and thus overcome the labor-intensive problem in current transplanting cropping system.

Cotton maturity and responses to harvest aids following chemical topping with mepiquat chloride during bloom period

Early maturity, complete defoliation and boll opening are essential for the efficient machine harvesting of cotton. Chemical topping, involving one extra application of mepiquat chloride(MC) in addition to its traditional multipleapplication strategy, may be able to replace manual topping. However, it is not known whether this chemical topping technique will influence maturity or cotton responses to harvest aids. In this 2-yr field study, we determined the effects of the timing of chemical topping using various rates of MC on boll opening percentage(BOP) before application of harvest aids(50% thidiazuron··ethephon suspension concentrate, referred to as TE), and the defoliation percentage(DP) and BOP 14 days after TE application. The results indicated that late chemical topping(near the physiological cutout, when the nodes above white flower is equal to 5.0) significantly decreased BOP before TE by 5.9–11.2% compared with early(at peak bloom) or middle(seven days after peak bloom) treatments in 2019, which was a relatively normal year based on crop condition. Also, a high MC rate(270 g ha) showed a significantly lower(22.0%) BOP before TE than low(90 g ha) or medium(180 g ha) rates. In 2020, which was characterized by stronger vegetative growth in the late season, the late chemical topping reduced the number of leaves before TE application relative to early or middle treatments, but had lower DP(23.2–27.2%) 14 days after TE application. The high MC rate showed a leaf count before TE application that was similar to the low and medium rates, but it showed the most leaves after TE and much lower(15.0–21.7%) DP in 2020. These results suggest that late timing of chemical topping and a high MC rate decreased the sensitivity of leaves to harvest aids. Further analysis indicated that the late chemical topping mainly affected the leaf drop from the mainstem and fruiting branches where the late regrowth occurred, and the high MC rate reduced leaf shedding from these parts and also from the vegetative branches. In conclusion, chemical topping with MC during the bloom period affected cotton maturity and responses to harvest aids in different ways according to the crop condition. To avoid the risks of delayed maturity and poor defoliation after the application of harvest aids, chemical topping should not be performed too late(i.e., near the physiological cutout) by using MC at more than 180 g ha. The optimum timing of chemical topping probably varies from peak bloom to around seven days later, and the safest MC rates for chemical topping should be less than 180 g ha.

Mepiquat chloride increases the Cry1Ac protein content of Bt cotton under high temperature and drought stress by regulating carbon and amino acid metabolism

The effects of mepiquat chloride(DPC)on the Cry1Ac protein content in Bacillus thuringiensis(Bt)cotton boll shells under high temperature and drought stress were investigated to provide a theoretical reference for Bt cotton breeding and high-yield and-efficiency cotton cultivation.This study was conducted using Bt cotton cultivar‘Sikang 3'during the 2020 and 2021 growing seasons at Yangzhou University Farm,Yangzhou,Jiangsu Province,China.Potted cotton plants were exposed to high temperature and drought stress,and sprayed with either 20 mg L^(-1)DPC or water(CK).Seven days after treatment,the Cry1Ac protein content,α-ketoglutarate content,pyruvic acid content,glutamate synthase activity,glutamic oxaloacetic transaminase activity,soluble protein content,and amino acid content were measured,and transcriptome sequencing was performed.DESeq was used for differential gene analysis.Under the DPC treatment,the Cry1Ac protein content increased by 4.7-11.9% compared to CK.Theα-ketoglutarate content,pyruvic acid content,glutamate synthase activity,glutamic oxaloacetic transaminase activity,soluble protein content,and amino acid content all increased.Transcriptome analysis revealed 7,542 upregulated genes and 10,449 downregulated genes for DPC vs.CK.Gene ontology(GO)and Kyoto Encyclopedia of Gene and Genomes(KEGG)analyses showed that the differentially expressed genes were mainly involved in biological processes,such as carbon and amino acid metabolism.For example,genes encoding 6-phosphofructokinase,pyruvate kinase,glutamic pyruvate transaminase,pyruvate dehydrogenase,citrate synthase,isocitrate dehydrogenase,2-oxoglutarate dehydrogenase,glutamate synthase,1-pyrroline-5-carboxylate dehydrogenase,glutamic oxaloacetic transaminase,amino-acid N-acetyltransferase,and acetylornithine deacetylase were all significantly upregulated.The DPC treatment increased pyruvate,α-ketoglutarate,and oxaloacetate by increasing the operational rate of the glycolytic pathway of the citric acid cycle.It also significantly upregulated the genes encoding glutamate synthase,pyrrolidine-5-carboxylic acid dehydrogenase,glutamate oxaloacetate transaminase,and N-acetylglutamate synthetase,while it downregulated the genes encoding glutamine synthetase.Therefore,the synthesis of aspartic acid,glutamic acid,pyruvate,and arginine increased after treatment with DPC,and the Cry1Ac protein content was increased by regulating carbon and amino acid metabolism.

Exogenous application of bio-stimulants and growth retardants improve nutrient absorption and fiber quality in upland cotton

Background Natural and synthetic plant growth regulators are essential for plant health,likewise these regulators also play a role in increasing organic production productivity and improving quality and yield stability.In the present study,we have evaluated the effects of foliar applied plant growth regulators,i.e.,moringa leaf extract(MLE)and mepiquat chloride(MC)alone and in combination MC and MLE on the conventional cotton cultivar(CIM 573)and transgenic one(CIM 598).The growth regulators were applied at the start of bloom,45 and 90 days after blooming.Results The application of MC and MLE at 90 days after blooming significantly improved the relative growth rate,net assimilation rate,the number of bolls per plant,and seed cotton yield.Likewise,the combined application of MLE and MC at 90 days after blooming significantly boosted the nitrogen uptake in locules,as well as the phosphorus and potassium uptake in the leaves of both cotton cultivars.The application of MLE alone has considerably improved the nitrogen uptake in leaves,and phosphorus and potassium contents in locules of Bt and conventional cotton cultivars.Similarly,Bt cotton treated with MLE at 90 days after blooming produced significantly higher ginning out turn and oil contents.Treatment in combination(MLE+MC)at 90 days after blooming produced considerably higher micronaire value,fiber strength,and staple length in conventional cultivar.Conclusion The natural growth enhancer,MLE is a rich source of minerals and zeatin,improving the nutrient absorption and quality of cotton fiber in both conventional and Bt cotton cultivars.

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.