Physiological Response Mechanism and Drought Resistance Evaluation of Passiflora edulis Sims under Drought Stress

In order to explore the response mechanism of Passiflora edulis Sims to drought stress,the changes in morpho-logical and physiological traits of Passiflora edulis Sims under different drought conditions were studied.A total of 7 germplasm resources of Passiflora edulis Sims were selected and tested under drought stress by the pot culture method under 4 treatment levels:75%–80%(Control,CK)of maximumfield water capacity,55%–60%(Light Drought,LD)of maximumfield water capacity,i.e.,mild drought,40%–45%(Moderate Drought,MD)of max-imumfield water capacity,i.e.,moderate drought and 30%–35%(Severe Drought,SD)of maximumfield water capacity,i.e.,severe drought.On the 40th day of drought treatment,13 indices,including seedling growth mor-phology,physiology,and biochemistry,were measured.The results showed that under drought stress,the height and ground diameter of P.edulis Sims gradually decreased with increasing drought stress,and there were signifi-cant differences in seedling height and ground diameter among the treatments.Drought stress significantly inhib-ited the growth of seven P.edulis Sims varieties.The contents of soluble sugar(SS),soluble protein(SP),proline(Pro),and other substances in P.edulis Sims basically increased with increasing drought stress.With the aggrava-tion of drought stress,the malondialdehyde(MDA)content of P.edulis Sims tended to increase to different degrees,the superoxide dismutase(SOD)activity and peroxidase(POD)activity both tended to increase atfirst and then decrease,and the change in catalase(CAT)activity mostly showed a gradual increasing trend.The con-tents of endogenous hormones in P.edulis Sims significantly differed under different degrees of drought stress.With the aggravation of drought stress,the abscisic acid(ABA)content of P.edulis Sims tended to increase,whereas the contents of gibberellin(GA),indoleacetic acid(IAA),and zeatin nucleoside(ZR)exhibited a down-ward trend.A comprehensive evaluation of the drought resistance of seven P.edulis Sims varieties was conducted based on the principal component analysis method,and the results showed that the drought resistance decreased in the order XH-BL>XH-TWZ>TN1>GH1>ZJ-MT>LP-LZ>DH-JW.

Physiological and Transcriptome Analysis Illuminates the Molecular Mechanisms of the Drought Resistance Improved by Alginate Oligosaccharides in Triticum aestivum L.

Alginate oligosaccharides(AOS)enhance drought resistance in wheat(Triticum aestivum L.),but the definite mechanisms remain largely unknown.The physiological and transcriptome responses of wheat seedlings treated with AOS were analyzed under drought stress simulated with polyethylene glycol-6000.The results showed that AOS promoted the growth of wheat seedlings and reduced oxidative damage by improving peroxidase and superoxide dismutase activities under drought stress.A total of 10,064 and 15,208 differentially expressed unigenes(DEGs)obtained from the AOS treatment and control samples at 24 and 72 h after dehydration,respectively,were mainly enriched in the biosynthesis of secondary metabolites(phenylpropanoid biosynthesis,flavonoid biosynthesis),carbohydrate metabolism(starch and sucrose metabolism,carbon fixation in photosynthetic organisms),lipid metabolism(fatty acid elongation,biosynthesis of unsaturated fatty acids,alpha-linolenic acid metabolism,cutin,suberine and wax biosynthesis),and signaling transduction pathways.The up-regulated genes were related to,for example,chlorophyll a-b binding protein,amylosynthease,phosphotransferase,peroxidase,phenylalanine ammonia lyase,flavone synthase,glutathione synthetase.Signaling molecules(including MAPK,plant hormones,H_(2)O_(2) and calcium)and transcription factors(mainly including NAC,MYB,MYB-related,WRKY,bZIP family members)were involved in the AOS-induced wheat drought resistance.The results obtained in this study help underpin the mechanisms of wheat drought resistance improved by AOS,and provides a theoretical basis for the application of AOS as an environmentally sustainable biological method to improve drought resistance in agriculture.

Drought-resistant Hybrid Millet under Watersaving Irrigation in Extreme Drought Area of Dunhuang City

[Objective]This study aimed to select hybrid mil et varieties those can produce high yield under water-saving irrigation conditions. [Method] From 2011 to 2013, drought-resistant experiments on 200 hybrid mil et combinations were carried out in the three consecutive years in Dunhuang City. Plastic film was covered on the soil surface in one treatment （F） and was not in the other treatment （NF）. Irri-gation was only performed once before sowing. At seedling stage, jointing stage, heading stage and fil ing stage, we measured the water contents of soil at 0-20, 20-40, 40-60, 60-80, 80-100 and 100-120 cm deep. Plant height, panicle length, til er number, grain weight per ear, grain weight per plant, grass weight and above-ground biomass were measured from a bulk of eight plants in each plot. Grain yield per plot was measured final y. [Result] Under the only irrigation of 1 200 m3/hm2 before sowing, 18 hybrid mil et combinations exhibited stronger resistance to drought, and four of them： 13DH2, 13DH3, 13DH8 and 13DH9 produced grain more than 3 000 kg/hm2. The yield of hybrid mil et combination 13DH8 was up to 6 000 kg/hm2 under the only irrigation of 1 200 m3/hm2, i.e. 1 m3 of water could produce 5 kg of grain on average. Therefore, application of this cultivation technology could increase arable land of irrigated arid area by several times. In addition, irrigation of 1 200 m3/hm2 is equivalent to 120 mm of rainfal; so this cultivation technology also can be applied in arid area with 200 mm of rainfal . [Conclusion] The cultivation technology can cope with the occurrence of extreme weather, protect water re-sources and enlarge global grain planting area. At the same time, it also ensures food production and food safety.

Increase in root density induced by coronatine improves maize drought resistance in North China

Drought stress caused by insufficient irrigation or precipitation impairs agricultural production worldwide.In this study,a two-year field experiment was conducted to investigate the effect of coronatine(COR),a functional analog of jasmonic acid(JA),on maize drought resistance.The experiment included two water treatments(rainfed and irrigation),four COR concentrations(mock,0μmol L^(-1);A1,0.1μmol L^(-1);A2,1μmol L^(-1);A3,10μmol L^(-1))and two maize genotypes(Fumin 985(FM985),a drought-resistant cultivar and Xianyu 335(XY335),a drought-sensitive cultivar).Spraying 1μmol L^(-1)COR at seedling stage increased surface root density and size,including root dry matter by 12.6%,projected root area by 19.0%,average root density by 51.9%,and thus root bleeding sap by 28.2%under drought conditions.COR application also increased leaf area and SPAD values,a result attributed to improvement of the root system and increases in abscisic acid(ABA),JA,and salicylic acid(SA)contents.The improvement of leaves and roots laid the foundation for increasing plant height and dry matter accumulation.COR application reduced anthesis and silking interval,increasing kernel number per ear.COR treatment at 1μmol L^(-1)increased the yield of XY335 and FM985 by 7.9%and 11.0%,respectively.Correlation and path analysis showed that grain yields were correlated with root dry weight and projected root area,increasing maize drought resistance mainly via leaf area index and dry matter accumulation.Overall,COR increased maize drought resistance mainly by increasing root dry weight and root area,with 1μmol L-^(-1)COR as an optimal concentration.

Improving water-use efficiency by decreasing stomatal conductance and transpiration rate to maintain higher ear photosynthetic rate in drought-resistant wheat

In wheat, the ear is one of the main photosynthetic contributors to grain filling under drought stress conditions. In order to determine the relationship between stomatal characteristics and plant drought resistance, photosynthetic and stomatal characteristics and water use efficiency(WUE) were studied in two wheat cultivars: the drought-resistant cultivar ‘Changhan 58' and the drought-sensitive cultivar ‘Xinong 9871'. Plants of both cultivars were grown in pot conditions under well-watered(WW) and water-stressed(WS) conditions. In both water regimes,‘Changhan 58' showed a significantly higher ear photosynthetic rate with a lower rate of variation and a significantly higher percentage variation of transpiration compared to control plants at the heading stage under WS conditions than did ‘Xinong 9871' plants. Moreover,‘Changhan 58' showed lower stomatal density(SD) and higher stomatal area per unit organ area(A) under both water conditions. Water stress decreased SD, A, and stomatal width(SW), and increased stomatal length in flag leaves(upper and lower surfaces) and ear organs(awn, glume,lemma, and palea), with the changes more pronounced in ear organs than in flag leaves.Instantaneous WUE increased slightly, while integral WUE improved significantly in both cultivars. Integral WUE was higher in ‘Changhan 58', and increased by a greater amount, than in‘Xinong 9871'. These results suggest that drought resistance in ‘Changhan 58' is regulated by stomatal characteristics through a decrease in transpiration rate in order to improve integral WUE and photosynthetic performance, and through sustaining a higher ear photosynthetic rate, therefore enhancing overall drought-resistance.

A drought resistance index to select drought resistant plant species based on leaf water potential measurements

The water deficit in arid and semi-arid regions is the primary limiting factor for the development of urban greenery and forestation. In addition, planting the species that consume low levels of water is useful in arid and semi-arid regions that have poor water management measures. Leaf water potential(Ψ) is a physiological parameter that can be used to identify drought resistance in various species. Indeed, Ψ is one of the most important properties of a plant that can be measured using a pressure chamber. Drought avoiding or drought resistant species have a lower Ψ than plants that use normal or high levels of water. To determine drought resistance of species that are suitable for afforestation in arid urban regions, we evaluated twenty woody species in the Isfahan City, central Iran. The experimental design was random split-split plots with five replications. The species were planted outdoor in plastic pots and then subjected to treatments that consisted of two soil types and five drip irrigation regimes. To evaluate the resistance of each species to drought, we used the Ψ and the number of survived plants to obtain the drought resistance index(DRI). Then, cluster analysis, dendrogram, and similarity index were used to group the species using DRI. Result indicates that the evaluated species were classified into five groups:(1) high water consuming species(DRI>–60 MPa);(2) above normal water consuming species(–60 MPa≥DRI>–90 MPa);(3) normal water consuming species(–90 MPa≥DRI>–120 MPa);(4) semi-drought resistant species(–120 MPa≥DRI>–150 MPa);and(5) drought resistant species(DRI≤–150 MPa). According to the DRI, Salix babylonica L., Populus alba L., and P. nigra L. are high water consuming species, Platanus orientalis L. and Albizia julibrissin Benth are normal water consuming species, and Quercus infectoria Oliv. and Olea europaea L. can be considered as drought resistant species.

Relationship Between Soluble Protein,Chlorophyll and ATP in Drought-Resistant Sweet Potato Under Water Stress

Some indices concerning the metabolism of substance and energy in sweet potato leaves under water stress were studied. The results showed an obvious increase in soluble protein content. Compared with control, Chl a, Chl b, total Chl contents and the ratio of Chl a to Chl b all decreased to some extent. ATP content increased in some varieties and decreased in others, but the stronger the drought resistance of the variety , the higher the ATP content. The correlation coefficient(r)of the soluble protein content, ratio of Chl a to Chl b and ATP content as a percentage of the drought-resistant sweet potato control variety are 0. 8968, - 0. 8509 and 0. 8200, respectively, P<0. 01. So these indices can be used to evaluate the drought resistance of different sweet potato varieties.

PoWRKY71 is involved in Paeonia ostii resistance to drought stress by directly regulating light-harvesting chlorophyll a/b-binding 151 gene

Although the functions of WRKY transcription factors in drought resistance are well known,their regulatory mechanisms in response to drought by stabilising photosynthesis remain unclear.Here,a differentially expressed PoWRKY71 gene that was highly expressed in drought-treated Paeonia ostii leaves was identified through transcriptome analysis.PoWRKY71 positively responded to drought stress with significantly enhanced expression patterns and overexpressing PoWRKY71 in tobacco greatly improved plant tolerance to drought stress,whereas silencing PoWRKY71 in P.ostii resulted in a drought-intolerant phenotype.Furthermore,lower chlorophyll contents,photosynthesis,and inhibited expression of photosynthesis-related light-harvesting chlorophyll a/b-binding 151(CAB151)gene were found in PoWRKY71-silenced P.ostii.Meanwhile,a homologous system indicated that drought treatment increased PoCAB151 promoter activity.Interactive assays revealed that PoWRKY71 directly bound on the W-box element of PoCAB151 promoter and activated its transcription.In addition,PoCAB151 overexpressing plants demonstrated increased drought tolerance,together with significantly higher chlorophyll contents and photosynthesis,whereas these indices were dramatically lower in PoCAB151-silenced P.ostii.The above results indicated that PoWRKY71 activated the expression of PoCAB151,thus stabilising photosynthesis via regulating chloroplast homeostasis and chlorophyll content in P.ostii under drought stress.This study reveals a novel drought-resistancemechanism in plants and provides a feasible strategy for improving plant drought resistance via stabilising photosynthesis.

Genetic dissection of drought resistance for trait improvement in crops

Reliance on agriculture for food security is a constant in all modern societies.Global climate change and population growth have put immense pressure on sustainable agriculture,exacerbating the effects of environmental stresses.Drought is one of the most pressing abiotic stresses that farmers face,presenting an annual threat to crop growth and yield.Crops have evolved extensive morphological,physiological,and molecular mechanisms to combat drought stress.Drought resistance is a polygenic trait,controlled by a complex genetic network and an array of genes working together to ensure plant survival.Many studies have aimed at dissecting the genetic mechanisms underlying drought resistance.Recent studies using linkage and association mapping have made progress in identifying genetic variations that affect drought-resistance traits.These loci may potentially be engineered by genetic transformation and genome editing aimed at developing new,stress-resistant crop cultivars.Here we summarize recent progress in elucidating the genetic basis of crop drought resistance.Molecular-breeding technologies such as marker-assisted selection,genome selection,gene transformation,and genome editing are currently employed to develop drought-resistant germplasm in a variety of crops.Recent advances in basic research and crop biotechnology covered in this review will facilitate delivery of drought-resistant crops with unprecedented efficiency.

Screening and Simple Identification of Drought-resistant Lines in Sugarcane Breeding

Six sugarcane plant lines were selected from seedlings owing to good performance in agronomic characters under drought conditions.A special test with drought stress to death under groove was carried out to select the best drought tolerant clones among them. The proportion of bound water to free water content in leaves,cell cytoplasm membrane permeability in leaves,yield components,etc.,which were regarded as reasonable indexes to identify drought resistance of sugarcane,were measured. The results showed that both YT06-868 and YT05-339 were winners. The two were high-class drought-resistant clones. On some measured indexes,both of them had higher values than ROC22( the main check variety) and on the other ones,they both had the same values as ROC22. The drought resistance of YT05-291 was moderate and between ROC22 and ROC16( the secondary check variety),while the others had poor drought-resistant according to these indexes.

Grassland-type ecosystem stability in China differs under the influence of drought and wet events

Ecological stability is a core issue in ecological research and holds significant implications forhumanity. The increased frequency and intensity of drought and wet climate events resulting from climatechange pose a major threat to global ecological stability. Variations in stability among different ecosystemshave been confirmed, but it remains unclear whether there are differences in stability within the sameterrestrial vegetation ecosystem under the influence of climate events in different directions and intensities.China's grassland ecosystem includes most grassland types and is a good choice for studying this issue.This study used the Standardized Precipitation Evapotranspiration Index-12 (SPEI-12) to identify thedirections and intensities of different types of climate events, and based on Normalized DifferenceVegetation Index (NDVI), calculated the resistance and resilience of different grassland types for 30consecutive years from 1990 to 2019 (resistance and resilience are important indicators to measurestability). Based on a traditional regression model, standardized methods were integrated to analyze theimpacts of the intensity and duration of drought and wet events on vegetation stability. The resultsshowed that meadow steppe exhibited the highest stability, while alpine steppe and desert steppe had thelowest overall stability. The stability of typical steppe, alpine meadow, temperate meadow was at anintermediate level. Regarding the impact of the duration and intensity of climate events on vegetationecosystem stability for the same grassland type, the resilience of desert steppe during drought was mainlyaffected by the duration. In contrast, the impact of intensity was not significant. However, alpine steppewas mainly affected by intensity in wet environments, and duration had no significant impact. Ourconclusions can provide decision support for the future grassland ecosystem governance.

Aβ-Carotene Ketolase Gene NfcrtO from Subaerial Cyanobacteria Confers Drought Tolerance in Rice

Nostoc flagelliforme is a terrestrial cyanobacterium that can resist many types of stressors,including drought,ultraviolet radiation,and extreme temperatures.In this study,we identified the drought tolerance gene NfcrtO,which encodes aβ-carotene ketolase,through screening the transcriptome of N.flagelliforme under water loss stress.Prokaryotic expression of NfcrtO under 0.6 mol/L sorbitol or under 0.3 mol/L NaCl stress significantly increased the growth rate of Escherichia coli.When NfcrtO was heterologously expressed in rice,the seedling height and root length of NfcrtO-overexpressing rice plants were significantly higher than those of the wild type(WT)plants grown on½Murashige and Skoog solid medium with 120 mmol/L mannitol at the seedling stage.Transcriptome analysis revealed that NfcrtO was involved in osmotic stress,antioxidant,and other stress-related pathways.Additionally,the survival rate of the NfcrtO-overexpression lines was significantly higher than that of the WT line under both hydroponic stress(24%PEG and 100 mmol/L H_(2)O_(2))and soil drought treatment at the seedling stage.Physiological traits,including the activity levels of superoxide dismutase,peroxidase,catalase,total antioxidant capacity,and the contents of proline,trehalose,and soluble sugar,were significantly improved in the NfcrtO-overexpression lines relative to those in the WT line under 20%PEG treatment.Furthermore,when water was withheld at the booting stage,the grain yield per plant of NfcrtO-overexpression lines was significantly higher than that of the WT line.Yeast two-hybrid analysis identified interactions between NfcrtO and Dna J protein,E3 ubiquitin-protein ligase,and pyrophosphate-energized vacuolar membrane proton pump.Thus,heterologous expression of NfcrtO in rice could significantly improve the tolerance of rice to osmotic stress,potentially facilitating the development of new rice varieties.

Application of Drought-resistant Varieties in Urban Green Spaces

As the connotations of urban green spaces and urban eco-green spaces have been more realized,drought-resistant green spaces have become a unique development trend,and drought-resistant flowers have been more applied in green spaces.This paper summarized characteristics of drought-resistant flowers,foreign and domestic researches in this field,advantages and disadvantages of their application in urban green spaces,and proposed key directions of the future researches.

Application Research of Water-saving and Drought-resistant Landscape Plants:A Case Study of Inner Mongolia Drought-resistant Mongolian Grasses

Construction of "water-saving landscape architecture" is a crucial content of building "conservation-minded society'',an important approach of ensuring the sustainable development of landscaping industry.It targets at exploring a reasonable means of using the nature,so as to improve ecological conditions and environment,save resources and energies,and promote the harmonious coexistence of man and nature.Landscape plant is a significant component of landscape architecture,it is a key section to choose proper drought-resistant plant species for the landscape construction.

Selection and Breeding of Drought Resistant,Water-saving and High-yield Wheat Variety Cangmai 028

Cangmai 028 was selected and bred according to the climatic characteristic of the winter wheat in Heilonggang Basin taking 98(083)as the female parent and the Canghe 030 as the male parent by "two-row parallel alternate selection" method.Cangmai 028 has characteristics of high resistance,water-saving,high and stable yield,and rich genetic background.This study elaborated selection and breeding background and methods,characteristics,quality,and yield of Cangmai 028.

Breeding of a Water-saving Drought-resistant Two-line Hybrid Rice Variety Wanliangyou 1008

Drought is one of the important factors limiting rice production,and the application of new water-saving rice varieties is urgently needed in rice production.Wanliangyou 1008 bred by Institute of Rice Research,Anhui Academy of Agricultural Sciences is a new two line hybrid rice variety with some good traits,including high drought resistance,high yield and good disease resistance.Wanlingyou 1008 was obtained by crossing drought-resistant high-quality restorer line DJ1008 and disease-resistant two-line sterile line Wan 25S.In this paper,the breeding process,characteristics and seed production technology of the variety were described in detail.

Drought Resistant Rice: an Integrated Crop Improvement Strategy

Rice physiological sensitivity to drought and its impact on crop productivity in water-limited environments are well-documented (O'Toole, 2004). However, rice yields in drought-prone rainfed lowlands and most

Changes in DNA Methylation Pattern at Two Seedling Stages in Water Saving and Drought-Resistant Rice Variety after Drought Stress Domestication

Recent studies revealed that DNA methylation plays an important role in plant growth and development. In this study, a water-saving and drought-resistant rice variety Huhan 3 was subjected to drought stress from tillering to grain-filling stages in six successive growth cycles. The variations in DNA methylation pattern between the original generation （Go） and the sixth generation （G6） were analyzed by using methylation sensitive amplification polymorphism method. The results revealed that the methylated loci accounted for 34.3% to 34.8% of the total loci. Among these methylated loci, 83.1% to 84.8% were full- and hyper-methylated and 15.2% to 16.9% were hemi-methylated. The DNA methylation level decreased from the three-leaf to four-leaf stages in Huhan 3. Differentially methylated loci （DML） between generations or/and between different developmental stages accounted for 4.0% of the total loci, most of which were only related to plant development （57.9%）. Compared to Go, the DNA methylation pattern of G8 changed after drought domestication, at the three-leaf stage, de-methylation accounting for 59.1%, while at the four-leaf stage, re-methylation for 47.9%. Genome-wide alternations of DNA methylation were observed between the two seedling stages, and DML mainly occurred on the gene＇s promoter and exon region. The genes related to DML involved in a wide range of functional biology and participated in many important biological processes.

Responses of Drought-Resistant Mutant vem1 to Stress and Cloning of VEM1 Gene in Arabidopsis

[ Objective] This study aimed to investigate the responses of drought-resistant mutant veml to stress and clone VEM1 gene in Arabidopsis. [ Method] A drought-resistant mutant veml was isolated from the Arabidops/s mutant pool. The germination rates of wild-type （WT） and mutant veml were detected to investigate the responses of mutant veml to mannitol, NaCl and ABA stress. [ Result] The mutant veml was resistant to mannitol and NaC1 stress but sensitive to ABA stress. VEM1 gene was cloned by Tail-PCR technology and sequenced. The sequencing result was submitted to NCBI for sequence alignment and gene mapping using BLAST. Database analysis suggested that VEM1 gene was a transposable clement gene. [ Conclusion] This study laid the foundation for functional analysis of drought-resistant gene VEM1.

Relationship Between Drought Resistance and Betaine Aldehyde Dehydrogenase in the Shoots of Different Genotypic Wheat and Sorghum

不同基因型小麦 (TriticumaestivumL .)和高粱 (SorghumvulgareL .)的抗旱性与其种芽中的甜菜碱醛脱氢酶(BADH)的含量存在密切关系。