Changes of Proline Content,Activity,and Active Isoforms of Antioxidative Enzymes in Two Alfalfa Cultivars Under Salt Stress

The plants of two elfalfa （Medicago sativa L.） cultivars differing in salt tolerance were subjected to three salt treatments, 70, 140, and 210 mM NaCl for 7 days. Root, shoot, and leaf growths were inhibited by increased salt treatments in both cultivars, and at 140 and 210 mM salt treatments, Zhongmu 1 had significantly higher root, shoot, and leaf dry weights per plant than Deft. The malondialdehyde （MDA） accumulation in Deft was considerably greater than in Zhongmu 1, indicating a higher degree of lipid peroxidation at 140 and 210 mM salt treatments. The changes in the activity and active isoforms of antioxidant enzymes such as superoxide dismutase （SOD, EC 1.15.1.1）, catalase （CAT, EC 1.11.1.6）, peroxidase （POD, EC 1.11.1.7）, and ascorbate peroxidase （APOX, EC 1.11,1.11）, accumulation of free proline, and rate of lipid peroxidation in leaves of two alfalfa cultivars were also investigated. After stress, the activity and active isoforms of antioxidative enzymes were altered and the extent of alteration varied between the cultivar Deft and Zhongmu 1. The proline accumulation in Deft was considerably greater than in Zhongmu 1 at 210 mM salt treatment. This indicated that proline accumulation may be the result, instead of the cause, of salt tolerance.

Changes of Antioxidative Enzymes and Lipid Peroxidation in Leaves and Roots of Waterlogging-Tolerant and Waterlogging-Sensitive Maize Genotypes at Seedling Stage

To better understand the physiological and biochemical mechanisms of waterlogging tolerance, waterlogging effects on lipid peroxidation and the activity of antioxidative enzymes were investigated in leaves and roots of two maize genotypes, HZ32 （waterlogging-tolerant） and K12 （waterlogging-sensitive）. Potted maize plants were waterlogged at the second leaf stage under glasshouse conditions. Leaves and roots were harvested 1 d before and 2, 4, 6, 8 and 10 d after the start of waterlogging treatment. Through comparing the activities of superoxide dismutase （SOD）, ascorbate peroxidase （APX）, glutathione reductase （GR）, catalase （CAT） and guaiacol peroxidase （POD） between waterlogging-tolerant and waterloggingsensitive genotype, we deduced that CAT was the most important H2O2 scavenging enzyme in leaves, while APX seemed to play a key role in roots. POD, APX, GR and CAT activities in conjunction with SOD seem to play an essential protective role in the O2^- and H2O2 scavenging process. Lipid peroxidation was enhanced significantly only in K12 （P 〈 0.001） and there was no difference （P 〉 0.05） in HZ32 up to 6 d after waterlogging stress. These results indicated that oxidative stress may play an important role in waterlogging-stressed maize plants and that the greater protection of HZ32 leaves and roots from waterlogging-induced oxidative damage results, at least in part, through the maintenance of increased antioxidant enzyme activity.

Nickel accumulation and its effect on biomass,protein content and antioxidative enzymes in roots and leaves of watercress(Nasturtium officinale R.Br.)

In order to understand its response towards nickel stress, watercress （Nasturtium officinale R. Br.） was exposed to nickel （1-25 mg/L） for 1, 3, 5 and 7 days. The accumulation and translocation of nickel were determined and the influence of nickel on biomass, protein content and enzymatic antioxidants was examined for both roots and leaves. It was determined that N. o fficinale could accumulate appreciable amounts of Ni in both roots and leaves. Nickel accumulated particularly in the roots of plants. Biomass increased at low nickel concentrations but certain measurable change was not found at high concentrations. Under stress conditions the antioxidant enzymes were up-regulated compared to control. An increase in protein content and enzyme activities was observed at moderate exposure conditions followed by a decline at both roots and leaves. The maximum enzyme activities were observed at different exposure conditions. Our results showed that N. officinale had the capacity to overcome nickel-induced stress especially at moderate nickel exposure. Therefore, N. officinale may be used as a phytoremediator in moderately polluted aquatic ecosystems.

Effect of Maturity Stage on the Gene Expression of Antioxidative Enzymes in Cucumber (Cucumis sativus L.) Fruits Under Chilling Stress

The gene expression pattems of antioxidative enzymes in cucumber （Cucumis sativus L.） fruits at four different maturity stages, immature （3-8 d after anthesis （DAA）, mature （9-16 DAA）, breaker （17-22 DAA）, and yellow （35-40 DAA）, were determined before and after cold storage at 2℃ for 9 d and after subsequent rewarming at 20℃ for 2 d. The electrolyte leakage and malondialdehyde content in cucumber fruits were increased after cold storage and subsequent rewarming. Increased expressions of peroxidase, ascorbate peroxidase （APX）, and monodehydroascorbate reductase after cold storage played an important role in cucumber fruits to cope with chilling injury. The elevated cyt-superoxide dismutase, catalase, APX and dehydroascorbate reductase after subsequent rewarming in cucumber fruits facilitated the recovery from chilling stress. The highest expression levels of all the seven antioxidative enzyme genes in yellow fruits might be responsible for the enhanced chilling tolerance. Cucumber fruits at earlier developmental stages was more susceptible to chilling stress than those at later stages. The relative higher gene expressions of antioxidative enzymes genes at earlier developmental stages may be the responses to the sever oxidative stress caused by chilling injury.

Contribution of Antioxidative Enzymes and Anoxia Responsive Genes to Submergence Tolerance in Rice: A Review

Flooding/submergence of rice fields is a severe problem in South and South-East Asia, affecting more than 20 million hectares of rice every year. Submergence creates hypoxic or anoxic condition causing poor germination, seedling establishment,and enormous yield loss. Standing water in the field from weeks to months also leads to significant yield losses when large part of aerial tissues is under water. For flash flooding, a rice variety FR1A3 with tolerant gene(SUB1A) was identified. SNORKEL1 and SNORKEL2 have been identified for their ability to survive deep-water flooding by rapid elongation. Submergence stress has also been reported to adversely affect cell division and damage cellular and organelle membranes. Research on antioxidative enzymes response and genes that confer tolerance to prolonged flooding is in progress. Here we review the different anoxia responsive genes and the potential involvement of antioxidative enzymes, such as superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase, which occur in cells of rice plant exposed to submergence stress.

Effect of Low Light Stress on Photosynthetic Pigments and Antioxidative Enzymes in Field Grown Indian Mustard(Brassica juncea L.)Genotypes

Oilseed Brassicas have prominent place after soybean and groundnut.More than 90%of the area under oilseed Brassicas is occupied by the Indian mustard(Brassica juncea)because of its relative tolerance to biotic and abiotic stresses as compared to other oilseed Brassica species.Light plays key a role in net primary productivity and is necessary for plant growth,morphogenesis and several physiological processes.The present investigation aimed to assess the effect of low light stress on photosynthetic traits and antioxidative enzymes in Brassica juncea genotypes.Shading was imposed with nets from mid-December to mid-January which cut 25%-30%of natural sunlight.Shading period coincided with the onset of flowering.The results showed that chlorophyll b and antioxidant activities of superoxide dismutase(SOD),guaiacol-peroxidase(G-POD)and catalase(CAT)increased under low light stress at two stages of investigations(10 and 30 days after removal of nets).With shading treatment,soil plant analysis development(SPAD)chlorophyll meter values,chlorophyll a,total chlorophyll,chlorophyll a/b ratio,carotenoid and protein content decreased significantly while malondialdehyde content increased due to damages of plant cells.This study provides valuable information for further deciphering genetic mechanism and improving agronomic traits in Indian mustard cultivated under optimal light requirements.

Osmoprotectants and Antioxidative Enzymes as Screening Tools for Salinity Tolerance in Radish (Raphanus sativus)

The research addresses the identification of a screening methodology for salt stress tolerance in radish cultivars. In the first experiment, two different radish cultivars(long white and round red) were compared in their morphological and physiological responses to different salinity levels. Round red radish showed better morphological and physiological responses to incremental salinity in terms of yield and better adaptation of overall water relations. In the second experiment, the most tolerant genotype from the first experiment was used as a control against other seven round red radish genotypes ranked by their salinity tolerance according to morphological, physiological and biochemical indices. Salt stress did not significantly affect malondialdehyde(MDA) and hydrogen peroxide(H2O2) content, and ascorbate peroxidase(APX) activity in the studied cultivars. Nonetheless, the relatively salt tolerant cultivar SAXA2 showed higher ability to accumulate compatible solutes(e.g.proline and proteins) and maintain osmotic adjustment. In addition, cultivar SAXA2 also showed considerable increase in glutathione reductase(GR) activity. Our results supported that accumulation of proline and higher GR activity are associated with radish salt tolerance, whereas no relationship with salinity was observed in superoxide dismutase(SOD), MDA and H2O2 content.

Foliar application of zinc promotes cadmium absorption by increasing expression of cadmium transporter genes and activities of antioxidative enzymes in winter wheat

Cadmium(Cd)is a deleterious non-essential metal in plants.To elucidate the mechanisms by which zinc(Zn)application alleviates cadmium(Cd)toxicity in wheat,we characterized plant growth,antioxidant system,leaf cell ultrastructure,and Cd transporter gene expression in winter wheat under Cd exposure(50μmol L^(-1)Cd)with foliar Zn application in a hydroponic experiment.Results showed that Zn addition(Zn+Cd)or pretreatment(pre-Zn+Cd)at 2 g L^(-1)as Zn_(S)O_(4)·7H_(2)O significantly exacerbated Cd-induced growth inhibition and diminished root morphological parameters,root cell viability,and chlorophyll content.In addition,the Cd content increased in roots and shoots in the Zn+Cd and pre-Zn+Cd treatments,but the Cd translocation factor decreased,when compared to the treatment without Zn application.After Zn application,the Cd content increased in the root cell wall fraction but decreased in the soluble fraction.The activities of antioxidative enzymes(superoxide dismutase,peroxidase,and catalase)and the contents of non-enzymatic antioxidants(malondialdehyde,ascorbic acid,and glutathione)significantly increased in the roots and shoots of wheat after Cd exposure,particularly in the Zn+Cd and pre-Zn+Cd treatments.Gene expression analysis showed that five genes(TaHMA2,TRIAE5370,TCONS1113,TRIAE5770,TRIAE1060,and TCONS5200)participated in root absorption of Cd,whereas TCONS5200 and TRIAE5660 contributed to Cd transfer to shoots.Foliar application of Zn increased the number of chloroplasts,but the chloroplast structure was destroyed in the Zn+Cd treatment.These results indicated that 2 g L^(-1)ZnSO4·7H2O increased the toxicity of 50μmol L^(-1)Cd.Increased Cd uptake due to the upregulated expression of Cd transporter genes and increased reactive oxygen species accumulation may be the reasons why Zn application aggravated Cd toxicity.

Study on Antioxidant Enzyme Activity and Physiology and Biochemistry of Solanum nigrum L. under Glyphosate Stress

[Objectives] This study was conducted to investigate the scientific prevention and control of Solanum nigrum L. [Methods] Through experiments on S. nigrum from different sources, it was found that glyphosate stress had significant effects on antioxidant enzyme activity and oxidative damage of sensitive S. nigrum plants. [Results] Sensitive S. nigrum showed oxidative damage under glyphosate stress, while resistant S. nigrum responded to adversity damage by improving its antioxidant enzyme activity. The experimental results showed that the antioxidant enzymes and reduced glutathione of S. nigrum had certain metabolic detoxification effects under glyphosate stress. [Conclusions] This study provides a theoretical basis for scientific prevention and control of S. nigrum , and has a certain reference value for revealing the glyphosate resistance mechanism of S. nigrum .

Activity of Stress-related Antioxidative Enzymes in the Invasive Plant Crofton Weed(Eupatorium adenophorum)

Crofton weed is an invasive weed in southwestern China. The activities of several antioxidative enzymes involved in plant protection against oxidative stress were assayed to determine physiological aspects of the crofton weed that might render the plant vulnerable to environmental stress. Stresses imposed on crofton weed were heat （progressively increasing temperatures： 25 ℃, 30 ℃, 35 ℃, 38℃ and 42 ℃ at 24 h intervals）, cold （progressively decreasing temperatures： 25 ℃, 20 ℃, 15℃, 10 ℃ and 5℃ at 24h intervals）, and drought （without watering up to 4days）. The three stresses induced oxidative damage as evidenced by an increase in lipid peroxidation. The effect varied with the stress imposed and the length of exposure. The activity of superoxide dismutase （SOD） increased in response to all stresses but was not significantly different from the controls （P 〈 0.05） when exposed to cold stress. Catalase （CAT） activity decreased in response to heat and drought stress but increased when exposed to cold conditions. Guaiacol peroxidase （POD） and glutathione reductase （GR） activities increased in response to cold and drought but decreased in response to heat stress. The activity of ascorbata peroxidase （APX） responded differently to all three stresses. Monodehydroascorbate reductase （MDHAR） activity decreased in response to heat and drought, and slightly increased in response to the cold stress but was not significantly different from the controls （P 〈 0.05）. The activity of dehydroascorbata reductase （DHAR） increased in response to all three stresses. Taken together, the co-ordinate increase of the oxygen-detoxifying enzymes might be more effective to protect crofton weed from the accumulation of oxygen radicals at low temperatures rather than at high temperatures.

Endophytic Bacteria Promote the Growth of Suaeda glauca in Saline-Alkali Stress:Regulation of Osmotic Pressure and Antioxidative Defense System

Endophytic bacteria are promising bacterial fertilizers to improve plant growth under adverse environment.For ecological remediation of coastal wetlands,it was necessary to investigate the effect and interaction of endophytes on halophytes under saline-alkali stress.In this study,an endophytic bacterium strain HK1 isolated from halophytes was selected to infect Suaeda glauca under pH(7 and 8)and salinity gradient(150,300 and 450mmolL^(-1)).Strain HK1 was identified as Pantoea ananatis and it had ability to fix nitrogen,dissolve inorganic phosphorus and produce indole-3-aceticacid(IAA).The results showed that strain HK1 could promote the growth of S.glauca seedings when the salinity was less than 300mmolL^(-1),in view of longer shoot length and heavier fresh weight.The infected plants could produce more proline to decrease the permeability of cells,which content increased by 26.2%–61.1%compared to the non-infected group.Moreover,the oxidative stress of infected plants was relieved with the malondialdehyde(MDA)content decreased by 16.8%–32.9%,and the peroxidase(POD)activity and catalase(CAT)activity increased by 100%–500%and 6.2%–71.4%,respectively.Statistical analysis revealed that increasing proline content and enhancing CAT and POD activities were the main pathways to alleviate saline-alkali stress by strain HK1 infection,and the latter might be more important.This study illustrated that endophytic bacteria could promote the growth of halophytes by regulation of osmotic substances and strengthening antioxidant activities.This finding would be helpful for the bioremediation of coastal soil.

Effect of powdery mildew on interleaf microbial communities and leaf antioxidant enzyme systems

Chinese peony(Paeonia lactiflora Pall.)is both medicinally and aesthetically beneficial.Powdery mildew is a common fungal disease that seriously jeopardizes the value of numerous species,including peonies as a crop.In order to provide a basis for the prevention and treatment of peony powdery mildew,we examined the microbial diversity,the malondialdehyde(MDA)concentrations and antioxidant enzyme activities of peony leaves infected with three levels of powdery mildew to determine any modifications to the leaf's antioxidant enzyme systems and microbial community structure following the onset of disease.The results show that the MDA content rose as the degree of infection became worse.Antioxidant enzyme activity rose and then declined.Following the initiation of powdery mildew,fungal community diversity decreased,whereas there was not any appreciable change in bacterial communities according to microbial diversity sequencing.The relative abundance of more than half of fungal species decreased,with the bacterial genera displaying both abundant and diminished communities with less pronounced alterations in their community structure after the disease spread.Significant different taxa that were critical to the organization of each microbiome were found.Correlation analysis showed that the relative abundance of powdery mildew pathogenic fungal genus Erysiphe was correlated with those of 11 fungal genera and one bacterial genus.Among them,Aureobasidium,Neosetophoma and Sclerostagonospora showed significant positive correlations with Erysiphe and MDA.

Osmotic Regulation,Antioxidant Enzyme Activities and Photosynthetic Characteristics of Tree Peony(Paeonia suffruticosa Andr.)in Response to High-Temperature Stress

Tree peony(Paeonia suffruticosa Andr.)is a traditional Chinese flower,which prefers cool weather.However,high temperature in summer in the middle and lower reaches of the Yangtze River restricts its growth and development.In this study,osmotic regulation,antioxidant enzyme activities,and photosynthetic characteristics of tree peony in response to high-temperature stress were investigated.The results showed that high-temperature stress had destroyed the cell membrane,manifested as the increased relative electrical conductivity and malondialdehyde content.Moreover,high-temperature stress led to excessive accumulation of reactive oxygen species,thereby,activating antioxidant enzyme activities.Also,photosynthetic parameters and chlorophyll fluorescence parameters directly reflected the damage to the photosystem II reflection center under high-temperature stress.In addition,high-temperature stress led to stomatal closure and chloroplast damage.This study revealed the physiological responses of tree peony to high-temperature stress,laying a foundation for the promotion of tree peony in high-temperature areas and the improvement of high-temperature resistance.

Ellagic Acid Enhances Antioxidant System Activity and Maintains the Quality of Strawberry Fruit during Storage

Ellagic acid(EA)is a natural antioxidant,widely present in a lot of forms’soft fruits,nuts,and other plant tissues,and helpful for promoting human health;however,its protective effect on postharvest fruit and improving the quality index of postharvest fruit have rarely been studied.In this experiment,the strawberries were soaked in 0,100,200,300,400,and 500 mg L^(−1) EA,respectively,and the influential EA on fruit quality and the antioxidant system of strawberries were studied.Compared with the control,EA treatment can reduce the browning degree and rotting rate of strawberry fruit during storage and augment the soluble solid content(SSC).EA treatment can also increase the content of related stuff and enzyme activity in antioxidant systems;the gene expression level of polyphenol oxidase(PPO)in strawberries treated with EA was always down-regulated,correspondingly,the expression of other antioxidant enzyme genes was enhanced.Among the strawberry fruits treated with EA of different concentrations,300 mg L^(−1) EA had the best effect in the process of strawberry preservation.The results suggested that the proper concentration of exogenous EA at 300 mg L−1 could maintain strawberries’quality and enhance the antioxidant system by improving the activities of antioxidative enzymes and the ascorbateglutathione(AsA-GSH)cycle during storage.

Effects of mechanical damage and herbivore wounding on H2O2 metabolism and antioxidant enzyme activities in hybrid poplar leaves

The changes of hydrogen peroxide （H2O2） metabolism and antioxidant enzyme activities in a hybrid poplar （Populus simonii xp. pyramidalis ＇Opera 8277＇） in response to rnechanical damage （MD） and herbivore wounding （HW） were investigated to determine whether H2O2 could function as the secondary messenger in the signaling of systemic resistance. Results show that H2O2 was generated in wounded leaves through MD and HW treatments and systemically in unwounded leaves around the wounded leaves. The activities of antioxidant enzymes such as superoxide dismutase （SOD）, catalase （CAT） and ascorbate peroxidase （APX） were also enhanced. However, the H2O2 accumulation and antioxidant enzyme activities were inhibited in MD leaves through the pretreatment with DPI （which is a specific inhibitor of NADPH oxidase）. The results of this study suggest that H2O2 could be systemically induced by MD and HW treatments, and H2O2 metabolism was closely related to the change in SOD, APX and CAT activities. A high level of antioxidant enzymes could decrease membrane lipid peroxidation levels and effectively induce plant defense responses.

Distribution of Calcium in Bagged Apple Fruit and Relationship between Antioxidant Enzyme Activity and Bitter Pit

[Objective]The aim was to study the distribution of Ca in bagged apple fruit and the relationship between antioxidant enzyme activity and bitter pit disease,which will provide a basis for resolving Ca metabolism disorder in apple cultivation. [Method]With Fuji Apple as the tested material,the changes of Ca2＋ content and antioxidant enzyme activity in different parts of apple fruit after picking bags and storage period were determined. [Result]The results showed that Ca contents in the light surface of fruits were higher than that in the backlight surface. The Ca contents of stalk cavity were higher than that of calyx-end. The activities of SOD,POD,CAT and APX in the light surface of fruits were higher than that in the backlight surface. The activities of SOD,POD,CAT and APX of stalk cavity were higher than that of calyx-end. The contents of MDA in the light surface of fruits were lower than that in the backlight surface. The contents of MDA of stalk cavity were lower than that of calyx-end. [Conclusion]The incidence rate of bitter pit in the light surface of fruits were lower than that in the backlight surface,and the incidence rate of bitter pit of stalk cavity were lower than that of calyx-end.

Effect of Different Arbuscular Mycorrhizal Fungi Strains on Mineral Nutrition and Antioxidant Enzymes of Chrysanthemum morifolium

[Objective] The purpose was to study the effects of different arbuscular mycorrhizal fungi strains（AMF）on the mineral nutrition and antioxidant enzymes of Chrysanthemum morifolium.[Method] The pot experiment was conducted in the greenhouse,C.morifolium ＇Jinba＇ was inoculated with five kinds of AMF,N,P,K,malondial dehyde（MDA）content,as well as the superoxide dismutase（SOD）,peroxidase（POD） and catalase（CAT） activity in roots,leaves and petals of C.morifolium were measured at seedling and flowering stages.[Result] The G.i,G.e and G.m treatments could promote mineral nutrient absorption,increase N,P,K content in roots,leaves and petals of C.morifolium compared with the control without inoculation.The G.d、G.e and G.m treatments could significantly reduce MDA content in roots and petals,thus alleviating membrane permeability and lipid peroxidation.The G.i treatments could also improve the SOD,POD and CAT activities of C.morifolium,thereby increasing the capability of scavenging oxygen free radicals.[Conclusion] According to the comprehensive analysis,G.i was screened out as the best strain to improve mineral nutrition and antioxidant enzyme activities of C.morifolium.

Research on Oxidative Stress Induced by Tenuazonic Acid from Alternaria augustiovoide and Changes in Antioxidant Enzyme Activities in Leaves of Echinochloa crus-galli

[Objective] The aim of the study was to determine whether phytotoxicity of TeA against Echinochloa crus-galli leaves was correlated with oxidative stress caused by generation of reactive oxygen and the changes of antioxidant enzymes activity.[Method] The changes of malondialdehyde（MDA）content,hydrogen peroxide（H2O2）,and activities of superoxide dismutase（SOD）,glutathione reductase（GR）and catalase（CAT）were studied by leaf segment method in vitro.[Result] After the treatment of 500 μmol/L TeA,the content of MDA and H2O2 increased by 247.86% and 67.00%,respectively,indicating that the accumulation of MDA and H2O2 in E.crus-galli leaves was due to the reactive oxygen burst induced by TeA.TeA induced a significant increase in activities of SOD,GR and CAT.At 500 μmol/L TeA,activities of SOD,GR and CAT increased more than one fold compared with the control.[Conclusion] TeA could not only cause oxidative stress in leaves of E.crus-galli through the induction of reactive oxygen,but also induce the increasing of antioxidant enzyme activity.

Extraction of Pumpkin Polysaccharide by Complex Enzyme Method and Its Antioxidant Research

[Objective] This paper aims to study a new method of extracting pumpkin polysaccharide from pumpkin. Single factor experiments were conducted to examine the effects of extracting time,temperature,the solid-liquid ratio and pH value on the extraction yield of polysaccharide from pumpkin. [Method] The best enzyme ratio and extraction conditions for complex enzymes extraction were determined through orthogonal tests. Scavenging ·OH and O-2 activities of pumpkin polysaccharides were also investigated by salicylic acid and improved self-oxidation of o-pheno methods respectively. [Results] The results showed that the biggest extraction yield of polysaccharide from pumpkin can be got when adding 1% cellulose enzyme,1.5% pectinase,1.0% papain and Na2HPO4-citric acid buffer solution (pH was 4.6),and oscillating for 30 min under water at 40 ℃ with the solid-liquid ratio of 1:30. In addition,pumpkin polysaccharides had a strong activity of eliminating ·OH,but very weak activity to scavenge O-2. [Conclusion] This study provided basic data for research and application of Pumpkin polysaccharide.

Microalgae(Chlorella vulgaris Beijerinck)alleviates drought stress of broccoli plants by improving nutrient uptake,secondary metabolites,and antioxidative defense system

Microalgae,such as Chlorella vulgaris Beijerinck(green algae),are beneficial microscopic organisms that may help plants to improve nutrient uptake,growth,and abiotic tolerance to stressors.The current study was performed to investigate the effectiveness of algae(Chlorella vulgaris Beijerinck)foliar applications[1%,3%,or 5%(v/v)]on mitigation of drought stress in broccoli plants subjected to water deficit at 25%of field capacity.The results showed that the broccoli plants grown under drought stress alone exhibited severe disturbance in growth with considerable reductions in the shoot length,and fresh and dry weights,leaf area,relative water content,leaf water potential,and photosynthetic pigment contents and elevated levels of the lipid peroxidation product malondialdehyde in the leaves.Additionally,the foliar application of microalgae mitigated the detrimental effects of drought,leading to better growth performance(increase of 9%–132%)when compared with the drought-stressed plants that had not received an application of microalgae.Microalgae-mediated beneficial effects were particularly evident in the enhancement of the photosynthetic pigment contents,including chlorophyll-a(6%–60%),chlorophyll-b(19%–55%),and total carotenoids(26%–114%).Exogenous microalgae also contributed to the reduction of membrane damage,as proven by significantly decreased levels of malondialdehyde(10%–39%)in the leaves of the broccoli plants exposed to drought stress.The application of microalgae increased the total flavonoid and phenolic contents,and nutrition uptake.Furthermore,the activities of enzymatic antioxidants like ascorbate peroxidase,catalase,glutathione reductase,and superoxide dismutase increased in response to mediation,resulting in significant alleviation of drought-induced oxidative damage.The most effective application concentration of microalgae was determined as 5%.Overall investigations revealed that the foliar application of microalgae could be recommended as a sustainable strategy to improve the defense system of drought-stressed broccoli plants.