Physiological,Molecular And Metabolic Effects Of Priming And Cold Plasma Treatment On Rice Seeds To Improve Resistance To Different Abiotic Stresses

Seeds of rice(Oryza sativa L),being a staple food for over half of the world's population,are sensitive during germination and early growth stages to various abiotic stresses,including heavy metal stress,salinity,chilling and drought stress.Abiotic stress is the main factor negatively affecting crop growth and productivity worldwide.Accordingly,the present study was carried out to elucidate the effects of seed priming and plasma treatment on seed germination and seed vigor of two cultivars(Qian You No.1(QY),Zhu Liang You 06(ZY))of rice under abiotic stress conditions through physiological,molecular and metabolomics approaches.It would be better to understand different mechanism of plant growth regulation to improve the germination and seedling growth under abiotic stress.Here different physiological and molecular analyses related with stress tolerance were performed which may provide a useful platform to improve stress-tolerant and increase rice seed vigor in response to different abiotic stresses.The main results were achieved as follows:1.Seed priming with polyethylene glycol regulating the physiological,molecular and metabolic mechanism in rice under nano-ZnO stressPlant growth parameters were significantly increased with seed priming with 30%PEG under nano-ZnO stress in both cultivars with a more prominent increase in QY as compared to ZY.Priming with PEG improved a-amylase activity and total soluble sugar contents of both cultivars under nano-ZnO stress.Significant increase in photosynthetic pigment with PEG priming was observed under the stress.PEG priming significantly decreased the antioxidant enzyme activities such as superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)as well as malondialdehyde(MDA)contents under nano-ZnO stress.Transcription analysis also suggested that expression level of APXa,APXb,CATa,CATb,CATc,SOD1,SOD2 and SOD3 were down regulated with PEG priming as compared to non-primed seeds under stress.The expression level of GR1,GR2,Amy2A and Amy3A in shoots and roots of both cultivars increased and had higher transcription levels under the stress conditions.The ultrastructural analysis showed that leaf mesophyll and root cells were significantly damaged under nano-ZnO stress in both cultivars with a more prominent in ZY cultivar.However,seed priming with PEG significantly alleviate the toxic effects of nano-ZnO stress and improved the cell structures of leaf and roots in both cultivars.In addition,glutathione reductase(GR)activity,reactive oxygen species(ROS)accumulation and proline contents decreased after the priming treatment in both cultivars under different nano-ZnO concentrations.Fourier transform infrared spectroscopy(FTIR)analysis did not show any significant effects of the priming treatment on the structure of functional groups in both cultivars under nano-ZnO stress.2.Regulation of ZnO nanoparticles-induced physiological and molecular changes by seed priming with humic acid in Oryza sativa seedlingsSeed germination and seedling performance were significantly improved by seed priming with humic acid(HA)under nano-ZnO stress as compared to the untreated control.Significant enhancement in total soluble protein,sugar,and starch contents were observed with seed priming over the control treatment under nano-ZnO stress.Abscisic acid(ABA)content in germinating seeds under nano-ZnO stress was also higher than that under control conditions.Meanwhile,gibberellins(GA)content decreased under nano-ZnO stress.Priming treatment reduced the expression level of ABA biosynthesis related genes(OsABA8ox2 and OsNCEDl)in rice seeds.In contrast,up-regulation in the expression levels of GA biosynthesis related genes(OsGA20ox2 and OsGA3ox1)were observed in primed seeds under stress.The contents of ROS and MDA,the activities of antioxidant enzymes were reduced by seed priming under the stress conditions.Higher uptake of Evans blue,nitro-blue tetrazolium(NBT)and 3,3-diaminobenzidine(DAB)by nano-ZnO stressed roots as compared with the control indicated loss of root cell viability and severe oxidative burst.The ultra-morphology analysis revealed that HA priming improved cell ultrastructure of the root tip and leaf mesophyll under nano-ZnO stress.3.Cold plasma treatment and exogenous salicylic acid priming enhances salinity tolerance of rice seedlingsSeed germination and seedling growth were enhanced by salicylic acid(SA)priming and cold plasma treatment either alone or in combination under salinity stress(150 mM NaCl).Photosynthetic pigments,photosynthetic gas exchange and chlorophyll fluorescence were improved by cold plasma treatment and SA priming under salinity stress as compared to the untreated seeds.The activities of antioxidant enzymes were significantly improved by the combination of SA priming and cold plasma treatment in both cultivars under salinity stress.The activities of enzymes involved in secondary metabolism activities were up-regulated with cold plasma and SA priming either alone or in combination under salinity stress.An increase in ROS accumulation and MDA content was also observed under salinity stress condition.However,seed treated with SA and plasma alone or combined resulted in a significant decrease in ROS and MDA contents under salinity stress.These results indicated that SA priming and cold plasma treatment either alone or combined improved plant uptake of nutrients in both cultivars under stress conditions.The ultrastructural changes were observed to be more prominent in ZY than QY cultivar;however,SA priming and cold plasma treatment alone or combined helped the plants to recover their cell turgidity under salinity stress.4.Seed priming with spermidine and 5-aminolevulinic acid improved seed polyamine metabolism under chilling stress in rice seedlingsPolyamines(PAs)have been demonstrated to be involved in plant in response to abiotic stresses including chilling stress.Germination percentage,seedling growth and seedling vigor index were decreased under chilling stress,however these physiological parameters were improved by priming with spermidine(Spd)and 5-aminolevulinic(ALA)in ZY and QY cultivars as compared with unprimed seeds.As well,total phenolics,flavonoids and glycine-betaine were improved by both priming treatment.Contrarily,significant decrease of a-amylase activity,the contents of soluble sugars and soluble protein in both cultivars was observed in chilling stressed plants as compared with optimum growth condition(25 ?).However,priming with Spd and ALA significantly increased a-amylase activity,the contents of soluble sugars and soluble protein with more prominent increase in QY cultivar.Results showed that chilling stress significantly improved SOD,POD,ascorbate peroxidase(APX)and glutathione peroxidase(GPX),and further enhancement was observed in Spd and ALA-primed seeds.Spd and putrescine(Put)was decreased under chilling stress,while a reverse tendency was observed in case of spermine(Spm)content.The enzymes involved in the PAs biosynthesis,arginine decarboxylase(ADC),ornithine decarboxylase(ODC)and S-adenosylmethionine decarboxylase(SAMDC)was improved by priming treatment.The relative expressions of genes encoding enzymes involved in PAs biosynthesis increased by Spd and ALA priming.Additionally,priming treatment improved the cell ultrastructure of leaf and embryo as compared with the unprimed seeds.5.Priming with methyl jasmonate alleviated polyethylene glycol-initiated drought stress by regulating metabolic pathway in rice seedRice seed germination and seed vigor was improved by priming with 2.5 mM of methyl jasmonate(MeJA)as compared with unprimed seeds,the application of MeJA(5 mM)diminished the germination and seed vigor under both the control and drought stress conditions.The root and shoot length,seedling fresh and dry weight were decreased under drought stress and enhanced by 2.5 mM MeJA-primed seeds as compared with priming with 5 mM of MeJA and unprimed seeds as well.The results suggested that the photosynthetic parameters such as net photosynthetic(Pn),stomatal conductance(Gs),intercellular CO2 concentration(Ci),and transpiration rate(Tr)were decreased in response to drought stress and were enhanced by priming with 2.5 mM MeJA as compared with unprimed seeds.Meanwhile,the chlorophyll content and the photochemical efficiency of PS?(Fv/Fm)were also improved by priming with 2.5 mM MeJA under drought stress as compared with 5 mM MeJA priming and unprimed seeds.Water potential,water use efficiency(WUE)and relative water content(RWC)was improved by 2.5 mM MeJA priming under drought stress condition,and a decrease tendency was observed in case of electrical conductivity.The GC-MS analysis revealed that drought stress induced changes in the concentration of the comprehensive metabolites in the root and shoot of both studied cultivars.Present results showed that proline content was significantly increased under drought stress as compared with the control.This study clarified the mechanism involved in rice tolerance to drought stress and provides possible widely cultivation of rice in highly water deficit-affected area.