Effect Of Uniconazole On Alleviating Carbon Metabolism Damage Of Mung Bean Under Chilling Stress At R1

Mung bean(Vigna radiata(L.)Wilczek)is indigenous to tropical areas and is regarded as sensitive to chilling stress.When temperature drops below 15°C,its growth and development are significantly retarded.Uniconazole(S3307)has been used as a plant growth retardant and plays an irreplaceable role in crop adaptation or resistance to abiotic stress.In order to clarify the mechanism of chilling injury in mung bean and the regulation mechanism of S3307 in growth and development under chilling stress at R1 stage.The experiment was conducted at Heilongjiang Academy of Agricultural Sciences located in Northeast China in 2017.Two different genotypes of mung bean varieties(Lufeng 2 and Lufeng 5)were used as experimental materials.The effects of chilling injury on growth and development of mung bean and the regulation effect of S3307 were studied by pot experiment.The main results and conclusions are as follows:1.Chilling stress at R1 stage reduced the number of pods per plant,the number of grains per plant and the yield of mung bean.With the prolongation of the low temperature treatment,the decline rate gradually increased.Compared with plants in the natural environment,Lvfeng 2 and Lvfeng 5,the yield significantly decreased by9.04%-44.85% and 9.17%-36.30%,respectively.The application of uniconazole effectively relieved the degradation of the above indicators in chilling-stressed plants.When treated with chilling injury for 4 day,S3307 pretreatment alleviated the yield loss by 24.86% and 17.42% for Lvfeng 2 and Lvfeng 5,respectively.2.Taking “Lvfeng 2” as experimental material,functional leaves were harvested at 1 d and 4 d after chilling stress treatment and untreated samples with chilling stress were used as controls.Transcriptome analyses were analyzed by Illumina RNA sequencing.A total of 19.62 Mb clean and high quality data were obtained after removing adaptors and low quality sequences.Among these differentially expressed genes(DEGs),2 023 were up-regulated and 2 002 down-regulated under chilling stress for 1 d.However,2 199 were up-regulated and 1 824 down-regulated under chilling stress for 4 d.In total,4 905 and 3 266 DEGs were identified after S3307 pretreatment for 1 d and 4 d under chilling stress,respectively.Gene ontology enrichment(GO)and biochemical pathways analyses of these DEGs showed thylakoid,Photosystem II(PSII),photosynthetic membrane structure,carbohydrate metabolism,etc.KEGG analyses of these DEGs showed that with the prolongation of chilling stress,the degree of damage on photosynthesis and carbohydrate metabolism in mung bean leaves were increased,and the involved number of DEGs were enhanced,but the number of DEGs in the total metabolic pathway were significantly higher than that in the early stage of R1 chilling stress.Exogenous application of S3307 during the same assay period could promote an increase in the number of DEGs in the above metabolic pathway.Nine DEGs were randomly selected to perform q RT-PCR and the result was basically consistent with RNA-Seq(R2=0.9119),demonstrating the reliability of transcriptome data.3.The photosynthetic pigment contents and the net photosynthetic rate(Pn)in both mung bean varieties declined with the prolongation of the low temperature treatment.In Lvfeng 2 and Lvfeng 5 chilling stress caused a marked decrease in photosynthesis amount and maximum net photosynthetic rate(Pnmax)which was40.87%,33.47%,59.88% and 40.87% lower than the plant in the natural environment,respectively.Starch and sucrose contents were declined in leaves with the low temperature treatment prolonging.The activities of invertase and sucrose phosphate synthase(SPS)were inhibited,the activities of amylase and sucrose phosphate synthase(SS)was improved by chilling stress.Exogenous application of S3307 can promote the up-regulation of key enzymes involved in chlorophyll synthesis,such as glutamyl t RNA reductase and Mg-chelating enzyme,and effectively alleviate the degradation of leaf photosynthetic pigments by chilling stress under chilling stress.S3307 pretreatment significantly increased the expression levels of 22 key enzymes of photosynthetic metabolism such as Psb O,Psb Q,Psb P and Pet H,which ensured that photosynthetic sources had strong photosynthetic capacity under chilling stress.4.The reaction center activity of photosystem II(PSII)and the energy transfer between PSII complex units were suppressed by chilling stress,which reduced the maximum quantum efficiency of PSII and resulted in photoinhibition of PSII.Exogenous application of S3307 was effective to improve the reaction center activity of PSII,promote the transfer of photosynthetic electrons,increase the energy transfer between PSII complexes,and avoid serious photoinhibition of PSII.5.Chilling stress accelerates the production of ROS and induction of oxidative stress,which eventually results in a significant increase of malondialdehyde and electrolyte permeability with the prolongation of the low temperature treatment.S3307 pretreatment observably enhanced the contents of non-enzymatic antioxidants and osmotic adjustment substances,and promoted the up-regulation of SOD and POD-related gene expression,and elevated the antioxidant enzyme activities in plants to detoxify of ROS.Overall,exogenous application of S3307 relieves oxidative damage caused by chilling stress in mung bean leaves.