| In the world,oilseed rape(Brassica napus L.)is one of the important oil crops.Low temperature is a main factor limiting the distribution of rapeseed.In China,rapeseed is mainly planted in the Yangtze River basin.The multi-ripe planting mode delays the rapeseed sowing period.The temperature is low when direct-seeding rapeseed emerges,which leads to slow germination,uneven emergence and weak seedlings.In addition,chilling stress is a common meteorological disaster in the Yangtze River basin,and rapeseed under normal sowing period is also vulnerable to low temperature threats.Therefore,to improve the chilling tolerance of Brassica napus L.by seed priming is important for ensuring rapeseed planting area and stabilizing final yield.In this paper,firstly,the cold tolerance of eight rapeseed cultivars was identified.Then the cold-resistant and cold-sensitive rapeseeds were used as experimental materials to study the effects of sodium silicate(Si)and γ-aminobutyric acid(GABA)on seed germination and seedling growth.The main results are as follows:1.Cold tolerance of eight rapeseed cultivars at germination stage was identified.The seed germination and seedling quality were measured under normal temperature(20℃)and low temperature(10℃),and the relative value of the index was used as the cold tolerance coefficient.Correlation analysis found that,relative germination energy,relative germination percentage,relative germination index,relative vigor index,relative average germination time and relative seedling fresh weight were significantly or highly significantly correlated with each other except for relative seedling dry weight,and the 6 index can be used to evaluate the tolerance of rapeseed.The comprehensive evaluation of 8 rapeseed cultivars was carried out by fuzzy membership function method.The cold tolerance of rapeseed from strong to weak was:ZYZ200,ZD619,ZY50,ZD630,ZD 622,GY605,ZS72,DXY53.2.The effects of Si and GABA on seed germination of different cold-tolerant rapeseed under low temperature stress were studied.The cold-tolerant(ZYZ200)and cold-sensitive(DXY53)rapeseed cultivars were used as experimental materials to determine the effects of Si and GABA priming on germination parameters,germination metabolism,energy mobilization and cold-induced gene under chilling(10℃)stress.The results showed that priming with 2 mM Si and 1 mM GABA significantly increased the germination speed,germination percentage and seedling vigor of rapeseed at low temperature,and the seedling quality was higher than that without treatment after 7 days of germination.Seed priming significantly increased the expression of isocitrate lyase and esterase gene BnICL and BnGDSL1 in the seed,enhanced the activities of isocitrate lyase and esterase,and the data of imbibition for 24 h at low temperature was significantly correlated with the seed germination parameters.The seed priming promoted the decomposition of soluble sugar and soluble protein and promoted the accumulation of proline in the seeds.The proline content at 48 h,the soluble protein at 72 h and the soluble sugar at 48 and 72 h were significantly correlated with the seed germination parameters.After priming,cold responsive genes BnCAMTA1,BnICE1,BnCBF and BnCOR25 were up-regulated in cv.DXY53,while ZYZ200 was down-regulated.After 24 h imbibition at the low temperature,the expression of BnICE1 increased significantly in cv.ZYZ200.Therefore,seed priming with Si and GABA promoted seed germination metabolism and energy mobilization,and regulated the expression of cold-responsive genes,alleviated the inhibition of seed germination by low temperature,and enhanced the chilling tolerance of rapeseed3.The eff-ects of priming with Si and GABA on the seedling growth of different cold-tolerant rape seeds under chilling stress were studied.Different cold-tolerant rapeseed cultivars were used as experimental materials to determine the physiological and biochemical changes and related gene expression of seedlings under three stages including normal temperature,low temperature(5℃)stress and recovery growth.The results showed that the seed priming significantly increased the leaf moisture content and proline content after low temperature stress,and decreased the soluble sugar and soluble protein content after restoration growth.Seed priming with Si and GABA significantly reduced the accumulation of superoxide anion and hydrogen peroxide,and decreased malondialdehyde content,lipoxygenase activity and relative conductivity.After low temperature stress,the seed priming significantly increased the expression of BnSOD,BnPOD and other genes,and enhanced the activities of superoxide dismutase(SOD)and peroxidase(POD).Low temperature stress inhibited the expression of cold responsive genes in cv.DXY53 rapeseed,promoted the expression of cold responsive genes in cv.ZYZ200,and induced the expression of BnCAMTA1,BnICE1 and BnCBF in cv.DXY53 leaves.The expression of BnCAMTA1,BnICE1 and BnCOR25 in cv.ZYZ200 was up-regulated.In conclusion,Si and GABA induced the accumulation of osmotic adjustment substances to reduce leaf water loss,enhanced antioxidant capacity,reduced reactive oxygen species accumulation and oxidative damage,maintained cell membrane integrity,meanwhile enhanced cold resonsive gene expression,and finally enhanced chilling tolerance of rapeseed. |
