Screening Of Magnesium-tolerant Brassica Napus L. And The Mechanism Of Response To Magnesium Deficiency Stress

More than half of China's soils have varying degrees of magnesium deficiency,and Chinese soils require a larger amount of magnesium fertilizer per year.As the most abundant divalent cation in plant,magnesium(Mg2+)is essential for the growth of plants.Mg2+ plays important roles in maintaining plant cell membrane stability.It regulates carbon fixation,chlorophyll synthesis,carbohydrate transport,enzyme activity and reproductive.Magnesium deficiency is a common nutritional disorder in plants,affecting agricultural production and quality,which will lead to morphological and physiological abnormalities.Brassica napus(B.napus)is the world's second largest source of human edible vegetable oil,especially in the southwestern part of China,and due to the soil type and acidity and alkalinity in the southwest,the soil's effective magnesium loss is more serious,leading to rapeseed are severely reduced.However,the mechanism of Mg2+ uptake and translocation in B.napus remains unknown.A magnesium-tolerant variety was screened in a large number of Brassica napus varieties,and the magnesium absorption and transport mechanism of the variety was studied.The related proteins and key genes involved in magnesium absorption and transport were identified,which was beneficial to the cultivation.The main results are as follows:(1)There are significant differences in the genotypes of Mg-T and Mg-S under different Magnesium conditions.Compared with Mg-normal conditions,the biomass of Mg-S was significantly reduced under Mg-deficient conditions,while the biomass of Mg-T did not change significantly between different concentrations of Mg treatment.Compared with Mg-normal conditions,the Mg content in the shoots of Mg-S was obviously reduced under Mg-deficient conditions,while the Mg content in the shoots of Mg-T did not change significantly.Compared with Mg-normal conditions,the Mg transport factor(TF)of Mg-S decreased significantly and the TF of Mg-T did not change under Mg-deficient conditions.The results showed that Mg-T was a magnesium-tolerant variety.(2)Compared with Mg-normal conditions,the net photosynthetic rate and chlorophyll content of Mg-T and Mg-S decreased under Mg-deficient conditions.And Mg-S showed a sharp downward trend,the change was significant,and Mg-T showed a slow decline trend with no significant change.Chlorophyll synthesis and photosynthesis of Mg-T were less strongly inhibited by magnesium deficiency,and Mg-T was more tolerant to Mg deficiency.(3)Compared with Mg-normal conditions,the malondialdehyde content and peroxidase activity of Mg-T and Mg-S increased under Mg-deficient conditions.And Mg-S showed a sharp upward trend,the change was significant,and Mg-T showed a slowly rising trend with no significant change.Lipid peroxidation of Mg-T was less affected by Mg deficiency,and Mg-T was more tolerant to magnesium deficiency.(4)Compared with Mg-normal conditions,the sucrose content of Mg-T and Mg-S increased under Mg-deficient conditions.And Mg-S showed a sharp upward trend,the change was significant,and Mg-T showed a slowly rising trend with no significant change.When MgT was exposed to magnesium deficiency,the sucrose export process in the source leaves was less inhibited,that is,Mg-T was more tolerant to Mg deficiency.(5)Transcriptome sequencing results showed that Bn MGT4-2,Bn MGT2-1 and Bn MGT9-3 had higher transcription levels in the shoots of Mg-T than Mg-S under Mg-deficient conditions.The transcription levels of Bn MGT9-3,Bn MGT4-2 and Bn MGT8-2 were significantly higher in Mg-T roots than those in Mg-S roots.These results were subsequently confirmed by q RT-PCR.Some other Bn MGTs closely related to the reported At MGTs were selected to analyze the relative expression differences under Mg-normal and Mg-deficient conditions.The results showed that under the conditions of Mg deficiency,the expression levels of Bn MGT1-2 and Bn MGT6-1 in the shoots of Mg-T were significantly up-regulated by more than 10 times,and the relative expression was significantly higher than other genes.Bn MGT1-2 and Bn MGT6-1 may play an active role in improving the Mg transport efficiency under Mgdeficient conditions,which promotes the Mg tolerance of Mg-T.(6)Bn MGT1-2 and Bn MGT6-1 were selected for further verification in yeast and Arabidopsis.Bn MGT1-2 and Bn MGT6-1 were able to restore the growth rate defect of under the condition of 50 or 200 ?M Mg2+.In addition,functional verification of Bn MGT1-2 and Bn MGT6-1 was performed in Arabidopsis.When grown on 1/2 MS medium containing 30 ?M Mg2+,the roots of wild-type Col-0,Bn MGT1-2 complement lines,Bn MGT6-1 complement lines and Bn MGT1-2 overexpression lines,Bn MGT6-1 overexpression lines were longer than those of the mutant atmgt1,and the root length of the overexpression lines was the longest.The results of fluorescent staining of roots with Magnesium Green-AMTM showed that,the fluorescence signal intensity in the roots of Bn MGT1-2 overexpression lines,Bn MGT6-1 overexpression lines,Bn MGT1-2 complement lines,Bn MGT6-1 complement lines and the wild type Col-0 was higher than that of the mutant atmgt1.Bn MGT1-2 and Bn MGT6-1 complement the function of At MGT1 and positively regulate the Mg transport efficiency under Mg-deficient conditions.