Characterization Of Mutant Rice With Giant Embryo And Its Metabolite Profiling During Germination And Grain Filling

Gamma Amino-Butyric Acid(GABA),a free amino acid that functions as an inhibitory neurotransmitter,accumulates mainly in rice embryos.GABA has multiple physiological functions such as normalizing blood pressure and aiding recover from disorders of the autonomic nervous system.As a country with great yield and consumption of rice,developing functional rice enriched with GABA has significant importance,which can raise and expand the added value of rice.Giant embryo rice is a kind of characteristic rice with giant embryo. In the practices of breeding,Giant embryo can be used as an important indirect selection method of rice enriched with GABA.In this study,using some varieties mainly cultivated in China as original materials.The research starting with the selection of giant embryo mutant which enriched with GABA,then analyzed the volume of GABA,the physical and chemical qualities,and the nutritional components and their metabolic profiling of mutants with giant embryo.We also observed the process of seeds' germination and grains filling in metabolic level.Further,we understood genetic control of the mutants with giant embryo,and we also did some primary work of molecular mapping.Followings are the main results:1)Selecting the seeds of core wild type 9311 and the leading restorer that produces famous super hybrid cultivarâ…¡youming 86---Minghui86,â…¡-32B,maintainer K17B and Gang46B,restorer 7954,R084 and 527,indica rice jinzao47,and the japonica rice Xiushui110,treating the seeds with the radiation of 60-Cobalt gamma rays and outer space, respectively,37 giant embryo mutants were induced,and the mutational frequency is among 1.89×10^-5-1.72×10^-4.Minghui 86 were irradiated by 60-Cobalt gamma rays with 300 Gy dose, and five giant embryo mutants,described as MH-ge1,MH-ge2,MH-ge3,MH-ge4,and MH-ge5,were isolated and characterized by 2.0,1.88,2.08,1.93,and 1.88 times larger embryo than that of the wild type.Mutant XS-gel's embryo is 2.14 times larger than the original cultivar Xiushui110.The embryos of the mutantsâ…¡-ge1 andâ…¡-ge2 are 2.87 and 2.21 times larger than the original cultivarâ…¡-32B,respectively.2)No obvious differences in physicochemical properties such as apparent amylose content(AAC),alkali spreading value(ASV),gel consistency(GC),and starch paste viscosity were observed between the giant embryo mutants and the wild type.Except inferior agronomic traits with mutant MH-ge5 and decreased 1000-grain weight in all mutants,the major agronomic traits of the giant embryo mutants were similar to that of the wild type.3)Compared to rice with normal embryo,obvious increases in the nutritional components.Significant increases in crude protein content(PC),crude lipid content(LC), VB₁,VB₂,VE,essential amino acids such as Asp,Glu,Met,Arg,and Lys,and mineral elements such as Fe,Ca,Zn,K,and P,were detected in the brown rice(BR)of the giant embryo mutants.The amounts of gamma aminobutyric acid(GABA),an inhibitory neurotransmitter,were similar in the BR of the giant embryo mutants and the wild type.4)After soaking,six nutritional components are obviously enrichment in the embryo of mutants compared to the wild type.They are GABA,Lysine,Magnesium,VB₁,VE and the Calcium.More GABA content was observed in the germinated brown rice(GBR)than BR. Significant enrichments were detected in the GBR of the giant embryo mutants,basically corresponding to the enlarged embryo.The volume of GABA increased synchronously with the times that the enlarged embryo,mutants of XS-ge1,MH-ge1,MH-ge2,MH-ge3,MH-ge4, MH-ge5,â…¡-ge1 andâ…¡-ge2 compared to their wild types.5)The mutated giant embryos were controlled by a single recessive gene,and except the mutated locus with MH-ge1 other four mutated loci were allelic to each other and the previous reported locus ge of japonica rice cultivar Kinmaze.The MH-ge1 is a new mutant gene.We selected 358 SSR which cover all the 12 chromosomes of rice to locate the MH-ge1 primarily.The giant embryo gene was located between two marker RM560 and RM346 on the 7th chromosome.The genetic distance from RM560 is 3.47cM,and the genetic distance from RM346 is 8.33cM.6)The property of grain-filling of the MH-ge1 is poorer than MH86.In the whole Grain filling days,the amount of the free sugar in MH-ge1 was higher than MH86 and the Grain filling quality of the seeds of MH-ge1 is worse than MH-86.The metabolite level is the highest in the seeds of DAF 10d,then slowed down with grain-filling,after DAF 25d,the metabolite level almost reached to the stable.The whole metabolite level of MH-ge1 is slightly higher than the wild MH86 and with the grain-filling,the free fatty acids,free sugars and amino acids all decreased.7)In the process of germination,the germinating energy,germination percentage,germination index,vigor index of the giant embryo mutant MH-ge1 are lower than MH86. With the increase of the activity ofα-amylase,the starch was continuously decomposed and the amount of the reducing sugar increased.Comparing to the wild type MH86,the activity of amylase in the giant embryo is lower all the time.After soaking,the activity of GAD increased obviously and the amount of GABA in MH-ge1 increases dramastically to six times of the amount in dry seeds.All soluble metabolites increased with germination and the changes of sugars and proteins is much more obviously than the lipids.