Characterization And Genetics Of A Novel Aurea Mutant In Wheat

1.A novel spontaneous aurea mutation of wheat (Triticum aestivum L.) was first described in this paper. It was find from a winter wheat culture genotype (Xinong 1718) in 1999-2000. When grown in the greenhouse and in the field, the mutant plants could be clearly distinguished from the green ones at any stage from seedling to near maturity. When the mutant plant selfed, three types offsprings couled be seen: green plant, intermediate of yellow-greenplants and yellow plant(aurea). The aurea plants died at the seedling stage for plants grown in soil, and the intermediate plants are viable but less vigorous and later development than the green plant. The mutant causes accumulation of chlorophyll reduce, resulting in a yellow color in the plant in different degreed. There were no significient differences in some agronomy traits between wild-type and yellownish-green plants, while the greenish-yellow mutant plants performed worse compared to the wild type in the field, with decreases in seed production of up to 70%.2.The chlorophyll content and the fluorescence parameters (Fo,Fm,Fv,Fv /Fm, qP,qN )were measured to evaluate the mutant. The result showed that the mutant wheat were shown to have a greatly diminished rate of chlorophyll accumulation compared to the wild type, and the ratio of Chl a / Chl b in the mutated plants were smaller than that in the wild type, and it tended to decrease as the etiolation degree increased. The net photosynthesis rate during booting stage and blooming stage in the golden types were only 5.7% and 2.4%, respectively, of that in the wilt type; while in the greenish-yellow type, it was about one-half (57.7% and 43.3%) of that in the wild type; and in the yellowish-green type, they were close to that in the wild type. The value of Fo in mutated plants were decreased significantly. The values of Fm,Fv,qP,qN in aurea type and greenish-yellow type, were decreased significantly. The values of Fm,Fv,qP,qN in yellowish-green type, have no significant difference with wild type. The value of Fv /Fm,Fv/F0 were decreased significantly in aurea type and in the greenish-yellow and yellowish-green plants, they were higher than that of the wild type.3.The aurea mutant wheat were analyzed genetically after inbreds and crosses with normal green plants. Selfing the M1 plant(chlorina) results in 1:2:1 segregation ratio of aurea : chlorina : green plants. The progeny of M1 green plants were all green. The test cross between a chlorina plant and a normal plant (as male or female) gave a 1 normal green: l yellow-green ratio. The result can be explained on the assumption that the aurea is homozygous for Au and the chlorina heterozygous for Au. It is concluded that the semi-dominant mutant is controlled by a single nucleus gene.This is the genetic constitution of the segregants being Au/Au, normal, Au/au, yellow-green, au/au, aurea.4.In order to better understand the mechanism of aurea mutant, comparative study on chloroplast ultrastructure was conducted between aurea mutant and its wild type(Xinong1718) under the electromicroscope. Using morphometrical measurements, the mutants chloroplast numbers, shape, size and the distribution in cell were similar with those of the parent of mutant. In contrast, the ultrastructure of chloroplasts among three phenotype types and the parent of mutant were markedly differences: in the yellowish-green mutant, a well-organized thylakoid system, differentiated into grana and intergrana thylakoids, resembled the parent of mutant; in the greenish-yellow chloroplasts, their thylakoid systems appeared to be disorganized, and the grana contained fewer lamellae, the number of grana per chloroplast section was reduced; in the golden type, the development of chloroplast was the most bad among the mutants, no grana but the stroma thylakoid were clearly, accumulation of osmiophilic droplet and starch granules were more than those of other phenotype types and wild type. The thylakoid morphology is more nearly wild type in appearance.5. The precursors of tetrapyrrole synthesis,δ-aminolevulinic acid (ALA), porphobilinogen (PBG), uroporphyrinogen(Urogen), Coprogen, ProtoⅨ, Mg-Proto and Pchlide were over accumulated in mutant wheat, while protoporphyrin IX(MgPP and MgPme were investigated. The result showed that the content of ALA,PBG,UrogenIII,Coprogen and ProtoⅨw ere all over to the wild type; in contrast, Mg-Proto and Pchlide were all decreased than wild type. This result indicated Coprogen and protoporphyrin accumulated in the mutant, and the rate of conversion of ProtoⅨto Mg- Proto was very low than that of wild type. It is concluded that, the mutation brings about a restriction in the rate of conversion of protoporphyrin to magnesium protoporphyrin; and in the mutant, the enzymes converting protoporphyrin into Mg- Proto are most likely absent or damaged. Mg-Chelatase catalyses this step.6. The pigment protein complexes are separated as shown by fully denaturing SDS-PAGE electrophoresis. Eleven chlorophyll-protein complexes of wheat were resolved in wild type. As compared with mutant parent wheat, in all type mutant, there were no significant changes in the composition of 60~64 kD polypeptide, which are mainly reaction center chlorophyll-protein complexes of PS I and 42~54 kD polypeptide, which are mainly PSII reaction center antenna protein. In contrast, a deficiency in 23~35 kD polypeptides, which are mainly light harvesting chlorophyll protein (LHCP) complex and reaction center chlorophyll-protein complexes of PSII, had been noted in all kinds of mutant wheat, particularly the two major polypeptides of LHCII, 23kD and 27kD polypeptides, were greatly diminished in amount in greenish-yellow and yellowish-green plants, and it had been absent in aurea plant. These data led to the suggestion that the LHCP complexes were more sensitivity to chlorophyll-deficiency than the other chlorophyll-protein complexes.