Studies On Chlorophyll-deficient Wheat Mutants Induced By Spaceflight Environment

Three chlorophyll-deficient wheat mutants, i.e., Mt135, Mt6172 and Mt18, which derived from spaceflight mutagenesis, were studied in terms of biological characteristics, main agronomic traits, chloroplast ultrastructure, photosynthesis and inherited model. The main results were as following:1. The leaf color of the mutants Mt135 and Mt6172 showed three phenotypes: albino, stripe and green, in which the albino plants with entire albino leaves died during seedling stage, while the plant height, grains per plant, grain weight per plant and 1000-grain weight of plants with green-and-white striped leaves were lower than those of the wild types; Mt18 was a temperature-sensitive winter wheat chlorophyll mutant. The leaf color varied from green to albino and regreen with the temperature from low to normal during the whole growth stage, and the main agronomic traits were lower than those of the wild type.2. Chloroplast ultrastructure observation showed that the chloroplast number in green tissue of Mt135 striped plants was less than that of the wild type, but no significant difference in the ultrastructure. The similar number of chloroplast but less number of granum-thylakoids in Mt135 striped plants was observed at the elongation stage. At the heading stage, the number of chloroplast and granum-thylakoids were increased significantly. Both at seedling and elongation stage, the chloroplast number of white tissue in Mt135 striped plants and albino plants was less than that of the wild type, and the number of granum-thylakoids reduced or completely disappeared, but the strom-thylakoid was obviously visible, and some chloroplasts without internal ultrastructure were found at heading stage. Mt6172 had less chloroplast in the green tissue at the elongation stage, but had normal ultrastructure at the three stages. There were different chloroplast variation of the white tissue in Mt6172 striped plants and albino plants, and the chloroplast number was less than that of the wild type among the three growth stages. There was no significant difference between Mt18 and the wild type during prior albino stage; at the albino stage, the number of granum-thylakoids and grana lamellae became fewer or completely disappeared, but the strom-thylakoid was obviously visible; after returning green, structure of most chloroplasts recovered into normal, but number of chloroplast was still lower than that of the wild type.3. The analysis of chlorophyll fluorescence kinetic parameters between the mutants and their wild type revealed that the photosynthetic efficiency of the green tissue in Mt135 striped plants reduced significantly at both seedling and elongation stages, and then increased at heading stage, while the white tissue of Mt135 striped plants and albino plants lost photosynthetic capacity completely; the photosynthetic efficiency of Mt6172 striped plants was normal at seedling stage, and was reduced significantly at elongation and heading stages, and albino plants still maintained very low photosynthetic capacity; the photosynthetic efficiency of Mt18 was normal at both prior albino and re-green stages and lower than that of the wild type at albino stage. In addition, with the increase of light intensity, the photosynthetic efficiency of the green tissue in Mt135 striped plants was lowest at elongation stage, and then increased significantly at heading stage. However, the white tissue of Mt135 striped plants and albino plants lost photosynthetic capacity completely; Mt6172 striped plants was significantly lower than that of wild type at different growth stages, while there was no significant differences in qP and Y(â…¡) between mutant and wild type, and albino plants still maintained very low photosynthetic capacity; the photosynthetic efficiency of Mt18 was significantly lower than that of the wild type only at albino stage.4. Preliminary genetic analysis showed that the inheritance model of Mt135 and Mt6172 was cytoplasmic, while Mt6172 a recessive nuclear. cDNA-AFLP analysis revealed significant differences between the chlorophyll-deficient mutants and their wild types at the molecular level. The type of different bands among the three mutants showed increment, deletion, strongth and weakness.It was concluded that different chlorophyll-deficient wheat mutants could be induced by spaceflight environment, with the characteristics of destructed chloroplast ultrastructure, deeply affected photosynthesis as well as decreased main agronomic traits. These chlorophyll-deficient wheat mutants could be new materials for basic study of wheat photosynthesis.