| Cucumber(Cucumis sativus L.)also called pickled cucumber or green cucumber, is an important annual and economic crop, widely cultivated in home and abroad.Previous studies have indicated that the leaf color mutant has important significance in both theory and practice.In this paper, a novel yellow green mutant Z3t of cucumber was used as research material. The main agronomic characteristics, biological characteristics, physiological biochemical characteristic (include the content of chlorophyll, photosynthetic characters, antioxidant enzyme system, the content of soluble sugar and soluble protein)and genetic characteristics of mutant Z3t were studied. Furthermore, used SSR molecular markers to preliminary screened out polymorphic markers in the mutant strain and the normal green leaf strains. To lay the foundation for the preliminary mapping of the mutant gene and for elucidating the physiological mechanism and the mechanism of the leaf color mutation.The results are as follows:1. The research results of Phenotype characteristics of mutant showed the cotyledon of mutant Z3t was yellow, and leaf color gradually change to yellow green with the plant growth and the yellow green leaf color is expressed in the whole growth stage. The mutant can complete its life cycle, including vine extension, flowering, fruit-setting. Compared with the control, the plant height, stem diameter, blade length, blade width, vine length, single fruit weight of the mutant are significantly decreased. In addition, the mutant Z3t leaves relatively thin, stem and petiole more brittle and easily fractured.2. Chloroplast ultrastructure observation indicated the chloroplast ultrastructure in the functional leaves of mutant abnormalities. Mainly manifested as the mutant Z3t has irregular chloroplast, cells of leaf shape mostly round, much circular cavity in cells, chloroplast derangements, few starch grains, chloroplast grana less, thin thylakoid stack and arranged irregularly, thin chloroplast matrix, and the control plant chloroplast evenly distributed, normal structure, thylakoid membrane system developed and highly differentiated, base particle layer and arranged in neat rows.3. The photosynthetic pigment contents in mutant Z3t analysis showed chlorophyll a, chlorophyll b and carotene were decreased in mutant, and all pigments content decreased about 50% compared with the normal plant. The total pigment content was gradually increased, the total chlorophyll content of mutant in seedling stage, vine stage and the fruit stage were 27.9%,41.3% and 44% respectively, but the content of chlorophyll b did not increase with the growth.Chlorophyll a/b in each stage were larger than the control which showd chlorophyll b decreased significantly than the control plant. There was no significant difference in the ratio of caro/total chlorophyll, it is about 0.3.Therefore, it is speculated that the mutation gene of the mutant may be caused the synthesis of chlorophyll b was blocked.4. The results of analysis of antioxidant enzyme activity and membrane lipid peroxide in mutant Z3t suggests SOD enzyme activity of mutant are significantly higher than the control at the seedling stage, vines stage, fruit stage, and the activity of SOD enzyme also increased with the plant growth; there is no obvious difference between mutant Z3t and the control plant of the activity of POD enzyme at seedling period, but at tendril elongation and fruit-set stage the activity of POD enzyme in mutant higher than normal plants, and the POD enzyme of mutant has high enzyme activity at fruit stage; the CAT activity of mutant in seedling stage was significantly lower than that of normal plant, but with the growth, the CAT activity was significantly higher than that of the control, the CAT activity decreased in the result period but still significantly higher than that of the control group. The results of MDA content and relative electrical conductivity showed the MDA content and relative electrical conductivity of the mutant leaves were significantly higher than that of the control plants in the seedling stage, the vines stage and fruit-setting period.5. Photosynthetic characteristics analysis indicates the net photosynthetic rate (Pn) in mutant Z3t and the normal plant gradually increasing along with photosynthetic radiation intensity enhancement in the illumination intensity of 0-2000?mol·m-2·s-1. The light compensation point and light saturation point of mutant were lower than control, the light compensation point of normal plant and light saturation point of mutants are increased in vines period. Compare with vines period, the light compensation point of mutant and control plant are decreased, the light saturation point in control plant increased, but no significant changes in mutant. The results of net photosynthetic rate, intercellular CO2 concentration, stomatal conductance and transpiration rate showed that the intercellular CO2 concentration and stomatal conductance were larger than that of control,but no significant difference in transpiration rate. The stomatal conductance and intercellular CO2 concentration in mutant Z3t is larger than that of control plants, but there was no significant difference in transpiration rate.6. Chlorophyll fluorescence kinetics parameters analysis in mutant Z3t indicates there are no significant different in maximal quantum yield of PS ?, maximal photochemical efficiency of the PS ? (Fv/Fm), photochemical quenching (qP), between mutant and control plants. However, the minimal fluorescence (Fo), the electron transport rate(ETR) was decreased in the mutant Z3t, non-photochemical quenching (NPQ) is significant larger than the control plants. These results showed that despite the mutant Z3t is yellow green, PS ? structure is not damaged, and it capture of light energy into electron,the electron transfer situation by the PS ? to PS ? is not affected. Despite relative electron transport rate reducted, the mutant can dissipation of excess light energy timely to protect the photosynthetic structure.7. The results of genetic analysis show the offsprings of self-production are all yellow green, and reciprocal crosses between the mutant and normal plants, F1 generation of crosses and reciprocal crosses are green. The proportion of offspring in backcross and F2 populations from yellow green leaf and green leaf phenotype were 1:1 and 1:3. The mutant was controlled by a recessive nuclear gene, tentatively named yl.8. The 280 pairs of SSR primers were used in mutant Z3t and mutant parent gene and yellow green gene pool and to screen polymorphic primers,21 pairs of polymorphic primers were screened, then use F2 to detecting polymorphic primers. The results showed that there are no linkage between mutation gene yl and screened polymorphic markers. |
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