| Purple corn is a pigmented variety of Zea mays L., originally cultivated in Andes of South America and was introduced to China long time ago. The grain of purple corn can be used as food, while it also was the raw material of extracting anthocyanin which used in health food、beverage and cosmetic industry(Han L,2003). Rich anthocyanin, low cost and perfect stability were the good reasons for purple corn as an ideal raw material to extract anthocyanin. If we could consider both of yield and biomass which be the raw material of anthocyanin extracting of purple corn, we could not only produce more grains for food, but also save the cost to produce natural pigment. Thus this can enhance the overall efficiency of agriculture of purple corn planting. In this study, seven purple corn hybrids including ZS11, ZS15, ZF39, FS11, SF38, FG01 and 68G1 were studied to investigate the yield, dry matter, anthocyanin accumulation, nitrogen uptake and utilization efficiency, photosynthetic and physiological characteristics of different purple corn hybrids under different nitrogen levels. The effect of secondary metabolites including polyphenols、flavonoid、phenylalnine ammonialyase and polyphenol oxidase on anthocyanin synthesis of purple corn were studied using multiple linear regression model. The accumulation of chlorophyll, carotenoids and anthocyanin in different organs of purple corn were studied. Furthermore, the identification, stability and antioxidant activity of anthocyanin which extracted from the cob, husk and grain of purple corn were also studied. In a word, this research will be helpful for high yield cultivation and anthocyanin industrialization of purple com. The main results were listed as follows:1. The differences of yield and dry matter of different purple corn hybrids were great. The yield and dry matter of different purple corn hybrids under N225 level were higher than that under NO. The yield of ZS11, ZS15, ZF39, FS11, SF38, FG01 and 68G1 increased 6.06%,2.97%,8.40%,6.75%, 12.64%,5.02%,3.57% respectively. While the dry matter of ZS11, ZS15, ZF39, FS11, SF38, FG01 and 68G1 increased 23.19%,4.33%,9.45%,12.14%,4.79%,15.89%,10.63% respectively. The yield of purple corn had significant positive correlation with 100-grain weight, but had no significant differences with ear grain. Path analysis indicated that the yield difference of purple corn was mainly caused by the difference of 100-grain weight. Dry matter accumulation of trumpet stage to anthesis was the most during the growing stage. Correlation analysis of dry matter accumulation and yield of purple corn showed that the dry matter accumulation of trumpet stage to anthesis and anthesis to filling stage had significant positive correlation with yield and the correlation coefficients were 0.852 and 0.800 respectively. While the dry matter accumulation of filling stage to maturity had negative correlation with yield. The correlation coefficient was-0.537, but the difference was not significant. Hence increasing the dry matter accumulation in late growth stage could provide more raw materials for purple corn anthocyanin extraction.2. The anthocyanin content of different purple corn hybrids increased along with the growing stage till to maturity. As for as the average of anthocyanin content of different purple corn hybrids were concerned, the anthocyanin content under N225 level was higher than that under NO level at every growing stage except trumpet stage. The anthocyanin accumulations of different organs were also different in the growing stage. Anthocyanin content of leaf and stem reached a maximum at trumpet stage and then dropped down, while increased slightly at maturity. Anthocyanin content of tassel reached a maximum at anthesis and then dropped down. While anthocyanin of sheaf, husk, cob and grain increased along with the growing stage till to maturity. Husk、cob and grain of purple corn had abundant anthocyanin and these organs could be main raw materials to extract purple com anthocyanin. The anthocyanin content of purple corn had significant negative correlation with yield, while the anthocyanin content of purple corn had extremely significant negative correlation with dry matter accumulation. The relationships among grain yield, dry matter and anthocyanin content must be coordinated in filed production. Thus the dry matter could be the foundation of yield formation on one hand and raw materials for anthocyanin extraction on the other hand.3. The anthocyanin content, polyphenols content, flavonoid content, activities of phenylalnine ammonialyase and polyphenol oxidase were extracted and determined during the development of purple corn. The result showed that the optimization of multiple linear regression model of anthocyanin synthesis was y=4.38386-0.20545x1+5.479638x2+0.195575x4. According to standard partial regression coefficient testing, the result indicated that polyphenols content was negatively correlated with anthocyanins and the relative influence to anthocyanin synthesis was-42.7%; flavonoid content and activity of polyphenol oxidase were significantly positively correlated with anthocyanins of purple corn and the relative influence to anthocyanin synthesis were 71.45% and 73.32% respectively. While there were no positive correlation between the activity of phenylalnine ammonialyase and anthocyanin of purple corn.4. The anthocyanin was closely related to the coloration and expression of different organs of purple corn. The coloration of purple corn was very complex which related the kinds of pigments, content of pigment and distribution in the cell of purple corn. The coloration of purple corn was mainly determined by the chlorophyll, carotenoid and anthocyanin. The result indicated that chlorophyll a, chlorophyll b, chlorophyll a+b, chlorophyll a/b and carotenoid were all significantly negatively related to anthocyanin of purple corn and the correlation coefficients were-0.59,-0.56,-0.59,-0.55 and-0.59 respectively.5. The differences of nitrogen content and nitrogen accumulation of different purple corn hybrids were great. All purple corn hybrids exhibited an obvious trend of decrease in nitrogen content from seedling stage to maturity. However, nitrogen accumulation had reversely changes. Among the seven purple corn hybrids, only SF38 and 68G1 were regarded as high yield, high nitrogen uptake and high nitrogen utilization efficiency hybrids. In addition, it was beneficial for grain yield of the produce that there were high nitrogen translocation rates of leaf and cob. However, it was beneficial for nitrogen utilization efficiency of the produce that there were high nitrogen translocation rate of leaf. Correlation analysis showed that increasing the nitrogen harvest index and nitrogen translocation rate could promote the nitrogen fertilizer utilization efficiency. The nitrogen utilization efficiency of purple corn was the main reason for grain increasing yield, secondly was nitrogen uptake. Analysis from the relationship between the nitrogen accumulation at different growing stage and yield, the nitrogen uptake amounts of grain yield mainly increased from anthesis to filling stage, secondly from the trumpet stage to anthesis.6. Physiological characteristics of different purple corn hybrids were studied in the experiment, the result showed that the soluble protein、nitrate-nitrogen、free amino acid、nitrate reductase activity and protease activity under N225 level increased 3.36%,3.41%,12.24%,33.93% and 8.33% respectively than that under NO. The nitrogen accumulation of purple corn had significantly positively correlation with free amino acid, nitrate-nitrogen, soluble protein and soluble sugar and the correlation coefficients were 0.919,0.793,0.999 and 0.863 respectively. While the nitrogen accumulation of purple corn had significantly negatively correlation with protease activity and the correlation coefficient was-0.687. 7. Photosynthetic characteristics of different purple corn hybrids were studied in the experiment, the result showed that the net photosynthetic rate, LAI, SPAD, Fv/Fm, Fv/F0 and leaf nitrogen content under N225 level increased 9.21%,7.51%,3.78%,1.94%,13.72%,5.75% respectively than that under NO. The LAI and SPAD decrease degree under N225 at late growing stage were lower than that at NO level, which indicated that nitrogen application could extend photosynthetic function duration of purple corn. The SPAD of upper ear leaf and ear leaf had significantly positively correlation with leaf nitrogen content at anthesis. The nitrogen utilization efficiency and yield had significantly positively correlation with SPAD at anthesis, filling stage and maturity and the correlation coefficients were 0.853,0.860, 0.973,0.819,0.827,0.985 respectively. The nitrogen utilization efficiency and yield had significantly positively correlation with net photosynthetic rate at anthesis and the correlation coefficients were 0.999 and 0.994 respectively. Difference of LAI was not the main reason for the differences of nitrogen utilization efficiency and yield of purple corn. The Fv/Fm had significantly negative correlation with nitrogen utilization efficiency and yield of purple corn and the correlation coefficients were-0.502 and-0.554 respectively. While Fv/Fo had no significant correlation with nitrogen utilization efficiency and yield of purple corn8. Purple corn anthocyanin was more stable under natural light than sunlight. It had better thermal resistance. It was sensitive to hydroperoxide (H2O2) and reductant (NaSO3). The purple corn anthocyanin showed high stability to some common metallic ion, but Fe3+ let the red solution been dark brown and slightly turbidity and Cu3+ turned the red solution yellow. Hence it should be avoided using iron and coppery containers to conserve the purple corn anthocyanin. The purple corn anthocyanin was stable to some common food additives such as glucose, sucrose and antioxidant VC.9. Ten anthocyanin pigments were detected in the grains of six purple com hybrids which included pelargonidin-3-o-glucoside, cyanidin-3-o-glucoside, peonidin-3-o-glucoside, delphinidin-delphinidin-3-o-glucoside, petunidin-3-o-glucoside, malvidin-3-o-glucoside, cyanidin-3-(6"-malonylglucoside), peonidin-3-(6"-malonylglucoside), pelargonidin-3-o-rutinoside, cyanidin-3-o-rutinoside. The main anthocyanin pigments in all of the six purple com hybrids were cyanidin-3-o-glucoside and pelargonidin-3-o-glucoside.10. There were great differences in anthocyanin, total phenolic, reducing power, hydroxyl radical and super-oxide anion radical scavenging activities among the six purple com hybrids. The anthocyanin of purple com extract had significantly positive correlation with reducing power, hydroxyl radical and super-oxide anion radical scavenging activities and the correlation coefficients were 0.992,0.999 and 0.995 respectively. |
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