| Chinese kale(Brassica alboglabra Bailey) is a special and important leafy vegetable in South China, and its flower stalk is mainly green, also with purple type. Color appearance is an important exterior quality of horticultural products. Anthocyanins are a large category of plant secondary metabolites, and it widely presents in many fruits and vegetables. Anthocyanins are natural edible pigment, and have special health functions for human body. Plant anthocyanins also have important ecological functions, helping to improve the adaptation of adversity, such as heat, strong light, nutritional deficiencies, pest and disease invasion. Anthocyanins biosynthesis are controlled by a series of enzymatic reactions, and regulated by internal and external factors. Therefore, the study for the formation physiology and regulation mechanism of anthocyanins, is of great theoretical and practical significance.In this study, different varieties of Chinese kale with diverse colors in flower stalk were used, to study the genetic regularity of flower stalk color, as well as the effect of different temperature, light, nitrogen levels, phosphorus levels on plant growth, quality, epidermal pigment content and related regulatory factors. The aim of the study is to reveal formation physiology and regulation mechanism of anthocyanins, from the view of genetic physiology and environmental regulation. The main results are as follows: 1. Genetic regularity of pigment in Chinese kale and its F1 heterosisUsing 2 types of Chinese kale(Brassica alboglabra Bailey) according to epidermis color of flower stalks(cultivar ‘Hongjiao’ with purple epidermis; cultivar ‘Zhonghua’ with green epidermis) as material, the color performance of the epidermis and flower for F1 hybrid and selfing F2, also the growth and yield traits of hybrids, were studied in the experiment. The results showed that, heredity of epidermis color was controlled by nuclear gene, without maternal effect. Epidermal anthocyanin content of flower stalk in Chinese kale showed ‘Hongjiao’ > ‘Hongjiao’ F1 > ‘Zhonghua’ F1 > ‘Zhonghua’. Mid-parent heterosis(MPH) was obvious while high-parent heterosis(HPH) was not clear for 2 F1 hybrids. Soluble phenols and flavonoid content of flower stalk were higher than their parents for both F1 hybrids, and MPH and HPH were quite evident. The plant height for 2 F1 hybrids was higher than those of their parents, while the stem diameter was significantly lower than their parents. Shoot fresh weight and economic yield for 2 F1 hybrids were significantly higher than their parents, and MPH and HPH were quite obvious. The biomass of ‘Zhonghua’ F1 was significantly higher than that of ‘Hongjiao’ F1. 2. The effect of temperature on plant growth and pigment formation in the flower stalks of Chinese kale.Two Chinese kale cultivars "Jianyexia"(green epidermis) and "Hongjiao"(purple epidermis) were used as material in the artificial climate chamber with normal temperature(day 22℃/night 17℃) and high temperature(35℃/28℃) treatments, to study plant biomass, pigment content in epidermal of flower stalk and related affecting factors. The results show that, shoot fresh weight of 2 Chinese kale cultivars was significantly reduced by high temperature treatment, and it was more clear for "Jianyexia". Anthocyanin content in flower stalk epidermis was significantly lower in "Jianyexia" than in "Hongjiao", while its chlorophyll content was significantly higher. Both anthocyanins and chlorophyll content were significantly reduced by high temperature treatment for the two Chinese kale cultivars, compared with normal temperature treatment. Epidermis fructose and glucose content were significantly reduced by high temperature treatment for the two Chinese kale cultivars. Fructose, glucose and total soluble sugar all had significant positive correlation with anthocyanin content. Anthocyanins were mainly distributed in the 4 or 5 epidermal cells of flower stalk. Anthocyanin distribution was reduced by high temperature treatment for both Chinese kale cultivars, and it was more obvious for "Hongjiao" cultivar. 3. The effect of light intensity on pigment formation in the flower stalks of Chinese kale.Using "Zhonghua" and "Jianyexia" cultivars of Chinese kale as materials, the effect of shading 40% and 60% on plant growth, quality and color formation were studied, with natural light as control(CK). The results showed that, compared with the CK, shading treatment inhibited the plant growth and product’s nutritional quality, but it also reduced the accumulation of anthocyanins in flower stalk epidermis, thus improving the appearance quality. Comprehensive nutritional quality and appearance quality point of view, shading 40% was appropriate for Chinese kale production in summer. Shading treatments reduced the soluble sugar content of flower stalk epidermis, and this was consistent with lower anthocyanin content. ABA content in flower stalk showed upward trend along with its development. Shading treatments reduced the ABA content of flower stalk, and this was consistent with lower anthocyanin content. Under shading treatments, anthocyanin biosynthesis in Chinese kale epidermis was reduced by decreasing soluble sugar and endogenous ABA content. 4. The effect of nitrogen nutrition on plant growth, quality and pigment formation in the flower stalks of Chinese kale.The effect of 5 nitrogen levels(0.25×N, 0.5×N, 1×N, 1.5×N, 2×N) on plant growth, quality and pigment formation in Chinese kale was studied. The results showed that, integrated biomass, nutritional quality and nitrate content point of view, 1×N treatment was appropriate for Chinese kale hydroponic production.In most flower stalk formation period, the epidermis chlorophyll content was negatively correlated with N level. Epidermis anthocyanin content was significantly higher in 2 low N level treatments than in the middle and high N level treatments.Flower stalk epidermis p H value gradually decreased during later bud develop period. p H value was the lowest for 0.5×N treatment, coming 0.25×N treatment, and it was relatively higher for 1.5×N and 2×N treatments. During the period from flower bud to harvesting, epidermis soluble sugar content gradually increased under different N treatments. N level and soluble sugar content had significant negative relation. N nutrition might control epidermis anthocyanin synthesis in Chinese kale by regulating p H and soluble sugar content. 5. The effect of phosphorus nutrition on plant growth and pigment formation in the flower stalks of Chinese kale.The effect of phosphorus(P) nutrition on plant growth and pigment formation in the flower stalk was studied under hydroponic conditions for 2 Chinese kale cultivars: ‘Jianyexia’(green flower stalk) and ‘Hongjiao’(mauve flower stalk). Three different P treatments were used: 30 mg/L(normal P), 7.5 mg/L(low P), and 0 mg/L(P-deficient). The results showed that the biomass, yield, plant height, stem diameter, and leaf number of Chinese kale were significantly reduced in low P and P-deficient treatments compared to the normal P treatment. The chlorophyll content in the flower stalk epidermis was not affected by different P levels in the ‘Jianyexia’ cultivar, but was significantly reduced by the P-deficient treatment in the ‘Hongjiao’ cultivar. Decreased P levels caused the flavonoid, soluble phenolic, and anthocyanin content of the flower stalks to gradually increase in both Chinese kale cultivars. The p H value of the flower stalk epidermis gradually decreased with declining P levels, and was significantly different among the 3 treatments. As P levels declined, phenylalanine ammonia-lyase(PAL) and chalcone isomerase(CHI) activities in the flower stalk epidermis gradually increased, and were significantly different among the 3 treatments. P nutrition may control the synthesis of anthocyanins in the flower stalk by regulating the epidermal p H value, and the activities of PAL and CHI.In summary, the biosynthesis of anthocyanin in flower stalk of Chinese kale was regulated by epidermis p H value, soluble sugar content, endogenous ABA content and the activity of PAL and CHI. Shading treatment reduced soluble sugar, endogenous ABA and anthocyanin content in flower stalk epidermis, and this proved that anthocyanin biosynthesis was related with the metabolism pathway of soluble sugar and hormone. Nitrogen regulated the p H value, soluble sugar content and anthocyanin synthesis of flower stalk epidermis, and anthocyanin content was negatively correlated with the p H value, and was positively correlated with soluble sugar content. Low phosphorus promoted anthocyanin synthesis of flower stalk epidermis, accompanied by increased activity of PAL and CHI, and the findings provided the direct evidence that plant could regulate the anthocyanin synthesis through its biosynthetic enzymes. |
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