| Anthocyanins and chlorophyll are two classes of very important pigments in higher plants. Anthocyanins are the pigments in vacuole of epidermal cell. They have caused the red, blue or purple colour in flowers, fruits and seed coats. Anthocyanins are provided with various important physiological functions in plants. For example, it appeals to pollinators and seed dispersers, defends protects plant against insect attracting and relieves the damage of UV-B radiation, as well as acts as powerful antioxidants etc. Recent studies show that anthocyanins could reduce the incidence of human cardiovascular disease, diabetes, arthritis and cancer. Chlorophyll is an extremely important kind of pigment in higher plants. It is not only an important pigment, but also the critical substance in photosynthesis of plant. Meanwhile, chlorophyll also occupies a very important role in human daily life. It is provided with good effects on hemopoiesis, detoxification, reduce cholesterol level and anti-mutation. Therefore, the further study on the synthesis metabolism of anthocyanins and chlorophyll and its regulation mechanism is essential to human health and increase in crop production. Cytokinins as a kind of phytohormones play critical roles in plant growth and development, including regulation of cell division and metabolism, stimulation chloroplast development, modulation of shoot and root development, and delay of leaf senescence in plants etc. In the present study, the model plant Arabidopsis thaliana was used as material, the effects of cytokinins on anthocyanin and chlorophyll content, and the regulatory role of red light receptor PHYB and PIFs (Phytochrome-interacting factors) in this process were investigated by physiological and molecular biology method. The results showed that:(1) In light, the marked accumulation of anthocyanins Arabidopsis thaliana seedlings was induce by treatment with exogenous cytokinin (6-benzyladenine,6-BA). Levels of mRNAs for three genes of the anthocyanin biosynthesis pathway, chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR) were obviously up-regulated by exogenous6-BA. These data suggested that exogenous6-BA promoted anthocyanins accumulation by inducing the expression of anthocyanin synthesis genes.(2) Chlorophyll content in newborn leaves of Arabidopsis thaliana was significantly decreased by6-BA in light. The decrease of chlorophyll content was not concentration-dependent manner. The treatment of0.1μM6-BA showed the maximum efficiency.(3) In Arabidopsis thaliana, there is three cytokinin receptors, AHK2(Arabidopsis his kinase2), AHK3and AHK4/CRE1. We found that AHK3and CRE1played an important role in the changes of anthocyanin and chlorophyll content induced by6-BA in light.(4) Effects of6-BA on anthocyanin and chlorophyll content were dependent on light and regulated by red light signal. The anthocyanin accumulation content in red light photoreceptor PHYB mutant seedlings was marked decrease and the change of chlorophyll content in newborn leaves of it was also less than that of the control in the exogenous6-BA treatment under light. The expression levels of three genes of anthocyanin biosynthesis pathway in phyB were much less than that of control (Col-0) in the exogenous6-BA treatment under light. These results indicated that PHYB signal was involved in regulating the effects of cytokinins on the changes of anthocyanin and chlorophyll content in Arabidopsis seedlings under light.(5) Our data indicated that PIF4negatively regulated the changes of anthocyanin and chlorophyll contents induced by6-BA. In6-BA treatments, the anthocyanin in control (Col-0), mutants (pif1, pif3, pif4, pif5) and over-expression line (PIF3OX and PIF5OX) seedlings obviously accumulated, and the chlorophyll contents in the newborn leaves of them were also marked decrease. But the anthocyanin accumulation content in PIF4OX seedlings was much smaller than that of in control in6-BA treatment. So was in changes of cholorphyll content in newborn leaves of it. Others, the expression levels of anthocyanin biosynthesis genes in PIF3OX and PIF5OX seedlings were much less than that of Col-0, PIF3OX and PIF5OX in6-BA treatment. The present data indicated that PIF4in Arabidopsis seedlings was the essential role in the changes of anthocyanin and chlorophyll contents induced by6-BA. |
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