| Rhododendrons belong to the family Ericaceae, and are among the ten famous traditional flowers in China with a long cultivation history since the Tang Dynasty. Azalea is one of the most popular ornamental species in Chinese market. The ability to control the timing of flowering is a key strategy on producing pot azaleas for the Spring Festival Market in China. In order to solve problems for production, we used two plant growth regulators and5-azaC (5-azacytosine, a demethylation agent) to test their influences on flowering of azaleas. Morphological parameters, carbohydrate contents, soluble protein contents, endogenous hormone contents and DNA methylation levels have been detected to explain the effects of plant growth regulators and5-azaC on flowering of azalea. The following are the main results:1、Preliminary investigation and evaluation on azalea cultivars in ChinaFifty-seven evergreen azaleas cultivars were investigated in this study based on seven characters, including flower colour, flower shape, flower diameter, lamina length, plant habit, natural flowering and sensitivity. The results show that all the flower colours fall into5categories, including white, red, red-purple, purple and variegated. Most cultivars have medium size of leaves and flowers. Over a half of the cultivars flower in mid-April. There are no relationship between the time of natural flowering and flower induction sensitivity.2、Effects of GA and5-azaC on the morphology and flowering of azaleaFrom the middle of November, we took an observation on Morphological changes, and kept a record with the timing of flowering, and investigated the effects of GA and5-azaC on the morphology and flowering of azaleas. The results show the treatments of5-azaC (40mg/L) and GA (300mg/L) can significantly promote flower bud growth. The volume of flower was bigger than control plants, and the time of flowering was significantly earlier than control plants, and promote the time of flowering in at least3-6days.3、Effects of plant growth regulators and5-azaC on the contents of carbohydrate, soluble protein and endogenous hormones There are four periods detected in this experiment according to the conversions of carbohydrates in leaves of pot azaleas:From July to August, the starch contents, sucrose contents and soluble sugar contents all decreased. From August to September, the starch contents decreased while sucrose contents and soluble sugar contents increased in leaves. From September to October, the starch contents, sucrose contents and soluble sugar contents all increased. From October to November, the starch contents, sucrose contents and soluble sugar contents all decreased again. Compared with the control plants, treatments of5-azaC and KH2PO4can increase the starch contents.The soluble protein content in flower buds was higher than that in leaves. All treatments of GA and5-azaC did not have a major influence on soluble protein content.GA and5-azaC can increase GA content to improve flowering. From December to February the next year, IAA content increased while ABA content decreased. IAA content of the plant treated with GA and5-azaC was higher than others. From December to March the next year, ZR content had a significant decrease. We supposed that GA and5-azaC promote flowering by decreasing GA content and increasing IAA/ABA.4、Effects of plant growth regulators and5-azaC on the level of DNA methylationThe level of DNA methylation was tested using High Performance Liquid Chromatography (HPLC). The results show that5-azaC and GA can decrease the level of DNA methylation in flower buds. The flowering time of cultivar ’Hongshanhu’ could be in advance for14to17days when both of the two treatments were used. Treatments of5-azaC (40mg/L) and GA (300mg/L) can significantly decrease the level of DNA methylation. The plants with lower level of DNA methylation flower earlier. It is suggested that5-azaC could make azaleas to flower earlier by decreasing the level of DNA methylation. |
PDF Full Text Request