The Study On The Mechanism Of Substrate PH And Al³⁺ Regulating Sepal Color Formation In Hydrangea Macrophylla

Hydrangea macrophylla is very famous for the changes of sepal color,and is widely cultivated in gardens,used as cut flowers and potted plants abroad.At present,there are many problems on changing the sepal color,because of the lack of the technology for regulating color lack in China.Therefore,there were difficulties in production and application of hydrangea in China.The sepals of many cultivars in hydrangea macrophylla showed different colors under different soil condition.When shrubs were planted in acidic soil,the sepal color is blue;while those in an alkaline soil have red sepals.However,the underlying mechanism of substrate pH on color variation remains unclear.In order to explore the mechanism of substrate pH regulating the formation of sepal color of hydrangea,hydrangea macrophylla ’Bailmer’ were tested to investigate the effect of substrate pH on growth and development of plants,synthesis of anthocyanin,and absorption of Al3+ in this study.In addition,the expression of genes was detected and the effect of substrate pH on expression of aluminum transport related genes was studied using qRT-PCR.The results are as follows:1.Firstly,the related physiological index(plant height,leaf pairs,leaf length,leaf width,sepal color,number of florets and inflorescence diameter)of growth and development in ’Bailmer’were measured and the effect of different substrate pHs(4.5,5.5,6.5)and temperatures(21 and 26℃)on the growth and development of plant were studied in this experiment.The results showed that 21℃ was better for flower development and ornamental morphogenesis,and 26℃ more suitable for vegetative growth in ’Bailmer’.In addition,the substrate pH 5.5 was the best for plant growth.2.Secondly,sepal color,component and content of anthocyanin and content of Al3+ were analyzed to study the effect of three adding aluminum treatments(adding aluminum on the whole growth stage,adding aluminum after budding and adding aluminum until the budding)on sepal color of hydrangea.The results showed that the optimum period of adding aluminum for’Bailmer’ was after budding.This result provided a foundation for the further research.3.Based on the research results mentioned above,sepal color,component and content of anthocyanin and content of Al3+ were detected to investigate the effect of different substrate pHs(4.0-4.5、5.0-5.5、6.0-6.5)and aluminum sulfate treatments on sepal color formation.The result showed that the substrate pH 6.0-6.5 was more suitable for developing pink sepals in ’Bailmer’under non-Al treatment.The substrate pH 5.0-5.5 was more benefit to blue sepal formation.4.The relative expression of two Al transporter genes(HmVALT and HmPALT)was detected using q-PCR to study the difference on expression of different blossom under different substrate pH(4.0-4.5、5.0-5.5、6.0-6.5)and aluminum sulfate treatment.The result showed that the relative expressions of Hm VALT and HmPALT reached peak value in early blooming and middle blooming under Al treatment and substrate pH 5.0-5.5.The result indicated the Al3+ was transported greatly to sepals during early blooming under substrate pH 5.0-5.5.In conclusion,21℃ was better for flower development and ornamental morphogenesis,and 26℃ more suitable for vegetative growth in ’Bailmer’.In addition,the substrate pH 5.5 was the best for plant growth in ’Bailmer’.The optimum period of adding aluminum in ’Bailmer’ was after budding.Moreover,the substrate pH 6.0-6.5 was more suitable for developing pink sepals in’Bailmer’ under non-Al treatment;the substrate pH 5.0-5.5 was more benefit to blue sepal formation under A1 treatment,and the great transportation of Al3+ to sepals started from early blooming.