| Michelia hedyosperma,an evergreen tree of the genus Mieria in the Magnoliaceae,is a precious and excellent timber tree in the tropical and subtropical regions.Its seeds can be used as medicine,and the essential oil can be extracted from its flowers and leaves,which has great potential and value for development and utilization.Light quality plays an important role in regulating plant growth and accumulation of active components.Therefore,it is necessary to investigate the effects of light quality on the growth and physiological metabolism of M.hedyosperma seedlings.In this study,we used 1-year-old M.hedyosperma as experimental material and LED as light source,used white light（W）as control and set up the treatments including red（R）,blue（B）monochromatic light and composite lights with ratios of red and blue light was2/1,4/1,6/1,8/1 and 10/1（2R1B,4R1B,6R1B,8R1B and 10R1B）,respectively.By analyzing the indicators of growth,photosynthetic physiology,endogenous hormones,soluble substances and contents of total phenols and total flavonoids,to investigate the effect of red and blue light quality on the growth physiology of M.hedyosperma seedlings and screening the optimum light quality for breeding seedlings.Based on the LC-MS platform,untargeted metabolomics analysis was conducted to explore the effects of red and blue light on the metabolites in leaves of M.hedyosperma seedlings,and explore the use and the potential role of the seedlings in coping with light quality changes of important metabolites.The aim of this study was to provide a theoretical basis for the cultivation of strong seedlings,the shortening of seedling growth period,the development and utilization of non-woody resources in terms of chemical composition,and the improvement of precious tree seedling cultivation technology.The main results are as follows:（1）Red and blue mono light decreased the dry weight and root shoot ratio of seedling compared with white light.The growth rates of seedling height and ground diameter,leaf area,dry weight of each organ,root-shoot ratio and seedling quality index of M.hedyosperma seedlings increased firstly and then decreased with the increase of red-blue composite light ratio.6R1B composite light was the most conducive to the morphosis of M.hedyosperma seedlings,and it could promote seedling height,ground diameter growth rate,leaf area,root shoot ratio,and dry weight of each organ.（2）Composite light with higher ratio of blue light（2R1B and 4R1B）was beneficial to the increase of photosynthetic pigment content and chlorophyll a/b ratio.Compared with red,blue and white light,red-blue composite light increased Fm and Fv/Fm.Blue light increased Y（II）,q P and NPQ,while red light decreased NPQ.Composite light with higher ratio of blue light（2R1B,4R1B,6R1B）could promote the increase the Pn of leaf,and it was the highest under 6R1B combination light treatment.Red-blue composite light except 4R1B could improve the water use efficiency of leaves.（3）Compared with white light,blue light and red-blue composite light except 4R1B could promote the increase of soluble sugar content,while red light inhibited the accumulation of soluble sugar and protein.Blue light obviously promoted the increase of ABA and ZR content,while red light did the opposite.Red and blue monochromatic light can increase the content of IAA.Compared with monochrome red light,adding a certain amount of blue light could help the synthesis of GA3 in leaves.The contents of total phenols and flavonoids were higher under 6R1B composite light treatment,indicating that6R1B composite light could significantly promote the accumulation of phenols.（4）Principal component analysis and membership function analysis show that,the light quality suitable for the growth of M.hedyosperma was 6R1B composite light.Therefore,the leaf of M.hedyosperma under 6R1B combined light,red,blue and white light were used for metabolomics analysis.The results of metabonomics analysis showed that there were 61 different metabolites between different light treatments.The results of up-regulation and down-regulation of differential metabolites showed that compared with red and blue monochrome light,6R1B composite light could enhance the metabolic activities of M.hedyosperma seedlings,and then promote the growth and accumulation of metabolites.Red,blue,and 6R1B composite light were compared with white light respectively,between Red and white light,the most significant metabolites wereβ-sitosterol,2-trans,6-trans-Farnesal and protocatechuic acid;between blue and white light,the most significant metabolites were linoleic acid and palmitic acid;between 6R1B composite light and white light,the most significant metabolites were perillyl alcohol and L-glutamine.These metabolites were key substances that could reflect the metabolic changes of leaves under different light treatments.D-Glucose,L-glutamine,L-isoleucine,gamma-aminobutyric acid,palmitic acid,pyruvic acid,and other metabolites are involved in multiple metabolic pathways,providing important information for studying the changes of leaf metabolites and pathways under different light quality treatments.Andβ-sitosterol,protocatechuic acid,linoleic acid,perillyl alcohol and other metabolites have many important uses.（5）Light quality mainly affected the amino acid metabolism,carbohydrate metabolism,lipid metabolism,nucleotide metabolism,terpenoids and polyketones metabolism,biosynthesis metabolism of other secondary metabolites and membrane transport of M.hedyosperma.Blue light and 6R1B combined light enhanced amino acid metabolism,red light and 6R1B combined light decreased lipid metabolism,6R1B composite light enhanced membrane transport pathways,while carbohydrate metabolism was less affected by light quality.Some metabolites related to the above key metabolic pathways may play a regulatory role in the growth physiology of M.hedyosperma in response to red and blue light.For example,blue light treatment may maintain higher Pn,Y（II）,q P and NPQ under monochromatic blue light stress by increasing the relative content of salicylic acid;blue light and 6R1B composite light treaments may promote the growth of height and ground diameter by increasing L-glutamine level.It is possible for the seedlings to cope with the changes of light quality through the mutual regulation betweenγ-aminobutyric acid and plant hormones.The effects of red and blue light qualities on the synthesis of secondary metabolites such as phenylalanine metabolism,terpenoid backbone biosynthesis and phenylpropane biosynthesis showed that red and blue light qualities treatment was a potential effective measure to regulate secondary metabolites of M.hedyosperma.In conclusion,red-blue composite light is more beneficial to the growth of M.hedyosperma seedlings than red and blue mono light,and 6R1B composite light is better for the growth of seedlings.Compared with white light,6R1B composite light could enhance the metabolic activity of M.hedyosperma and facilitate the accumulation of metabolites. |
