Study On The Coloring Mechanism Of Birch Autumn Leaves Based On Metabolomics

Leaf color is one of the most important ornamental characteristics of autumn leafy trees.The white birch(Betula platyphylla)is a typical autumn leaf tree in Northeast China,with its ornamental characteristic of golden leaves in autumn.In this study,the leaf color values,growth,and physiological indicators of B.platyphylla leaves during five coloration periods were measured,and the physiological characteristics during the coloration process of B.platyphylla leaves,as well as the metabolic characteristics of primary and secondary metabolites that affect color conversion,were investigated using the non targeted primary metabolomic analysis technique(GC-MS)and the targeted phenolic metabolomic analysis technique(UPLC-MS),This provides a basic theoretical basis for studying the mechanism of leaf color formation and leaf color regulation in B.platyphylla.Through this study,the following conclusions are obtained:(1)Through phenotypic analysis,it was found that the brightness of the autumn leaves of B.platyphylla increased during the coloration process,and the leaves became more colorful.Through the analysis of leaf color using the Lab model,it was found that the yellowness b~*and color value C~* better explained the color characteristics of white birch leaves.The analysis of pigment content showed that the content and proportion of chlorophyll,carotenoids,and total flavonoids played a key role in the coloration of B.platyphylla leaves,while there is very few anthocyanin in B.platyphylla leaves.Ionic analysis of mineral elements indicates that the decrease of N and P during the coloration period of B.platyphylla leaves may be related to nutrient transfer caused by leaf senescence.CAT and POD enzymes are more active in the antioxidant system.When birch leaves enter the metaphase of color transition(S3),they produce a large amount of CAT to remove oxygen radicals.POD replaces CAT during S4,further slowing down the oxidative stress caused by natural aging in plants.(2)Correlation analysis found that there was a significant correlation between the brightness value L~*,yellowness value b~*,and color value C~* and the content of carotenoids/chlorophyll,soluble sugar,total flavonoids,copper,potassium,and chlorophyll(p<0.01).The N,P,and K elements in mineral elements indirectly affect leaf color by influencing the content of chlorophyll,carotenoids,and total flavonoids.The results of redundancy analysis showed that the carotenoid/chlorophyll,total flavonoid content,and chlorophyll content had the highest interpretation rate for the differences in leaf color values of B.platyphylla at different color conversion stages,and were the decisive factors affecting the color appearance of B.platyphylla.(3)Through GC-MS analysis,it was found that substances such as sucrose and lactose as substrates enter metabolic pathways such as glycolysis,providing a basic carbon skeleton for leaf color conversion;In addition to the TCA cycle providing energy for birch leaves during color conversion,cell wall degradation assists in energy conversion during color conversion through glyoxylic acid metabolism;The decrease in the content of amino acid metabolites is related to the basic growth and metabolism of plants caused by changes in leaf color;The significant increase in phytol levels related to chloroplast degradation and metabolism further confirmed that chloroplast degradation and carotenoid retention are one of the main factors affecting the autumn color transition of B.platyphylla leaves.(4)Through UPLC-MS analysis,it was found that most C3C6C3 type flavonoids and their derivatives accumulated significantly in the late stage of birch leaf color transformation.The results of correlation analysis showed that there was a significant positive correlation between7 flavonoids such as naringin and the yellowness value b~*(p<0.05),indicating that these substances had a promoting effect on the appearance of yellow leaves;Chlorogenic acid,vanillic acid,and eugenoic acid are beneficial for plants to improve their antioxidant capacity and indirectly assist in maintaining the yellow color of their leaves.In addition,there is a very significant positive correlation between naringin and the content of its downstream products,kaempferol,rutin,etc.(p<0.01),indicating that in the biosynthetic pathway of flavonoids and flavonols,related substances promote each other.In summary,this study combined pigment content,physiological characteristics,ionomics,and metabolomics to comprehensively analyze the leaf color changes of B.platyphylla during the coloration period.It was found that the coloration mechanism of B.platyphylla leaves is relatively complex and is determined by multiple factors.The main reasons for the change in leaf color of B.platyphylla are the decrease in chlorophyll content in the leaves,the retention of carotenoids,and the accumulation of flavonoids.Among flavonoids,apigenin,naringin,luteolin,kaempferol,quercetin,astragaloside,and rutin are the seven substances that have the greatest impact on the color appearance of leaves.The reactions and changes of N,chlorogenic acid,and antioxidant system in mineral elements confirm that the yellow transition of leaves is related to the seasonal adaptation mechanism of plants and leaf senescence.In addition,soluble sugar,K element,P element and other indicators indirectly participate in the coloration of B.platyphylla leaves by influencing the content of various pigments.This study provides a reference for the study of color change mechanism and seasonal adaptation of autumn leaf plants.