Study On Mechanism Of Leaf Color Variation Of Ligustrum Obtusifolium ’Jinye’ And Its Application In Landscaping

Ligustrum obtusifolium ‘Jinye’ as a colored leaf shrub,belongs to the Oleaceae family Ligustrum genus,which shows obvious golden leaf traits throughout the growth period,and the leaves differentiate into different Its unique leaf color variation pattern may indicate a special leaf color variation mechanism and is worthy of further study.In this paper,Ligustrum obtusifolium ‘Jinye’ as the research material,the leaf color parameters were determined by colorimeter,the pigment contents of leaf were determined by spectrophotometer,the structural characteristics of leaf chloroplasts were observed by ultra-thin section,the intermediate product contents of chlorophyll synthesis were determined by spectrophotometer,and the chromosome number of root tip cells was determined by press slice method,the mechanism of leaf color variation of Ligustrum obtusifolium ‘Jinye’ was comprehensively analyzed.The ornamental characteristics and application advantages of Ligustrum obtusifolium ‘Jinye’ were analyzed,the precautions,application methods and practical application effects of Ligustrum obtusifolium ‘Jinye’ in landscaping were discussed.The results of the study are as follows.(1)During the period from April to December,the brightness(L*)of Ligustrum obtusifolium ‘Jinye’ return-green leaves,semi-yellow leaves and yellow leaves were yellow leaves>semi-yellow leaves>return-green leaves,indicating that the brightness of yellow leaves was always higher than that of semi-yellow leaves and return-green leaves during the whole growth period;the red-green phase(a*)were yellow leaves>semi-yellow leaves>return-green leaves,and the leaves of the three leaf color phenotypes were all negative during the whole growth period,indicating that the green phase of yellow leaves was the lowest,followed by semi-yellow leaves and the highest in return-green leaves;the yellow-blue phase(b*)were yellow leaves>semi-yellow leaves>return-green leaves,indicating that yellow phase of yellow leaves was the highest,followed by semi-yellow leaves and the lowest in return-green leaves.The changes of leaf color parameters of three leaf color phenotypes of Ligustrum obtusifolium ‘Jinye’ were consistent with the changes of leaf color phenotypes.(2)During the period from April to December,the chlorophyll content,carotenoid content,and anthocyanin content of semi-yellow and yellow leaves of Ligustrum obtusifolium ‘Jinye’ were significantly lower than those of return-green leaves except at the early and late growth stages,and the chlorophyll b content were extremely low,indicating that Ligustrum obtusifolium ‘Jinye’ belonged to total chlorophyll and carotenoid content.The total chlorophyll and chlorophyll b synthesis were reduced in Ligustrum obtusifolium ‘Jinye’ mutant.The high relative content of carotenoids in semi-yellow and yellow leaves was the direct cause of the yellow color of the leaves of Ligustrum obtusifolium ‘Jinye’.(3)The chloroplast structure of Ligustrum obtusifolium ‘Jinye’ return-green leaves is intact,while the chloroplast structure of semi-yellow leaves and yellow leaves has different degrees of defects,the cystoid lamellar system in the yellow tissues of semi-yellow leaves and yellow leaves is seriously degraded,lacking normal stromal cystoid and basal cystoid,and the cystoid membrane is degraded into the remaining membrane structure and vesicles,which is the intrinsic reason for the leaf color variation.(4)The relative contents of ALA in semi-yellow and yellow leaves of Ligustrum obtusifolium ‘Jinye’ were significantly low,indicating that the entire tetrapyrrole system was severely blocked at the initial stage of chlorophyll synthesis,resulting in low chlorophyll contents in semi-yellow and yellow leaves;the relative contents of ALA in semi-yellow and yellow leaves of Ligustrum obtusifolium ‘Jinye’ were significantly low.The relative contents of Mg-Proto IX and Pchlide were significantly lower in semi-yellow and yellow leaves,indicating that the chlorophyll biosynthesis pathway of semi-yellow and yellow leaves of Ligustrum obtusifolium ‘Jinye’ was blocked,and the blocked sites were not in the chlorophyll synthesis pathway.The pathway of chlorophyll biosynthesis in Ligustrum obtusifolium ‘Jinye’ semi-yellow and yellow leaves was blocked,and the blocked sites might be found in the conversion process of CoprogenⅢand Proto IX.(5)The chromosome base number of Ligustrum obtusifolium ‘Jinye’ was x=23,which was consistent with the reported chromosome base number of Myrtaceae.(6)With the change of seasons,the leaf color of Ligustrum obtusifolium ‘Jinye’shows a change from soft yellow to golden yellow to wax yellow,and there are scenes to be seen throughout the year,which is advantageous in building colorful landscapes in landscap applications.In practical application,we should follow the principles of ecological adaptation and color coordination,choose a reasonable layout,ensure sufficient light conditions,and timely prune the growing re-return-green leaves to keep the leaf color of Ligustrum obtusifolium ‘Jinye’ consistent.