Diversity assessment on triterpene metabolites in different tissues of ten types of loquat germplasms

Abstract:【Objective】The loquat [Eriobotrya japonica (Thunb.) Lindl.] has long been used as a phar-maceutical plant, its leaves, flower as well as other tissues have been used for the treatment of many diseases. Dry loquat leaves are widely used in traditional Chinese medicine to treat cough and asthma. Trit-erpene acids have been found in the leaves, peel, flesh, seeds and flowers of loquat, and some of these compounds have been proved to have bioactivities such as anti-inflammatory, antitussive, diuretic, anti-tumor and diabetes. The aim of this work was to study the diversity of triterpene acids in different tis-sues of loquat germplasm resources, so as to provide basis for resource identification and functional uti-lization of this species.【Methods】The contents of ursolic acid, corosolic acid and oleanolic acid in leaves, peel, flesh and seeds collected from 10 types of loquat germplasms were determined by high per-formance liquid chromatography (HPLC), and the diversity and correlation among triterpene acids in different loquat germplasms as well as correlation of triterpene enrichment capacities in tissues of the same germplasm accession were analyzed.【Results】Three triterpene acids (ursolic acid, corosolic acid and oleanolic acid) were identified in all tissues of 10 loquat resources, the triterpene acids compounds  and contents in different tissues varied greatly with the variation coefficient ranging from 21.8% to 213.4%, the variation coefficient of ursolic acid in flesh was the highest, and the variation coefficient of oleanolic acid in leaves was the lowest. In leaves, the average contents of ursolic acid, corosolic acid and oleanolic acid of 10 types of loquat germplasms were 4.10, 3.47 and 1.10 mg·g^-1, respectively, the differences between the highest and lowest content were 2.7, 2.7 and 2.3 times for ursolic acid, coro-solic acid and oleanolic acid, respectively. In peel, the content of ursolic acid was the highest (average2.27 mg·g^-1, 51.4%), the second was corosolic acid (average 1.58 mg·g^-1, 35.7%), the content of oleano-lic acid was the lowest (average 0.57 mg·g^-1, 12.9%), and the differences between the highest and low-est content were 4.3, 3.2 and 5.2 times for ursolic acid, corosolic acid and oleanolic acid, respectively.In flesh, the content of corosolic acid was the highest (average 54.12 µg·g^-1, 83.6%). The contents of ur-solic acid and oleanolic acid were lower (average 7.03 and 3.61 µg·g^-1, 10.9% and 5.7%, respectively),and the differences between the highest and lowest content were 48.1, 8.8 and 21.4 times for ursolic acid,corosolic acid and oleanolic acid, respectively. In seeds, the content of corosolic acid was the highest (average 30.25 µg·g^-1, 47.6%), the next was ursolic acid (average 24.01 µg·g^-1, 37.7%), the content of oleanolic acid was the lowest (average 9.36 µg·g^-1, 14.7%), and the differences between the highest and lowest content were 40.0, 5.8 and 3.3 times for ursolic acid, corosolic acid and oleanolic acid, respec-tively. The total triterpene acid content in leaves was higher than that in peel, and both of them were much higher than those in flesh or seed. In most detected materials, ursolic acid was the highest triter-pene compound in leaves, and the peak ursolic acid in Anhuidahongpao leaves was 4000 fold more than that in flesh of Xiaomaopipa. All these results demonstrated that most loquat leaves were suitable for traditional Chinese medicine. Loquat peel and flesh, with high ursolic acid and /or corosolic acid, were potential table supply of triterpene components. The amount of ursolic acid, corosolic acid and total trit-erpenoid acid in leaves showed significant positive correlation with each other (r=0.81, 0.95 and 0.94),while oleanolic acid showed weaker positive relationships with ursolic acid, oleanolic acid and total triterpenoid acid (r=0.64, 0.60 and 0.69). In peel, ursolic acid, corosolic acid and total triterpenoid acid also showed significant positive correlation with each other (r=0.82, 0.97 and 0.92) and oleanolic acid showed weaker positive relationships with total triterpenoid acid. In flesh, very significant positive cor-relations existed among ursolic acid, corosolic acid and total triterpenoid acid (r=0.97, 0.98 and 1.00). In seed, ursolic acid and corosolic acid showed positive correlation with total triterpenoid acid (r=0.87and 0.78) while ursolic acid content was just slightly related with corosolic acid (r=0.65).【Conclusion】Comprehensive analysis on triterpene metabolite enrichment capacities of diverse tissues in 10 loquat accessions in this study identified specific germplasms including tissues for novel metabolite utilization of this species. Leaves with stable high triterpene content were suitable for traditional Chinese drug preparation. High ursolic acid and corosolic acid accumulation capacity was found in peel of germ-plasm like Luoyangqing, and high corosolic acid was detected in flesh of germplasm like Marc. Totally,here the comprehensive analysis on triterpene compounds among loquat germplasms supported metabo- lome basis that dry loquat leaves are vital and widely used in traditional Chinese medicine. The high specific triterpene accumulated in fruit tissues is potential for table dietary to benefit human health and the residual seed after loquat fruit consumption is valuable for food deep processing.