Objective The amount of nuclear DNA（C-value）is a key biodiversity character that provides strong unifying elements in revealing the phylogenetic regularity and relationship between genome size and functional traits for plant resource.The estimation of C-values could primarily extend our knowledge on the genetic background and genome diversity for medicinal plants,and thereby the variation of pharmacological constituents and phylogenetic mechanism of medicinal plant taxa will be revealed.However,a large number of medicinal plants（e.g.Cornus officinalis）typically contain a series of secondary metabolites,especially tannic acid,which would significantly affect the estimation of DNA content by flow cytometry（FCM）.Methodological discussions and improvement need to be made to solve this problem.Methods Two isolation buffers LB01 and Otto 1 were selected to prepare nuclear suspension with additional treatments of pre-soaking and centrifugation combination of gradient centrifugal force and duration.The best isolation and estimation methods were determined by FCM measurement in C.officinalis.Results The dry leaves were pre-soaked in Otto I buffer for 15 min and the Otto I nuclear suspension was centrifugated at 1.0×103 g for 2 min.The results showed that debris and nuclei were better separated and the scatterplots of good quality were obtained with low coefficient of variation（CV）.Contrarily,the nuclear DNA content of C.officinalis could not be accurately estimated for nuclei extracted by LB01 buffer.Finally,2C-value and genome size of C.officinalis were first estimated as 5.92 pg and 2893 Mbp,respectively.Conclusion The new methods proposed here are able to accurately estimate DNA content of C.officinalis,which provides valuable references for the estimation of genome size in other tannin-rich medicinal plants.
