Preliminary Studies On Cytology And Genome Sizes Of Rhodiola In Hengduan Mountains

Rhodiola belongs to Crassulaceae,most of which are rare medicinal plants.It is known as "plateau ginseng" and "snow mountain fairy grass" in China.There are 96 species in the world,mainly distributed in the northern hemisphere in the cold region,China,Korea,Japan,and North America also have distribution;China is the central producing region of Rhodiola,with 73 species,two subspecies and seven varieties,mainly distributed in the northwest,southwest,northeast and some parts of north China.There are few cytological be reported on Rhodiola.Among the 96 species of Rhodiola distributed globally,only 16 species have chromosome reports,accounting for only 16% of Rhodiola.Only 11 Rhodiola species distributed in China have been reported to have chromosomes,which is only 15% of the 73 Rhodiola species distributed in China.Among the 36 Rhodiola species distributed in the HDM,only R.kirilowii? R.bupleuroides? R.quadrifida and R.wallichiana have been reported,so the cytological research needs to be strengthened urgently.Besides,there are no reports on the determination of Rhodiola genomic size by flow cytometry,so it is of specific scientific significance to study the genomic size of Rhodiola.In this study,cytological experiments were carried out on six species,and seven populations of Rhodiola collected from HDM and adjacent mountainous areas.Furthermore,the genomic size and ploidy of 46 populations of 17 species of Rhodiola from HDM and adjacent mountain areas were determined for the first time by flow cytometry.Based on previous cytological studies and molecular systems,the discussion on the chromosome evolution of Rhodiola can be concluded as follows:1.The chromosome Numbers of two populations of R.kirilowii were 2n = 2x=46,2n =6x= 66,and the two populations were 2x and 6x.R.bupleuroides,R.fastigiata,and R.crenulata are all 2x,and chromosome number is 2n = 22.R.chrysanthemifolia is 2x,and chromosome number is 2n = 14,R.macrocarpa is 8x,the chromosome number is 2n = 104.The cytological results showed that Rhodiola had a significant variation of chromosome base in HDM,including x = 7,11,23,26,etc.Four of the above results were reported for the first time.These results enriched the cytological data of Rhodiola and provided the primary data for the chromosome evolution and systematic classification of Rhodiola.2.By summarizing the chromosome number,radix and ploidy of Rhodiola and related genera,it is found that the chromosome number,radix and ploidy of Rhodiola vary greatly:(1)Chromosome base number of Rhodiola is x = 7,10,11,13,17,18,23 etc.,and x = 11 percentage is the highest,accounted for 11.45%,combined with related taxa chromosome data x = 11 is the base of basic chromosome;(2)the chromosome number of Rhodiola somatic cells was 2n = 14,20,22,32,34,36,44,46,66,86,98,110,etc.,of which 2n = 22 accounted for the highest proportion,reaching 7.81%,followed by 2n = 32,34,both is 7.51%.(3)Rhodiola has rich ploidy,most of which are diploid,accounting for 66.07% of the total;Tetraploid,hexaploid,octoploid,and decaploid were also found,and the proportion of tetraploid was 27.33%.It is preliminarily measured that the evolution of Rhodiola at the cellular level is mainly reflected in the diversity of chromosome number,ploidy,and aneuploidy,which may be the cytological mechanism for Rhodiola to adapt to the harsh mountain environment.3.The genome size of Rhodiola was studied for the first time in 46 populations of 17 species.The results show that :(1)the genome size ranged 564.98-5764.71 Mbp,DNA-2C ranged from 0.58-5.93 pg.(2)the proportion of ploidy was 71.11%,and that of other ploidy(tetraploid,hexaploid,and octoploid)was 22.89%.(3)all Rhodiola genome size averages are 2001.62 Mbp,the average genome size above 5000 m altitude is 4037.09 Mbp,the average genome size above 4500 m altitude is 2579.76 Mbp.The average genome size below 4500 m altitude is the only 917.59 Mbp.From the size of the genome and elevation of the average relationship can be seen that Rhodiola species with increasing altitude,its region genome increases gradually.It's biological significance remains to be further discussed.4.Based on the results of the molecular phylogenetic tree of Rhodiola,the law of chromosome evolution of Rhodiola was discussed.Based on the analysis of cytological characteristics and genome size,it was found that the polyploidy of Rhodiola was not obvious,which did not support the hypothesis of the "polyploid pre-adaptation mechanism" and "low temperature accelerated polyploidy formation".