Genome Size Variation And Foliar Epidermal Micromorphology In Sorbus Subgenus Aria(Rosaceae) From China

Sorbus subgenus Aria comprises about 34 species and 6 varities in China.Division arise over the species'relationships among different taxonomists.This study aims to assess ploidy by means of genome size using flow cytometry and observe leaf epidermal micromorphology using light microscope and scanning electron microscope with 16 species and 4 varieties of the subgenus in China and S.japonica in Japan,and to provide extra taxonomical evidence for species identification.The results are as follows:1.Genome size and ploidyGenome size of the subgenus Aria was determined with the internal standard Oryza sativa subsp.japonica‘Nipponbare'.2C-values variation of 21 taxa is 1.299 pg~1.586 pg,among which S.pallescens was the smallest and S.zahlbruckneri was the largest.The genome size was significantly different among different taxa.According to the 2C value variation on different ploidy of Sorbus in C-value database and the previous chromosome counting,21 taxa were inferred to be diploids.2.Epidermal cell formThe shape of leaf epidermal cells is polygonal or irregular,with straight,curved to sinuated anticlinal walls.The anticlinal wall of the epidermal cells is convex or concave.21 taxa can be divided into 5 groups on the basis of epidermal cells and anticlinal walls:(1)the shape of adaxial and abaxial epidermal cells are polygonal,with straight and curved anticlinal walls,observed in S.dunnii and S.meliosmifolia;(2)the shape of adaxial and abaxial epidermal cells are irregular,with sinuated anticlinal walls,only observed in S.zahlbruckneri;(3)the shape of adaxial and abaxial epidermal cells are polygonal and irregular,with straight,curved to sinuated anticlinal walls,observed in 8 taxa including S.caloneura,S.coronate and S.folgneri,etc.(4)the shape of adaxial epidermal cells are polygonal and irregular,with straight,curved to sinuated anticlinal walls,while the abaxial epidermal cells are irregular,with sinuated anticlinal walls,observed in 4taxa including S.alnifolia,S.alnifolia var.lobulate,S.aronioides and S.keissleri;(5)the shape of adaxial epidermal cells are polygonal,with straight and curved anticlinal walls,while the abaxial epidermal cells are polygonal and irregular,with straight,curved to sinuated anticlinal walls,observed in 6 taxa including S.alnifolia var.angulate,S.hemsleyi and S.kohimensis,etc.Cell area of adaxial epidermis ranges from 428.7?m2 to 1083.48?m2 for 21 taxa,among which S.pallescens is the smallest and S.megalocarpa is the largest.Cell area of abaxial epidermis ranges from 363.84?m2 to 826.62?m2 for 21 taxa,among which S.coronata var.glabrescens is the smallest and S.zahlbruckneri is the largest.Significant difference existes in epidermal cell area among different taxa.Significant differences are found in epidermal cell area among different taxa(P<0.05).Fine relief of the cell wall of studied taxa is reticulate,striate,irregular bulge,smooth or invisible.Two types of trichomes are observed-ribbon-like and cylindrical-bended near the trichome base.21 taxa can be divided into 4 groups based on fine relief of the cell wall and trichomes in abaxial epidermis:(1)the abaxial epidermis is covered by dense trichomes and the ornamentation is invisible,which are observed in 4 taxa,including S.coronate,S.pallescens,S.dunnii and S.folgneri;(2)reticulate,observed in 8 taxa including S.japonica?S.zahlbruckneri,S.hemsleyi,etc.,5 taxa among them S.japonica,S.zahlbruckneri,S.hemsleyi,etc.have ribbon-like trichomes,while S.lushanensis has two types trichomes;(3)striate,observed in 7 taxa,including S.kohimensis,S.caloneura,S.keissleri,etc.,only S.meliosmifolia among them has ribbon-like trichomes;(4)irregular bulge,only observed in S.alnifolia var.angulata and S.megalocarpa which has not trichomes.Abundant epicuticular waxes are observed in this subgenus,mainly including crust,granules,platelets,rodlets and threads.Significant differences are found in epicuticular wax type among different taxa(P<0.05).3.Stomatal complex characteristicsThe stomata of 21 taxa are distributed in the abaxial epidermis and are anomocytic type.Every stomata is composed of two kidney-shaped guard cells,which is raised or sunken.The guard cells have prominent outer stomatal rims.Except in S.japonica and S.kohimensis,T-type thickening structure are observed in the guard cells of the other 19 taxa.Stomatal waxes of 21taxa are diversified,including crust,granules,platelets and threads.Stomatal length ranges from19.17?m to 30.81?m,stomatal width ranges from 16.29?m to 22.87?m,stomatal area ranges from 288.41?m2to 564.55?m2,stomatal density ranges from 101.82 stomata/mm2 to 532.83stomata/mm2,stomatal index ranges from 8.74%to 24.09%.Stomatal area,stomatal density and stomatal index are significantly different among different taxa(P<0.05).4.Cluster21 taxa can be divided into 3 groups on the basis of foliar epidermal micromorphology.The first group contains 9 taxa,including S.caloneura var.kwangtungensis,S.keissleri and S.caloneura,etc.The second group contains 5 taxa,including S.coronate,S.folgneri and S.pallescens,etc.The third group contains 7 taxa,including S.alnifolia,S.japonica and S.lushanensis,etc.In conclusion,significant differences are found in genome size,the shape of leaf epidermal cells,fine relief of the cell wall,epicuticular waxes,stomatal characteristics and trichomes among Chinese Subgenus Aria species,which is valuable in understanding the species identification.At the same time,S.alnifolia var.angulata and S.alnifolia var.lobulata are not supported as synonymies of S.japonica.