Evolutionary transitions from sexual to asexual reproduction should have significant influences on genetic divergence and polymorphism at the genome level.Plant lineages with diverse reproductive systems provide opportunities to investigate this question using comparative approaches and studies of molecular evolution.We investigated evidence for differences among the transcriptomes of 19 Dioscorea species(wild yams)with diverse reproductive systems.These included sexual species,those that propagate primarily by bulbils,and those with mixed sexual and asexual reproductive modes.We examined how transitions between these reproductive systems affected between-species divergence and within-species polymorphism.Primarily asexual species exhibited a reduced efficacy of natural selection and accumulation of deleterious mutations for both divergence and polymorphism.In contrast,species with mixed reproductive strategies involving both seed and clonal reproduction showed no evidence of an increased fixation of harmful mutations at the divergence level,while an accumulation of genetic load present in polymorphism was evident.Our study indicates that the genetic consequences of evolutionary transitions from sexual to predominantly clonal reproduction is likely to depend on both the duration and extent of asexuality occurring in populations.
The aim of this research was to find and assay phytochemical compounds and various biological macromolecules of the tender stems of Dioscorea praehensilis benth and evaluate their antioxidant activity and to compare the content of oxalates and cyanogenetic glucosides between raw and cooked tender stems.The plant collection and identification,phytochemical evaluation:phytochemical screening,preliminary(qualitative)analyses and in vitro assays.Phytochemical screening was performed by qualitative methods.The estimation of the content of secondary metabolites was evaluated by spectrophotometry-UV.Antioxidant activity was evaluated using the ABTS and DPPH assays and preliminary composition by the gravimetric method.The results obtained show that the stems of Dioscorea praehensilis are devoid of certain important chemical groups,the flavonoids were not detected and they were rich in total polyphenols(17.22±0.16),tannins(19.32±0.52)and anthocyanins(25.22±0.04).Our extracts showed a lower antioxidant activity than that of positive controls.The samples are rich in carbohydrates and fiber,with low levels of proteins,lipids and ash.Dioscorea praehensilis has a high toxicity in HCN,but after a good cooking of about 1 hour,99.97%of the cyanide are eliminated and does not have many oxalates.The results obtained show that Dioscorea praehensilis has a high dietary value and can therefore be used as a nutritive food.
Most species in the genus Tacca （Dioscoreaceae） feature green to black purple, conspicuous inflorescence involucral bracts with variable shapes, motile filiform appendages （bracteoles）, and diverse types of inflorescence morphology. To infer the evolution of these inflorescence traits, we reconstructed the molecular phylogeny of the genus, using DNA sequences from one nuclear, one mitochondrial, and three plastid loci （Internal Transcribed Spacer （ITS）, atpA, rbcL, trnL-F, and trnH-psbA）. Involucres and bracteoles characters were mapped onto the phylogeny to analyze the sequence of inflorescence trait evolution. In all analyses, species with showy involucres and bracteoles formed the most derived clade, while ancestral Tacca had small and plain involucres and short bracteoles, namely less conspicuous inflorescence structures. Two of the species with the most elaborate inflorescence morphologies （T. chantrieri in southeast China and T. integrifolia in Tibet）, are predominantly self-pollinated, indicating that these conspicuous floral displays have other functions rather than pollinator attraction. We hypothesize that the motile bracteoles and involucres may facilitate selfing; display photosynthesis in the dim understory, and protect flowers from herbivory.
Ling ZhangHong-Tao LiLian-Ming GaoJun-Bo YangDe-Zhu LiCharles H. CannonJin ChenQing-Jun Li
