| Trapa L.,also known as water chestnut,is a traditional medicine-food aquatic crop in China with important ecological and economic values.The pericarps of Trapa are rich in phenols,which have significant anticancer and antioxidant activities.However,the lack of the information about the differences of secondary metabolites in the pericarps among Trapa species,and the correlations between secondary metabolites in the pericarps and the genetic relationships,environmental factors and fruit morphology,will not be benificial for the effective utilization of the polyphenols resources of Trapa pericarps.In the present study,19 Trapa species(53 populations)were collected throughout China,especially from the Middle and Lower Reaches of Yangtze River and Sanjiang Plain in Northeast China,including 13 wild(42 populations)and 6 cultivated species(11 populations).The pericarps from all Trapa species and populations were collected and extracted using the system of ethanol: water(7:3).We measured the total phenols content(TPC)and the antioxidant activity from the ethanol extract of pericarps(EEP)of Trapa.Meanwhile,seven representative species,including six wild species(T.maximowiczii Korsh.,T.quadrispinosa Roxb.,T.bispinosa Roxb.,T.manshurica Flerow,T.kozhevnikovirum Pshennikova and T.japonica Flerow)and one cultivated species(T.acornis Nakano),were selected to test the secondary metabolites based on the Ultra Performance Liquid Chromatography-Tandem mass spectrometry(UPLC-MS/MS).Then,we analysised the correlations between the TPC,antioxidant activity and secondary metabolite profiling and the genetic relationship,environmental factors and morphological characteritics.The results were as follows:1.The TPC of the ethanol extracts from Trapa pericarps ranged from 26.75 to 115.40mg/g GAE(dry weight).For the wild species,TPC in the EEP of T.quadrispinosa,T.potanini V.Vassil and T.kozhevnikovirum significantly differed among populations,and the antioxidant activity of all species showed significant differences among populations,which might be influenced by the stress of climate and water environmental factors in different sample sites.For the cultivated species,TPC and antioxidant activities in the EEP of T.bicornis Osbeck var.cochinchinensis(Lour.)H.Gluck and T.bicornis Osbeck differed significantly among populations,which were contributed to their planting environment and management.Meanwhile,the TPC and antioxidant capacity in the Trapa EEP showed significant differences among species,and both of them in the cultivated species were higher than those in the wild species.The TPC in the EEP positively correlated with the antioxidant capacity in 53 Trapa populations(P<0.01).A total of 273 secondary metabolites were detected from 7 representative Trapa species.Among them,the metabolite compositions of T.bispinosa and T.quadrispinosa were the most similar and significantly correlated(r=0.989);the metabolites of T.manshurica and T.kozhevnikovirum also strongly correlated(r=0.941).The metabolic components and contents of T.maximowiczii have significant difference with other species,neither did the T.japonica.2.The results from AFLP and chloroplast(cp)genome sequencing consistently showed that Trapa genus was devided into two genetic branches: small-and large-fruit branches.The small-fruit branch included two species(T.incisa and T.maximowiczii);the large-fruit branch included all other large-fruit Trapa species.The results also showed a close relationship between T.quadrispinos and T.bispinosa,and the four species(T.manshurica,T.kozhevnikovirum,T.litwinowii V.Vassil and T.sibirica Fler)shared one genetic group.T.japonica was genetically distinctive with other Trapa species.The genetic distances were negatively correlated with similarity of secondary metabolite profilings among Trapa species,indicating that the relationships among species were closer,the secondary metabolites in the pericarps among different Trapa species more similar.3.The TPC and antioxidant activity in the different Trapa EEP were affected by different environmental factors.The TPC in the T.potanini EEP were positively correlated with mean of small evaporation(SE)and mean of sunshine hours(MAS).Meanwhile,the antioxidant activities in the EEP were negatively correlated with minimum relative humidity(Min RH),mean of wind speed(MWS)and maximum wind speed(Max WS).However,the TPC in T.bispinosa EEP showed positive correlations with SE,MAS,mean of ground surface temperature(MGT)and minimum temperature(Min T),but no relationship with water environmental factors,which suggested that the phenolics were more sensitive to climate indicators than water environment factors.In contrast,the antioxidant activity in T.bispinosa EEP showed negative correlations with MAS and Min T,positive correlations with dissolved oxygen(DO)and ammonium nitrogen(NH4+-N).The results might be caused by the different secondirary meatbolites composition in the T.bispinosa EEP.Redundancy analysis(RDA)analysis showed that Min RH,mean of nighttime precipitation(MNP)and MWS were the main factors to the composition and content of secondary metabolites in different Trapa species.4.For Trapa,fruit size(fruit height and fruit width)was relatively stable morphological trait.The TPC and antioxidant capacity in the EEP of T.bispinosa and T.potanini were correlated with the characteristics of fruit crown and neck,and the TPC and antioxidant capacity in different species were related to different morphological characters.The TPC of T.potanini EEP negatively correlated with crown width(CW)and crown length(CL),while those of T.bispinosa only negatively correlated with CL.The antioxidant activity of the T.potanini EEP showed negative correlations with crown size(CW and CL),neck height(NH)and fruit width(FW).However,in the T.bispinosa EEP,the antioxidant activity showed positive correlations with NH and CW based on FRAP,and positive correlation with NH/ND based on ABTS.RDA showed that CW/CL,tuber height(TH)and NH were the mainly influence factors to metabolite composition of different Trapa species.Moreover,the morphological characteristics of the tuber,fruit crown and fruit neck from different Trapa species were affected by different environmental factors.This study provides baseline for the germplasm resources exploitation and utilization of Trapa,which benefits the molecular biology and metabolic regulation of the plant. |
