Effects Of UV-B Radiation And Salt Stress On Growth And Physiological And Biochemical Characteristics Of Two Licorice Seedlings

Soil salinity and high doses of UV-B(UV B radiation,wavelength is 280 ~ 320 nm)radiation is as important abiotic stress factor,especially in arid and semiarid regions where plant production and resources development and utilization of environmental factors can never be ignored.Salt stress and UV-B radiation stress can inhibit plant growth and development process,including making plant proteins,DNA molecular structure and biological membrane damage,plant morphological growth inhibition,photosynthetic physiology and the adjustment of the aspects such as the synthesis of secondary metabolites,and even lead to the death of plants.Most previous studies focused on the control of artificial climate box and greenhouse experiment research,while lessstudy is under the condition of field.Moreover,the unbalance of the spectral intensity effectively under experimental conditions may cause the negative impact of UV B radiation on plant.Some previous researches of medicinal plant radix glycyrrhizae are on seedling stage,the radiation time is shorter,and most of the researches did not consider licorice photosynthetic physiological characteristics and the change in chemical properties under a long-term UV B radiation.Because of plant response to separate the UV-B stress responses and UV-B and other composite effect of stress response is different.In the present study,we used Glaycyrrhiza.inflata Bat.and Glycyrrhiza glabra L.as the research object,and explored the seed germination,radicle growth,physiological index change and photosynthetic physiological study to the two species in the artificial climate box and greenhouse control experiment setting UV-B radiation,different concentrations of salt stress and UV-B radiation alone and salt composite stress of two factors respectively.In addition,in the field under the condition of long-term use UV-B radiation processing,we further studied the growth,photosynthetic physiology and secondary metabolism process of research.The study is significant for deeper understanding in the field cultivation under the condition of long-term high doses of UV-B radiation influence on triterpene compound such as licorice glycosides,and is helpful in understanding the response of two kinds of plants to soil salt stress and enhanced UV B radiation reaction.The results showed that:1.In this study,high concentration of salt stress and under combined intimidation with UV-B radiation resulted in lower germination rate and germination index of two licorice,and a separate UV B radiation has no effect on two kinds of licorice root germination.In comparison,the Glaycyrrhiza.Inflata Bat.has higher germination ability,and the Glycyrrhiza glabra L.is more sensitive to stress.2.Except the dry weight of the aboveground and underground parts,root length,plant height,aboveground and underground fresh weight of two kinds of Glycyrrhiza were significantly reduced by high salt stress and combined effects with UV-B.Under the condition of field cultivation,enhanced UV-B radiation treatment decreased the height of Glaycyrrhiza.Inflata Bat,the fresh mass and dry mass of aboveground and underground parts.3.All the stress conditions increased the proline content of two kinds of plants,especially for the high salt stress group and UV-B treatment group of Glycyrrhiza inflata;salt stress significantly increased the activity of POD of two kinds of licorice and Glycyrrhiza glabra SOD activity,but the activity of CAT decreased significantly;all the stress conditions of plant anthocyanin and the content of flavonoids have been improved.The tolerance of Glycyrrhiza inflata to salt stress and UV-B stress was higher than that of Glycyrrhiza glabra.4.Under the conditions of greenhouse cultivation,UV-B radiation,salt stress,and the combination stress reduced the chlorophyll a and b content of the leaves and chlorophyll content in the leaves of Glaycyrrhiza.Inflata and Glycyrrhiza glabra.The UV-B radiation did not affect the carotenoids in the leaves,but the salt stress and the compound stress of the two factors reduced the carotenoid content.UV-B radiation,salt stress and the combination of two factors reduced the content of carotenoids.The content of chlorophyll a,b,total chlorophyll,Chla/b and carotenoid content in the leaves of Glaycyrrhiza inflata and Glycyrrhiza glabra were enhanced by UV-B radiation under field cultivation conditions.5.Under the condition of glasshouses,the results showed that the lowest net photosynthetic rate was found for the combination of UV-B radiation and low-concentration salt.For the net photosynthetic rate,UV-B radiation and salt stress were superimposed on each other.The net photosynthetic rate of the leaves of licorice leaf was the lowest in high concentration of salt stress and UV-B radiation and high concentration of salt,and the high concentration of salt and UV-B radiation showed antagonistic effects.Under the culture condition of the field,leaf net photosynthetic rate size order for Glycyrrhiza glabra(UV-B)> Glycyrrhiza glabra(CK)> Glaycyrrhiza.Inflata(UV-B)> Glaycyrrhiza.Inflata(CK),indicates that the enhanced UV B radiation appropriate improves the two kinds of licorice leaf net photosynthetic rate.6.For the greenhouse cultivation condition,UV-B radiation,high salinity and high UV-B radiation combined with low concentration of salt stress significantly reduced Glycyrrhiza and Glycyrrhiza glabra leaf net photosynthetic rate(Pn),stomatal conductance(Gs)and intercellular CO2 concentration(Ci),transpiration rate(Tr)exchange parameters,the efficiency of gas and water.Glycyrrhiza glabra L.showd lower tolerance under the high concentration of salt stress and UV-B radiation stress.For two licorice varieties grown in field enhancement,except for water use efficiency(WUE),Glycyrrhiza inflata has higher net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),intercellular CO2 concentration(Ci below)than that of Glycyrrhiza glabra.All the results indicate that stress tolerance of Glycyrrhiza glabra to enhanced UV-B radiation is higher than that of Glycyrrhiza inflata.7.Results of field cultivation experiment showed that enhanced UV-B radiation significantly increased leaf maximum fluorescence(Fm)and apparent photosynthetic electron transport rate(ETR)of Glycyrrhiza inflata,while decreased the non photochemical quenching coefficient(NPQ)and photochemical quenching(q P),but the initial fluorescence(Fo),and PS II the photochemical quantum yield(Fv/Fm)and PS II effective photochemical quantum yield(Fv'/Fm')and PS II quantum yield(PS II)were not significant among two species.Under greenhouse conditions,Fv/Fm and NPQ of licorice increased significantly with the increase of salt concentration,while Fo,Fm,,and Fv'/Fm',with PS II and ETR and q P decreased.Combined effects of UV-B and salt stress,Fo,Fm parameters of Glycyrrhiza glabra increased significantly,Fv/Fm,Fv'/Fm',PS,ETR II and q P parameters were significantly reduced,indicating that UV-B radiation and high salt concentration are superimposed on each other.8.For field cultivation,effect of long-term enhanced UV-B radiation on the three terpene effective chemical substance content of Glycyrrhiza leaves is significantly greater than the effect on the root and stem.Especially,the content of liquiritin licorice in leaves was significantly greater than that in root and stem,and is also greater than the content in the leaves of Glycyrrhiza glabra.The content of liquorice,glycyrrhizic acid and glycyrrhetinic acid in root of Glycyrrhiza glabra increased significantly under enhanced UV-B radiation.The content of glycyrrhizin in leaves of Glycyrrhiza inflata increased with UV-B radiation,and was higher than that of Glycyrrhiza glabra,and Glycyrrhiza inflata was sensitive to UV-B radiation.The variation of the content in different effective chemicals under UV-B radiation showed that UV-B radiation induced selectivity to three terpenoid chemicals in different Glycyrrhiza varieties.