Adaptability Study Of Didymodon Tectorum Under Different Calcium Environments

A large area of calcium-rich loess parent material can be seen on the gully cliffs and slopes on both sides of the road in Xinghe–Qingshuihe loess hilly region of Inner Mongolia Province.Due to low soil fertility and serious surface soil erosion,it is difficult for herb plants to form a stable community.However,Didymodon tectorum often forms a large population of moss crust in this area,and it must have a series of adaptation characteristics in response to the high calcium environment.In this study,the calcicole moss Didymodon tectorum was the research object,and the content of soil elements was used as a guide to optimize the tissue culture system.At the same time,it is treated with different concentrations of Ca²⁺,and the physiological indicators of the moss,chloroplast ultrastructure and ion flow rate were measured,revealing the physiological adaptation mechanism of Didymodon tectorum to the high-calcium environment.In addition,combined with transcriptome sequencing to conduct preliminary research on related genes,and discover functional genes that respond to the high calcium environment.The main results were as follows:1.Optimizing the ratio of element content and hormones in the culture medium of Didymodon tectorum can significantly increase its growth rate.The results of determination of the content of all elements in Didymodon tectorum and soil showed that the content of calcium in both the plant and the soil was the highest.Except for the trace element manganese and the heavy metal elements rubidium,yttrium,antimony,lead and uranium,the content of all other elements in the soil is significantly lower than Didymodon tectorum.According to the results of the determination of all elements,the Knop medium was optimized.The modified Knop liquid medium combined with 1.0 mg/L IBA and 0.5 mg/L 6-BA can obtain a large number of protons after 5 weeks.2.Promote the growth of Didymodon tectorum under 200 m M CaCl₂environment.The chlorophyll content of Didymodon tectorum is the highest under the environment of 200 m M CaCl₂.The content of MDA and Proline is the lowest and the activity of POD is the lowest.As same as,a clear thylakoid lamella structure can be seen,without accumulation of starch grains and osmiophilic granules.Conversely,higher or lower than 200 m M CaCl₂all lead to a decrease in chlorophyll content,an increase in MDA and Pro content,and an increase in POD activity.The chloroplast morphology is full but the accumulation of starch grains and osmiophilic granules appears.Especially in the 400 m M CaCl₂environment,the chloroplast morphology is destroyed.With the increase of the concentration of Ca²⁺in the medium,the rate of Ca²⁺efflux from the protons increased,and the rate of Ca²⁺efflux reached the highest under the treatment of 400 m M CaCl₂.When medium is lower than 200 m M CaCl₂,it promotes the absorption of Mg²⁺and the efflux of O₂.Under the treatment of 200 m M CaCl₂,the absorption of Mg²⁺and the rate of O₂efflux are the highest.When it is higher than 200 m M CaCl₂,Mg²⁺changes from absorption to efflux,and O₂changes from efflux to absorption.3.Under the high calcium concentrations of 300 m M CaCl₂,Ca²⁺accumulates in Didymodon tectorum.At the same time,transcriptome screening obtained 18348significantly differentially expressed genes.Under the treatment of 300 m M CaCl₂,the Ca²⁺fluorescence intensity in the protonema and gametophyte mesophyll cells of Didymodon tectorum increased significantly.Transcriptome sequencing analysis assembled 51961 unigenes,and screened out 18,348 significantly differentially expressed genes.There were 12,214 up-regulated genes and 6,134 down-regulated genes.Preliminary studies on the differentially expressed candidate genes found that Unigene DN6466 is predicted to encode serine/threonine kinase,subcellularly located in the chloroplast,and its expression is down-regulated in a high calcium environment.Unigene DN6689 is predicted to encode calmodulin-like protein CML25,which is subcellularly located in the cell membrane,and its expression is down-regulated in a high calcium environment.Unigene DN8859 is predicted to encode a voltage-gated calcium channel,which is subcellularly located in the chloroplast,and its expression is up-regulated in a high calcium environment.