Mechanism Analysis Of Chrysanthemum Crassum Responsing To Stress And Leave Incrassation Under Salinity Stress

As one of the Chinese ten traditional flowers and world four cutting flowers,Chrysanthemum(Chrysanthemum morifolium)possessing great ornamental and economic value.As the changes of climate and environment and the abuse of chemical fertilizer,the soil salinization of China is getting more and more serious,which is disturbing the survive and growth of chrysanthemum.And in general,the salinity tolerance of ornamental species of Chrysanthemum is weaker than some related species of Dendranthema,so the study of the mechanism and functional genes of related species of Dendranthema under salinity stress would provide the reference and guideline to how improve the salinity tolerance of ornamental species of Chrysanthemum.Chrysanthemum crassum is one of the related species of Dendranthema that habitated in areas nears the sea,which possessing remarkable salinity tolerance and can survive and maintain growth under 200mM NaCl conditions.Our research studied the physiological and morphological changes made by C.crassum under salinity stress,and sequence the total RNA of it after salt treatment,illuminated the strategies and dug out functional genes that help the C.crassum adopt the salinity stress.Here are the main results:1.Treated with 0,80,120 and 200mM NaCl,the stressed plants displayed the delay of growth rate compared with the control,and there is no significant difference among 80,120 and 200mM NaCl treated plant.Planted in 120mM NaCl for 30 d,we found that the growth rate of stressed plants were delayed and their leaves displayed incrassation and expansion compared with the control.The paraffin sections showed that the leave incrassation were caused by the expansion of leave cells.By the leave surface observation,we found that the leave epidermal cells expanded,the stoma destiny decreased.We also used the scanning electron microscope(SEM)to observe the detail of the leave surface and found that the wax layer became thicker,trichome dropped off,and glands cracked under salinity stress.Additionally,besides leaves,some tissues have better plasticity like petiole also displayed incrassation under salinity,which also caused by the expansion of cells.2.We measured some physiological changes of C.crassum leaves after salt treatment.After salt treatment,the activity of ROS-scavenging enzymes were increased immediately and recovered to a lower level gradually.After salt treatment,the Na+ content increased and the increasing rate became slowly as time goes by,and the Na+ accumulated in base leaves priorly;the K+ content in base leaves increased slightly,while changed little in the top leaves;the Ca2+ content in base leaves decreased significantly,while changed little in the top leaves.After salt treatment,the hormones of functional leaves displayed that,the content of ABA and IAA increased,and GA decreased;in the base leaves,the content of ABA increased and IAA and GA decreased;in the top leaves,the content of IAA increased,and ABA and GA just changed slightly;in the top buds,the content of ABA and IAA increased,and GA decreased.After salt treatment,the content of water,lipoclastic,and hydrotrope matters increased significantly,and content of polysaccharides that make up to cell wall like cellulose,pectin,and lignin decreased.3.We collected the samples after 0 h,12 h,and 24 h salt treatment,extracted the total RNA and run the RNA sequencing.Following de novo assembly,154,944 transcripts were generated,and 97,833(63.14%)transcripts were annotated,including 55 Gene Ontology(GO)terms and 128 Kyoto Encyclopedia of Genes and Genomes(KEGG)pathways.The expression profile of C.crassum was globally altered after salt treatment.We selected functional genes and pathways that may contribute to salinity tolerance and identified some factors involved in the salinity tolerance strategies of C.crassum,such as signal transduction,transcription factors and plant hormone regulation,enhancement of energy metabolism,functional proteins and osmolyte synthesis,ROS scavenging,photosystem protection and recovery,and cell wall protein modifications.Forty-six genes were selected for quantitative real-time polymerase chain reaction detection,and their expression patterns were shown to be consistent with the changes in their transcript abundance determined by RNA sequencing.