Research Of Photosynthetic Physiology And Leaf Thickening Of Chrysanthemum Crassum Under Salt Stress

Chrysanthemum(Chrysanthemum grandiflorum Ramat.),one of ten traditional flowers and one of four the world's major cut flowers,is widely cultivated for ornamental purposes,which plays an important role in modern flower production.Soil salinization has seriously affected the production and quality of chrysanthemum,and breeding new varieties of salt tolerant has therefore become an important goal of chrysanthemum breeding.C.crassum as a salt-tolerant species,exploring salt tolerance mechanisms of it can lay the foundation for enhancing the salt tolerance of chrysanthemum,and promote breeding new chrysanthemums varieties of salt tolerance.The main results are as follows:1.C.crassum(salt tolerant)and C.ornatum(salt sensitive)were took as test materials to research the effects of NaCl on plant growth,photosynthesis and chlorophyll fluorescence characteristics.The results showed that,salt stress inhibited plant growth,decreased pigment content of leaves.And Pn,Tr,Gs decreased gradually as time passed by,while Ci gradually increased.Under NaCl stress,Fv/Fm,qP and ?PS II of C.crassum decreased slightly,?NPQ and qN increased significantly,?NO was unchanged,and chloroplasts were hardly damaged.For C.ornatum,Fv/Fm,qP,?PS ? and qN declined,?NPQ was unchanged,?NO significantly increased and chloroplast structure was irreversibly damaged.Compared with salt-sensitive C.ornatum,ABS/RC and TR0/RC of salt-tolerant C.crassum under salt stress increased less,RC/CS0 decreased less,OEC on the PS ? donor side and electronic transfer were slightly damaged,cpR0,Plabs and PItot also declined slightly.Therefore,under salt stress,C.crassum can alleviate the damage of excess energy on the photosynthetic mechanism by increasing the thermal dissipation,maintaining the integrity of chloroplast structure,ensuring the orderly conduct of photosynthesis,making the plants to grow up slightly slowly,which is one of the important reasons it can resist salt stress.2.Changes of part of photosynthetic characteristics and antioxidant enzyme activity under long-term salt stress were investigated.The results showed that after 60-days stress,the height,stem diameter,root length,fresh and dry weight and leaf area were significantly decreased,the leaves were significantly thickened,and chloroplast structure was seriously damaged.Besides,its carboxylic efficiency and maximum net photosynthetic rate decreased first and rised then fell again,while the CO2 compensation point showed the opposite trend.And the activity of antioxidant enzymes showed a tendency to rise after the first drop.The results indicated that in the early stage of salt stress,antioxidant enzymes can protect plants to some extent,to ensure the conduction of photosynthesis.But after long-term salt stress,antioxidant enzyme activity decreased,which caused damage to plant growth.3.The effect long-term of salt stress on the leaf structure of C.crassum was studied including the reasons.The results showed that the leaves of C.crassum covered with trichomes and vesicles and long-term salt stress lead to significant thickening of its leaves.Then the paraffin sections showed that the direct cause of C.crassum leaf thickness was cell stretch also with the volume increasing,but mesophyll cell layers unchanged.The increase of cell volume was presumably due to cell wall expansion casused by IAA content increasing and expansion gene upregulation after salt stress.