Salt Tolerance Evaluation Of Taxa From Chrysanthemum And Its Relative&the Stugy Of Salt Tolerant Mechanisms Of Dendranthema

Chrysanthemum(Dendranthema grandiflorum (Ramat.) Kitamura), 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. Serious impact on soil salinization in chrysanthemum production and quality, and breeding new varieties of salt tolerant has therefore become an important goal of chrysanthemum breeding. Wild species germplasm resources often carried some important resistance that lack in cultivars is an important basis for resistance breeding materials. In order to discover the salt tolerant germplasm in Dendranthema, an evaluation system for salt-tolerance of Chrysanthemum was established. The paper also explores its salt mechanism for promoting innovation and new chrysanthemum varieties of salt-tolerant germplasm breeding foundation. The main results are as follows:Four species from Dendranthema and its relative genera were studied, the proper screening concentration of NaCl was determined as120mmol.L"1among NaCl at different concentrations of0,40,80,120,160and200mmol.L-1according tothe ratio of injured leaf area per plant, and salt tolerance of32species from Dendranthema and its relative genera were screened. Hierarchical clustering analysis showed that32taxa could be divided into extremely salt tolerant, salt tolerant, moderately salt tolerant and salt sensitive grade, respectively. Artemisia japonica, Aster spathulifolius, Crossostephium chinense are extremely salt tolerant, Tanacetum vulgare and Chrysanthemum crassum are salt-tolerant, seven taxa represented by Artemisia vulgaris, Leucanthemum vulgare are moderately salt tolerant,20taxa represented by Dendranthema zawadskii, D. chanetii, D. vestitum, D. lavandulifolium are salt sensitive ones. Salt tolerance screening of plants from Dendranthema and its relative genera can be achieved effectively and rapidly by morphological indexes.The content of chlorophyll, proline, malondialdehyde, relative leaf water, K+and Na+, net photosynthesis rate etc.,15indicators of NaCl stressed and unstressed seedlings of13taxa from Dendranthema and its relative genera were measured. The relation between these physiological traits and morphology injured index were analysed, the results showed that among45variables, dry and fresh weight plus the ratios of K+Na+of unstressed plants, and the content of chlorophyll a, total chlorophyll, relative leaf water, malondialdehyde, proline, dry and fresh weight, relative value of chlorophyll a, chlorophyll b, total chlorophyll, malondialdehyde, proline, net photosynthesis rate of salt stressed seedlings, all14variables were significantly or highly significantly correlated with morphology injured extent. And it can be the indicators of comprehensive evaluation of salt tolerance of Dendranthema and its relative genera.Applying principal component analysis and subordinate function value analysis comprehensive salt tolerance evaluation of the material were made. Four multiple-linear regression equation between the comprehensive evaluation value of salt tolerance and physiological traits of salt stressed and unstressed seedlings, relative value(index after stress/index without stress) and variables including aforementioned three group index were established separately. The salt tolerance prediction of tested species used the established equation were highly consistent with comprehensive salt tolerance evaluation value. The predict effect by using ratios of K+/Na+of unstressed plants, chlorophyll content and proline content of plants being stressed is best among4regression equation, so, we suggested that the three indexes could be used to predict the salt tolerance in Dendranthema and its relative genera in seedlings.The effects of NaCl stress on the chlorophyll contents, photosynthetic gas exchange parameters and injury degree of two species of Dendranthema with different salt tolerance, i.e., Dendranthema crassum and D. ornatum were investigated. The results showed that under salt stress, Chl content decreased in two species. The net photosynthetic rate, stomatal conductance and transpiration rate declined significantly, while intercellular CO2concentration increased in the both species under salt stress. However, MDA content increased under salt stress. The inhibiting effect of D. ornatum was significantly greater than that of Dendranthema crassum. The partly cause of salt tolerant is that Dendranthema crassum under salt stress could keep the total chlorophyll contents stable, maintain the net photosynthetic rate stays at a certain level, and keep membrane system in relatively perfect working order. In the reasons for the decline in photosynthetic rate of two species of Dendranthema, non-stomatal limitation has always played a role, the stomatal limitation of D. ornatum began to affect photosynthesis when the stress concentration reached to120mmol.L-The ratio of injured leaf area per plant of two species increased, and the ratio of new developed leaf area per plant decreased, leaf relative electricity conductivity increased. Dendranthema crassum showed slighter injured symptom under NaCl stress than D. ornatum. The Na+and Cl-content in seedlings of two species, also the K+content in stem and new developed leaves increased as the NaCl concentrations increased, the Na+and Cl+accumulation in upper part of the seedlings was more than the amount in root. Na+and Cl-were primarily concentrated in mature leaves. Compared with salt tolerant D. crassum, the salt sensitive D. ornatum showed high Na+and Cl-accumulation in every organ, and its growth showed much correlation with the Na+and Cl-content in its organ. The ratios of K+/Na+in different parts of D. crassum seedlings were higher than D. ornatum’s except the ratio in root under severe NaCl stress. D. crassum had a higher transportation selectivity of K+to Na+from root to stem, a lower of K+to Na+from stem to middle mature leaves under same salinity, and a higher K+to Na+from stem to upper new developed leaves under high NaCl salinity. That D. crassum accumulate lower Na+and Cl-, retained more Na+in root, be able to maintain ratios of K+Na+well, and have lower transportation selectivity of Na+from stem to upper leaves were the main reasons for the stronger salt-tolerance of it, while the higher transportation selectivity of Na+from stem to middle mature leaves was one of mechanisms of accommodation to salt stress. Cl-influenced D. ornatum’growth little more than Na+from multiple-linear regression analysis.By the method of X-ray microanalysis, the effects of different concentration NaCl on the absorption, transportation and compartmentalized distribution of K+, Na+and Cl-on the sub-organ level of2species of Dendranthema seedlings were studied, The results showed that under NaCl stress the Na+and Cl-accumulation in every part of the leaf and stem was more than the amount in root. Compared with D. crassum, D. ornatum showed high Na+and Cl" accumulation in every part of each organ, more section of Na+were stored in the inner cortex and marrow of its stem, while less Na+were inpoured into the vessels, as a result the Na+transported to leaves become less. Except for the of leaves and roots, outer and middle in root, K+/Na+was higher than the value in D. ornatum, Ca2+/Na+of every part in D. crassum, was also higher than the amount in D. ornatum, Except for the marrow in stem, which suggested that the ability of maintaining ion balance in D. crassum is better than that in D. ornatum. Both Na+and Cl-were withheld by cortex as their were transport Laterally from epidermis to stele in two species, but D. crassum could retained more Na+in root cortex and possess the ability of withholding Na+but not for Cl-when ion were transported vertically from root to stem, while neither Na+nor Cl-was observed being withheld in root of D. ornatum. The disparity of Cl-content between two species is great than the Na+content, also the retardarce of Cl-transport in cortex to stele is more remarkable than the Na+, which indicated that the difference of absorption and compartmentalized distribution of Cl-may explain the difference of salt resistance.When the seedlings of D. crassum and D. ornatum were treated with NaCl, soluble amino acids, the content of soluble sugar and the contents of Na+and Cl-in leaves all increased with salt concentration increased, Ca2+、Mg2+、NO3-decreased and K+was first increased and then decreased. Overall, the contribution of inorganic ions to osmotic adjustment in leaves was greater than the organic osmotica, and Na+and Cl-played the most important role. In organic osmotica, though the content of soluble sugar was much higher than soluble amino acids, increase extent of them were similar after stress. The Na+/K+and Pro/AA value of two plants also increased after the stress. The measured osmotic potential (MOP) of D. crassum is bigger than computational osmotic potential (COP), which implies that there still exists other osmotic in the plants except for the8osmotica determined in the experiment. Osmotic adjustment ability of salt-sensitive D. ornatum was much stronger after salt stress, which implies that the salt tolerance of D. crassum was stronger than D. ornatum was not the result of osmotic adjustment ability.The effects of long term (68d) NaCl stress on the compartmentalized distribution of K+, Na+and Cl-on the organ level of4salt tolerant taxa from Dendranthema and its relative, Dendranthema crassum, Tanacetum vulgare, Aster spathulifolius, Crossostephium chinense seedlings were studied, The results showed that after NaCl stress, no obvious injured symptom were exhibit in4species, and the Na+and Cl-content of4species increased significantly in comparison with the control, also the content were higher than the amount in salt sensitive D. ornatum when the plant exhibit chlorosis. Na+and Cl-accumulation in the leaf was more than the amount in root. The Na+and Cl-content of stem, lower leaves and mature leaves were highest among different organs. Compared with Na+distribution, the distribution of Cl-among different organs were more balanced. The content of K+and ratio of K+/Na+decreased, significantly in comparison with the control, but the K+/Na+on active metabolic organs remained on a higher value. That these four species accumulate lower Na+and Cl-in root, absorb more KT from environment, retained more Na+in root, be able to maintain ratios of K+/Na+well, and have higher transportation selectivity of K+from stem to upper leaves were the main reasons for the stronger salt-tolerance of them. while the higher transportation selectivity of Na+from stem to middle mature leaves was one of mechanisms of accommodation to salt stress. Cl-influenced D. ornatum’ growth little more than Na+from multiple-linear regression analysis. The ability of Cl-absorption on Aster spathulifolius, Crossostephium chinense was lower than other two species, while the ability of Na+absorption of Tanacetum vulgare was lowest among these four species. So the difference on the strategy of ion absorption and compartmentalized distribution of plants may play an important role on the mechanism of salt resistance.Leaf thickness became thinning and the characters of isobilateral leaf disappeared or weakened in Tanacetum vulgare and Crossostephium chinense under prolong stress, but in D. crassum and Aster spathulifolius, the character of salt-dilution is obviously, such as thicken mesophyll and parenchyma tissue and increased cell volume. Under shot-term stress, the cells collapsed lending to distortion of organ morphology, reducing the number of cells in the chloroplast and distortion of organ morphology in Salt-sensitive species D. ornatum. Relative leaf water content in Aster spathulifolius and D. crassum increased while decreased in Tanacetum vulgare and Crossostephium chinense and maintained a high level under long-term stress.