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Comparison Of Adaptation Mechanism To Alkali Stress And Salt Stress In Sunflower (Helianthus Annuus L.)

Posted on:2012-04-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:J LiuFull Text:PDF
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Soil alkalization is becoming increasingly prominent, and its destructive power is greater than soil salinization. Salt stress and alkali stress are two kinds of stresses not only in aspects of their effects on plant, but also in the response of plant to them. Sunflower is the only oil crop under alkaline condition, but the tolerance, especially, the mechanisms of alkali-tolerant have not been reported systematically. In this paper, our experiment formation is different from the previous laboratory experiment, to be closer to natural conditions. In this study, we firstly simulated saline and alkaline conditions, and then the sunflower seeds-baikuiza 6-were sowed and stressed under salt stress and alkali stress. We analyzed the effects of salt stress, alkali stress and salt-alkaline mixed stress on sunflower and eco-physiological adaptive mechanisms of sunflower to its salt-aklaline habitat. Major experiment results and conclusions were as follows:1. Effects of salt stress and alkali stress on seed germination and seedling survival in sunflowerIt is a critical statge of plant from seed germination and seedling growth to adapting to saline and alkaline environment, and to some exent which decide whether plant can live and reproduce or not. Our experiment showed the emergence time was delayed under salt stress when≤120mM,but the emergence rate and seedling survival rate did not decrease significantly. With increasing stress intensity, the emergence rate and seedling survival rate delayed signigicantly. Under alkali stress, the emergence rate and emergence time did not change, but the seedling survival rate decreased sharply, even when salinity was 60 mM,the seedlings were all died under alkali stress. This indicated the effects were significantly different among different growth stages under alkali stress. High pH did not interfere with seed water absorption, but was directly on the root cells when radicel borke through seed coat and destroyed their stucture and function, and led to increase in toxic ions, making it difficult to seedlings. This showed high pH caused by alkali stress was main factor to limiting seedlings.2. Effects of salt stress and alkali stress on growth and photosynthesis in sunflowerAlthough some seedlings could survive under salt stress and alkali stress, photosynthesis and growth were inhibited, and the inhibition was greater under alkali stress than that under salt stress. The decreases of dry matter, leaf area, height, net photosynthetic rates, stomatal conductance and transpiration rates under alkali stress were greater than those under salt stress. By analyzing the photosynthetic electron transfer processes (chlorophyll fluorescence parameters), we found alkali stress damaged the photosynthetic systemⅡ, and reduced the efficiency of photosynthetic electron transport, but salt stress did not. These data indicated that high pH damaged the photosynthetic systemⅡand interferred photosynthetic electron transport, this might be the main reason that PN was lower under alkali stress than that under salt stress.3. Effects of salt stress and alkali stress on mineral nutrition in sunflowerThe experimental results indicated that the accumulation of mineral elements was markedly different under salt and alkali stresses. The contents of N, P, S and Fe did not decrease, but increased under salt stress; while contents of almost all mineral nutrients declined under salt-alkaline mixed stress. It was clear that mineral nutrition deficits was a main reason that the inhibitions of growth and photosynthesis under alkali stress were more severe than those under salt stress.4. Effects of salt stress and alkali stress on osmotic adjustment and ion balance in sunflowerWe compared the contributions of various osmolytes under stress. The results showed K+ was the main inorganic osmolyte in shoots, but the solute sugar was the main organic osmolyte in sunflower. At moderate stress, it may be a special mechanism which controls Na+,K+ transport in the roots of sunflower. Sunflower roots could control Na+ but promote K+ transfer to leaves, maintaining low Na+ high K+ status of leaves. This may be the main reason that sunflower is the relative salt and alkali-tolerant crop. Alkali stress especially high alkali stress could cause ion imbalance and pH instability, and sunflower synthesized organic acids to keep ion balance and adjust pH.5. The response characteristics of DNA methylation in sunflower under salt stress and alkali stressThe results showed the DNA methylation in leaves were much higher than that in roots and the simultaneous CG/CHG methylation was the main pattern. Under two stresses, the roots had greater variation than that in leaves. Moreover, the methylation variation of roots and leaves were both concentrated in CG/CHG sites. Because the roots have contact with various soil stresses directly, and can feel and transport the signals, and then make the adaptive responses quickly. DNA methylation patterns in roots were different from in leaves, and the variation was significantly greater than that in leaves. Those proved that DNA methylation might be directly involved the signals generation and transminssion in roots and the regulation of the roots on DNA level was faster and more complex than that leaves. In addition, the DNA methylation variations in roots and leaves under alkali stress were both significantly greater than those under alkali stress, this proved salt stress and alkali stress were two kinds of stresses once again. The regulation of sunflower roots is a key in alkali-tolerant, and DNA methylation plays an important role in the regulation processes, but the mechanisms deserve further investigation.
Keywords/Search Tags:Sunflower, Salt stress, Alkali stress, Photosynthesis, Mineral nutrition, Ostomic adjustment, Ion balance, DNA methylation
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