| Natrium, the main ingredient and one of the indicators, is the essential microelement for the growth of most C4 and CAM and is profitable fof the growth of some C3 plants. If the salt concentration is too high, it will do such harm to crops as water stress, ion stress, membrane lipid peroxidation, physiological disorder. The crops themselves will adjust to the stress, which is called saline tolerance. The harm to crops caused by salt stress and mechanism of saline tolerance differ in different genotypes. This experiment was carried out in salt experimental plot and salt lake in seed multiplication farm in Dezhou agricultural research center in Shandong province; in principal lab and test center in Biology Department, Dezhou College; in principal lab in Shandong Agricultural University; and in national geological experiment and test center. With farmland, salt lake, sand culture and water culture in the lad, the systematically corns'mechanism of saline tolerance and different genotypes were studied. In 2004 and 2005, the 25 popularized corn crossbreed were planted in farmland, then analyzed the ability of different genotypes to saline tolerance, as well as the output under the salt stress. In the year 2005 and 2006, based on farmland planting, the experimenter picked out 6 crossbreeds with different ability to saline tolerance, put them in different concentration in salt lake, and therefore made a further analysis on the ability to saline tolerance and output. In 2006 and 2007, on the basis of growing in salt lake, the 2 corn crossbreed with different ability to saline tolerance chose out of the 6 were placed into labs by means of sand culture and water culture, and finally analyzed their biochemistry under the stress of NaCl. The major study results are as follows:1. Effect of salt stress on photosynthesis physiological characteristic on leaf and output of different genotypes of cornBy farmland planting, long term stress of NaCl in labs, the photosynthesis characteristic, the ability to saline tolerance of different corn genotypes and the output under salt stress were observed. The results showed that corn is sensitive; under salt stress, its growth is apparently restricted, net photosynthetic rate, chlorophyll content and root system energy are clearly declined, therefore, it causes the reduce in growth, plant height, leaf area, fresh weight and dry weight of each individual plant. Besides, the influence is greater in overground than in underground. So the root to shoot ratio becomes high. Amplitude of variation of Jundan 18 is greater than that of Denghai 9, which illustrated that different variety of corn have different abilities to saline tolerance; the tolerance is featured by genotype dominating and heritable.According to clustering analysis, among the varieties for experiment, Ludan 850 and Jundn 20 are the best genotypes for saline tolerance. Their output and index to saline tolerance are highest, and the control output is high, therefore, they can be adopted in both saline land and non-saline land. Zhongke 4 and Yuyu 22 are good genotypes; their output and control output are also high and the index to saline tolerance are up middling, so they can be used in non-saline alkali land and medium saline alkali land. Ludan 984 andLiaoyu 18 are also in the middle. Their output, control output and the index to saline tolerance are up middling. They can be selected in non-saline land and medium saline land. Denghai 9 is one with highest index to saline tolerance. Its output and control output are in the middle and it is the best choice in medium and grave saline land. Liao 93-1 has a comparatively high output, but has poor ability to saline tolerance, and salt stress exerts great influence on tassed sprouting and number of pollen. Under the condition that single variety is planted in large area, salt stress will have strong influence on output because of lack of pollen. Zhengdan 958 has highest control output but has poor ability to saline tolerance, and can be chosen in non-saline land and slight saline land. The output and the index to saline tolerance of Yedan 19 are the lowest. This variety has the worst ability to saline tolerance. It is best not to use this variety in saline land.2. The effect of salt stress on ion content of different genotypes of cornDifferent varieties of corn with different ability to saline tolerance germinated, grew in nutrient solution with various concentration of NaCl (0,50,100,150,200mmolL-1). ICP Mass was used to test the amount of Na+,K+,Ca2+ in the seed coat, embryo, albumen of germinated seed and the root , leaves of seedlings. The results showed that under stress of NaCl, the homeostasis of ion is broken. With the increase of concentration of NaCl in nutrient solution, the content of Na+ becomes higher, while the amount of K+ and Ca2+ is decreased. The variation and absolute amount in corn is: crown>root>embryo>seed coat>leaf>albumen. The amount of Na+ in crown, root, seed coat and leaf, as well as the amount of Ca2+ in crown, root and leaf are related to the ability to saline tolerance. All the seed coat, crown and root have the ability to regionalization of Na+, and the crown has the ability of retention of Na+. The leaves can refuse Na+, and the root has higher content of Na+ than the overground. 3. Effect of salt stress on antioxidant enzyme activity of different genotypes of corn and the relationship with output The experiment chooses the variety Denghai 9 which has ability to saline tolerance and the variety Yedan 22 which is sensitive to salt. In different salt concentration, the activity of SOD,POD,CAT, and the content variation of MDA as well as the relationship with output are analyzed in different stages, that is, trefoil stage, male tetrad, anthesis and grain filling stage. The results demonstrated that under salt stress, the activity of the three enzymes gets high with the increase of the concentration of salt. But then it gets lower after reaching a point. The activity of antioxidant of Denghai 9 is higher than that of Yedan22, which means that the activity of enzyme has positive correlation with the ability of saline tolerance. The content of MDA in Denghai 9 is lower than that in Yedan22, which means that the content of MDA has negative correlation with the ability of saline tolerance. The changes of content of MDA told us that with the increase of concentration of salt, the cell membranes of corn suffer more and that the variety with sensitivity to salt endures much more than the variety with ability to saline tolerance.male tetrad is the stage when SOD and POD are most active and the content of MDA is the lowest. It is also the stage that corn has strongest tolerance of salt. At this stage, the activity of SOD and POD has positive correlation with the concentration of salt. Anthesis is the stage when SOD is comparatively passive and POD is the most passive and the content of MDA is the highest. At this stage, the activity of SOD doesn't have positive correlation with the concentration of salt. Under salt stress, the plants growth is influenced, the output is reduced and the concentration of salt has negative correlation with the output. The variety with different sensitivity to salt receive different degrees of influence and their indexes to saline tolerance differ greatly.4. The changes of the membrane permeability and ultrastructure of mesophyll cell of corn lamina under salt stressMaize cultivars of different salt-sensitive was grown under the stress condition of NaCl(0,50,100 mmolL-1)nutrient solutions, and thereby the changes in membrane permeability were measured and the biomembrane ultrastructural changes of mesophyll cells were observed using transmission electron microscopy.The experiment results showed that the membrane permeability of mesophyll cell increases and the number of mitochondrion becomes large under NaCl stress. Under subsalt (50mmolL-1NaCl) stress, all kinds of membrane structure of mesophyll cell are slightly hurt. Under higher concentration of salt stress(100mmolL-1), cell wall, all kinds of membrane structure such as cytoplasmic membrane, karyotheca, vacuole membrane, chloroplast and mitochondrion were destroyed; even the whole cell vanished. The results above showed that biomembrane, especially the membrane structure of chloroplast, the destruction is closely related to the final death of mesophyll cell under salt stress.Under salt stress, the hurt of mesophyll cell of corn lamina was not synchronous. Some of the cells were completely vanished while some neighbor cells are only slightly hurt. This phenomenon wes not outstanding in variey sensitive to salt.As for different genotypes, the differences of membrane permeability are not obvious. The hurt of biomembrane of sensitive corn variety to salt was slightly hurt.5. The regulation and control of 5-SA to sprout of seeds and growth of seedlings of Maize under salt stressBy the experiment of seed sprout,the effect of 5-SA on sprout of seeds and growth of seedlings of corns with different genotypes under NaCl stress were studyed.The results suggested that salt stress severely restrict the growth of sprout of seeds and the growth of seedlings of corns. Using5-SA can remit the restriction of salt. The rate of spout is highly increased. The root and bud grow obviously. With the increase of concentration of 5-SA, the release is also improved. But it declines after getting to a point. The seeds cannot even burgeon. 0.1-1.0mmolL-1 is best to improve the sprout of seeds and growth of seedlings. When it has high level of salt, 5-SA's optimum concentration is the lowest; while in low level of salt, its optimum concentration is the highest. The stimulation of 5-SA to Denghai9, which is a variety with saline tolerance, is greater than that of Jundan18, which is sensitive to salt. Since salt stress exerts greater influence on the overground than the underground, it is also true with 5-SA's function.6. The effect of NaCl stress on the amount of organic osmoregulation matter of the aboveground part of corn seedlings with different genotypesUsing different genotypes of corn with various abilities to saline tolerance as the material, the amount of soluble sugar, proline and free amino acids overground were measured under NaCl stress.The results showed that under salt stress, the amount of soluble sugar and free amino acids increases, but soluble sugar doesn't increase much, free amino acids amplitude is high, especially proline has the highest amplitude. The absolute value of content and amplitude of variety with saline tolerance is higher than that of the variety with sensitivity to salt. |
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