The Studies Of DNA Methylation Occuured In Alkali-resisitant Halophyte Chloris Virgata And Glycophyte Cotton Under Kinds Of Salt And Alkali Stresses

Soil salinization and alkalization is a worldwide environmental problem, and isdrawing more and more people’s attentions. Soil salinization and alkalization is oftenco-occurred in nature. Many studies have proved that salt stress and alkali stress aretwo different stresses with different properties, they have different effects on plantgrowth and physiology, and the mechanisms that plants reacted to them are alsodifferent. Although there were many reports about the resistance mechanism of C.virgata and cotton, most of them concentrated in the physiological response. Therewas still no study about the effects on plant DNA methylation of salt stress and alkalistress. Chloris virgata is a kind of alkali-resistant halophyte, while cotton is a kind ofimportant economic glycophyte. Two kinds of salt and alkali stresses were used in thispaper, and we discussed the resistance mechanisms of C. virgata and cotton fromphysiological response and DNA methylation response, and the experiments werebased on two organ levels that were leaf and root. The main results and conclusionswere as follows:1. Salt stress and alkali stress have different effects on ionic balance and osmoticregulation of C. virgata under different treated time.Two kinds of neutral salts （NaCl and Na₂SO₄） and alkaline salts （NaHCO₃andNa₂CO₃） were used to treat C. virgata seedlings. By comparing the different effects onphotosynthetic pigment, ion content and organic acids content, we found that Na⁺increased with the increased treated time of both stresses, and the increasment underalkali stress was more obvious. K+content didn’t change under both stresses. Thecontents of anions were decreased with the increament of treated time of alkali stress.The mainly accumulated organic acid was succinic acid to adjust the long-term saltstress, and was citric acid to adjust long-term alkali stress. Overall, alkali stress hadmore significant influence on C. virgata than salt stress, and the effects were more andmore significant along with the extension of the treated time.2. Compared with salt stress, alkali stress had more significant influence on DNAmethylation of C. virgata and cotton.Two kinds of neutral salts （NaCl and Na₂SO₄） and alkaline salts （NaHCO₃andNa₂CO₃） were used to treat C. virgata seedlings, and through the analysis of MSAP（methylation sensitive amplified polymorphism） technology, we found that DNAmethylation variation frequency was0-0.24%in leaf and0.09-1.85%in roots undersalt stress, while DNA methylation variation frequency was0-0.41%in leaf and0.09-5.48%in roots under alkali stress. In cotton we also found that salt stress had noeffect on the overall level of methylation, while alkali stress significantly decreasedthe overall methylation level. The total variation frequency was1.38%in leaf undersalt stress, and the frequencies were2.20%in root respectively. Meanwhile, the total variation frequency was2.59%in leaf under alkali stress, and the frequencies were11.44%respectively.Therefore, this experiment confirmed that salt stress and alkali stress are reallytwo different stresses from the point of DNA methylation. The effect of the alkalistress on plant DNA methylation was more serious with higher pH value. Under thelong-term salt and alkali stress, plants could regulate stress-related gene expressionthrough DNA methylation, which has no impact on the DNA sequence and genomestability. It was also a quick response to stress and a kind of evolution model with theleast effect on plant genome.3. Four kinds of single salt and their mixed salt had significantly different effectson C. virgata DNA methylation.Using four kinds of single salt （NaCl, Na₂SO₄, NaHCO₃, Na₂CO₃） and the mixedfour salts （molar ration was1:1） to treat C. virgata seedlings, and through theanalysis of MSAP technology, we found that alkaline salts （NaHCO₃and Na₂CO₃）,had more significant effect than neutral salts （NaCl, Na₂SO₄）. After the treatment ofthe mixed four salts, the influence in the leaves was much more serious than neutralsalts and alkaline salts, while in root it showed a soothing effect. According to thedifferent properties of different anions, all the methylation variation were classifiedinto8types: Na⁺specific bands; Cl-specific bands; SO42-specific bands;HCO₃-specific bands; CO₃2-specific bands; Mix specific bands; Higher pH specificbands; SS （neutral salts specific） bands. The main variation bands were Mix specificbands in leaf, while that were high pH specific bands in roots. This article showed thatalthough four kinds of single salt were sodium salts, but they had different influenceon DNA methylation because of its specific anion, and the mixed four salts hadcomplex effects on plants, there were some alleviation effects, and the impact ofhigher pH in the soil surrounding root was significant.4. Under salt stress and alkali stress, DNA methylation variation was moremarked in roots.The variation frequencies occurred in C. virgata and cotton showed that nomatter in a neutral salt stress or in alkaline salt stress or in single salt stress or inmixed salt stress, the phenomenon of DNA methylation variations was more markedin root than in leaf. And among all the methylation variations, the hypomethylationwas the main type. In salt and alkali environment, roots was the primary organ whichcontacted directly with ion poison and osmotic pressure, it’s responses to the outsidestresses were more directly and quickly than other organs. The lower DNAmethylation level and the higher variation frequencies in root justified the importantrole of root in the process of adjusting alkali stress.