The Effect Of NaCl Stress On Different Ploidy Watermelon Seedling And DNA Methylaiton Analysis

The activity of the antioxidase, the content of chlorophyll,the content of Na⁺、K⁺andCa²⁺were measured in different ploidy watermelon seedling including diploid （2x）, triploid （3x）and tetraploid （4x） under the concentration gradient level0、100、200、300、400mmol.L^-1NaCl.The changes of ultrastructure and molecular mechanism through MSAP after salt stress were alsostudied.The results would be provided theoretic basis for breeding, studying on salt stress inwatermelon. The main results were as follows:1. Changes of physiological biochemical character of different ploidy watermelon underNaCl stress.1.1The degree of impairment in different ploidy watermelon seedling under NaCl stress:Along with the increase of the salt concentration, watermelon seedlings suffer index also withincreased. Part of the2x plant had died, the suffer index reached6.03at the400mmol.L^-1 NaClconcentration. Damage degree in different ploidy was different under different NaCl levels, thesalt resistance was4x＞3x＞2x,through the analysis on morphological index.1.2The activity of SOD increased slightly along with the increase of stress days, it show thechange law first increased, then decreased of the ativity of SOD in different ploidy watermelonseedling, the change law of the ativity of SOD less effected by the change of salt concentration.The result showed that the change law of the ativity of SOD effected by planting conditions andvariety.1.3The change law of the ativity of POD in2x was not very remarkable under low saltconcentration stress. It increased observably along with the increase of stress days under high saltconcentration, and the ativity of POD achieved maximum on the eight day in the three ploidywatermelon seedling.The variation tendency in4x was the most obvious one in the three ploidy,atthe same time the ativity of POD in4x was the biggest,4x＞3x＞2x,it coincided with themorphologic indexes.1.4The change law of the ativity of PAL was not very remarkable under low saltconcentration stress, while it increased observably along with the increase of stress days underhigh salt concentration. The order of the ativity of PAL in three ploidy was4x＞3x＞2x, the resultalso showed that the change law of the ativity of SOD effected by planting conditions and variety.1.5The order of MDA content of the three ploidy was2x＞3x＞4x under salt stress, thechange law of the content of MDA in three samples were the same, polyploid had advantagesunder salt stress.1.6The change of chlorophyll content was not very remarkable under low salt concentrationstress, while it decreased observably with the increase of stress days in high salt concentration, the variation tendency in three ploidy was same, there wasn’t any different in different ploidy.2. The content of Na⁺was higher in4x than it in the2x and3x, the order of the content of K⁺was4x＞2x＞3x under high salt concentration,2x got more serious damage than4x because of itwas more sensitive to Ca²⁺, there were bigger K⁺/Na⁺and Na⁺/Ca²⁺ratio in4x than it in2x.3. The shape of chloroplast changed with the higher salt concentration,grana lamella becamelooser, chloroplast became shorten and round, the membrane structure damaged, the number ofosmiophilic particles increased. The more damage of chloroplast in the plant were increased inhigher salt concentration, the damage of2x was more bigger than3x and4x.4. The full methylation ratio, hemi methylation ratio and total methylation ratio all decreasedwith the increasing salt concentration, but the order of methylation ratio in three ploidy was2x＞4x＞3x at the same leavel salt concentration. The demethylation ratio decreased, while thehypermethylation ratio increased after the salt stress, the order of the rangeability was4x＞3x＞2x.