| In the natural evolution of plants history, genome duplication is a very important way to adapt to the environment. More genetic information could be stored when the genome increased that plants could survive better, however, it was not that the larger genome the better for plants. To verify the drought resistance in different ploidy rice, the same naturally occurring sources of haploid, diploid and triploid rice were used in this study, the changes of the soluble sugar (SS), soluble protein, free proline, malondialdehyde (MDA) and abscisic acid (ABA) content in different ploidy rice, and the activity changes of Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) were studied, by simulated natural drought stress. And Six ABA-related genes,OsCIPK15,Polcalcin,OsGASA2,OsCBL4,Myb and WGP1 in different ploidy rice were evaluated under drought stress by real-time fluorescence quantitative PCR. The results were:1. The proportion of yellow leaves were analyzed under drought stress, there were 81% leaves turn yellow in haploid, diploid were 37% and triploid were 45%. It inferred that the order of the drought resistance in different ploidy rice was diploid> triploid> haploid.2.7 drought resistant related physiological indicators were analyzed, the results were:the soluble sugar (SS), soluble protein, free proline, malondialdehyde (MDA) and abscisic acid (ABA) content were increased, and the SOD, POD and CAT activity were increased under drought stress. In the treatment group, Soluble protein in peak time were 2.12 times(N), 2.08 times(2N) and 1.45 times(3N) of the control group, soluble sugar in peak time were 1.38 times(N),1.41 times(2N) and 1.18 times(3N) of the control group, free proline in peak time were 2.65 times(N),4.31 times(2N) and 3.30 times(3N) of the control group, MDA in peak time were 3.44 times(N),2.57 times(2N) and 2.94 times(3N) of the control group, SOD in peak time were 1.41 times(N),2.05 times(2N) and 1.77 times(3N) of the control group, CAT in peak time were 1.15 times(N),1.44 times(2N) and 1.16 times(3N) of the control group, POD in peak time were 1.88 times(N),1.86 times(2N) and 2 times(3N) of the control group. So the drought resistance of the haploid rice was weaker than that of diploid and triploid, diploid was stranger than triploid.3. Quantitative RT-PCR analysis showed, in the control group, diploid's WGP1 and OsCIPK15 genes expression level were high, were haploid's 3.74 and 3.04 times, triploid 5 's WGP1 gene expression was highest, was 12.83 times of haploid. the expression of haploid OsGASA2 gene was higher than diploid and triploid. Under drought stress, compared with the control group, the expression of OsCBL4 gene in haploid was increased, other genes expression did not change significantly, the expression of Myb and WGP1 gene in diploid decreased, the expression of OsCBL4, OsGASA2, and OsCIPK15 gene was increased, Polcalcin gene expression did not change significantly, the expression of Myb and WGP1 gene in triploid decreased, the expression of OsCBL4, OsGASA2 and OsCIPK15 gene was increased, Polcalcin gene expression did not change significantly.Based on the known results, in adverse circumstances, the drought resistance of diploid was strongest, because in the stress condition the content of the soluble sugar, soluble protein, free praline increased much more than others, and the MDA which reflects the degree of membrane damage was lower than any other. As a common choice for most species in nature, the gene expression of diploid perfectly adapt to the present natural environment. But the triploid had one more set of chromosome, maybe cause the coordination of gene expression weaker than the diploid. As there was only one set of chromosomes in haploid, the severe shortage of biomass, lower output of osmotica and protection enzymes, made it weaker than others. So we can draw the conclusion that the order of the drought resistance of different ploidy rice is diploid> triploid> haploid.
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