| PCD is very important for normal development of both animals and plants. It has been a new hot topic in the field of biology. Although it is not so good in plants as in animals, studies of PCD in plants have made a far progress in resent years, such as in morphology, biochemistry, genetic regulation and signal transduction. As one of the model plant, Arabidopsis thaliana plays a big role in plant study. In this study, we compared the differences between wild-type Arabidopsis and the AtDADl overexpression type in their phenotype, in their tolerance to hydrogen peroxide and the difference in sugar. The main results are as follows:DAD1 (Defender against Apoptotic Death1) is an evolutionarily conserved gene. It was first founded in hamster in 1997.Homologs of DAD1 have been proved to exist in other vertebrates such as human and mouse, invertebrates such as Xenopus and C.elegans, and in a variety of plant species. Its plant homologs have been cloned from Arabidopsis (AtDADl) , rice (OsDAD1) , pea(PSDAD1) , barley (HvDAD1) , citrus (CitDAD1) , apple (MdDAD1) , and tomato (LeDAD1) .But the functions of these genes have not been very clear. AtDADl {Arabidopsis thaliana Defender against Apoptotic Death1) has an open reading frame of 345 nucleotides starting with an ATG, a 25-nucleotide 5'untranslated region and a 192-nuclaertide 3' untranslated region. The complete peptide sequence is of 115 amino acids (calculated molecular mass: 12.7 kD).It is 48-49% identical (63% similar) to each of the vertebrate proteins and 46% identical (68% similar) to that of C.elegans.In this study, we found that the overexpression plant of AtDADl was strongerthan the wild type, especially in the young seedlings. For example, its leaves were a little bigger and a little thicker. But all of these were not much obvious.We compared the differences between the wild-type Arabidopsis thaliana and the AtDADl overexpression type in their tolerance to high dosages of H2O2 in this research , we found that when there was no H2O2 in the media, the germination rate of them was identical. On the 50 m mol / L H2O2 medium, the germination time of the wild type was latter than the overexpression and the germination rate was lower than the overexpression. When it was up to 100 m mol / L, both of these two types'germination was inhibited, but some of the overexpression type seeds still germinated. It has been inhibited completely when there was 150 m mol / L H2O2 in the 1/2 MS media. All of this proved that the transgenic plant was more resistant to H2O2 stress than the wild type.After the treatment of H2O (as a control) , the wild plant leaves and the transgenic plant leaves were both been dyed bright yellow-green fluorescein with FDA. It had little difference in color. After the treatment of I^C^, the colour of the wild plant leaves was much thinner than the colour of transgenic plant leaves. It may be inferred that AtDADl transgenic Arabidopsis leaf cell viability was stronger than the wild type under the treatment of H2O2.In our research, we have already compared the difference in sugar between the wild type plant and the transgenic plant. It was found that the latter was 1.4 fold to the first. It has been proved that sugar was important in leaf senescence and cell death previously. So, our result suggested AtDADl is perhaps related to sugar and then has some effect on Arabidopsisi resistance to PCD.
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