Isolation And Expression Of Key Genes Relating To PAs Biosynthesis And Response To Stresses In Malus Hupehensis(Pamp) Rehd

Annual seedlings and 3-years-old trees of Malus hupehensis were used as materials in this experiment. Have cloned three genes which were key enzymes in the polyamines synthesis in plants, such as arginase, arginine decarboxylase and ornithine decarboxylase. Studied this genes transcription levels in different development stages and different tissues in Malus hupehensis. Discussed the principal way of the polyamines biosynthesis under heavy metal and salt stress. Studied the effects of exogenous polyamines in alleviating the damage under heavy metal stress. The results as follows:1. Designed primer pairs based on highly conserved nucleotide sequences of other plant genes previously submitted to the Genebank database. We have cloned arginase, arginine decarboxylase and ornithine decarboxylase genes using RT-PCR and RACE technology. And we named these three genes MhArg, MhADC and MhODC, and submitted them in Genebank, the accession numbers is EF427896, EU431331 and EU431332 respectively.2. The MhArg had high levels when the stored nutrition hydrolyzed to soluble proteins. And the MhADC and MhODC had high expression levels in the young tissues.3. The ADC gene transcription levels increased under salt stress, and it had highest transcription levels after 6h treatment in leaves and 3h in roots. The impact of salt stress on the ADC gene expression levels is very little, however, the expression levels had a marked increase in roots after 12h treatment. Put can be accumulated in the plants under salt stress. And the Put content can achieve a peak after 12h treatment, however the content of Spd and Spm were decreasing. The heavy metal stress induced the ODC gene expression markedly, however, it could not induce ADC gene expression. The plants could accumulate Put under heavy metal stress, and the Spd content was decreased, the Spm content was not changed. The ADC pathway may be the main way to synthesis Put in Malus huspehensis under heavy metal and salt stress. Compared to salt stress, the ODC pathway may play a more important role under heavy metal stress. 4. Foliar spraying Spm or Spd in Malus hepehensis under CdCl2 stress significantly increased the content of endogenous Spm and Spd, and significantly decreased the content of endogenous Put, so can markedly increased the content ratio (Spd + Spm)/Put. That can keep the membrane stability and reduce the active oxygen generation through promoting the oxidant enzyme activity or/and scavenging active oxygen directly, so alleviate the lipid peroxidation under CdCl2 stress.