| In this thesis, two Jerusalem artichoke varieties (Nanyu No.1and Qinyu No.2) were conducted in soil pot experiments. Growth and physiological characteristics were investigated under30days’treatment of different concentrations of NaCl. Based on the above results, time course experiments were carried out to study the effects of salt stress on accumulation and distribution of dry matter and soluble sugar under2g-kg"1NaCl treatment. A1-FEH gene from Jerusalem artichoke was isolated and examined by heterologous expression of the cDNA in Pichia pastoris. Besides, the gene expression pattern analysis was then carried out in order to elucidate the regulation mechanism of fructan metabolism under salt stress. The results obtained were listed as follows:1. Compared with the control, the biomass of Jerusalem artichoke were not significantly changed under1g-kg"1NaCl treatment. When soil salinity goes up to2g·kg-1, biomass, chlorophyll content and net photosynthetic rate were significantly decreased, while the total soluble sugar in leaf were increased. Under2g-kg-1NaCl treatment, the biomass of Nanyu No.1and Qingyu No.2were decreased48.39%and59.05%, respectively; the biomass decreased65.8%and72.1%under3g·kg-1NaCl treatment, respectively. Compared with Qingyu No.2, Nanyu No.l had bigger stem diameter, more soluble sugar content in stems and leaves. On the contrary, Qingyu No.2maintained higher chlorophyll content and net photosynthetic rate in order to adapt to salt stress.2. Salt stress reduced tuber dry weight per plant of Nanyu No.l and Qingyu No.2by57.78%and85.61%, respectively. Tuber reduction was caused by two reasons: First, the dry matter accumulation and translocation in shoot were restricted; second, the dry matter accumulation rate in tuber was decreased. Salt stress changed the dry matter distribution between shoot and tuber:more distribution ratio of shoot but less tuber ratio.The effect of salt stress on tuber development was greater than shoot. Nanyu No.1had lower decreased degree of dry matter accumulation rate than Qingyu No.2under salt stress.3. In the time course experiments, the total soluble sugar content of stem was decreased under constant salt treatment, but its non-reducing sugar content was increased. The increase of non-reducing sugar in stem may be an osmotic adjustment strategy to salt stress, but it could limit the sugar traslococation in stem. During the period of tuber initiation (90-130d), tuber fructan content was increased under salt stress, but it was decreased during the period of tuber filling (130-210d). This result showed that salt stress induced the fructan synthesis in the stage of tuber initiation, but it limited the sustainable accumulation of fructan in tuber during the stage of tuber filling. Under salt stress, Nanyu No.1had lower decreased degree of tuber fructan accumulation rate than Qingyu No.2.4. The semi-quantitative RT-PCR analysis showed that the expression of1-SST and1-FFT in tuber were up-regulated by salt stress during the period of tuber initiation (90-130d) while down-regulated in tuber filling period (130-210d). The transcript level of1-FEH in leaf was enhanced after50days’ salt treatment and it suggests that1-FEH plays a role in physiological defense under salt stress.5. A1-FEH cDNA from Helianthus tuberosus (Ht1-FEH) was cloned by RT-PCR using specific primers based on the EST database. The Ht1-FEH encodes a polypeptide of560amino acids. The relative molecular mass and isoelectric point (pI) of the deduced polypeptide are calculated to be62.7kDa and4.86. The deduced amino acid sequence contains three conserved motifs (NDPN, RDP and EC) which are suggested be essential for β-fructosidase activity. Ht1-FEH shows96%and75%identity to sunflower cwINV1and chicory1-FEH I, respectively. The expression pattern analysis of Ht1-FEH revealed it was mainly expressed in sprouting tubers, while expression in development tubers, leaves, stems and roots was not detectable or only present at a low level.6. Functional characterization of the recombinant Ht1-FEH protein in Pichia pastoris showed that it could hydrolase inulin but not sucrose, demonstrating that the enzyme is indeed a fructan1-exohydrolase. |
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