| Soil salinization and drought are the mainly environmental factors, which can severely limited the growth and development of a large amount of higher plants worldwide, especially displayed more obvious for crops. Desert xerophytes Zygophyllum xanthoxylum that grow well in extreme arid region can compartmentalize Na~+ into vacuolars by topoplast Na~+/H~+ antiporter. The process is not only protects the cytoplasm from Na~+-toxicity, but also allows plant to use Na~+ as a benefit osmiticum for decreasing its cellular osmotic potential and preventing water loss. Sugar beet(Beta vulgaris L.) have grown in more fertile soil for a long period, their genetic potential for salt- and drought-tolerance is very limitied, especially its seedings are very sensitive under high salinity and drought conditions. Thus, Breeding saltand drought-resistant sugar beet cultivars is vital for sustainable husbandry development and reusing salinity land in arid and semi-arid areas of northwest china.The aims of the studies are use suger beet as material to explore the physiological adaptive mechanisms under salt or osmotic stress. The Zx NHX and Zx VP1-1 genes encoding tonoplast Na~+/H~+ antiporter and H~+-PPase from Zygophyllum xanthoxylum were co-transfromed in sugar beet by Agrobacterium tumefaciens-mediated methods. These plants also were analysed about salt- and drought-tloerance. The main foundings are as follows:1. Compared with control(0 mmol/L Na Cl), it was found that 50~150 mmol/L Na Cl increased the shoots fresh weight and dry weight by 70%~90%, and Na~+ concentration by 4~5 folds, whereas K~+ concentrations in leaf and lateral root were decreased by 35%~50%. The content of proline were also incerased 93%, but decreased sucrose and fructose contents by 40%~50%, glucose contents have not significant difference in storage root from sugar beet plants under salt treatment.2. Osmotic stress(-0.5~-1.5 MPa) inhibited the growth of sugar beet, and leaves showed chorosis, even plants started to died. Compared with control(0 MPa), osmotic stress reduced the fresh weight and tissue water content in shoots by 40%~50%, and its Na~+ concentration were increased by 30%~40%, while K~+ concentrations in lateral root decreased by 40%~50%. The contents of proline were increased 2~3 folds in shoot and storage root, whereas fructose and gloucose contents have not remarkable differences in storage root from sugar beet plant under osmotic stress.3. We totally obtained 40 sugar beet plants co-expressing Zx NHX and Zx VP1-1 genes by PCR amplification, respectively. The expression levels of Zx NHX and Zx VP1-1 were monitored by RT-PCR, and a stable transformation efficiency of 9.95% was observed using a total of 402 plants.4. It is obvious that the leaves of wild-type(WT) sugar beet plants started to chorosis and wilt, while the plants(T0) co-expressing Zx NHX and Zx VP1-1 genes were vigorous with largely fresh weight and tissue water content in shoot under salinity stress(400 mmol/L Na Cl). Compared with WT plants, it was clear that T0 plants can accumulate more Na~+, K~+ and proline concentration in shoots, and decrease the solute osmotic potentials(Ψs) and malondialdehyde(MDA) contents in leaf, meanwhile the sucrose, fructose and glucose contents in storage root were remarkable increased under salt stress.5. It was observed that the growth of WT and T0 plants were significant inhibited, whereas WT plants showed more obvious under osmotic stress. Compared with WT plants, the concentrations of Na~+ and Ca2~+ in shoots were increased by 15%~30%, and proline contents were increased by 40%~50%, and fresh weight and tissue water content in shoots were also increased by 40%~50%, meanwhile the sucrose and fructose contents was largely accumulated in storage root from T0 sugar beet plants under osmotic stress.In summar, our results suggested that salinity(50~150 mmol/L) can improved the growth of sugar beet plants, and the largely accumulations of Na~+ and proline in shoots is one of mainly adaptive strategies under salt and osmotic stress. The T0 sugar beet plants co-expressing of Zx NHX and Zx VP1-1 genes increased the sequestration of Na~+ into vacuole, and the accumulations of more soluble solute, such as Na~+, K~+ and proline, which lead to decrease the osmotic potential and cell membrane damage, and increase the salt- and drought-tolerance. |
PDF Full Text Request