Studied On The Brassinosteriod In Regulation Of Plant Vascular System Development

Vascular tissue provided an important mechanical supporting function for the plant and also played a role in transporting water, minerals, photosynthetic products and plant growth and development-related nutrients. The plant vascular tissue had an important function in plant growth and development, and the study on mechanism of plant vascular tissue development was very meaningful. Brassinotserds(BRs) play an important role in vascular tissues during development, which had rare content of plant and high activity in the plant. Arabidopsis brassinotserds gene BAS1 encoded a hydroxylase, whose overexpression could transform brassinotserds to 26-hydroxybrassinotserds and decreased BRs activity.In order to study the effect of BRs content on vascular tissue development, we constructed plant expression vectors which contained BAS1 genes driven by 35 S and p LXM5 promoter. We transformed tobacco by Agrobacterium-mediated leaf discs and investigated on transgenic plants. Made the following findings: 1 Construction of plant expression vectors and acquisition of transgenic plantsWe constructed two recombinant vectors on the basis of vector PSH737, which gus::npt II fusion gene acted as a selection marker gene and a reporter gene named p SH-35S-BAS1 and p SH-p LXM5-BAS1. The recombinant vectors were transformed into Agrobacterium tumefaciens LBA4404. We obtained 46 lines of transgene 35S::BAS1 tobacco and 52 lines of p LXM5-BAS1 tobacco by leaf discs after screening and identification. 2 Effect of overexpression BAS1 on transgenic tobacco plant height and stem diameterBy measuring tobacco plant height and stem diameter, we found that plant height of transgene 35S::BAS1 tobacco plants was lower 18.6% than that of wild type, stem diameter of transgenic tobacco was higher 26.2% than that one, while numbers of internodes of transgenic tobacco was higher 13% than that one. Plant height of transgene p LXM5::BAS1 tobacco plants had no significant difference with that one and stem diameter of transgenic tobacco was higher 27.3% than that one, while numbers of internodes of transgenic tobacco was higher 40%. 3 Effect of overexpression BAS1 on photosynthetic rate of tobaccoThe result of research to photosynthesis characteristic of tobacco showed that net photosynthetic rate of transgene 35S::BAS1 tobacco was higher 57.9% than that of wild-type tobacco and net photosynthetic rate of transgene p LXM5::BAS1 tobacco was higher 84.1% than that one. 4 Effect of overexpression BAS1 on photosynthetic pigment content of tobaccoThe result of research to photosynthetic pigment content of tobacco showed that chlorophyll a and b content of transgene 35S::BAS1 tobacco was higher 67.8% and 67.5% than that of wild-type tobacco. Also that chlorophyll a and b content of transgene p LXM5::BAS1 tobacco were higher 89.4% and 90.1% than that one, respectively, which indicated that BAS1 gene in transgenic tobacco improved net photosynthetic rate of tobacco. The chlorophyll a, b and carotene content of transgene 35S::BAS1 tobacco had no obvious difference compared to transgene p LXM5::BAS1 tobacco. 5 Effect of overexpression BAS1 on tobacco stem vascular bundles and pithThe study found that rephloem layer of transgene 35S::BAS1 and p LXM5::BAS1 tobacco were 2.1 and 2.2 fold than wild type. And between phloem layer and size of phloem cells of transgene 35S::BAS1 tobacco and that of transgene p LXM5::BAS1 tobacco had no significant difference. We observed pith of wild type and transgene 35S::BAS1 and p LXM5::BAS1 tobacco and discovered pith length of transgene 35S::BAS1 tobacco was lower 30% than wild type, whereas the pith length had no significant difference between wild type and transgene p LXM5::BAS1 tobacco. Studies have shown that overexpression BAS1 in the plant and vascular tissues increased phloem layers of tobacco vascular bundles and could not affect size of phloem cells. Transgene 35S::BAS1 had a 35 S promoter which was a constitutive promoter. It was expressed in tobacco plants, but also affected other cellular morphology. Transgene p LXM5::BAS1 had a vascular bundles specific promoter p LXM5, which only expressed in vascular bundles and could not affect other cellular morphology.