| Maize was not only the largest food crops for human consumption and the main raw material of the production of feed, but also the highest total output of crops in the world. Drought was the first element to limit China’s corn production development and production increased, which influence on maize yield of 20% to 50%, and cultivate high-yielding drought-resistant varieties was one of the most cost-effective way to resist drought stress. In the drought-tolerant corn cultivation of new varieties,the using of traditional breeding techniques played a positive role, but the traditional breeding techniques was time-consuming, high-costed and less effective.High-yielding drought-resistant crops cultivation for agricultural development by genetic engineering techniques was very important. The using of transgenic technology for crop varieties orientation transformation not only accelerated processes of screening and breeding excellent biological species, and broken reproductive isolation across species to transfer excellent gene, greatly expanded available genetic resources. However, before using of transgenic technology to cultivate fine crop varieties, we had to figure out drought resistance mechanism.Research clearly to drought-resistant maize mechanism provided a theoretical basis for improving drought resistance of crops, but also provided theoretical guidance for the cultivation of new varieties of drought-resistant corn.We studied effects on the growth and physiochemical mechanism of transgenic maize with trehalose-6-phosphate synthase gene TPS1 from Saccharomycescerevisiae and found that gene TPS1 improve drought tolerance by promoting root growth, accumulating anthocyanidin and improving photosynthetic capacity under drought stress. The following findings were obtained.1.Trehalose-6-phosphate synthase gene TPS1 from Saccharomyces cerevisiae improve root growth in transgenic maize under drought stressIn this paper, TPS1 improve root growth of maize and the condition of transgenic maize had an advantage over wild type under drought stress. Root length and diameter of transgenic maize was 10.4 cm and 1.02 mm, while that of wild type maize was 5.8 cm and 0.90 mm, which increased 79.3% and 13.3%, respectively. The number of first-order lateral roots of transgenic maize was 20.1, which increased 3.4folds than wild type. Wild type maize had no second-order lateral roots, but transgenic maize had obvious second-order lateral roots that average number was 1.5.Meanwhile root absorption area, active absorption area, specific surface area and root activity in genetically modified maize was 1.92 m2, 0.95 m2, 1.47 m2·cm-3 and 0.070mg·g-1·h-1 while that of wild type was 1.27 m2, 0.63 m2, 1.27 m2·cm-3 and 0.059mg·g-1·h-1, which increased 51.2%, 50.8%, 15.7% and 18.6% compared to wild type.The determination of auxin and cytokinin content indicated auxin content of transgenic maize was 2.03 μg·g-1, which increased 35.7% compared to wild type, but that of cytokinin of transgenic maize was 26.95 μg·g-1, which decreased 26.5%compared to wild type. Further, results showed that genes associated with auxin（PLT1, AUX/IAA, PIN1 and CRL1） were up-regulated, and relative expression level of PLT1, AUX/IAA, PIN1 and CRL1 was 2.8, 1.5, 4.4 and 2.0 folds of wild type, while expression level of genes associated with cytokinin（WOX11, ARR2 and ARR1）dropped 20.8%, 59.7% and 90.3% than wild-type.2.Improve drought tolerance via accumulating anthocyanidin under drought stress in TPS1 transgene maizeIn this paper, we studied mechanism of transgene maize plants drought-resistant enhancement based on former studies. Under different concentrations of PEG-6000 solution simulated drought stress conditions, leaf relative water content and drought-resistant coefficient of wild type and transgenic maize plants decreased withaggravating drought degree; and under conditions of each degree, both leaf relative water content and drought-resistant coefficient of genetically modified maize plants was higher than wild type, which indicated drought resistance of transgenic plants was more than wild type. At the same time, with drought aggravating, anthocyanin content also increased in wild type and transgenic maize plants, and that of transgenic maize plants were higher than wild type in each drought stress condition. Correlation analysis showed anthocyanin content in transgenic plants had significantly correlated to drought resistance. Anthocyanin content in roots, stems and leaves of wild-type and TPS1 transgene maize plants was no significant difference before drought stress, but that of transgenic corn was significantly higher than wild type under drought stress,which anthocyanin content in roots, stems and leaves of TPS1 transgene maize plants was 0.516 nmol·g-1（FW）, 0.674 nmol·g-1（FW） and 0.754 nmol·g-1（FW）,representing an increase of 8.5, 5.4 and 1.8 fold, respectively. Gene relative expression analysis of transcription factors that regulating anthocyanin biosynthesis showed that relative expression of positive regulator gene PL1, R1, PAC1 was up-regulated, and that of negative regulator gene c1-I-2K1 was down-regulated in roots, stems and leaves of transgenic maize that dropped 63.8%, 60.2% and 85.1%,which suggested that transcription factors were influenced anthocyanin accumulation by TPS1 in roots, stems and leaves of TPS1 transgene maize, and then improved drought resistance of plants. Results also showed that CAT activity and MDA content were no significant difference between transgenic plants and wild type before drought stress, but compared with wild type plants, CAT activity was 20.12 U·mgprot-1 which increased 56.3% and MDA content was 1.12 nmol·mgprot-1 which decreased by36.7% in transgenic plantsafter drought stress, which suggested TPS1 gene increased the antioxidant capacity of corn result in improving maize drought resistance.3.Transgene TPS1 improved photosynthetic capacity of maize under drought stressWe determined photosynthetic parameters of transgene TPS1 maize under drought stress by using LI-6400 photosynthesis system. The results showed that net photosynthetic rate of transgene TPS1 maize was 17.03 μmol CO2·m-2·s-1 whichincreased 69.2% compared to wild type. The stomatal conductance, intercellular CO2 concentration and transpiration rate of transgene TPS1 maize under drought stress was0.12 mmol H2O·m-2·s-1, 150.55 μmol CO2·mol-1 and 2.25 mmol H2O·m-2·s-1, which decreased 40.5%, 33.2% and 38.9%, respectively. The transgene TPS1 maize had lower light compensation point than wild type and utilized wide illumination range efficiently than wild type, which transgenic plant photosynthetic capacity was stronger than wild type under drought stress. The content of chlorophyll a, chlorophyll b and total chlorophyll of transgenic maize under drought stress was 0.94 mg·g-1, 0.25mg·g-1 and 1.19 mg·g-1, which increased 40.5%, 33.2% and 38.9%, but chlorophyll（a/b） value had no significant change before and after drought stress, which chlorophyll degradation degree of transgene TPS1 maize was lower than wild type under drought stress. Meanwhile, studies suggested that RBC activity of transgene TPS1 maize was 237.78 U·g-1 which increased 35.4% and its RBC gene relative expression was 3.6 fold compared to wild type under drought stress. Also PEPC activity of transgenic maize was 40.00 U·g-1, which increased 15.7% and its PEPC gene relative expression was 1.6 fold than wild type under drought stress. However,ME activity and its gene relative expression of transgenic had no significant change with wild type. Which indicated that TPS1 gene improved light synthase activity of transgenic plant under drought stress.4.Effects of TPS1 gene on flowering time and yield of transgenic maizeMaize would be subjected to stress, such as drought, under complex natural conditions such as drought stress. Studies shown that TPS1 gene express under natural conditions due to the promoter rd29 A we studied as stress-inducible promoter. The study found that bloom of transgenic maize was earlier and flowering time of transgene TPS1 maize was less 15.3 d than wild type. Real-time PCR analysis indicated that gene relative expression of FT and CO gene had no significant change between transgenic maize and wild type, while gene relative expression of AP gene of transgenic maize was 13.2 fold than wild type, which flowering time of maize was influenced by TPS1 gene. And ear length, bald, ear diameter, rows per ear,grains per row and axis diameter had no significant change between transgenic maizeand wild type, but hundred-grain-weight of transgenic maize was increased 48.6%than wild type, which indicated that expression of TPS1 gene affected hundred-grain-weight of transgenic maize. The result showed that TPS1 gene affectes maize grain matter accumulation and increased production. |
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