| Abscisic acid (ABA) is a plant hormone that plays important roles in many physiological and developmental processes, including seed development, dormancy, germination, vegetative growth and fruit maturation. In addition, ABA has a vital function in plant adaptation to environment stress, such as draught, salt, chilling et al. Endogenous ABA level is a crucial part of determining ABA action in plant growth and physiological responses. In our previous study, the NCED gene has been isolated from Thellungiella hahphila, named ThNCED. Using the LBA4404 carrying the vectors which contain sense or antisense ThNCED cDNA, the tobacco leaf discs were transformed. The regenerated plantlets were verified by PCR and Southern blotting analyses. The transgenic tobacco plants will be used to analyse physiological process in response to draught stress and plant development.Responding to drought stress, ABA regulates Stomatal aperture by inhibiting Stomatal opening and inducing Stomatal closure in guard cells. A polyethylene glycol solution is expected to mimic the effect of water deficit stress, thus incubation in 10% PEG6000 could impose osmotic stress on guard cells. The overexpression transgenic plants could promote Stomatal closure, and conversely the transgenic plants with antisense inhibit Stomatal closure under the stress conditions compared with wild type plants.T1 seed of transgenic plants was selected to test the efficacy of ThNCED in the transgenic tobacco. The seed of transgenic plants overexpressing ThNCED gene exhibited delayed germination, and expression of an antisense ThNCED resulted in rapid germination. According to the result of Stomatal aperture and seed germination, the overexpression transgenic CN+8 and antisense transgenic CN-40 lines were used in further assay.The overexpression ThNCED lines displayed the more resistance to dehydration from their leaves or whole plants, but the antisense transgenic plants were more sensitive to dehydration. The total soluble sugars and free amino acids increased under drought stress for 3d were significantly higher in transgenic overexpression lines than that of WT plants. In addition, the MDA levels in overexpression transgenic lines were significantly lower than that in WT after drought stress.When plants were grown in unstressed conditions there was an observed reduction in Stomatal conductance (gs) in ovexpression lines cn+8 compared to the wild type, and gs in antisense lines cn-40 was similar with wild type. On the other hand, ABA induces Stomatal closure to reduce water loss by transpiration. The net photosynthetic rate of overexpression lines show lower level than wild type, conversely, the antisense lines have the higher level. There are the evidences that the net photosynthetic rate of leaves was according with Stomatal conductance change. Under unstressed environment, there are no different in Non-photochemical quenching of chlorophyll (NPQ) between transgenic plants and wild type, and NPQ was enhanced following the light intensity increase. When draught treatment was exposed, NPQ of transgenic plants and wild type started to decrease significantly. This decrease in NPQ was much greater in overexpression line (cn+8) than in wild-type plants and antisense line (cn-40) at 6 days after the drought treatment,.It was clear from numerous observations under glasshouse condition that cn+8 and cn-40 taken to establish growth rate is subsequently similar in all genotypes under well-watered conditions before the ten-twelve leaf stage. Then, transgenic plants often appeared to produce different types of plant. The plant height in overexpression line is about 92.7cm, while it is 89.0cm cm and 81.5cm antisense line and wile type, respectively.The pollen germinations of transgenic plants were significantly different compared with wild type. Nearly 53% of pollen grains from the overexpression line germinated after incubation for 4 h, and 85% and 81% in antisense line and wile type, respectively. Moreover, the pollen tubes of overexpression lines were grown slowly than wild type after 4 h incubation.In this paper, we study the effect on drought resistance and photosynthesis characteristic of transgenic tobaccos. These conclusions provide a basis for further study about the effect of ABA on drought resistance and photosynthesis characteristic.
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