Salt Stress-Induced Physiological Responses And The Cloning Of PT-HKT1in Poplar

Poplar has the following characteristics:fast-growing, strong adaptability, distributed, many kinds of species, easily hybridization, modified hereditary, asexual reproduction, is used for intensive cultivation widely.In this thesis, two Poplar strains (Nanyang1and Nanyang2) were conducted in quartz sand pot experiments. Growth and physiological characteristics were investigated under21days’treatment of different concentrations of NaCl. The physiological response, chlorophyll fluorescence characteristics, cell morphology and ultrastructure and ion uptake and distribution of poplar Nanyang1and Nanyang2under different salt stress were studied. Meanwhile, the genomic DNA sequence of Pt-HKT1from Poplar was isolated. The results were listed as follows:1. Under lower salt stress (75mmol·L-1NaCl), the inhibitions of the plant dry weight of Nanyang1were more than that of Nanyang2, and the dry weight of Nanyang1and Nanyang2were decreased61.3%and21.4%; the decrease of water potential of Nanyang1was higher than that of the Nanyang, and the inhibitions of plant dry weight and root/shoot of Nanyang1were more than those of Nanyang2. The damages of cell morphology and ultrastructure in Nanyang1were more obvious than that in Nanyang2by lower salinity. However, under higher salt stress (150mmol·L-1NaCl), there was no significant difference of growth inhibition between two poplar strains.2. Under lower NaCl stress, the inhibitions of chlorophy11content, qP, Yield and ETR of Nanyang1were more than that of Nanyang2, compared with the control, Fm/Fv and Fm’/Fv’ did not change significantly. But, there was no significant difference between Nanyang1and Nanyang2under higer NaCl stress. The average value of Pc for Nanyang2was higher than that of Nanyang1under the salt stress, but Hd was lower than Nanyang1. There was no significant difference of the average value of Ex for Nanyang1and Nanyang2. 3. Under lower NaCl stress, Na+and Cl-increased in root, new branch and leaf, especially in root, Nanyang1was obviously higher than Nanyang2, while K+, Ca2+and Mg2+declined. K+, Ca2+and Mg2+in Nanyang1were markedly lower than those in Nanyang2. Na+/K+, Na+/Ca2+of root, new branch and leaf of Nanyang2were markedly lower than those of Nanyang1. RSK,Na and RSCa,Na in Nanyang2were higher than those in Nanyang1, which indicated the ability of selective transport of K+and Ca2+in Nanyang2were higher than Nanyang No.1. However, under higer NaCl stress, there was no significant difference between two poplar strains. X-ray microanalysis suggested that Na+contents in different cells of root of Nanyang1were obviously higher than Nanyang2by salt stresses. Under salt stress, in new branch, Na+contents in epidermis, cortex and xylem cells of Nanyang1were higher than that of Nanyang2, and in root and new branch, Na+priority distribution in epidermal and cortical cells of both poplar which indicated root and new branch had strong ability of Na+retention, however, no significant Na+increase in both poplar leaves. In leaf, the Na+contents in upper epidermis, palisade and spongy cells of Nanyang1were higher than those in Nanyang2under salt stress, and excepct in the upper epidermis cells, the Mg2+contents in the other cells of Nanyang2were significantly higher than those of Nanyang1.4. A HKT1gDNA from Poplar(Pt-HKT1) was cloned by PCR using specific primers based on the EST database. The Pt-HKT1encodes a polypeptide of519amino acids. The relative molecular mass and isoelectric point (pI) of the deduced polypeptide are calculated to be56.5kDa and9.37. Gene sequence analysis showed that:Pt-HKT1may be a potassium ion transporter protein.Analysis of protein predicted that there are eight transmembrane of Pt-HKT1.