The Physiological Response And Expression Of The PfSOD Gene From Pleioblastus Fortunei Under Lead Stress

Pleioblastus fortunei is one kind of excellent landscape greening plants, with good adaptabilities, fast growth, developed root system, strong resistance to cutting, rare occurance of pests and diseases, and other excellent features. It is significant to study the effects of lead stress on the growth and expression of resistance gene in Pleioblastus fortunei for selecting plants of lead stress tolerant.In this study, 2-year-old Pleioblastus fortunei clones, in1/2 Hoagland solution were treated with different Pb²⁺ concentration (0, 4, 8, 12, 16mmol·L^-1). some physiological and biochemical parameters such as activities of SOD, POD and CAT, plasma membrane permeability, contents of chlorophyll, free proline, soluble protein, soluble suguar ,MDA and so on under lead stress were measured, as well as expression of PfSOD gene was detected by the real-time PCR. The main results were:1,Pleioblastus fortunei could tolerant a certain degree of lead stress. It looks normally in1/2 Hoagland solution with 4 mmol·L^-1 Pb²⁺ treatment. High concentrations of lead stress inhibit the growth of the Pleioblastus fortunei. It was hurt under high concentrations of lead stress, leaves got wilting from tips and edges, burn-like spots appeared on leaves, and gradually extended to the entire leaves. Then whole plant showed yellow and wilt, and then died and biomass decreased significantly.2,The initial time of response to lead stress was relative with Pb²⁺ concentration. The higher the Pb²⁺ concentration, the earlier the initial time. With in 24 hrs lead treatment, no response for any Pb²⁺ concentrations. The initial time to lead was 264h,168h,96h and 48h for Pb²⁺ concentration of 4 mmol·L^-1,8 mmol·L^-1,12 mmol·L^-1and 16mmol·L^-1, respectively.3,Lower Pb²⁺ concentration, e.g. 4 mmol·L^-1, inhibited growth of Pleioblastus fortunei lightly, but not mortal injury, and the ratio of Fv/Fm was not significant compared with the ones in check. Meanwhile some other physiological parameters, i.e. membrane permeability, activities of SOD,POD and CAT, content of soluble sugars, MDA, changed significantly compared with the ones in check under the lead stress.4,PfSOD gene was cloned by RT-PCR. With a size of 925 bp, the cDNA contains a 456 bp open reading frame(ORF) encoding a putative protein of 152 amino acids, the molecular weight and pI of the protein PfSOD were predicted to be 15 105.73Da and 5.76, respectively. Analysis by Blast on website NCBI, the predicted protein encoded by PfSOD gene contains 6 active sites, 4 Cu²⁺ binding sites, 4 Zn²⁺ binding sites, it was completely consistent with the one coded by Cu/ZnSOD from the other species such as Bambusa oldhamii, Oryza sativa et al., which implied that it could be one gene encoded SOD enzyme from Pleioblastus fortunei.5,The expression of PfSOD gene was detected as target and theβ-actin gene as reference. The resulst indicated that PfSOD existed in all the organs of Pleioblastus fortunei. In root systems, PfSOD increased firstly then fell with different treatment concentrations. Expression of PfSOD was lower in leaves under the Pb stress than that in control, which was consistent with the changes of activity of SOD. It suggested that the expression of PfSOD gene was involved in SOD synthesis.6,The 3 activities of protective enzyme rose at the beginning of lead treatment, which implied that active oxygen content increased under lead stress and Pleioblastus fortunei started response machanism. With treatment time expanding, the balance of active oxygen was broken and expression of PfSOD was refrained, while SOD synthesis was inhibited. This may be the injury machanism of Pleioblastus fortunei under lead stress: synthesis of protective enzyme was inhibited; active oxygen accumulated and damaged membrane permeability, led to MDA accumulation.