Abstract:

Unsymmetrical dimethyl-hydrazine (UDMH) is a highly volatile and reactive compound widely used as a liquid rocket propellant fuel in manned and unmanned space and missile systems. Exposure to UDMH is an important occupational health issue, which will increase in significance as space applications increase. Several methods have been tested for removing UDMH from the environment, such as catalytic oxidation, active carbon absorption and ion exchange resins. However, little attention has been given to the application of constructed wetlands to remove UDMH from groundwater even though constructed wetlands are a promising measure for wastewater treatment.
In expectation of constructing of an effective wetland by the variant reed lines to deal with UDMH polluted groundwater, attempts were made to screen for UDMH tolerant variant lines of reeds using cellular engineering technology in this study.
Seeds of the reed (Phragmites communis) collected from the river banks near by a satellite-launching basement were sterilized with 70% ethanol and 2% hypochlorous acid and then transferred to a MS medium for germination. After germination, hypocotyl seedling segments were used to induce callus on the MS medium supplemented with 1 mg·L^-1 2,4-dichlorophenoxyacetic acid. The UDMH-tolerant cell lines were obtained by continuous selection on the UDMH containing medium supplemented with 0.5 mg·L^-1 2,4-dichlorophenoxyacetic acid. Three levels of UDMH tolerant cell lines were screened for that contained either 1.63, 3.26, or 8.15 mmol·L^-1 UDMH after 3-6 times of subculture. Relative growth, measured at the end of a 23-day incubation, was 90.4%, 84.3%, and 43.4% of the control in the three treatments, respectively, and, at the end of a 43-day incubation, was 95.6%, 91.7%, and 46.8% of the control, respectively. These results showed that UDMH could inhibit the growth of the callus at 8.15 mmol·L^-1. Regeneration of plantlets from the selected cell lines was conducted on UDMH containing MS medium supplemented with 0.1 g·L^-1 6-Benzylaminopurine and 0.01 g·L^-1 1-naphthyl acetic acid. However, only the cell lines grown in the lower two treatments could be successfully differentiated, the 8.15 mmol·L^-1 UDMH failed to differentiate. These results indicated that the suppressive effect of UDMH on callus differentiation was greater than on callus growth. Plantlets screened under UDMH stress were more tolerant to UDMH than the control, which were plantlets regenerated from callus without UDMH stress. Root growth of the differentiated plantlets was enhanced by transferring them to a hormone-free MS medium supplemented with UDMH for 35 days prior to successful transplantation of the plantlets into the soil. Finally, more than 70% of regenerated plantlets could be successfully transferred to the greenhouse. Further experiments estimating the growing status and remediation efficiency in UDMH polluted water of these variant seed lines were undertaken.

Key words: UDMH, Reed, In vitro selection, variant lines, Cellular engineering