Protect And Repair Role Of CO₂ Laser On Mung Bean Seedling Damaged By Enhanced UV-B Radiation

In order to determine whether CO₂ laser has the protect and repairs capacity to the seedlings from enhanced UV-B damage. The mung bean (Phaseolus raditus L.) seeds and the seedlings damaged by enhanced UV-B radationO.lO kJ.m(-2).d^-1 were exposed to CO₂ laser (20 m W mm^-2) radiation. The methods of physiology, biochemistry, molecule and laman spectroscopy were used in this research. The results from the experiments indicated chiefly that:1.The growth of seeds pretreated by CO₂ laser was better than the control. The results indicated that the content of chlorophyll, soluble protein and biomass, the rate of photosynthesis and stomatal conductance and the water use efficiency were all enhanced after pretreated by CO₂ laser.2.At the same time, the content of GSH, AsA, UV absorbling and proline and the enzymes activities of SOD, POD, CAT were also enhanced, while the content of MDA were reduced by the CO₂ laser pretreatment.3.The seedlings were injured by UV-B irradiation. The results indicated that the content of chlorophyll, soluble protein and biomass, the rate of photosynthesis and stomatal conductance and the water use efficiency were all reduced with UV-B irradiation.4. The content of MDA, UV absorbing compounds and proline were enhanced after UV-B irradiation. On the contrary, the content of GSH, AsA and the enzymes activities of SOD, POD, CAT were reduced. The seedling lipid peroxidation was appeared because superfluous free radicals were produced.5.The results showed that CO₂ laser pretreatment can protect Mung Bean seedlings from enhanced UV-B damage. The seeds pretreated with CO₂ laser were irradiated with UV-B radiation. Afterward, The results showed that the effects of UV-B irradiation on the content of chlorophyll, soluble protein and biomass, the rate ofphotosynthesis and stomatal conductance and the water use efficiency were restrained at a certain extent. And the damage effects of UV-B irradiation on the content of soluble protein, MDA, GSH, AsA and the enzymes activities of SOD, POD, CAT were also restrained at a certain extent. It means that CO2 laser pretreatment could improve the resistibility of the seedlings from enhanced UV-B damage.6. In addition, the results also showed that CO2 laser has the better repair capacity of the seedlings from enhanced UV-B damage. The seedlings irradiated by UV-B radiation were then treated with CO2 laser. The results showed that the promoting effects of CO2 laser alleviated the detrimental effects of UV-B radiation on the content of chlorophyll, soluble protein, soluble protein, MDA, GSH, AsA and biomass, the rate of photosynthesis and stomatal conductance and the water use efficiency and the enzymes activities of SOD, POD, CAT at a certain extent. It means that the CO2 laser radiation could activate the UV-B resistance capacity of the seedlings.7. The results showed that the best treat-time is about five minutes in the protect experiment and the best treat-time is about ninety seconds in the repair experiment.8.The results of laman spectra indicated that enhanced UV-B irradiation caused mung bean DNA damage and yielded a lot of CPDs. It showed that the bands of T and C moved obviously and the their intensity reduced. At the same time, the damage of hydrogen bonds and groups among the purine and pyrimidine bases were yielded. However, all the UV-B-damaged mung bean DNA could be repaired at a certain extent when the seedling were then treated with CO2 laser. The repair pathway might be breaking bands directly in CPDs by CO2 laser.