Preliminary Study Of Thermal Effect Mechanism Of Laser Protecting And Repairing Wheat From UV-B Radiation Damage

It is reported that there will be a 16% decrease of ozone in 2060, and then the ultraviolet-B radiation reached the earth will become a great threat to the survival of all livings including the humans. Therefore how to investigate the UV-B influence on organism and how to prevent them from UV-B damage have become one of international problems. In order to test if laser radiation and its thermal effect can protect plant from UV-B damage or heal it up and to estimate the proportion of thermal effect in laser's total biological effect, a series of experiments on wheat seeds and seedlings were conducted, in which changes of chlorophyll and antioxidants content and activity were measured. The results may provide more theoretical foundation on how to control and use laser in biology field more efficiently. The results indicated that:1. The temperature of dry and wet seeds rosed to different extent after irradiated by He-Ne laser with power density 3.5mW·mm^-2 or CO₂ laser with power density 6.62mW·mm^-2 correspondingly. Thereinto, the temperature variations of dry and wet seeds radiated by He-Ne laser were less than 0.5 ℃, while those of seeds treated by CO₂ laser were 7℃and 3℃, which indicated that the thermal effect of CO2 laser was more apparent than that of He-Ne laser.2. After radiated by CO₂ laser with power density 6.62mW·mm^-2 for 30s, the germination percentage and seed vigor index of wet seeds were increased, MDA content was decreased, meanwhile the dry seeds were damaged slightest after irradiated for 30s.3. The temperature of dry seeds rose so rapidly after treated by CO₂ laser for 30s that the thermal pretreatment reinforced UV-B damage instead of wakening it. As to wet seeds, chlorophyll content was higher and the MDA content was lower in combined treatment of thermal pretreatment and UV-B radiation than that of UV-B treatment alone,however it did not counteract UV-B damage compared with control. However, the growth of wheat seedlings in different treatments was not influenced judging by the biomass.4. In repair experiment the temperature adopted was the same as that of protect experiment. It was indicated that the chlorophyll content and dry weight of wheat seedlings in combined treatments (BT> BL) were decreased, UV-absorbing substances was increased, meanwhile MDA content and the autoxide rate were higher than that of control and UV-B treatment alone. So CO2 laser radiation and its thermal treatment were not helpful in repairing UV-B damage for wheat seedlings.5. In protect and repair experiments, fluctuation trends of UV-absorbing substances content in laser irradiation and simulated its thermal treatments during 5 days after freed wheat seedlings from UV-B stress were similar to each other, both were like a reversed letter V, so maybe they influence the organism in the same way. Namely, when the temperature fluctuation resulted by laser radiation is higher than that in surroundings, the thermal effect is dominant in laser's total biological effect;or else, another effect of laser such as pressure effect, electromagnetic effect or optic effect, will be the leading one.In conclusion, it is hard to estimate the biological effect of thermal on wheat from the results abovementioned, in order to distinguish whether the laser biological effect is a single effect or a result of multiplex effects, more comprehensive researches are needed.