Influence of He-Ne laser irradiation on seeds thermodynamic parameters and seedlings growth of Isatis indogotica

In this study, the seed embryos of Isatis indogotica were exposed to He-Ne laser irradiation (5.23 mW mm−2, radiated for 5 min) to determine whether or not He-Ne laser caused changes to thermodynamic parameters of seeds and had a long-term physiochemical effects. A microwave (180 mW mm−2) was also employed in place of laser to pretreated seeds for 8 s as a parallel experiment with the laser pretreatment in order to identify the temperature effects of laser. The thermodynamic parameters were calculated according to thermograms of seed germination tested with a calorimeter at 25 °C for 40 h. The changes in physiological characters (net photosynthetic rate, stomatal conductance, water utilization efficiency and concentration of chlorophyll), biochemical characters (soluble saccharides, soluble protein, pyruvic acid, and the activities of three kinds of enzymes) and the growth parameters of seedlings (biomass and leaf area) were measured when the seedlings, which seeds were pretreated with He-Ne laser, developed to the stage of 24-25 days. It was found that the thermodynamic parameters in ΔH, (ΔS)e, (ΔS)c, (ΔS)e/Δt and (ΔS)c/Δt of seeds pretreated with He-Ne laser and microwave were similar during 40 h germination at 25 °C, while they changed significantly compared with that of the control. Similarly, the physiological characters of the seedlings, e.g. stomatal conductance, water utilization efficiency, net photosynthetic rate and chlorophyll concentration, and the biochemical characters of the seedlings, e.g. the concentration of soluble saccharides, soluble protein and the activities of α-amylase, GPT and GOT were increased significantly by the laser pretreated. Meanwhile, the biomass and leaf area of the seedlings were significantly improved. These changes suggested that the pretreatment with He-Ne laser had not only a short-term biological effect, which enhanced inner energy of seeds, but also a long-term effect, which contributed to the acceleration of the growth and development of seedlings. The present study has benefits in the elucidation of mechanisms underlying the effect of laser irradiation on organisms, as well as in the application of laser in agriculture and horticulture.