Effect of Narrow Bandwidth Infrared Radiation on Arabidopsis thaliana Growth and Gene Expression

The purpose of this study is to design an infrared emitter, and utilize its narrow bandwidth infrared radiation to irradiate Arabidopsis for 72 hours, in order to identify the specific waveband of infrared radiation which may affect the seed germination and seedling development of Arabidopsis thaliana. Infrared radiation emitters used in this study are fabricated based on the principle of surface plasmon. The heat is generated by sending electric current to the molybdenum film on silicon substrate. The infrared source can be achieved by heating the triple layer structure which consists of a SiO2 layer between two Ag films on the molybdenum film. The top Ag layer is perforated by periodic holes, and the emission wavelength can be altered by changing the lattice constant and diameter of the hole arrays. In this study, plasmonic thermal emitters with different emission peak wavelengths, i.e., 3, 3.5, 4.0, 4.5, and 5.0 μm, were designed and fabricated. The smallest full width at half maximum (FWHM) could be shrunk down to 0.5μm. The highest emitting power can reach 80mW/cm2 at a temperature of 160oC. After 72 hours exposure to infrared radiation with different wavelength, the hypocotyl lengths of Arabidopsis thaliana seedlings were measured. HSP101 (heat shock protein) was used to verify that this phenomenon is not caused by thermal effects. Furthermore, Northern blot analysis is also applied to investigate the gene expression pattern of chosen genes GASA4, CHS and RbcS. Thus, different wavebands of infrared radiation affecting gene expression could be found. The infrared of wavelengths 5.0 and 4.0 μm inhibit the elongation of hypocotyl lengths by 9.0 and 13.1%, respectively. The 3.0, 3.5 and 4μm infrared irradiation do not affect the hypocotyl length of Arabidopsis thaliana. The gene expression of CHS and RbcS has significant change in this experiment, showing that the gene expressions of these two genes are not only induced by visible light but also influenced by infrared exposure.