異なる背景光強度におけるイネ生葉のＬＩＦスペクトルと光合成速度の変化

Abstract

Chlorophyll fluorescence is known to be a sensitive probe of photosynthesis. Laser induced fluorescence (LIF) is useful for remotely sensing physiological information of plants by optical measurement. However, it is difficult to assess the LIF independently because of changes in background light. Background light, like sunlight, not only stimulates photosynthetic reaction but also induces fluorescence.To demonstrate the possibility of detecting changes in photosynthetic reaction according to background light from the LIF spectra, the correlation between LIF spectra and intensity of incident light on leaves was investigated.The LIF spectra from rice (Oryza sativa L.) leaves, which were illuminated with a metal halide lamp as background light, were measured. A gated CCD camera with monochrometer was synchronized to a pulsed UV-laser (Nd: YAG, 355nm) to detect the LIF spectrum under background light of different intensities. The LIF magnitude increased linearly with the laser intensity at each intensity of background light. The slope of fluorescence against laser intensity was considered to be a measure of fluorescent efficiency. The fluorescent efficiency increased with intensity of illumination. This increase of fluorescent efficiency was mainly caused by the increase of blue-green fluorescence (BGF) but chlorophyll fluorescence was constant. These changes of LIF spectra can be explained by the interaction of the fluorescent efficiency of chlorophyll and re-absorption of BGF; these phenomena reflect the redox state of the first electron acceptor (QA) in the photosynthetic reaction. The ratio of regression coefficients of BGF to chlorophyll fluorescence against the laser intensity changed in accordance with the change of photosynthetic rate of rice leaves.Photosynthetic information of leaves was detectable by analyzing the correlation between induction intensity and LIF spectra under changing background light.