Spectral Efficiency of in vivo Photochemical Energy Storage in SO 2 Fumigated Sugar Maple Leaves

Abstract

Photosynthetic action spectrum and quantum yield of photochemical energy storage were determined by recording photoacoustic spectra of sugar maple (Acer saccharum Marsh.) leaves at a modulation frequency of 80 Hz. At this low frequency, the difference between the intensity of spectra in the presence and in the absence of a non-modulated background light indicated the relative magnitude of the photochemical energy storage, which is generally measured at high frequencies. The amount of energy stored per unit absorbed light energy is low in blue, intermediate in green and high in red regions of the spectrum, indicating the excitation energy transfer efficiency of photosynthetic pigments. Similarly, the relative quantum yield of energy storage was low in blue and high in red regions showing the red-drop phenomenon. The energy storage spectrum per unit incident energy showed a similar profile except for a decline between 520 and 570 nm. In 2 µL L-1 SO2 fumigated leaves, the photochemical activity decreased relative to the control, confirming the SO2 inhibitory site on the electron transport chain.