Recently, molecular biological techniques are well developed and used to make transgenic plants. However, physiological analyzes of transgenic plants are suffered due to the lack of in vivo measurement system. Therefore, we have developed the multi-wavelength absorption spectrometer for plant by using modulation methods. These techniques were used to uncover the adaptation mechanisms of photosystems for halotolerance. Photoacoustic measurements indicated that appreciable energy storage by photosystem I mediated cyclic electron flow at high salinities. Significant electron donation to photosystem I reaction centers through NAD (P) H-dehydrogenase complexes was observed in high salt media. The contents of Cyt.b6/f and PS II were almost constant under various salinity conditions, whereas the levels of Chl a, PS I,soluble Cyt.c-553, and NAD (P) H-dehydrogenase increased in the cells grown with high salinitie, indicating the improtance of cyclic electron flow around PS I for the adaptation to salt stress. The modulated multiwavelength florometer was als used for the analyzes of photosynthesis in transgenic plants.