Abstract: The ultrastructure of Spirodela polyrrhiza, which belongs to the family of Lemnacea, was investigated using transmission electron microscope. We have discovered that: when supplied with strong light intensity, the chloroplasts in mesophyll cells of S. polyrrhiza increased. Though the number of chloroplasts decreased with weak light intensity, the grana lamella of chloroplasts thickened to increase its photosynthesis reaction area. In terms of temperature effects, S.polyrrhiza was under stress to a certain degree in 10℃ and 35℃ treatments, as shown by shriveled chloroplasts and large cell cavity at 10℃, and dissolved chloroplast envelope, exuded stroma and increased plastoglobulus at 35℃. S.polyrrhiza transformed its internal structure inside the cell morphology in order to adapt to different light intensity and temperature conditions, making it be a certain tolerant to light and temperature stress.

Key words: duckweed, mesophyllic cell, chloroplast, ultrastructure