The Effect of Light on the Structure and Organization ofLemnaPeroxisomes

The effect of light on a number of Lemna minor enzyme activities was investigated. The levels of activity of glycolate oxidase, catalase and RuBPCase increased with increasing irradiance, paralleling the increase in Lemna growth rate. In contrast with results obtained for other species, no glycolate oxidase activity could be detected in etiolated Lemna fronds or when these were treated with light or glycolate, in vivo or in vitro, for up to 24 h. The number of peroxisome profiles per cell section was determined in Lemna grown under different light conditions. When fronds were grown under dim light, the number of peroxisome profiles per cell section appeared to increase with increasing irradiance, although no further increase in the peroxisome number was apparent when the fronds were grown under higher irradiances. The level of glycolate oxidase activity per peroxisome was shown to increase with increasing irradiance, whereas that of catalase remained relatively constant, indicating that differential addition of enzymes to pre-existing peroxisomes is possible. Peroxisomes from Lemna grown under high irradiance were subjected to serial sectioning and examined under the electron microscope. Some peroxisomes were found to have a three dimensional structure suggesting either fission and/or fusion or branching of these organelles, supporting the hypothesis of a peroxisomal reticulum. The dynamic relationship between the various shapes is discussed.