Effect of phytochrome on development of catalase activity and isoenzyme pattern in mustard (Sinapis alba L.) seedlings : A reinvestigation.

In contrast to an earlier publication (Drumm et al., Cytobiol. 2, 335, 1970), a definite enhancement by phytochrome of the catalase level in mustard (Sinapis alba L.) cotyledons can be demonstrated. This response can be obtained either with continuous far-red light or with short red pulses, the effect of which is reversible by short far-red pulses. From the comparison of the time courses of catalase activity with the time courses of glyoxysomal (isocitrate lyase) and peroxisomal (glycolate oxidase, glyoxylate reductase) marker enzymes in dark grown and far-red irradiated cotyledons, there appears to be a close relationship between the catalase present in darkness and glyoxysomes and between the phytochrome-stimulated portion of total catalase and peroxisomes, respectively.The isoenzyme pattern of catalase shows 3 strong and several weaker bands in dark grown cotyledons. Irradiation with white or far-red light leads to a more complex pattern with at least 12 detectable bands. The isoenzymes increased by light supplement rather than replace the isoenzymes present in darkness. This is true also in cotyledons and true leaves of white light grown plants which do not possess glyoxysomes. In the hypocotyl of the seedling, catalase formation is depressed by far-red light and no change in the isoenzyme pattern is observed.It is concluded that the development of peroxisomes in the cotyledons is specifically controlled by phytochrome and that this subcellular differentiation also involves the control of catalase, a marker enzyme for both glyoxysomes and peroxisomes. The implications of these results with respect to the developmental origin of peroxisomes in cotyledons of fat-storing, potentially photosynthetically active cotyledons is discussed.