Lecithin synthesis during microbody biogenesis in watermelon cotyledons

During the normal development of watermelon seedlings, leaf peroxisomes succeed glyoxysomes as the major microbody component in the cotyledons. The possibility has thus been raised that the two organelles are ontogenetically related; that leaf peroxisomes are derived from glyoxysomes. The behavior of lecithin, an important constituent of the membranes of both kinds of organelle was examined in this study. Using labeled choline as a precursor of lecithin, its incorporation into various membrane fractions was followed during the period when glyoxysomal activity was declining and that of leaf peroxisomes increasing after exposure to light. The results showed that glyoxysomal membrane was selectively destroyed during this period. Furthermore, from double-labeling experiments using ¹⁴C]- and ³H]choline it was shown that newly synthesized lecithin was incorporated into the membranes of the developing leaf peroxisomes. These results support the thesis that leaf peroxisomes are not derived from glyoxysomes and instead represent two distinct microbody populations.