Catalase Synthesis and Turnover during Peroxisome Transition in the Cotyledons of Helianthus annuus L.

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Abstract
Based on measurements of total catalase hematin and the degradation constants of catalase hematin, zero order rate constants for the synthesis of catalase were determined during the development of sunflower cotyledons (Helianthus annus L.). Catalase synthesis reached a sharp maximum of about 400 picomoles hematin per day per cotyledon at day 1.5 during the elaboration of glyoxysomes in the dark. During the transition of glyoxysomes to leaf peroxisomes (greening cotyledons, day 2.5 to 5) catalase synthesis was constant at a level of about 30 to 40 picomoles hematin per day per cotyledon. During the peroxisome transition in the ligh, total catalase activity rapidly decreased. In continuous darkness, total catalase hemating decreased considerably from a peak at day 2. The results show that by light. The turnover characteristics of catalase are in accordance with the concept that glyoxysomes are transformed to leaf peroxisomes as described by the one population model and contradict the two population model and the enzyme synthesis changeover model which both postulate de novo formation of the leaf peroxisome population and degradation of the glyoxysome population.