Glyoxylate Cycle Enzymes in Peroxisomes Isolated from Petals of Pumpkin (Cucurbita sp.) during Senescence

The activities of the two unique enzymes of the glyoxylate cycle,isocitrate lyase (EC 4.1.3.1 EC] ) and malate synthase (EC 4.1.3.2 EC] ),were undetectable in petals of pumpkin (Cucurbita sp. AmakuriNankin) until the end of blooming, but they appeared duringsenescence. The activity of catalase (EC 1.11.1.6 EC] ) increased,glycolate oxidase (EC 1.1.3.1 EC] ) activity did not change, whilehydroxypyruvate reductase (EC 1.1.1.81 EC] ) activity peaked at fullblooming stage and declined thereafter. After fractionationof cellular organelles on a sucrose density gradient, we detectedisocitrate lyase and malate synthase activities in peroxisomalfractions only from petals at the senescing stage. Northernblot analysis revealed that malate synthase mRNA increased duringpetal senescence. Citrate synthase (EC 4.1.3.7 EC] ) and malate dehydrogenase(EC 1.1.1.37 EC] ) activities were also present, while aconitase(EC 4.2.1.3 EC] ) was not detectable in peroxisomal fractions. Moreoverthe presence of 3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35 EC] )and urate oxidase (EC 1.7.3.3 EC] ) in the peroxisomal fractionsfrom senescing petals indicates that peroxisomes could be involvedboth in the ß-oxidation pathway and in the purinecatabolism during petal senescence. (Received May 25, 1991; Accepted September 25, 1991)