Occurrence and biosynthesis of catalase at different stages of seed maturation

Abstract

It was to be shown whether during the biogenesis of microbodies some of their components were already present in the cell prior to the organelle's assembly. To this end, the occurrence and properties of catalase in soluble and particular fractions of ripening cucumber seeds were examined. Homogenates of seeds from ripening fruits were fractionated by isopycnic density gradient centrifugation, and thus catalase was found in three different fractions: as a soluble enzyme in the gradient supernatant, as a membrane fraction at density d=1.18 kg l(-1), and in association with microbodies. In the early steps of seed formation, catalase was detected at density d=1.18 kg l(-1) and in the gradient supernatant. At a later stage of seed maturation, however, catalase was primarily associated with microbodies which exhibited an equilibrium density of d=1.23 kg l(-1). M r as well as subunit M r of catalase were determined, and their close immunological relationship to leaf peroxisomal catalase and glyoxysomal catalase was demonstrated. Biosynthesis of catalase at different stages of seed maturation was investigated by in vivo labeling with L-[(35)S]methionine, L-[(14)C]leucine and δ-[(3)H]aminolaevulinic acid. Electrophoretic analysis of de novo synthesized catalase subunits revealed the occurrence of a heavy form (M r 57,500) in the soluble fraction; this form was preferentially labeled. A light form, M r 53,500, was detected in microbodies and also in the soluble fraction. The findings lend support to the hypothesis that the rate of catalase synthesis is highest in an early stage of seed formation, when globulins have already been formed, but before de novo synthesis of malate synthase has commenced. Prior to microbody assembling, a cytoplasmic pool of catalase was labeled.

Occurrence and Biosynthesis of Glyoxysomal Enzymes in Ripening Cucumber Seeds

“…In contrast, work done in our laboratory! 15~ 17 1 rather supports the concept that in germinating seeds glyoxysomal proteins are synthesized into a cytoplasmic pool and are then imported into the organelle in a way analogous to that for mitochondrial proteins [ 18,19] In the present paper we have extended the investigations to ripening seeds at defined stagesl 15 1 which enabled us to study the biosynthesis of glyoxysomal enzymes. Although the studies were hampered by the presence of protein body components dominating at this stage of embryogenesis, the investigations showed that glyoxysomal proteins were presumably formed in a way similar to the one found for glyoxysomal proteins in germinating seedst 20 !.…”

“…Seeds selected according to size and biochemical parametersf 15 1 were peeled and then either immediately chopped using razor blades or first incubated with the radioactive precursor, L-[ 35 S]methionine (25 TBq/ mmol; Radiochemical Centre, Amersham, U.K.).…”

Purification and biosynthesis of cottonseed (Gossypium hirsutum L.) catalase

“…Yamaguchi et al [17] also found only one catalase polypeptide on blots of tissues possessing various types of peroxisomes. In contrast, two different-Mr catalase subunits were reported for maize scutellum [33] and cucumber cotyledons [6,7,34,35], and two immunoreactive catalase polypeptides (subunit Mr 55000 and 59000) were detected on Western blots of three greening cucurbit species [16,17,361. Confirming this, we observed two immunoreactive catalase polypeptides on Western blots of cucumber and pumpkin seedlings probed with anti-(cotton catalase) serum (Fig.…”

Biogenesis of Glyoxysomes

“…Hence, the recent evidence for algal, fungal, and oilseed (and mammalian) matrix and peripheral membrane enzymes indicates they are synthesized on unbound ribosomes and released into the cytosol at some time prior to their import into glyoxysomes. Most of these enzymes are not synthesized as higher Mr precursors (clear exceptions are oilseed MDH and ChIarella isocitrate lyase), although not all results are in agreement (72,129). Considerable controversy exists, however, on whether matrix and peripheral proteins are glycosylated.…”

“…The in vitro synthesis of oilseed catalase from poly(A +)-mRNA has been done only with cucumber cotyledons (72,129). These independent studies indicate that translation products are larger than authentic subunits.…”