Development of Enzymes in the Cotyledons of Watermelon Seedlings

Exposure of dark grown resting Euglena to ethanol produced a transient increase in the specific activity of the glyoxysomal enzyme malate synthase. Enzyme specific activity increased during the first 24 hours of ethanol treatment and then declined. Light exposure or malate addition failed to increase enzyme specific activity. The increase and decrease in enzyme specific activity represented changes in the amount of active enzyme. In both wild type cells and the plastidless mutant W3BUL, enzyme levels were always higher in the dark than in the light.The specific activity of the peroxisomal enzyme glycolate dehydrogenase began to increase 24 hours after dark grown resting Eugkena were exposed to light. Ethanol, but not malate, prevented the increase and promoted a decrease in glycolate dehydrogenase levels. Cycloheximide produced a decline in enzyme levels similar to the decline produced by ethanol addition. Glycolate dehydrogenase was present in the plastidless mutant W3BUL indicating that it is coded in the nucleus and synthesized on cytoplasmic ribosomes. Streptomycin, a specific inhibitor of chloroplast protein synthesis and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of photosynthetic CO2 fixation, inhibited the photoinduction of glycolate dehydrogenase while having no effect on the photoinduction of NADP dependent glyceraldehyde-3-phosphate dehydrogenase, another light induced, nuclear coded, cytoplasmically synthesized enzyme. Taken together, these results suggest that microbodies are continuaDly synthesized in resting Euglena and their enzyme complement is determined through substrate induction of glyoxysomal and peroxisomal enzymes.

mentioning

confidence: 99%

mentioning

confidence: 99%

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Nutritional Regulation of Organelle Biogenesis in Euglena

Horrum

Schwartzbach²

1981

“…During early germination, glyoxylate cycle enzymes such as isocitrate lyase (threo-D-isocitrate glyoxylate lyase, EC 4.1.3.1) undergo a well characterized increase and subsequent decline in activity, with peak activity corresponding to the period of maximum fat metabolism (3,4,7,16,32,35). Much is already known about the developmental physiology of the glyoxylate cycle enzymes and the glyoxysomal compartment in which they are localized, but little is presently understood about the regulatory mechanisms which underlie their appearance and subcellular compartmentation in the germinating seed.…”

Section: Introductionmentioning

confidence: 99%

Regulation of Glyoxysomal Enzymes during Germination of Cucumber

Lamb

Riezman²,

Becker³

et al. 1978

The glyoxysomal enzymes isocitrate lyase and catalase have been isolated from etiolated cucumber (Cucumis satdvus) cotyledons. The enzymes co-purified through polyethyleneimine precipitation and (NH4)2SO4 precipitation, and were resolved by gel filtration on Sepharose 6B foUlowed by chromatography on diethylaminoethyl-cefulose (isocitrate lyase) or hydroxylapatite (catalase). Purity of the isolated enzymes was assessed by sodium dodecyl sulfate-polyacrylamide electrophoresis, isoelectric focusing, and immunoelectrophoresis. Antibodies raised to both enzymes in rabbits and in tumor-bearing mice were shown to be monospecific by immunoelectrophoresis against total homogenate protein. Isocitrate lyase and catalase represent about 0.56% and 0.1%, respectively, of total extractable cotyledonary protein. Both enzymes appear to be present in a single form. Molecular weights of the native enzymes and its subunits are 225,000 and 54,500 for catalase, and 325,000 and 63,500 for isocitrate lyase. The pH optimum for isocitrate lyase is about 6.75 in morpholinopropane sulfonic acid buffer, but varies significantly with buffer used. The Km for D-isocitrate is 39 micromolar. A double antibody technique (rabbit antiisocitrate lyase followed by 1251-labeled goat anti-rabbit immunoglobulin G) has been used to visualize isocitrate lyase subunit protein on sodium dodecyl sulfate-polyacrylamide with high specificity and sensitivity.Seed germination in fat-storing species requires a functional glyoxylate cycle to effect net gluconeogenesis from the acetyl-CoA derived by fl-oxidation of storage triglycerides (4). During early germination, glyoxylate cycle enzymes such as isocitrate lyase (threo-D-isocitrate glyoxylate lyase, EC 4.1.3.1) undergo a well characterized increase and subsequent decline in activity, with peak activity corresponding to the period of maximum fat metabolism (3,4,7,16,32,35). Much is already known about the developmental physiology of the glyoxylate cycle enzymes and the glyoxysomal compartment in which they are localized, but little is presently understood about the regulatory mechanisms which underlie their appearance and subcellular compartmentation in the germinating seed. 'To whom reprint requests should be addressed.enzyme with a characteristic increase and subsequent decline in activity during germination (35). We are interested both in the level(s) at which the activities of glyoxysomal enzymes are regulated during cucumber germination (3) and in the relationship between appearance of enzyme activity and organelle biogenesis.Critical to such studies is the availability of purified glyoxysomal enzymes and of monospecific antibodies to them. Few reports have appeared to date concerning the isolation of glyoxysomal enzymes from plant sources. Specifically, ICL4 has been isolated from bacterial (25), fungal (14), algal (15), and nematode (9, 28) sources, but its purification from angiosperms has thus far been described only for flax by Khan et al. (18) and for cucumber in our own preliminary communica...

“…A unique feature of these seeds is that, in distinct contrast to the reserve organ endosperm in castor bean endosperm, under natural conditions the cotyledons will develop into photosynthetically functional leaf tissues. This process, which is commonly called greening, occurs when the cotyledons are exposed to light, and leads to some dramatic morphological structural changes such as the developmental formation of chloroplasts and leaf peroxisomes together with the degradation of glyoxysomes (8,9). Since there is no cell division in the cotyledons of fatty seedlings during the process of seed germination and subsequent greening (18), all the developmental events take place in a fixed number of preexisting cells.…”

mentioning

confidence: 99%

Developmental Formation of Glutamine Synthetase in Greening Pumpkin Cotyledons and Its Subcellular Localization

Nishimura

Bhusawang²,

Strzałka³

et al. 1982

During the germination of pumpkin (Cucurbita sp. Amakuri Nankin) seeds in dark, the activity of glutamine synthetase in cotyledons gradually increased, reaching a maximum at 5 to 6 days. A measurable enhancement (about 4-fold) of the enzyme activity occurred when the seedlings were exposed to continuous illumination from day 4 up to day 8. Glutamine synthetase activity was detectable only in the cytosolic fraction in the etiolated cotyledons, whereas it was found both in the cytosolic and chloroplast fractions in the green cotyledons. The two isoenzymes of glutamine synthetase have been separated by DEAE-ceilulose column chromatography of extracts from the green cotyledons. These data indicate that during the greening process the chloroplastic glutamine synthetase is newly synthesized. The roles of cytosolic and chloroplastic glutamine synthetase in germinating pumpkin cotyledons concerning assimilation of NH3 are discussed.