PHOTOCONTROL OF ORGANELLE BIOGENESIS IN Euglena

Schwartzbach, Steven D.

doi:10.1111/j.1751-1097.1990.tb01708.x

Cited by 30 publications

(35 citation statements)

References 225 publications

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“…One is the red/blue system, which is localized in the plastids and uses Pchl(ide) as the photoreceptor (10,36). The other is the blue system, which seems to be localized outside of the plastids and whose photoreceptor has not been unequivocally defined (32,36).…”

Section: Discussionmentioning

confidence: 99%

“…The phytoflagellate Euglena gracilis is a useful model organism in studies of chloroplast differentiation because, like higher plants, it has a light requirement for the synthesis of Chl and development of photosynthetic competence (36). As with plant tissues, Euglena cells grown in complete darkness fail to accumulate Chl and, instead, form small quantities of 'Supported by National Science Foundation grant DMB85-18580. Pchl(ide).…”

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confidence: 99%

“…One of these responds to both red and blue light, is localized in the plastids, is apparently absent in certain mutant strains in which plastids are absent or nonfunctional, and has Pchl(ide) as its photoreceptor (10, 36). The other photoregulatory system responds only to blue light and retains its activity in mutant cells lacking functional plastids (32,36 (23,24). …”

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confidence: 99%

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δ-Aminolevulinic Acid Biosynthesis from Glutamatein Euglena gracilis

Mayer

Beale²

1991

Plant Physiol.

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Wild-type Euglena gracilis cells synthesize the key chlorophyll precursor, 5-aminolevulinic acid (ALA), from glutamate in their plastids. The synthesis requires transfer RNAG'U (tRNAG'U) and the three enzymes, glutamyl-tRNA synthetase, glutamyl-tRNA reductase, and glutamate-1-semialdehyde aminotransferase. Nongreening mutant Euglena strain W14ZNalL does not synthesize ALA from glutamate and is devoid of the required tRNAGIU. Other cellular tRNAG'Us present in the mutant cells were capable of being charged with glutamate, but the resulting glutamyl-tRNAs did not support ALA synthesis. Surprisingly, the mutant cells contain all three of the enzymes, and their cell extracts can convert glutamate to ALA when supplemented with tRNAGlU obtained from wild-type cells. Activity levels of the three enzymes were measured in extracts of cells grown under a number of light conditions. All three activities were diminished in extracts of cells grown in complete darkness, and full induction of activity required 72 hours of growth in the light. A light intensity of 4 microeinsteins per square meter per second was sufficient for full induction. Blue light was as effective as white light, but red light was ineffective, in inducing extractable enzyme activity above that of cells grown in complete darkness, indicating that the light control operates via the nonchloroplast blue light receptor in the mutant cells. Of the three enzyme activities, the one that is most acutely affected by light is glutamate-1-semialdehyde aminotransferase, as has been previously shown for wild-type Euglena cells. These results indicate that the enzymes required for ALA synthesis from glutamate are present in an active form in the nongreening mutant cells, even though they cannot participate in ALA formation in these cells because of the absence of the required tRNAG'U, and that the activity of all three enzymes is regulated by light. Because the absence of plastid tRNAGIU precludes the synthesis of proteins within the plastids, the three enzymes must be synthesized in the cytoplasm and their genes encoded in the nucleus in Euglena. Pchl(ide). Exposure to light brings about the conversion of these pigments to Chl(ide), and in continuous light this is followed by a phase of rapid Chl accumulation (17) and transformation of the developing plastids into photosynthetically functional chloroplasts (37).The source of plastid tetrapyrrole pigments in Euglena, as in higher plants, algae, cyanobacteria, and other oxygenic organisms, is ALA2 that is formed from glutamate via the tRNA-dependent five-carbon pathway (26, 39). The fivecarbon pathway begins with activation of glutamate by ligation to tRNAGIU, catalyzed by glutamyl-tRNA synthetase, followed by reduction of the activated glutamate to GSA, catalyzed by glutamyl-tRNA reductase, and transamination of the GSA, catalyzed by GSA aminotransferase, to yield ALA (2).Unlike other oxygenic organisms, Euglena also has the ability to form ALA via the route used by animals, yeasts, and certain bacterial groups,...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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δ-Aminolevulinic Acid Biosynthesis from Glutamatein Euglena gracilis

Mayer

Beale²

1991

Plant Physiol.

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“…The phytoflagellate Euglena gracilis shares with higher plants a light requirement for Chl synthesis and the development of photosynthetic competence (33). As with plant tissues, Euglena cells grown in complete darkness fail to accumulate Chl, and instead form small quantities of Pchl(ide).…”

mentioning

confidence: 99%

“…One of these responds to both red and blue light, appears to be localized in the plastids, is lacking in certain mutant strains having nonfunctional or absent plastids, and is thought to have protochlorophyllide as its photoreceptor (10,33). The other photoregulatory system responds only to blue light and retains its function in mutant cells lacking functional plastids (30,33).…”

mentioning

confidence: 99%