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1.
Chlorophyll synthesis in Euglena, as in higher plants, occurs only in the light. The key chlorophyll precursor, δ-aminolevulinic acid (ALA), is formed in Euglena, as in plants, from glutamate in a reaction sequence catalyzed by three enzymes and requiring tRNAGlu. ALA formation from glutamate occurs in extracts of light-grown Euglena cells, but activity is very low in dark-grown cell extracts. Cells grown in either red (650-700 nanometers) or blue (400-480 nanometers) light yielded in vitro activity, but neither red nor blue light alone induced activity as high as that induced by white light or red and blue light together, at equal total fluence rates. Levels of the individual enzymes and the required tRNA were measured in cell extracts of light- and dark-grown cells. tRNA capable of being charged with glutamate was approximately equally abundant in extracts of light- and dark-grown cells. tRNA capable of supporting ALA synthesis was approximately three times more abundant in extracts of light-grown cells than in dark-grown cell extracts. Total glutamyl-tRNA synthetase activity was nearly twice as high in extracts of light-grown cells as in dark-grown cell extracts. However, extracts of both light- and dark-grown cells were able to charge tRNAGlu isolated from light-grown cells to form glutamyl-tRNA that could function as substrate for ALA synthesis. Glutamyl-tRNA reductase, which catalyzes pyridine nucleotide-dependent reduction of glutamyl-tRNA to glutamate-1-semialdehyde (GSA), was approximately fourfold greater in extracts of light-grown cells than in dark-grown cell extracts. GSA aminotransferase activity was detectable only in extracts of light-grown cells. These results indicate that both the tRNA and enzymes required for ALA synthesis from glutamate are regulated by light in Euglena. The results further suggest that ALA formation from glutamate in dark-grown Euglena cells may be limited by the absence of GSA aminotransferase activity. 相似文献
2.
3.
Summary NADPH : protochlorophyllide oxidoreductase (pchlide reductase, EC 1.6.99.1) catalyzes the light-dependent reduction of protochlorophyllide in higher plants. Cloned cDNAs encoding two distinct pchlide reductases were isolated from a gt11 library constructed from poly(A)+ RNA prepared from the cotyledons of dark-grown white pine (Pines strobes) seedlings and a nuclear gene (lpcr) analogous to one of these cDNAs has been characterized from loblolly pine (P. taeda). The pine gene encodes an approximately 43 kDa precursor polypeptide consisting of a 334-amino acid mature protein and a 66-amino acid transit peptide. The deduced primary structures for the pine proteins are highly homologous to those reported from monocots and dicots. The coding portion of the pine lpcr gene is interrupted by four introns. The placement of these introns within the pine lpcr gene is identical to that observed in pea (Pisum sativum), suggesting conservation in gene organization between dicot and gymnosperm species. Western blot analysis using polyclonal antiserum against oat pchlide reductase detected in extracts of dark-grown pine cotyledons a single immunoreactive protein, which declined in abundance during a 48 h period of illumination with white light. Cotyledons of dark-grown seedlings were also found to accumulate high levels of pchlide reductase mRNA; however, little or no change in the steady-state levels of mRNA encoding pchlide reductase was observed in these tissues following illumination. Stem tissue of dark-grown seedlings did not contain significant levels of pchlide reductase mRNA, whereas stems of light-grown plants of the same age accumulated substantial amounts of the message. These results suggest that light and the developmental age of the tissue affect regulation of lpcr expression in pine. 相似文献
4.
Isolation of the Red-light-absorbing Form of Phytochrome from Light-grown Pea Shoots 总被引:1,自引:0,他引:1
Shimazaki Yukio; Moriyasu Yuji; Pratt Lee H.; Furuya Masaki 《Plant & cell physiology》1981,22(7):1165-1173
Phytochrome was extracted from both light-grown and dark-grownshoots of Pisum and partially purified by brushite chromatographyand ammonium sulfate fractionation. About 160270 ng ofphytochrome per g green tissue extracted was recovered afterthe partial purification while about 5.18.6 µgof phytochrome per g etiolated tissue was recovered. Only thered-light-absorbing form of phytochrome was detected in extractsprepared from both light- and dark-grown tissue, even thoughthe light-grown tissue was harvested in daylight and purificationwas done entirely at 04°C with only a dim green safelight. No significant differences were found between phytochromepurified from green and etiolated tissues, either in their spectralproperties or in their immunochemical reactivity against antietiolated-zucchini-phytochromeserum.
1 Permanent address: Botany Department, University of Georgia,Athens, Georgia 30602, U.S.A (Received June 10, 1981; Accepted August 6, 1981) 相似文献
5.
The transfer and integration of tRNA genes from organellar genomes to the nuclear genome and between organellar genomes occur
extensively in flowering plants. The routes of the genetic materials flowing from one genome to another are biased, limited
largely by compatibility of DNA replication and repair systems differing among the organelles and nucleus. After thoroughly
surveying the tRNA gene transfer among organellar genomes and the nuclear genome of a domesticated rice (Oryza sativa L. ssp. indica), we found that (i) 15 mitochondrial tRNA genes originate from the plastid; (ii) 43 and 80 nuclear tRNA genes are mitochondrion-like
and plastid-like, respectively; and (iii) 32 nuclear tRNA genes have both mitochondrial and plastid counterparts. Besides
the native (or genuine) tRNA gene sets, the nuclear genome contains organelle-like tRNA genes that make up a complete set
of tRNA species capable of transferring all amino acids. More than 97% of these organelle-like nuclear tRNA genes flank organelle-like
sequences over 20 bp. Nearly 40% of them colocalize with two or more other organelle-like tRNA genes. Twelve of the 15 plastid-like
mitochondrial tRNA genes possess 5′- and 3′-flanking sequences over 20 bp, and they are highly similar to their plastid counterparts.
Phylogenetic analyses of the migrated tRNA genes and their original copies suggest that intergenomic tRNA gene transfer is
an ongoing process with noticeable discriminatory routes among genomes in flowering plants.
Electronic Supplementary Material Electronic Supplementary material is available for this article at
and accessible for authorised users.
Reviewing Editor: Dr. David Guttman 相似文献
6.
Ultrastructural and biochemical approaches were used to investigate the mode of action of tagetitoxin, a nonhost-specific phytotoxin produced by Pseudomonas syringae pv. tagetis (Hellmers) Young, Dye and Wilkie, which causes chlorosis in developing — but not mature — leaves. Tagetitoxin has no effect on the growth rate or morphology of developing leaves of wheat (Triticum aestivum L.) seedlings. Its cytological effects are limited to plastid aberrations; in both light-and dark-grown leaves treated with toxin, internal plastid membranes fail to develop normally and plastid ribosomes are absent, whereas mitochondrial and cytoplasmic ribosomes are unaffected. The activity of a plastid stromal enzyme, ribulose-1,5-bisphosphate carboxylase (RuBPCase, EC 4.1.1.39), which is co-coded by nuclear and chloroplast genes, is markedly lower in extracts of both light-and dark-grown toxin-treated leaves, whereas the activity of another stromal enzyme, NADP-glyceraldehyde-3-phosphate dehydrogenase (NADP-G-3P-DH, EC 1.2.1.13), which is coded only by the nuclear genome, is significantly lower in extracts of light-grown, but not of dark-grown, treated leaves. The mitochondrial enzymes fumarase (EC 4.2.1.2) and cytochrome-c oxidase (EC 1.9.3.1) are unaffected by toxin in dark-grown leaves, but fumarase activity is reduced in light-grown ones. Four peroxisomal enzyme activities are lowered by toxin treatment in both light- and dark-grown leaves. Light- and dark-grown, toxintreated leaves contain about 50% and 75%, respectively, of the total protein of untreated leaves. There are threefold and twofold increases in free amino acids in light-grown and dark-grown treated leaves, respectively. In general, the effects of tagetitoxin are more extensive and exaggerated in light-grown than in dark-grown leaves. We conclude that tagetitoxin interferes primarily with a light-independent aspect of chloroplast-specific metabolism which is important in plastid biogenesis.Abbreviations NADP-G-3-DH
NADP-glyceraldehyde-3-phosphate dehydrogenase
- PLB
prolamellar body
- RuBP-Case
ribulose-1,5-bisphosphate carboxylase
- SADH
shikimic acid dehydrogenase 相似文献
7.
IS elements were identified in the genomes of five Acidithiobacillus ferrooxidans strains isolated from various media. IST2 elements were revealed in all the strains grown in a medium with ferrous iron,
ISAfe1 elements were detected in four strains (TFBk, TFL-2, TFV-1 and TFO). Three strains (TFV-1, TFN-d and TFO) were found
to contain IS elements, ~600 bp long. These were named preliminary as ISAfe600. Partial sequencing of the 5′- and 3′-terminal
nucleotide stretches of an ISAfe1 element in TFBk and TFL-2 strains and complete sequencing of the ISAfe1 element in the TFBk
strain has revealed nucleotide substitutions as compared to the prototype, i.e., the ISAfe1 element of an ATCC 19859 strain.
Partial sequencing of the 5′- and 3′-terminal nucleotide stretches of the IST2 elements in TFO, TFBk and TFL-2 strains has
shown numerous nucleotide substitutions when compared to the IST2 element of an ATCC 19859 strain. Complete sequencing of
the IST2 element in the TFBk strain has revealed: the divergence between the IST2 elements in the TFBk strain and the prototype
was 21.2%. Southern hybridization of EcoRI fragments of the chromosomal DNA from five A. ferrooxidans strains grown in a medium with ferrous iron using an internal region of ISAfe1, a full-length ISAfe1 or a full-length IST2
as probes has shown them to differ in the number of copies of IS elements and their localization on the chromosomes. Adaptation
to elemental sulfur in A. ferrooxidans strains caused changes in the number, intensity and localization of hybridization bands. The authors discuss the role of
IS elements in the adaptation of A. ferrooxidans to the new energy substrate.
The nucleotide sequence data reported in this paper were deposited in GenBank under accession numbers: AY823401, the ISAfe1
from A. ferrooxidans TFBk; AY825254, the IST2 from TFBk; DQ002894, the 5′-terminal nucleotide sequence of ISAfe1 from TFL-2; DQ002895, the 3′-terminal
nucleotide sequence of ISAfe1 from TFL-2; DQ005952, the 5′-terminal nucleotide sequence of IST2 from TFV-1; DQ005953, the
3′-terminal nucleotide sequence of IST2 from TFV-1. 相似文献
8.
The amounts of plastid DNA in the primary leaves of 4-d-oldlight- and dark-grown seedlings of Avena sativa were measuredby microspectrofluorometry using the DNA-fluorochrome DAPI (4',6-diamidino-2-phenylindole). In the light-grown primary leaves (4045 mm long) therewas a marked increase in DNA level per plastid from 10.2 to18.5 ? 1015 g between 2.0 mm and 10 mm from the leafbase, resulting from the rate of plastid DNA synthesis beinghigher than the rate of plastid division. Beyond 30 mm the plastidDNA level was reduced to 14 ? 1015g due to chloroplastdivision rates being higher than the rate of plastid DNA synthesis,while from 20 mm plastid DNA levels were constant at 2.2 ? 1012g per cell, which corresponds to 16000 plastome copies per cell. Observations of dark-grown leaves establish that, in Avena,light is not necessary for plastid division and the dark-grownleaf cells accumulate higher amounts of plastid DNA than light-grownleaf cells. Plastid nucleoids showed a change of distribution after completionof plastid DNA synthesis in light-grown leaves. A change inthe distribution of plastid nucleoids was also observed duringthe greening of etioplasts of dark-grown leaves while plastidDNA level remained constant. Such changes in plastid nucleoiddistribution appear to be independent of plastid DNA synthesisand correlate with the formation of grana stacks. Key words: Avena sativa, microspectrofluorometry, plastid DNA 相似文献
9.
The contents in minor nucleotides of total transfer RNA (tRNA) of etiolated and light-grown wheat (Triticum aestivum L.) seedlings and of seedlings illuminated for 24 or 48 h were examined. The total tRNA of seedlings illuminated 24 h contained more, and that from seedlings illuminated 48 h still more modified nucleotides than that from etiolated ones. Thus, the appearance of the characteristic minor nucleotides of tRNA of light-grown wheat seedlings needs a rather long greening period, of at least 48 h. 相似文献
10.
Pinus palustris has a greatly reduced need for light to initiate chloroplast development in comparison to angiosperms. Light is not required for chlorophyll synthesis in dark-grown Pinus palustris seedlings. However, embryos do not contain chlorophyll, and synthesis is limited to seedlings having cotyledon lengths between about 0.5 cm and 2.0 cm. The final amount of chlorophyll accumulated by dark-grown seedlings is about one fifth of that in light-grown seedlingsat the same stage. The major light-harvesting chlorophyll a/b-polypeptides of Photosystem II (LHC IIb) are absent in the embryos but begin to accumulate in seedlings of 0.5 cm cotyledon length, irrespective of the light conditions. Although dark-grown seedlings accumulate most of the pigmented complexes seen in light-grown seedlings, there are differences in the subunit structure of some of them. These findings suggest that the majority of the components of the photosynthetic membrane do not require light for induction of synthesis or assembly into complexes, but that the final forms seen in light-grown seedlings may require light.Abbreviations ALA
5-amino levulinic acid
- glucoside
-D-glucopyranoside
- LHC
light-harvesting complex
-
lhc
genes encoding LHCs
- PS
photosystem 相似文献