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K Apel

Publications and source records attributed to K Apel.

At least 73 records · Page 4Linked to original sources
PubMed1989

Nucleotide sequence of a cDNA coding for the NADPH-protochlorophyllide oxidoreductase (PCR) of barley (Hordeum vulgare L.) and its expression in Escherichia coli.

The primary structure of the NADPH-protochlorophyllide oxidoreductase of barley has been deduced from the nucleotide sequence of a cloned full-length cDNA. This cDNA hybridizes to a 1.7 kb RNA whose steady-state level in dark-grown seedlings is drastically reduced upon illumination. The predicted amino acid sequence (388 residues in length) includes a transit peptide of 74 amino acids whose end point has been delimited by sequencing the N-terminus of the mature protein. Expression of the cDNA in Escherichia coli leads to the synthesis of an enzymatically active precursor of the NADPH-protochlorophyllide oxidoreductase. Activity of this protein in bacterial lysates is completely dependent on the presence of NADPH and protochlorophyllide and requires light.

Amino Acid Sequence↗
PubMed1988

Phonological and spatial processing abilities in language- and reading-impaired children.

In the present study, we further examined (see Kamhi & Catts, 1986) the phonological processing abilities of language-impaired (LI) and reading-impaired (RI) children. We also evaluated these children's ability to process spatial information. Subjects were 10 LI, 10 RI, and 10 normal children between the ages of 6:8 and 8:10 years. Each subject was administered eight tasks: four word repetition tasks (monosyllabic, monosyllabic presented in noise, three-item, and multisyllabic), rapid naming, syllable segmentation, paper folding, and form completion. The normal children performed significantly better than both the LI and RI children on all but two tasks: syllable segmentation and repeating words presented in noise. The LI and RI children performed comparably on every task with the exception of the multisyllabic word repetition task. These findings were consistent with those from our previous study (Kamhi & Catts, 1986). The similarities and differences between LI and RI children are discussed.

Child↗
PubMed1987

Cognitive strengths and weaknesses in language-impaired children: one more look.

The hypothesis-testing abilities of 15 language-impaired and 15 normally developing children matched for mental age were investigated using discrimination-learning tasks. The subjects in both groups were presented with two sets of discrimination-learning problems. One set of problems featured explicit input concerning the correct response choice. The other set of problems featured nonexplicit input. The results revealed both differences in the performance of the MA-matched and language-impaired children and differences in performance on the two types of problems. The children in both groups solved more of the explicit input problems than the nonexplicit input problems. In addition, the MA-matched children performed significantly better than the language-impaired children, particularly on the nonexplicit problems. The findings suggested that the language-impaired children exhibited deficits in solving discrimination-learning problems. The deficits exhibited by the language-impaired children seemed related to deficits in their ability to encode information.

Child↗
PubMed1986

The light-dependent accumulation of the P700 chlorophyll a protein of the photosystem I reaction center in barley. Evidence for translational control.

The light-dependent accumulation of the P700 chlorophyll a protein of the photosystem I reaction center has been studied in greening barley (Hordeum vulgare L.) seedlings. Immunoblot analysis of total cellular protein fractions and immunogold labelling of the P700 chlorophyll a protein in ultrathin sections of Lowicryl-embedded leaf tissue revealed that the concentration of this chlorophyll-binding protein in plastids of dark-grown barley seedlings is below the limit of detection. Upon illumination with white light, a rapid accumulation of this protein is induced. This light effect seems not to be regulated at the level of transcription. The gene for the P700 chlorophyll a protein has been mapped within the large single-copy region of the plastid DNA of barley. High levels of transcripts of this gene are present already in dark-grown seedlings and remain fairly constant throughout an extended illumination period. Polysomes were isolated from etioplasts and chloroplasts. The same high relative concentration of mRNA encoding the P700 chlorophyll a protein was present in both polysome fractions. This result suggests that the light-dependent accumulation of the P700 chlorophyll a protein during chloroplast formation in barley seedlings is regulated at the translational, or posttranslational, level.

Chlorophyll↗
PubMed1986

Tissue-specific and light-dependent changes of chromatin organization in barley (Hordeum vulgare).

The DNase I sensitivity of the nuclear genes encoding the NADPH-protochlorophyllide oxidoreductase, the light-harvesting chlorophyll a/b protein (LHCP), the hordeins and a 15-kDa protein of unknown function was assayed in chromatin of etiolated and green leaves and endosperm tissue of barley (Hordeum vulgare L.). A tissue-specific differentiation of chromatin structure was found for the LHCP, hordein and 15-kDa protein genes. The genes for the LHCP and the 15-kDa protein, which are expressed in leaf tissue, display DNase I sensitivity in leaves but not in endosperm. Hordein genes which are expressed solely in endosperm, were insensitive to low levels of digestion with DNase I in leaves but sensitive in endosperm. The effect of light on chromatin structure was determined by comparing leaves of etiolated plants and plants which had been grown under a day/night cycle. Only in the case of the 15-kDa protein is there a remarkable change from a DNAse-I-sensitive configuration in etiolated leaves to a more resistant one in leaves from illuminated plants. The gene for the NADPH-protochlorophyllide oxidoreductase was found to be equally sensitive to DNase I in leaves and endosperm.

Chlorophyll↗
PubMed1986

The implication of a plastid-derived factor in the transcriptional control of nuclear genes encoding the light-harvesting chlorophyll a/b protein.

In carotenoid-deficient albina mutants of barley and in barley plants treated with the herbicide Norflurazon the light-dependent accumulation of the mRNA for the light-harvesting chlorophyll a/b protein (LHCP) is blocked. Thus, the elimination of a functional chloroplast, either as a result of mutation or as a result of herbicide treatment, can lead to the specific suppression of the expression of a nuclear gene encoding a plastid-localized protein. These results confirm and extend earlier observations on maize [Mayfield and Taylor (1984) Eur. J. Biochem. 144, 79-84]. The inhibition of mRNA accumulation appears to be specific for the LHCP; the mRNAs encoding the small subunit of ribulose-1,5-bisphosphate carboxylase and the NADPH: protochlorophyllide oxidoreductase are relatively unaffected. The failure of the albina mutants and of Norflurazon-treated plants to accumulate the LHCP mRNA is not exclusively caused by an instability of the transcript but rather by the inability of the plants to enhance the rate of transcription of the LHCP genes during illumination. Several chlorophyll-deficient xantha mutants of barley, which are blocked after protoporphyrin IX or Mg-protoporphyrin, and the chlorophyll-b-less mutant chlorina f2 accumulate the LHCP mRNA to almost normal levels during illumination. Thus, if any of the reactions leading to chlorophyll formation is involved in the control of LHCP mRNA accumulation it should be one between the formation of protochlorophyllide and the esterification of chlorophyllide a. While the nature of the regulatory factor(s) has not been identified our results suggest that, in addition to phytochrome (Pfr), plastid-dependent factors are required for a continuous light-dependent transcription of nuclear genes encoding the LHCP.

Carotenoids↗
PubMed1985

Phytochrome control of in vitro transcription of specific genes in isolated nuclei from barley (Hordeum vulgare).

The transcriptional rates of four different genes in shoots of barley grown under different light regimes were quantified by monitoring nuclear RNA transcripts using gene-specific hybridization probes. Isolated nuclei were pulse-labelled with [alpha-32P]UTP and the relative rates of light-harvesting chlorophyll a/b protein (LHCP) mRNA, NADPH:protochlorophyllide oxidoreductase mRNA, B1 hordein mRNA, and 26-S rRNA synthesis were measured. Irradiation of dark-grown plants with a red light pulse increased the rate of LHCP mRNA synthesis tenfold within 3 h, and the rate of rRNA synthesis more than twofold within 9 h. The relative rate of synthesis of the oxidoreductase mRNA decreased following a red light pulse reaching a minimum after 3-6 h. As a direct proof of phytochrome involvement in the light-induced stimulation of LHCP and the repression of the oxidoreductase transcripts for both responses, red/far-red reversibility could be demonstrated. We conclude that phytochrome is able both to increase the transcription of certain nuclear genes and decrease the transcription of others.

Cell Nucleus↗
PubMed1984

An inverse control by phytochrome of the expression of two nuclear genes in barley (Hordeum vulgare L.).

During the light-dependent transformation of etioplasts to chloroplasts a rapid decrease of the NADPH-protochlorophyllide oxidoreductase is induced. At the same time the mRNA activity coding for this enzyme protein also declines rapidly under the influence of phytochrome (Pfr). On the other hand the apoprotein of the light-harvesting chlorophyll a/b protein and its mRNA activity are inversely affected by the same photoreceptor. Cloned cDNA sequences which are complementary to these mRNAs have been used to assess the effect of phytochrome (Pfr) on the concentration of the two transcripts. The phytochrome-induced changes of the two translatable mRNAs are paralleled by corresponding changes in the steady-state concentration of the mRNA sequences. This inverse relationship between the light-dependent regulation of the NADPH-protochlorophyllide oxidoreductase and the light-harvesting chlorophyll a/b protein suggests that a single reversible triggering event can increase the transcription of certain genes and decrease the transcription of others.

Chlorophyll↗
PubMed1984

The proteolytic degradation in vitro of the NADPH-protochlorophyllide oxidoreductase of barley (Hordeum vulgare L.).

A cell-free membrane system has been developed from isolated barley etioplasts which displays a highly selective decrease of the NADPH-protochlorophyllide oxidoreductase in vitro which is indistinguishable from that observed previously in the intact plant. The rapid breakdown of the enzyme protein in vitro is caused by a membrane-bound proteolytic activity. The protease is essentially independent of pH in the physiological pH range of 6 to 8.5. The optimum temperature for the reaction is approximately 40 degrees C. In the presence of excessive protochlorophyllide the enzyme is no longer degraded or inactivated during illumination of dark-grown plants. In the isolated membrane fraction protochlorophyllide also enhances the stability of the enzyme, a similar effect is exerted by NADPH but not by NADH. The results suggest that the inactivation of the NADPH-protochlorophyllide oxidoreductase is influenced by the interaction of the enzyme with protochlorophyllide and NADPH. In the absence of these two components the enzyme becomes susceptible to proteolytic degradation.

Edible Grain↗
PubMed1983

The phytochrome-controlled accumulation of mRNA sequences encoding the light-harvesting chlorophyll a/b protein of barley (Hordeum vulgare L.).

Double-stranded cDNA was synthesized from polysomal poly(A)-containing RNA of illuminated barley plants and was inserted into the PstI site of the bacterial plasmid pBR322. Two different strategies were used for the screening of the bacterial colonies. Light-regulated sequences were detected by differential hybridization with cDNA of polyadenylated RNA from dark-grown and illuminated barley plants. For a second screening step partially purified mRNAs encoding the light-harvesting chlorophyll a/b protein were used for the synthesis of another cDNA probe. By using these procedures a cDNA clone was isolated which encodes a constitutive polypeptide of the light-harvesting chlorophyll a/b protein. This cloned cDNA has been used to assess the effect of phytochrome on the steady-state level of mRNA sequences encoding the light-harvesting chlorophyll a/b protein. The mRNA is almost undetectable in dark-grown plants. Following treatment with red light, the concentration of this mRNA sequence increases rapidly during the subsequent dark period. This red light effect can be reversed substantially by irradiation with far-red light. These results indicate that not only the amount of mRNA activity as shown previously, but also the steady-state level of mRNA sequences encoding the light-harvesting chlorophyll a/b is controlled by phytochrome.

Base Sequence↗
PubMed1983

The light-dependent control of chloroplast development in barley (Hordeum vulgare L).

The light-induced greening of etiolated barley plants is used as a model to study the light-dependent control of plastid development. Upon illumination a rapid transformation of etioplasts to chloroplasts is induced. The effect of illumination does not only include the light-dependent chlorophyll synthesis but also the appearance or decline of specific proteins within the plastid membrane fractions. So far two of these proteins have been studied in detail. The light-harvesting chlorophyll a/b protein (LHCP) is one of the major protein constituents of the thylakoid membrane of chloroplasts. However, this protein is not detectable among the membrane polypeptides of etioplasts. Illumination of dark-grown barley plants induces a massive insertion of the LHCP. The appearance of the protein is controlled by the cooperation of at least two distinct photoreceptors: protochlorophyllide and phytochrome. In dark-grown barley plants not only the LHCP but also its mRNA is not detectable. The light-dependent appearance of mRNA activity for the LHCP is under the control of phytochrome (Pfr). Even though the appearance of mRNA activity is induced via Pfr by a single red light pulse, the assembly of the complete LHCP takes place only under continuous illumination, which allows chlorophyll synthesis. The second protein analyzed so far is the NADPH-protochlorophyllide-oxidoreductase. This enzyme catalyzes the light-dependent reduction of protochlorophyllide to chlorophyllide and thus controls one of the first detectable light-dependent reactions during the greening period. It is generally assumed that this enzyme is responsible for the overall chlorophyll synthesis and accumulation during the greening period.(ABSTRACT TRUNCATED AT 250 WORDS)

Chlorophyll↗
PubMed1981

The protochlorophyllide holochrome of barley (Hordeum vulgare L.). Phytochrome-induced decrease of translatable mRNA coding for the NADPH: protochlorophyllide oxidoreductase.

During the illumination of dark-grown barley plants light induces a rapid decrease of a translatable mRNA which codes for a polypeptide of Mr 44000. This component was identified as a precursor of the NADPH:protochlorophyllide oxidoreductase. The precursor has an Mr larger than the authentic protein by approximately 8000. The light-induced change in the level of translatable mRNA can be induced by a 15-s red-light pulse followed by 5 h of darkness. The red-light effect is reversed by a subsequent far-red-light treatment. It is concluded that the light-induced decline of translatable mRNA for the NADPH:protochlorophyllide oxidoreductase is controlled by phytochrome. The significance of this finding for present concepts of light-dependent control of chloroplast development and chlorophyll synthesis is discussed.

Electrophoresis, Polyacrylamide Gel↗
PubMed1981

The protochlorophyllide holochrome of barley (Hordeum vulgare L.). The effect of light on the NADPH:protochlorophyllide oxidoreductase.

During the illumination of etiolated barley plants a rapid decline of the NADPH: protochlorophyllide oxidoreductase is observed. Within the first 5 min of continuous light approximately 90% of the enzyme activity present in dark-grown barley plants disappears and, at the same time, the amount of enzyme protein is diminished by more than 60%. No stable polypeptide fragments have been found which might be formed during the light-induced degradation of the enzyme protein. The rate of enzyme protein synthesis is not drastically affected at the beginning of the illumination period. During the subsequent light-dependent chloroplast development a phytochrome-induced decline in the rate of protein synthesis, concomittant with a continuous light-dependent degradation of the enzyme protein, leads to a progressive decrease of the concentration of the enzyme. After 6 h of continuous light, when the rate of chlorophyll accumulation is at its greatest, only traces of the enzyme protein are visible and the enzyme activity is no longer detectable within the plants. In contrast to previous concepts of chlorophyll biosynthesis in higher plants, our results present evidence that the NADPH: protochlorophyllide oxidoreductase functions only for a short time period after the onset of light.

Darkness↗
PubMed1980

The protochlorophyllide holochrome of barley (Hordeum vulgare L.). Isolation and characterization of the NADPH:protochlorophyllide oxidoreductase.

The NADPH:protochlorophyllide oxidoreductase of barley has been solubilized from etioplast membranes and purified to apparent homogeneity. The highest specific activity measured for the purified enzyme was 1.6 nmol chlorophyllide formed (mg protein-1) per flash. Electrophoretic analysis of the purified enzyme on sodium dodecylsulfate/polyacrylamide gels revealed only one polypeptide of Mr 36000. Durig glycerol gradient centrifugation the enzyme migrates as a low-molecular-weight component. It is proposed that each enzyme molecule contains only one polypeptide chain. Assuming a molecular weight of 36000 for the enzyme, it was calculated that two or three protochlorophyllide molecules are bound to each enzyme molecule.

Chlorophyll↗
PubMed1978

The plastid membranes of barley (Hordeum vulgare). Light-induced appearance of mRNA coding for the apoprotein of the light-harvesting chlorophyll a/b protein.

Illumination of dark-grown barley plants induces a massive insertion of the light-harvesting chlorophyll a/b protein into the developing thylakoid membrane. In addition to the onset of chlorophyll synthesis, light induces specifically the appearance of a prominent mRNA species which codes for a polypeptide of Mr 29500. This component was identified as a precursor of the apoprotein of the light-harvesting chlorophyll a/b protein. The precursor has an Mr larger than the authentic protein by approximately 4000. Studies of the chlorophyll-b-less mutant chlorina f2 of barley offer the first clue to the mechanism which controls the light-dependent mRNA formation. The induction of the mRNA coding for the aproprotein of the light-harvesting chlorophyll a/b protein does not seem to be linked directly to the assembly process of the light-harvesting structure and does not require chlorophyll b. It is proposed that light exerts its influence on the mRNA formation by a reaction which is different from the phototransformation of protochlorophyll(ide) to chlorophyll(ide).

Cell Membrane↗
PubMed1977

The light-harvesting chlorophylla a/b.protein complex of the green alga Acetabularia mediterranea. Isolation and characterization of two subunits.

In the green alga Acetabularia mediterranea a light-harvesting chlorophyll a/b.protein complex of 67 000 daltons has been found which contains two polypeptide chains of 21 500 and 23 000 daltons. These two polypeptides were isolated on a preparative scale and were further characterized by several different methods. Both polypeptides proved to be very similar. While their amino acid and sugar compositions as well as their immunochemical properties were almost identical the tryptic peptides and the cyanogen bromide fragments of the two polypeptides revealed minor but significant differences. The 67 000-dalton chlorophyll a/b.protein complex and its two polypeptide components were compared to the light-harvesting chlorophyll a/b.protein of higher plants.

Acetabularia↗