Biomedical subjects

A Batschauer

Publications and source records attributed to A Batschauer.

25 records · Page 2Linked to original sources

PubMed1989

The effect of light on the biosynthesis of leaf-specific thionins in barley, Hordeum vulgare.

In barley seedlings grown in the dark large amounts of thionin-specific mRNAs are present, the concentration of which rapidly declines once the seedling is exposed to light. This rapid light effect is mediated by a complex interaction of possibly two photoreceptors, phytochrome and a blue-light-absorbing photoreceptor. Parallel to the decline in mRNA content, the de novo synthesis of leaf-specific thionins ceases rapidly upon illumination of etiolated seedlings. However, thionins which have accumulated before the onset of illumination remain stable within the seedling at high concentrations. In younger leaves of mature, nonstressed barley plants grown under a 16-h-light/8-h-dark cycle thionins are still present, although at much lower concentrations. In these plants, synthesis and accumulation of thionins occur predominantly in the meristematic zone at the leaf basis, which is shielded from light through the sheath of the preceding leaf. In mature light-adapted barley plants, mRNA encoding leaf-specific thionins may reaccumulate if these plants are exposed to pathogens or other stresses. Thus, the inhibitory effect of light on the biosynthesis of thionins may be overruled by stress- and pathogen-induced signals.

Chloroplasts↗

PubMed1988

Phytochrome regulation of greening in barley : effects on mRNA abundance and on transcriptional activity of isolated nuclei.

Red light treatment of etiolated barley (Hordeum vulgare L.) seedlings causes an increase in the relative abundance of the mRNA for light-harvesting, chlorophyll a/b-binding polypeptides, and a decrease in the relative abundance of the mRNA for the NADPH:protochlorophyllide oxidoreductase. It also increases transcriptional activity of subsequently isolated nuclei for the mRNA for the chlorophyll-binding polypeptides and reduces it for the reductase. These results confirm those published previously. Fluence-response and kinetic studies support the hypothesis that the abundance of mRNA for the chlorophyll-binding polypeptides may be transcriptionally limited. They do not support the same hypothesis for the reductase. Red light treatments in the very low fluence range significantly decrease transcriptional activity in isolated nuclei for RNAs hybridizable by the reductase probe, but have little effect on mRNA abundance. By contrast, red light treatments in the low fluence range bring about a sharp decrease in reductase mRNA abundance with little further effect on transcription, suggesting light regulation at the level of mRNA stability rather than transcription. The fluence-response relationships for increase in abundance of mRNA for the chlorophyll-binding polypeptides is similar to that published elsewhere for elimination of the lag period of chlorophyll accumulation in barley. However, kinetic studies published elsewhere show that for elimination of the lag in chlorophyll accumulation, the dependence on the far red-absorbing form of phytochrome concentration is significantly different from the dependence of the transcriptional changes, suggesting that although transcription might be what limits mRNA abundance for the chlorophyll-binding proteins, the mRNA abundance can not be what limits chlorophyll accumulation per se.

Journal Article↗

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↗

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↗