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Biomedical subjects

H K Lichtenthaler

Publications and source records attributed to H K Lichtenthaler.

At least 19 recordsLinked to original sources
PubMed2001

Chlorophyta exclusively use the 1-deoxyxylulose 5-phosphate/2-C-methylerythritol 4-phosphate pathway for the biosynthesis of isoprenoids.

The biosynthesis of the C5 building block of isoprenoids, isopentenyl diphosphate (IPP), proceeds in higher plants via two basically different pathways; in the cytosolic compartment sterols are formed via mevalonate (MVA), whereas in the plastids the isoprenoids are formed via the 1-deoxyxylulose 5-phosphate/2-C-methylerythritol 4-phosphate pathway (DOXP/MEP pathway). In the present investigation, we found for the Charophyceae, being close relatives to land plants, and in the original green flagellate Mesostignma virilde the same IPP biosynthesis pattern as in higher plants: sterols are formed via MVA, and the phytol-moiety of chlorophylls via the DOXP/MEP pathway. In contrast, representatives of four classes of the Chlorophyta (Chlorophyceae, Ulvophyceae, Trebouxiophyceae, Prasinophyceae) did not incorporate MVA into sterols or phytol. Instead, they incorporated [1-2H1]-1-deoxy-D-xylulose into phytol and sterols. The results indicate that the entire Chlorophyta lineage, which is well separated from the land plant/Charophyceae lineage, is devoid of the acetate/ MVA pathway and uses the DOXP/MEP pathway not only for plastidic, but also for cytosolic isoprenoid formation.

Carbon Radioisotopes↗
PubMed2001

Biosynthesis of 2-methyl-3-buten-2-ol emitted from needles of Pinus ponderosa via the non-mevalonate DOXP/MEP pathway of isoprenoid formation.

The volatile hemiterpene 2-methyl-3-buten-2-ol (MBO) is emitted from the needles of several pine species from the Western United States and contributes to ozone formation in the atmosphere. It is synthesised enzymatically from dimethylallyl diphosphate (DMAPP). We show here that needles of Pinus ponderosa Laws. incorporated [1-2H1]-1-deoxy-D-xylulose (d-DOX) into the emitted MBO, but not D,L-[2-13C]mevalonic acid lactone. Furthermore, MBO emission was inhibited by fosmidomycin, a specific inhibitor of the second enzyme of the mevalonate-independent pathway of isopentenyl diphosphate and DMAPP formation, i.e. the 1-deoxy-D-xylulose 5-phosphate/2-C-methyl-D-erythritol 4-phosphate (DOXP/MEP) pathway. We thus prove that MBO emitted from needles of P. ponderosa is primarily formed via the DOXP/MEP pathway.

Hemiterpenes↗
PubMed2000

Non-mevalonate isoprenoid biosynthesis: enzymes, genes and inhibitors.

The essential steps of the novel non-mevalonate pathway of isopentenyl diphosphate and isoprenoid biosynthesis in plants are described. The first five enzymes and genes of this 1-deoxy-D-xylulose 5-phosphate/2-C-methyl-D-erythritol 4-phosphate (DOXP/MEP) pathway are known. The herbicide fosmidomycin specifically blocks the second enzyme, the DOXP reductoisomerase. The DOXP/MEP pathway is also present in several pathogenic bacteria and the malaria parasite. Hence, all herbicides and inhibitors blocking this novel isoprenoid pathway in plants are also potential drugs against malaria and diseases caused by pathogenic bacteria.

Aldose-Ketose Isomerases↗
PubMed2000

Properties and inhibition of the first two enzymes of the non-mevalonate pathway of isoprenoid biosynthesis.

Enzymes of the 1-deoxy-D-xylulose 5-phosphate/2-C-methylerythritol 4-phosphate (DOXP/MEP) pathway are targets for new herbicides and antibacterial drugs. Until now, no inhibitors for the DOXP synthase have been known of. We show that one of the breakdown products of the herbicide clomazone affects the DOXP synthase. One inhibitor of the non-mevalonate pathway, fosmidomycin, blocks the DOXP reductoisomerase (DXR) of plants and bacteria. The I(50) values of plants are, however, higher than those found for the DXR of Escherichia coli. The DXR of plants, isolated from barley seedlings, shows a pH optimum of 8.1, which is typical for enzymes active in the chloroplast stroma.

Aldose-Ketose Isomerases↗
PubMed1999

Inhibitors of the nonmevalonate pathway of isoprenoid biosynthesis as antimalarial drugs.

A mevalonate-independent pathway of isoprenoid biosynthesis present in Plasmodium falciparum was shown to represent an effective target for chemotherapy of malaria. This pathway includes 1-deoxy-D-xylulose 5-phosphate (DOXP) as a key metabolite. The presence of two genes encoding the enzymes DOXP synthase and DOXP reductoisomerase suggests that isoprenoid biosynthesis in P. falciparum depends on the DOXP pathway. This pathway is probably located in the apicoplast. The recombinant P. falciparum DOXP reductoisomerase was inhibited by fosmidomycin and its derivative, FR-900098. Both drugs suppressed the in vitro growth of multidrug-resistant P. falciparum strains. After therapy with these drugs, mice infected with the rodent malaria parasite P. vinckei were cured.

Aldose-Ketose Isomerases↗
PubMed1999

Cloning and heterologous expression of a cDNA encoding 1-deoxy-D-xylulose-5-phosphate reductoisomerase of Arabidopsis thaliana.

Various plant isoprenoids are synthesized via the non-mevalonate pathway of isopentenyl diphosphate formation. In this pathway, 1-deoxy-D-xylulose 5-phosphate (DOXP), the first intermediate, is transformed to 2-C-methyl-D-erythritol 4-phosphate (MEP) by an enzyme which was recently cloned from Escherichia coli. In order to find a plant homologue of this 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) we cloned a cDNA fragment from Arabidopsis thaliana which has high homology to the E. coli DXR. By expression of this fragment in E. coli we could demonstrate that it encodes a protein which transforms DOXP to MEP. The antibiotic fosmidomycin specifically inhibits this DXR enzyme activity.

Aldose-Ketose Isomerases↗
PubMed1998

Distribution of the mevalonate and glyceraldehyde phosphate/pyruvate pathways for isoprenoid biosynthesis in unicellular algae and the cyanobacterium Synechocystis PCC 6714.

Isopentenyl diphosphate, the universal isoprenoid precursor, can be produced by two different biosynthetic routes: either via the acetate/mevalonate (MVA) pathway, or via the more recently identified MVA-independent glyceraldehyde phosphate/pyruvate pathway. These two pathways are easily differentiated by incorporation of [1-13C]glucose and analysis of the resulting labelling patterns found in the isoprenoids. This method was successfully applied to several unicellular algae raised under heterotrophic growth conditions and allowed for the identification of the pathways that were utilized for isoprenoid biosynthesis. All isoprenoids examined (sterols, phytol, carotenoids) of the green algae Chlorella fusca and Chlamydomonas reinhardtii were synthesized via the GAP/pyruvate pathway, as in another previously investigated green alga, Scenedesmus obliquus, which was also shown in this study to synthesize ubiquinone by the same MVA-independent route. In the red alga Cyanidium caldarium and in the Chrysophyte Ochromonas danica a clear dichotomy was observed: as in higher plants, sterols were formed via the MVA route, whereas chloroplast isoprenoids (phytol in Cy. caldarium and O. danica and beta-carotene in O. danica) were synthesized via the GAP/pyruvate route. In contrast, the Euglenophyte Euglena gracilis synthesized ergosterol, as well as phytol, via the acetate/MVA route. Similar feeding experiments were performed with the cyanobacterium Synechocystis PCC 6714 using [1-13C]- and [6-13C]-glucose. The two isoprenoids examined, phytol and beta-carotene, were shown to have the typical labelling pattern derived from the GAP/pyruvate route.

Animals↗
PubMed1998

The stress concept in plants: an introduction.

The current concept of stress in plants has been well developed over the past 60 years. Any unfavorable condition or substance that affects or blocks a plant's metabolism, growth, or development is regarded as stress. Vegetation stress can be induced by various natural and anthropogenic stress factors. One has to differentiate between short-term and long-term stress effects as well as between low-stress events that can be partially compensated for by acclimation, adaptation, and repair mechanisms, on the one hand, and strong stress or chronic stress events causing considerable damage that may eventually lead to cell and plant death, on the other hand. Some essential stress syndrome responses of plants are summarized in a unifying stress concept. The major abiotic, biotic, and anthropogenic stressors are listed. Some stress tolerance mechanisms are mentioned. Stress conditions and stress-induced damage in plants have so far been detected using the classical ecophysiological field methods as well as point data measurements of particular chlorophyll fluorescence parameters and of reflectance spectra. The novel laser-induced high-resolution fluorescence imaging technique, which integrates chlorophyll and blue-green fluorescence, marks a new standard in the detection of stress in plants.

Acclimatization↗
PubMed1997

Incorporation of 1-deoxy-D-xylulose into isoprene and phytol by higher plants and algae.

In further substantiating the novel mevalonate-independent pathway for isoprenoid biosynthesis, which generates isopentenyl diphosphate (IPP) via 1-deoxy-D-xylulose-5-phosphate, labeling experiments with 1-[2H(1)]deoxy-D-xylulose were performed with various higher plants and algae: efficient incorporation was observed into isoprene emitted by Populus, Chelidonium, and Salix, into the phytol moiety of chlorophylls in a red alga (Cyanidium), in two green algae (Scenedesmus, Chlamydomonas), and a higher plant (Lemna). By contrast, 13C-mevalonate applied was incorporated into isoprene and phytol to a much lower extent or not at all. This demonstrates that this '1-deoxy-D-xylulose-5-phosphate pathway' for biosynthesis of plastidic isoprenoids is widely distributed in photosynthetic organisms.

Butadienes↗
PubMed1997

Biosynthesis of isoprenoids in higher plant chloroplasts proceeds via a mevalonate-independent pathway.

Isopentenyl diphosphate (IPP) is the biological C5 precursor of isoprenoids. By labeling experiments using [1-(13)C]glucose, higher plants were shown to possess two distinct biosynthetic routes for IPP biosynthesis: while the cytoplasmic sterols were formed via the acetate/mevalonate pathway, the chloroplast-bound isoprenoids (beta-carotene, lutein, prenyl chains of chlorophylls and plastoquinone-9) were synthesized via a novel IPP biosynthesis pathway (glyceraldehyde phosphate/pyruvate pathway) which was first found in eubacteria and a green alga. The dichotomy in isoprenoid biosynthesis in higher plants allows a reasonable interpretation of previous odd and inconclusive results concerning the biosynthesis of chloroplast isoprenoids, which so far had mainly been interpreted in the frame of models using compartmentation of the mevalonate pathway.

Chloroplasts↗
PubMed1996

Biosynthesis of isoprenoids (carotenoids, sterols, prenyl side-chains of chlorophylls and plastoquinone) via a novel pyruvate/glyceraldehyde 3-phosphate non-mevalonate pathway in the green alga Scenedesmus obliquus.

Isoprenoid biosynthesis was investigated in the green alga Scenedesmus obliquus grown heterotrophically on 13C-labelled glucose and acetate. Several isoprenoid compounds were isolated and investigated by 13C-NMR spectroscopy. According to the 13C-labelling pattern indicated by the 13C-NMR spectra, the biosynthesis of all plastidic isoprenoids investigated (prenyl side-chains of chlorophylls and plastoquinone-9, and the carotenoids beta-carotene and lutein), as well as of the non-plastidic cytoplasmic sterols, does not proceed via the classical acetate/mevalonate pathway (which leads from acetyl-CoA via mevalonate to isopentenyl diphosphate), but via the novel glyceraldehyde 3-phosphate/pyruvate route recently detected in eubacteria. Formation of isopentenyl diphosphate involves the condensation of a C2 unit derived from pyruvate decarboxylation with glyceraldehyde 3-phosphate and a transposition yielding the branched C5 skeleton of isoprenic units.

Carbon Isotopes↗
PubMed1993

Studies on the constancy of the blue and green fluorescence yield during the chlorophyll fluorescence induction kinetics (Kautsky effect).

Blue (F450) and green (F530) leaf fluorescence were studied together with the red chlorophyll fluorescence (emission maxima F690 and F735) during light-induced chlorophyll fluorescence induction kinetics (Kautsky effect) in predarkened leaves of wheat (Triticum aestivum L.) and soybean (Glycine max L.). The intensity of the red chlorophyll fluorescence decreased from maximum fluorescence Fm to steady-state fluorescence Fs, and the fluorescence ratio F690/F735 decreased by about 10% from Fm to Fs. However, blue and green fluorescence intensities remained constant throughout the measuring time. Consequently, the ratio of blue to red fluorescence (F450/F690) increased during chlorophyll fluorescence induction kinetics, whereas the ratio of blue to green fluorescence (F450/F530) remained unchanged within the same period. The knowledge of these ratios will be a prerequisite for the interpretation of remote sensing data from terrestrial vegetation.

Chlorophyll↗
PubMed1992

Chlorophyll fluorescence lifetime determination of waterstressed C3- and C4-plants.

This article describes the effect of water stress on the room temperature chlorophyll fluorescence lifetime of plants of wheat (C3) and maize (C4). In addition, net CO2 assimilation rate (PN), stomatal conductance and the fluorescence quenching coefficients qP and qNP at steady state conditions were recorded. The overall fluorescence decay of the control plants can be described by an average decay time of 1 ns for both plant types. Water stress did not modify this parameter in the case of wheat, whereas a shortening of the decay was observed for waterstressed maize plants (tau = 0.45 ns). This shortening in the chlorophyll fluorescence decay was accompanied by an increase in the non-photochemical quenching (qNP). The photochemical quenching (qP) and therefore the electron transport via photosystem II remains unaffected by water stress. The most pronounced effect of the stress for both plant types was a decrease in PN due to a closure of the stomata.

Chlorophyll↗
PubMed1992

A CCD-OMA device for the measurement of complete chlorophyll fluorescence emission spectra of leaves during the fluorescence induction kinetics.

A new device for the measurement of complete laser induced fluorescence emission spectra (maxima near 690 and 735 nm) of leaves during the induction of the chlorophyll fluorescence is described. In this the excitation light (cw He/Ne laser, 632.8 nm) is switched on by a fast electro-mechanical shutter which provides an opening time of 1 ms. The emitted fluorescence is imaged onto the entrance slit of a multichannel spectrograph through a red cut-off filter (greater than 645 nm). A charge coupled device (CCD) sensor with 2048 elements simultaneously detects the complete chlorophyll fluorescence emission spectrum in the 650-800 nm wavelength range. Scanning is accomplished electronically and the integration time for a complete fluorescence emission spectrum can be selected from 10 ms up to 260 ms. Shutter, detector system and data acquisition are controlled by an IBM-PC/AT compatible computer. A maximum of 32 spectra can be measured at selected times during the fluorescence induction kinetics with the shortest time resolution of 10 ms. The instrument permits the determination of various fluorescence parameters: a) the rise-time of the fluorescence to the maximum level fm, b) the changes in the shape of the fluorescence emission spectra during the induction kinetics, c) the induction kinetics in the fluorescence ratio F690/F735 as well as d) the fluorescence decrease ratio Rfd at any wavelength between 650 to 800 nm. These fluorescence parameters provide information about the functioning of photosynthesis. The ratio F690/F735 allows the non-destructive determination of the chlorophyll content of leaves. The application of this instrument in ecophysiological research and stress physiology of plants is outlined.

Chlorophyll↗
PubMed1992

Increase of the chlorophyll fluorescence ratio F690/F735 during the autumnal chlorophyll breakdown.

The chlorophyll content and the fluorescence induction kinetics at two wavelengths (690 nm and 735 nm) have been measured in leaves of nine common broadleaf tree species during the autumnal chlorophyll breakdown. The ratio of the chlorophyll fluorescence maxima F690/F735 was determined at fluorescence maximum (fm) and at steady-state conditions (fs) by the laser-induced fluorescence emission using the two-wavelength fluorometer. The ratio F690/F735 increases with the leaf discolouring during the autumnal chlorophyll breakdown. The relationship between the chlorophyll content and the ratio F690/F735 can be expressed by a power function (curvilinear relationship) which is valid for all the species examined. In most cases the ratio F690/F735 measured in the upper leaf side is lower than that in the lower leaf side, but the trend is the same along the decreasing chlorophyll content. The ratio F690/F735 is always higher at maximum fluorescence than at steady-state fluorescence in the upper as well as lower leaf side and these values are well fitted in a linear correlation. This study confirms the usefulness of the ratio F690/F735 as a suitable non-destructive indicator of the in-vivo chlorophyll content, especially at medium and low chlorophyll content.

Chlorophyll↗
PubMed1991

Fluorescence emission spectra of plant leaves and plant constituents.

The UV-B radiation (e.g. 337 nm) induced blue fluorescence (BF) and red chlorophyll fluorescence spectra (RF) of green leaves from plants with different leaf structure were determined and the possible nature and candidates of the blue fluorescence emission investigated. The blue fluorescence BF is characterized by a main maximum in the 450 nm region and in most cases by a second maximum/shoulder in the 530 nm region. The latter has been termed green fluorescence GF. The red chlorophyll fluorescence RF, in turn, exhibits two maxima in the 690 and 730 nm region. In general, the intensity of BF, GF and RF emission is significantly higher in the lower than the upper leaf side. The ratio of BF to RF emission (F450/F690) seems to vary from plant species to plant species. BF and GF emission spectra appear to be a mixed signal composed of the fluorescence emission of several substances of the plant vacuole and cell wall, which may primarily arise in the epidermis. Leaves with removed epidermis and chlorophyll-free leaves, however, still exhibit a BF and GF emission. Candidates for the blue fluorescence emission (lambda max near 450 nm) are phenolic substances such as chlorogenic acid, caffeic acid, coumarins (aesculetin, scopoletin), stilbenes (t-stilbene, rhaponticin), the spectra of which are shown. GF emission (lambda max near 530 nm) seems to be caused by substances like the alkaloid berberine and quercetin. Riboflavine, NADPH and phyllohydroquinone K1 seem to contribute little to the BF and GF emission as compared to the other plant compounds. Purified natural beta-carotene does not exhibit any blue fluorescence.

Chloroplasts↗
PubMed1990

Decrease of the chlorophyll fluorescence ratio F690/F730 during greening and development of leaves.

Using the two-wavelength chlorophyll fluorometer the fluorescence induction kinetics (Kautsky effect) were measured simultaneously in the 690 nm and 730 nm region for ten common tree species during the greening period (April to July). The chlorophyll-fluorescence ratio F690/F730 (i.e. ratio of fluorescence intensity at the two maxima near 690 and 730 nm) was calculated from the laser-induced induction kinetics (He/Ne-laser 632.8 nm) at the fluorescence maximum and the steady state. The ratio F690/F730 decreases with increasing chlorophyll content of developing leaves. Its dependence on the chlorophyll content can be fairly well expressed by a power function which has a general validity for leaves, pigment extracts and chloroplast suspensions. The ratio F690/F730 is somewhat higher at maximum (fm) than at steady-state fluorescence (fs), but there is a very good correlation between both values. The ratio F690/F730 is a good indicator of the chlorophyll content and can be used as a non-destructive measure of the chlorophyll content of leaves. It also appears to be a suitable fluorescence parameter in the future remote sensing of the physiological state of the vegetation by laser-equipped airborne systems.

Chlorophyll↗