Zeitschrift für Pflanzenphysiologie最新文献

The growth of two Neurospora crassa methionine auxotrophs (met-6, 35809, FGSC 1330 and mac, 65109, FGSC 3609), that have lesions affecting folylpolyglutamate synthetase, was examined by culture in defined, liquid media. Both mutants responded to L-methionine supplements but additions of homocysteine, cysteine, serine, formate, thymine and adenine, supplied singly or in various combinations were not effective in stimulating growth. Mycelial yields after 22 hr growth in 0.5 mM L-methionine-supplemented media were comparable to those of a wild type strain (Lindegren A, FGSC 853) cultured in defined minimal medium. Pulse feeding radio-labelled cysteine, glycine, serine and formate showed that both mutants had less ability to generate methionine than the wild type. Standard microbiological assays, conjugase treatments and DEAE-cellulose chromatography showed that folylpolyglutamates were lacking in met-6 and mac but accounted for about 70% of the wild type folate pool. The polyglutamyl chain lengths of these folates were determined following tritium labelling, acid cleavage and Chromatographic separation as diazo dye derivatives. The wild type contained mainly tri- and hexaglutamyl folates. In met-6, mono- and diglutamates predominated but in mac only monoglutamates were found. Extracts of met-6: mac heterokaryons contained folates that were hexaglutamate derivatives. These findings provide additional evidence that folylpolyglutamates have an essential role in the methionine synthesis of N. crassa.

The chloroplast-specific glycolipids monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol and the prenylquinones α-tocopherol, plastoquinone-9 and phylloquinone were formed in the 70S ribosome-deficient leaf tissue of rye seedlings grown at a non-permissive temperature of 32°C. In light 32°-grown 70S ribosome-deficient leaves were chlorotic. Etiolated 32°-grown leaves contained about 50% of the protochlorophyll(ide) content of control leaves from permissive growth conditions (22°C). As in chloroplasts, monogalactosyldiacylglycerol and digalactosyldiacylglycerol were the predominating polar lipids in isolated bleached ribosome-deficient plastids. Sulfoquinovosyldiacylglycerol and the phospholipids phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol were also present. The 32°-grown 70S ribosome-deficient leaves contained the same molecular species of monogalactosyldiacylglycerol and digalactosyldiacylglycerol as 22°-grown control leaves. As under permissive conditions linoleic and linolenic acid were the prevailing fatty acids of the galactolipids from 70S ribosome-deficient leaves. All enzymes of the biosynthesis of protochlorophyll(ide) and of the chloroplast glycolipids and prenylquinones must be synthesized on cytoplasmic 80S ribosomes. In accord with the reduction of the thylakoid system the ratio of monogalactosyldiacylglycerol to digalactosyldiacylglycerol was lower in 70S ribosome-deficient than in normal green leaves. In etiolated leaves grown at either 32°C or 22°C the amounts of the glycolipids and prenylquinones did not differ markedly. However, in light the glycolipid and prenylquinone contents remained almost as low in the bleached 70S ribosome-deficient leaves as in darkness, while several-fold increases accompanied greening of normal leaves in light. The data suggest that the light-mediated increase of glycolipids and prenylquinones depends on the availability of chlorophyll. The contents of steroidal saponins in oat leaves were slightly higher in light than in darkness and showed no specific relationship to the presence of etioplasts. They did not notably differ in 22°- or 32°-grown leaves.

Since gravistimulation is followed by alterations in the external current symmetry (Behrens et al., 1982), the effect of gravistimulation on cellular membrane potential was investigated using conventional glass microelectrode techniques. The resting potential of statocytes in a vertically oriented root is approx. -118 mV. Upon gravistimulation, the membrane potential is temporarily depolarized (lag time = 2 s) to a potential of approx. -93 mV. This depolarization is only observed in statocytes located on the physically lower root flank while those on the corresponding upper flank become weakly hyperpolarized (approx. -13 mV). These results reflect altered ion fluxes across the plasma membrane.

The perception of gravistimulus was suggested to result from a pressure of the amyloplasts on the distal endoplasmic reticulum (ER) of the statocytes (Sievers and Volkmann, 1972).

A causal relationship between changes in ER-amyloplast interactions and the rapid alterations in plasma membrane potential described above is not known. A candidate for such an intracellular messenger is Ca²⁺. As a first step in establishing the validity of such an assumption, we have isolated ER membranes from roots. When incubated with micromolar concentrations of Ca²⁺, the vesicular membrane fraction accumulates Ca²⁺. The accumulation is ATP-dependent and -specific and is directly coupled to ATP hydrolysis since a protonophore shows no inhibitory effect. Thus, in analogy to the sarcoplasmic reticulum of muscle, regulation of an ER-localized Ca²⁺ compartment might be an important step in such complex processes as stimulus-transduction in gravitropism.

Stock callus cultures of Carica papaya L. maintained in modified White's medium were grown in twenty media types. Growth, protease activity and total protein in extratives is reported. The basic Wood and Braun medium produced good growth and high protease activity. Reduction of macro- and/or microelements in Murashige and Skoog basic medium increased protein content and enzyme activity of the callus. In most cases, peptone was found to significantly increase growth, protease activity and protein content of callus cultures.

The relationship between light induced and dark metabolic processes occurring during synchronous germination of unicellular spores of the fern Pteris vittata was investigated. Light was almost totally ineffective as an inducer during a 12 to 16 h preinduction phase. Spores imbibed in the cold before illumination could not be induced to germinate, indicating that metabolic events occurring during the preinduction phase are required for the photomorphogenetic response. Two brief irradiations separated by two hours of darkness during a later, photoinductive phase were more effective in inducing germination than a single one of equal fluence. These short red-light illuminations induced more than 40% synchronous germination and enabled the separation between hydration and light effects. Chlorophyll formation is a phytochrome induced dark process in germinating spores, preceding the first nuclear division and rhizoid emergence. The formation of chlorophyll in ferns in the dark differs from light mediated chlorophyll synthesis in both angiosperms and gymnosperms as it is an enzymatic process, yet is mediated by phytochrome photoconversion.

In maize leaves, the intercellular distribution of photorespiratory enzymes was investigated with bundle sheath strands and mesophyll protoplasts isolated enzymically and obtained with a high degree of purity. Phosphoglycolate phosphatase was found to be exclusively located in bundle sheath which also contained about 90% of the whole leaf activities of catalase, glycolate oxidase, and hydroxypyruvate reductase. The spatial compartmentation of the photorespiratory process in corn leaves is discussed on the basis of the data reported in this study, together with those of other reports.

We investigated the influence of monospecific antisera to monogalactosyl diglyceride and to digalactosyl diglyceride on the photosynthetic electron transport in chloroplasts of higher plants. Both antisera inhibit the photoreduction of dichlorophenolindophenol (DCPiP) with water as the native electron donor as well as the reduction of anthraquinone-2-sulfonate with the electron donor couple DCPiP/ascorbate. The degree of inhibition of the galactolipid antisera in the region of photosystem I depends on the pH and the temperature of the reaction assay. Treatment of the chloroplasts with sodium periodate or with lipase results in a complete loss of any inhibition by the galactolipid antisera. Treatment with β-galactosidase, however, had no influence on the reactions with galactolipid antisera. The sites of inhibition of the galactolipid antisera could be localized on the donor side of photosystem I as well as on the donor side of photosystem II. From this we conclude that the mono- and digalactosyl diglyceride molecules that are localized on the stroma side of the membrane are components of the photosystem I- and also of the photosystem II-protein-lipid-complex. We may conclude that there are obviously interactions between the galactolipid molecules and the photosynthetically active proteins, since the binding of antibodies leads to a partial blocking of electron transport.

The NaCl resistance of enzymes in crude extracts from the extreme halotolerant alga Dunaliella parva was investigated. Enzymes exhibit a very broad scale of sensitivity against NaCl, ranging from half maximal inhibitions at 100 mM up to the molar range. Salt resistance depends on the type of the enzyme as well as on the substrate concentrations: Enzymes with nonelectrolytes exhibit a relatively higher salt tolerance than those with anionic substrates. Salt — inactivation is caused by Cl^- and not by K⁺ or Na⁺. A competitive type of interaction of the Cl^- anion with the anionic substrate is observed. Consequently high concentrations of anionic substrates protect enzymes in vivo against Cl^- inactivation.

Half maximal inhibition of enzymes from D. parva cells adapted to different salinities were not significantly different under substrate saturating conditions, but the KM-Values for the substrates increased with the salinity of the preculture.

The effect of various substrate analogues and some of the intermediates and endproducts of the phenylpropanoid pathway on the development of L-phenylalanine ammonia-lyase (PAL) in relation to the growth of the embryonic axes in germinating lettuce seeds was investigated. Externally supplied L-phenylalanine and its D-isomer did not affect extractable PAL activity at 50 and 100 μM concentrations, whereas at 500 μM L-phenylalanine, there was a slight but significant inhibition of PAL activity. In the presence of 500 μM D-phenylalanine a slight stimulation of PAL activity was observed. Two other substrate analogues, p-fluorophenylalanine and tryptophan, strongly inhibited both the growth of the radicle as well as the development of PAL activity, whereas tyrosine significantly stimulated both the radicle elongation and PAL activity. All the intermediates of the phenylpropanoid pathway used were inhibitory to growth and PAL activity, the order of effectiveness for inhibition being cinnamic acid > p-coumaric acid > ferulic acid > caffeic acid. Some of the end products of the phenylpropanoid pathway, viz., coumarin, quercetin and chlorogenic acid were also found to be very strong inhibitors both of radicle elongation and PAL activity. In all these treatments a strong correlation between PAL activity and radicle elongation was observed supporting the earlier observations that in germinating lettuce seeds any chemical or physical treatment that inhibits radicle elongation also inhibits PAL activity.

An enzymatic NAD(P)H oxidase activity that generates species of toxic oxygen was located at the level of the lutoidic tonoplast. The partial characterization of this enzyme shows that it is insensible towards classical inhibitors of respiratory chains, and still functions at very low oxygen concentrations. It is greatly activated by physiological concentrations of metallic cations (Fe³⁺ and Cu⁺⁺), and by quinone-like compounds, among which naphtoquinones and ubiquinones may act as physiological activators or electron carriers.

The diverse species of toxic oxygen emitted, lead to the peroxidatic degradation of the unsaturated lipids of the membrane and then to destabilisation and lysis of the organelles, in a way similar to that described for the NAD(P)H induced O₂^- production and consecutive membrane alteration by mammalian microsomes or granulocytes.

Intensive hormonal treatment of bark («over-stimulation» with ethrel, an ethylene generator), or too frequent bark wounding (i.e. over-tapping) increase the O₂^- generating activity, and simultaneously decrease the level of cytosolic scavengers. This leads to lysis of the latex organelles and especially of the lutoids (vacuolysosomes), and to subsequent liberation into the latex of the «coagulating factors» which they normally compartmentalize. It results in latex coagulation within the bark of the stressed trees: the so-called «dry-cuts syndrome».

However, the NAD(P)H oxidase activity remains very low and the scavenging activities (superoxyde-dismutase, catalase, glutathion reductase) and chemical scavengers (e.g. reduced thiols) fully efficient, in the latex from healthy non-stressed Heveas (stable latex).

Computer data analysis allowed us to draw a model describing the biochemical events leading to this type of cell degeneration.