Zeitschrift für Pflanzenphysiologie最新文献

The aim of this work was to study the effects of metabolic intermediates on pyrophosphate: fructose 6-phosphate phosphotransferase (PFP) from endosperm of germinating castor bean (Ricinus communis). Glucose 1-phosphate, glucose 6-phosphate, UDPglucose, glucose, fructose, sucrose and pyruvate, each at 1 mM, and malate, succinate and glycolate, each at up to 5mM, had no significant effect on enzyme activity. PFP was inhibited by 3-phosphoglycerate, 2-phosphoglycerate, phosphoenolpyruvate, citrate and all nucleotides tested. Inhibition by MgATP, 3-phosphoglycerate, phosphoenolpyruvate and citrate was due primarily to their effect on the affinity of PFP for fructose 2,6-bisphosphate, a potent activator of the enzyme. These inhibitors each increased the concentration of fructose 2,6-bisphosphate required for half maximum activation of PFP up to 30-fold, from 6 to 180 nanomolar. The possible roles of these compounds in the control of PFP are discussed.

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.

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.

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.

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.

Exposure of Beta vulgaris to various levels of Na₂SO₄ (1 to 100 mM) resulted in an enhanced plant growth at 10 and 50 mM Na₂SO₄ and in a reduced plant growth at 100 mM. On a total lipid basis, the content of phospholipids, sulfolipids and sterols + sterol esters of shoots and roots was unaffected at all tested Na₂SO₄ levels. Glycolipid content of the roots was unaffected by Na₂SO₄. However, both on a total lipid and chlorophyll basis, the glycolipid content of the shoots was decreased at enhanced Na₂SO₄ concentrations. The significance of the role of lipids in adaptation to an excess of Na₂SO₄ is discussed.