Zeitschrift für Pflanzenphysiologie最新文献

Fronds of Spirodela polyrhiza (L.) Schleiden (duckweed) were grown under axenic conditions. Three series of two-week experiments were performed. In each series the concentration of iron, magnesium or zinc was varied, but all other elements remained in a constant concentration. Thirty-five different concentrations of iron were used, the iron content varying from 0 to 0.72 mol·m^-3. In the case of magnesium and zinc fifty concentrations of each metal were used, the metal content varying from 0 to 4.12 mol·m^-3 for Mg and from 0 to 1.53 mol·m^-3 for Zn. For each culture the frond multiplication rate and the rate of increase in biomass were measured. After two weeks the fronds were analysed for their Fe, Cu, Ca, Zn, Mn and Mg content. Whereas high concentrations of Fe and Zn resulted in decreased frond multiplication rates, high Mg concentrations did not affect this rate. Although the increase in biomass per unit time showed an optimum curve for each of the varied elements, the weight per frond remained quite constant with varying Fe, showed an optimum value for Mg and increased with increased Zn concentration.

The data obtained point to the possible existence of coupled uptake mechanisms for Fe and Cu, Mg and Mn and for Zn and Ca.

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.

Electrostatic properties of the isolated plasma membrane of maize roots were studied using the fluorescent ANS probe and microelectrophoresis of membrane vesicles. Variations of the net surface charge of membrane were obtained by adding ionic surfactants or by acidifying the medium. Parallel experiments were performed on excised roots. We showed that surface electrostatic interactions can affect major membrane functions such as ATPase activity, trans-membrane PD, and permeability to NO₃.

Ultracytological and ultracytoenzymological studies indicate that there are no adverse alterations in either fungal or plant plasmalemma during intracellur host-fungus interactions in symbiotic ericoid and vesicular-arbuscular endomycorrhizas. These observations are discussed in relation to those reported for biotrophic pathogen infections in plants.

We separated two membrane fractions containing H⁺-ATPase. One fraction with H⁺-ATPase was enriched in plasma membranes while the other one contained no plasma membranes. Since mitochondrial or plastidial origin of H⁺-ATPase could be excluded, the latter one presumably contained H⁺-ATPase in tonoplast vesicles.

With a plasma membrane-enriched fraction, the effect of auxin on ATPase activity was investigated. Auxin decreased the apparent K_M of ATPase so that auxin stimulation of ATPase activity can be measured best at very low ATP concentrations (< 50 μM). The stimulation of ATPase activity is specific for auxin in that 2,3-dichlorophenoxyacetic acid, a weak auxin, had a much lower effects than 2,4-dichlorophenoxyacetic acid or indolyl-3-acetic acid.

These experiments support the hypothesis that auxin stimulates H⁺-extrusion by stimulation of a H⁺-ATPase in vivo and in vitro.

In order to elucidate the origin of the transtonoplast potential difference (PD) measured on isolated vacuoles, the possible contribution of the surface potential to the transmembrane PD was studied. The PD and the electrophoretic mobility were measured on vacuolar preparations, isolated from Beta vulgaris roots and Acer pseudoplatanus cells. Zeta potential was calculated from the electrophoretic mobility. The changes in zeta potential, in response to pH or to a cationic surfactant, were shown to induce parallel variations in the PD. These results suggest that the surface potential could contribute to the transmembrane PD of isolated vacuoles. Various hypotheses on the origin of this transtonoplast PD are discussed.

The resistance of cotton to water stress can be modified by the photoperiod: plants grown under short day conditions are resistant to water stress, and FR enhances their resistance. It has been shown that FR improves water economy.

The determination of the composition of fatty acids during water stress was carried out under drought resistance induced by FR. In roots, FR treatment causes saturation of fatty acids. During water stress, there is a general decrease in the content of fatty acids, with saturation of fatty acids. This is true in 9 h light period and in 9 h light + FR. These changes can be related to variations in membrane fluidity.

Without FR, water stress causes a marked decrease in the content of the fatty acids in the buds. When FR is given, water stress has no effect on fatty acids content, which, under these conditions, is always lower than in non water stressed plants without FR.

We describe a method for the isolation of cytosol from mesophyll protoplasts of sweet clover (Melilotus alba Desr.). Polybase induced lysis of protoplasts under gentle conditions, followed by centrifugations at increasing velocities resulted in the progressive sedimentation of intact subcellular organelles. The final supernatant obtained at 100,000 × g was assumed to be the cytosol. Its contamination was found to be low, according to the activities of marker enzymes, and mainly due to vacuolar sap (ca. 10 %) and soluble constituents of peroxisomes (ca. 20 %). Enzymes of the sucrose pathway are exclusively located in the cytosol and can therefore be used as markers of this subcellular compartment.

The salt-tolerant legume Sesbania aculeata was grown in hydroponic culture with or without the addition of 100 mol m^-3 NaCl. The stressed plants had higher sodium and chloride contents and lower potassium, calcium, magnesium and nitrate levels. The fresh weight/dry weight ratio, shoot/root ratio, wax contents and relative growth rates were only slightly affected by salt treatment. Pinitol and, to a lesser extent, glycinebetaine increased in the leaves of salt stressed plants. The possibility of pinitol acting as a compatible cytosolute in this and other stress tolerant legumes is discussed.

Lutoids, the vacuo-lysosomes of the Hevea latex cells, compartmentalize, in vivo, numerous ions such as H⁺, Mg⁺⁺, Ca⁺⁺, Pi, citrate, some of them strongly toxic for the cytosolic metabolism. Evidence is given for the correlation of the in vivo compartimentation of some of these ions inside the lutoids with the latex production by Hevea.

Two opposing H⁺ pumps were localized on the lutoidic tonoplast; the one is a Mg⁺⁺-dependent ATPase, the other a NADH-consuming redox system (cytochrome c: artificial acceptor). The functioning of these H⁺ pumps may account for a major part of the transtonoplastic ΔpH variations, and therefore the cytosolic pH control, which probably regulates the highly pH-dependent latex metabolism.

The resulting proton-motive force energizes the accumulation and compartmentation of the inhibiting ions inside the lutoïds, and ensures the control of the «detoxification» and ionic equilibrium of the cytoplasm of the laticiferous cells.

Treatment of Hevea bark with ethrel, an ethylene generator which «stimulates» latex production, induces an increase in the H⁺-pumping ATPase activity, resulting in the activation of the metabolism in the latex cells.

All the results reviewed lead us to propose that the lutoids play a double role as a «biophysical pH-STAT and a «detoxicating trap», thus controlling the cytosolic homeostasis.