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Marrè, Maria‐Teresa; Albergoni, F. G.; Venegoni, A.; Moroni, A.
doi: 10.1111/j.1438-8677.1991.tb00216.xpmid: N/A
The early effects of penconazole (PCZ) at relatively high concentration (10−4 to 5 × 10−4 M) on changes in pH and in titratable acidity of the medium, transmembrane electrical potential difference (Em), electrolyte leakage and cell morphology were investigated in Egeria densa leaves. At the lowest (10−4 M) concentration and in the presence of a very low (10 μM) K+ concentration, triazole induced an early, moderate hyperpolarization of Em, associated with a decrease of net K+ uptake, suggesting some increase in the passive permeability to K+. This Em hyperpolarization was no longer detectable at high (2 mM) K+out concentration. At high PCZ concentrations (3 × 10−4 M and 5 × 10−4 M) the early hyperpolarization detectable in the presence of a low K+out concentration became transient, and was followed by a marked depolarization. PCZ, at these concentrations, suppressed acidification of the medium, stimulated electrolyte leakage and, in the mesophyll cells, induced some shrinking of the cytoplasm and its disconnection from the cell walls. These results are interpreted as due to an early effect of this triazole leading to the disorganization of the plasma membrane.
doi: 10.1111/j.1438-8677.1991.tb00217.xpmid: N/A
The movement responses of the cellular slime mold Dictyostelium discoideum to multiple stimuli were investigated. The responses were found to differ depending on the developmental stage of the organism. A novel response, positive gravitaxis, was found in Dictyostelium slugs but not in amoebae. In the presence of a simultaneous light stimulus, gravitaxis is effective only at low fluence rates. Slugs showed positive thermotaxis in a thermal gradient (0.2 °C cm−1) and ignored the simultaneous light stimulus at low fluence rates (< 10−3 W m−2), while at higher fluence rates they moved toward the light source. With a combination of a thermal gradient and gravity Dictyostelium slugs clearly oriented thermotactically ignoring the gravistimulus.
doi: 10.1111/j.1438-8677.1991.tb00218.xpmid: N/A
Dynamic changes of microtubule (MT) configuration have been examined during the cell cycle progression in tobacco BY‐2 cells, which have been highly synchronized by aphidicolin treatment. Although it has been shown previously that four cell cycle stages display characteristic features of MTs (Hasezawa et al., 1991), distinct changes of MT configuration were observed at the interfaces of G2/M, M/G1 and G1/S, and the frequency of appearance of such distinct structures were quantitatively examined. Among others, it is the first observation that at M/G1 disintegrating phragmoplasts coexisted with short MTs in the perinuclear envelopes, but the MTs disappeared in the later stage, when cortical MTs were organizing. Thus it is supposed that cortical MTs originate from the transiently observed short MTs in the perinuclear region. This observation offered also an experimental system to analyze the molecular changes of MTs at the three interfaces during cell cycle progression in plant cells, as the mass culture of tobacco BY‐2 cells is readily available.
Kirches, E.; Frey, N.; Schnabl, Heide
doi: 10.1111/j.1438-8677.1991.tb00219.xpmid: N/A
Experiments on transient gene expression were performed with mesophyll protoplasts isolated from young leaves of the sunflower (Helianthus annuus L.). Both PEG‐mediated DNA transfer as well as electroporation, were shown to be suitable for the introduction of a foreign gene. The expression of the reporter gene β‐glucuronidase was measured by a fluorimetric GUS assay. Inhibiting RNA synthesis by cordycepine (3‐deoxyadenosine) or translation of mRNA by cycloheximide suggests that biologically active plasmid‐DNA as well as functional mRNA transcripts are available for only short time periods in transfected protoplasts. Electroporation was carried out using rather high pulses in the microsecond range. Results indicate, that DNA uptake is more efficient using PEG, while electroporation causes less damage in DNA treated mesophyll protoplasts.
Biedinger, Ursula; Bickert, Chr; Youngman, R. J.; Schnabl, Heide
doi: 10.1111/j.1438-8677.1991.tb00220.xpmid: N/A
Membrane lipid degradation of plant protoplasts of Vicia faba was characterized by the determination of ethane formation after electrofusion and electropermeabilization. Incubation of protoplasts with ascorbate or α‐tocopherol before electromanipulation led to a decrease in ethane production. Fusion product yield could be increased by incubation with α‐tocopherol.
Hodick, D.; Gilroy, S.; Fricker, M. D.; Trewavas, A. J.
doi: 10.1111/j.1438-8677.1991.tb00221.xpmid: N/A
Rhizoids of Charafragilis Desv. were iontophoretically loaded with the Ca2+‐sensitive ratio dye indo‐1. After loading, the rhizoids regained their preinjection‐membrane potential within 2 to 5 min and survived the procedure for more than 24 h, but their growth in length was permanently inhibited. Microfluorimetric measurements of the indo‐1 fluorescence‐ratio showed spontaneous fluctuations of the cytoplasmic Ca2+‐concentration, usually declining from high values after loading to 425 ± 80 nM (± SD, n = 7) as determined by in‐vitro calibration. Increasing the extracellular K+‐concentration (0.1 mM to 10 mM) or Ca2+‐concentration (1 mM to 10 mM) led to increases of 100 to 200 nM in cytoplasmic Ca2+‐concentration. The spatial distribution of cytosolic Ca2+ in the rhizoid tips was visualised in ratio images computed from low‐light video‐pictures. These images showed a fairly homogeneous distribution of Ca2+ throughout the tip cytoplasm with concentrations being in the same range as determined by microfluorimetry. A tip‐to‐base gradient in cytoplasmic Ca2+, thought to be a prerequisite for cell polarity and tip growth, was found in only 1 out of 16 successfully microinjected cells. Additionally, a progressive compartmentalization of the fluorochrome indo‐1, probably in the proplastids and the very abundant endoplasmic reticulum of the rhizoids, was observed.
doi: 10.1111/j.1438-8677.1991.tb00222.xpmid: N/A
Young plants of Phaseolus and Canavalia were grown in nutrient solutions where calcium had been partially or totally replaced by either strontium or sodium. The deleterious effect of this replacement on growth and development was greater with strontium than with sodium. As the calcium content of the nutrient solution was decreased fewer calcium oxalate crystals were formed in leaf tissues. There were fewer crystals formed when calcium was replaced by strontium than by sodium. Changes in solubility characteristics of the crystals indicated that they had incorporated strontium.
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