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The Mimosa pudica leaf has motor organs allowing movements driven by cell osmotic changes in the parenchyma cells in response to various stimuli. Short white light pulses induce rapid and large seismonastic‐like movements (denoted “photostimulation”) of the primary pulvini in various leaves within 120 s after the onset of light. An early event recorded is a wavelength‐related modification of the plasma membrane difference: potential depolarization under white, blue, green, and red wavelengths, and hyperpolarization under far red wavelengths (and also in darkness). The photoreactivity of the pulvini is controlled by a circadian rhythm and modulated by the applied diurnal photoperiod cycle (photophase ranging from 6 to 18 h). The reactivity varied among plants and even between leaves on the same plant. The level of reactivity is related to the photon fluence rate in the range from 10 to 140 μmol m−2 s−1 under white light and to the experimental temperature in the range 15°C–35°C. An “accommodation” to light supply is evidenced by a modulation of the reactivity in relation to the schedule of light application under low fluence rates and the introduction of short darkness intervals during the first 30‐s light pulse. The blue light‐induced photostimulation is under phytochrome control. [ABSTRACT FROM AUTHOR]

Actin microfilaments (F‐actin) are major components of the cytoskeleton essential for many cellular dynamic processes (vesicle trafficking, cytoplasmic streaming, organelle movements). The aim of this study was to examine whether cortical actin microfilaments might be implicated in the regulation of nutrient uptake in root and leaf cells of Beta vulgaris. Using antibodies raised against actin and the AtSUC1 sucrose transporter, immunochemical assays demonstrated that the expression of actin and a sucrose transporter showed different characteristics, when detected on plasma membrane vesicles (PMVs) purified from roots and from leaves. The in situ immunolabeling of actin and AtSUC1 sites in PMVs and tissues showed their close proximity to the plasma membrane. Using co‐labeling in protoplasts, actin and sucrose transporters were localized along the internal border and in the outermost part of the plasma membrane, respectively. This respective membrane co‐localization was confirmed on PMVs and in tissues using transmission electronic microscopy. The possible functional role of actin in sucrose uptake (and valine uptake, comparatively) by PMVs and tissues from roots and leaves was examined using the pharmacological inhibitors, cytochalasin B (CB), cytochalasin D (CD), and phalloidin (PH). CB and CD inhibited the sucrose and valine uptake by root tissues in a concentration‐dependent manner above 1 μM, whereas PH had no such effect. Comparatively, the toxins inhibited the sucrose and valine uptake in leaf discs to a lesser extent. The inhibition was not due to a hindering of the proton pumping and H+‐ATPase catalytic activity determined in PMVs incubated in presence of these toxins. [ABSTRACT FROM AUTHOR]

Eutypa dieback is a devastating disease induced in vineyards by the fungal pathogen Eutypa lata. The fungus colonizes the xylem tissues of trunk and cordons but is never found in the annual canes. Nevertheless, dwarfed shoots and leaf necrosis observed in diseased plants indicate that a necrotic signal can spread at a distance from the infected area. Eutypine, a small cyclic molecule, and related compounds have been postulated as the toxins inducing these symptoms. In this work, we evidence that E. lata secreted other metabolites of polypeptidic nature which induced toxic effects on canes and leaves of vines, and on leaves of other plant materials. The polypeptide fraction (PF) isolated from culture medium of mycelium induced transitory H+ fluxes and membrane depolarization of plant cells. Complementary assays with plasma membrane vesicles (PMV) showed that H+-ATPase is a primary site of action as indicated by inhibition of the enzyme activity and increase of H+ conductance of plasma membrane. The toxic effect was also obvious on respiration and photosynthesis. All these impairments led to a hindering in cell energetics and, as a consequence, to an inhibition of uptake of assimilates. Treatment with PF also triggered biological events, characteristics of elicitation as suggested by the early responses on cell membrane described above, the activation of NADPH oxidase and the activation of Phenylalanine ammonia lyase (PAL). [ABSTRACT FROM AUTHOR]

Uptake of [3H]‐glycine by sections of Mimosa pudica L. pulvini is pH dependent (maximum at pH 5.5) and exhibits biphasic saturation kinetics in the range of concentrations tested (1–75 mM). Effects of compounds which increase [fusicoccin (FC)] or decrease (uncouplers, ATPase inhibitors) the proton‐motive force were tested both on the pH variations induced in the incubation medium and on glycine uptake by the pulvinar tissues: there is a close relationship between the time required for the effect of these compounds on the acidification (for FC) and the pH rise (for the inhibitors) of the medium and that needed respectively for promotion and inhibition of glycine uptake. Experiments with sulfhydryl‐reacting compounds show that N‐ethylmaleimide induces a large rise in pH in the incubation medium and strongly inhibits glycine uptake, whereas p‐chloromercuribenzenesulfonic acid has less effect on these processes. These results argue for a proton‐glycine symport mechanism in the pulvinar tissue and thus support the previously postulated involvement of a proton pump in the regulation of pulvinar movement. [ABSTRACT FROM AUTHOR]

Dimethylsulfoxide (DMSO) acts on dark‐ and light‐induced movements exhibited by leaflets of isolated leaves of Cassia fasciculate Michx. The closing movement (scotonasty), induced when the leaves are placed in darkness during the normal period of daylight, was inhibited, whereas the opening movement (photonasty), when the leaves arc transferred to light during the normal period of darkness, was promoted. The concentration for significant effects of DMSO was 1% (v/v) when applied over a 3‐h period. After five days, a necrosis of the leaflets was observed for DMSO concentrations as small as 0.1%, applied over a 6‐h period. Complete abscission took place if 3% DMSO was applied for more than 30 min. [ABSTRACT FROM AUTHOR]