Different zinc sensitivity of Brassica organs is accompanied by distinct responses in protein nitration level and pattern

Zinc is an essential microelement, but its excess exerts toxic effects in plants. Heavy metal stress can alter the metabolism of reactive oxygen (ROS) and nitrogen species (RNS) leading to oxidative and nitrosative damages; although the participation of these processes in Zn toxicity and tolerance is not yet known. Therefore this study aimed to evaluate the zinc tolerance of Brassica organs and the putative correspondence of it with protein nitration as a relevant marker for nitrosative stress. Both examined Brassica species (B. juncea and B. napus) proved to be moderate Zn accumulators; however B. napus accumulated more from this metal in its organs. The zinc-induced damages (growth diminution, altered morphology, necrosis, chlorosis, and the decrease of photosynthetic activity) were slighter in the shoot system of B. napus than in B. juncea. The relative zinc tolerance of B. napus shoot was accompanied by moderate changes of the nitration pattern. In contrast, the root system of B. napus suffered more severe damages (growth reduction, altered morphology, viability loss) and slighter increase in nitration level compared to B. juncea. Based on these, the organs of Brassica species reacted differentially to excess zinc, since in the shoot system modification of the nitration pattern occurred (with newly appeared nitrated protein bands), while in the roots, a general increment in the nitroproteome could be observed (the intensification of the same protein bands being present in the control samples). It can be assumed that the significant alteration of nitration pattern is coupled with enhanced zinc sensitivity of the Brassica shoot system and the general intensification of protein nitration in the roots is attached to relative zinc endurance.

Comparing the effects of excess copper in the leaves of Brassica juncea (L. Czern) and Brassica napus (L.) seedlings: Growth inhibition, oxidative stress and photosynthetic damage

Hydroponic experiments were conducted to compare the effects of excess copper (Cu) on growth and photosynthesis in young Indian mustard (Brassica juncea) and oilseed rape (Brassica napus). We compared the effects of excess Cu on the two Brassica species at different physiological levels from antioxidant levels to photosynthetic activity. Nine-day-old plants were treated with Cu (10, 25 and 50 μM CuSO4) for 7 and 14 days. Both species took up Cu from the external solution to a similar degree but showed slight root-to-shoot translocation. Furthermore, after seven days of treatment, excess Cu significantly decreased other microelement content, such as iron (Fe) and manganese (Mn), especially in the shoots of B. napus. As a consequence, the leaves of young Brassica napus plants showed decreased concentrations of photosynthetic pigments and more intense growth inhibition; however, accumulation of highly reactive oxygen species (hROS) were not detected. After 14 days of Cu exposure the reduction of Fe and Mn contents and shoot growth proved to be comparable in the two species. Moreover, a significant Cu-induced hROS accumulation was observed in both Brassica species. The diminution in pigment contents and photosynthetic efficiency were more pronounced in B. napus during prolonged Cu exposure. Based on all the parameters, B. juncea appears to be more resistant to excess Cu than B. napus, rendering it a species with higher potential for phytoremediation.

Effects of Pyridazinone Herbicides during Chloroplast Development in Detached Barley Leaves I. Effects on Pigment Accumulation and Fluorescence Properties

The effects of three differently substituted pyridazinone herbicides on the accumulation of photosynthetic pigments and on the fluorescence properties of greening barley leaves were studied. The two trifluoro-methyl derivatives, SAN 6706 and 9789 caused inhibition in the accumulation of carotenes only after the first 24 h of greening. By the 48th hour of greening no detectable amounts of carotenes were present in the treated leaves. Considerable amounts of xanthophylls however remained present, and no bleaching of the leaves was observed. It is suggested that SAN 6706 and 9789 prevent the formation of the enzyme(s) catalyzing the desaturation of phytoene and phytofluene. Fluorescence spectra indicate that the organization of pigment forms altered seriously in the treated leaves. This experimental system may be useful to study the action of pyridazinone herbicides without causing complete photobleaching of the photosynthetic apparatus. SAN 9785 had only minor effects on pigment accumulation and also on the organization of pigment forms. The possible explanations of the effects observed are dis­cussed.

Effects of Pyridazinone Herbicides during Chloroplast Development in Detached Barley Leaves II. Effects on Lipid Content, Fatty Acid Composition and Ultrastructure of Chloroplasts

The effects of three differently substituted pyridazinone herbicides were studied on the lipid content, fatty acid composition of glycerolipids, fatty acid synthesizing capacity and ultrastruc­ture of chloroplasts after 72 h of greening of etiolated barley leaves. SAN 9789 caused a nearly threefold increase in the total fatty acid content of chloroplasts. and this increase was accom­panied by an increase in the DGDG- and phospholipid-content as well. SAN 6706 and 9785 caused reduction in the linolenic to linoleic acid ratio in nearly all lipid classes, only PC was unaffected. Both herbicides reduced the saturated to unsaturated ratio in the PG, SAN 9789 had no effect on the fatty acid composition of the PG. Fatty acid synthesis was inhibited in the SAN 6706- and 9789-treated leaves as monitored by incorporation of labelled acetate, but all of the three pyridazinones stimulated the incorporation of labelled galactose into chloroplast galactolipids. SAN 6706 and 9789 also caused abnormal organization of chloroplast lamellar system.

Isohydric and anisohydric strategies of wheat genotypes under osmotic stress: biosynthesis and function of ABA in stress responses

Changes in water potential (ψw), stomatal conductance, abscisic acid (ABA) accumulation, expression of the major genes involved in ABA biosynthesis, activities of abscisic aldehyde oxidase (AO, EC 1.2.3.1) and antioxidant enzymes were studied in two wheat cultivars with contrasting acclimation strategies subjected to medium strength osmotic stress (-0.976MPa) induced by polyethylene glycol (PEG 6000). Because the biosynthetic pathway of ABA involves multiple gene products, the aim of this study was to unravel how these genes are regulated in isohydric and anisohydric wheat genotypes. In the root tissues of the isohydric cultivar, Triticum aestivum cv. Kobomugi, osmotic stress increased the transcript levels of 9-cis-epoxycarotenoid dioxygenase (NCED) gene, controlling the rate limiting step of ABA biosynthesis. Moreover, this cultivar exhibited a higher basal activity and a higher induction of aldehyde oxidase isoenzymes (AAO2-AAO3), responsible for converting ABAldehyde to ABA. It was found that the fast activation of the ABA biosynthesis in the roots generated an enhanced ABA pool in the shoot, which brought about a faster closure of the stomata upon increasing osmotic stress and, as a result, the plants could maintain ψw in the tissues close to the control level. In contrast, the anisohydric genotype, cv. GK Öthalom, exhibited a moderate induction of ABA biosynthesis in the roots, leading to the maintenance but no increase in the concentration of ABA on the basis of tissue water content in the leaves. Due to the slower response of their stomata to water deficit, the tissues of cv. GK Öthalom have to acclimate to much more negative water potentials during increasing osmotic stress. A decreased activity of superoxide dismutase (SOD) was found in the leaves and roots of both cultivars exposed to osmotic stress, but in the roots elevated activities of catalase (CAT), peroxidase (POX), glutathione reductase (GR) and glutathione transferase (GST) were detected in the isohydric cultivar, suggesting that this genotype was more successful in the elimination of reactive oxygen species caused by the stress conditions.

Physiological and morphological responses of the root system of Indian mustard (Brassica juncea L. Czern.) and rapeseed (Brassica napus L.) to copper stress

Copper (Cu) is an essential microelement for growth and development, but in excess it can cause toxicity in plants. In this comparative study, the uptake and accumulation of Cu as well as the morphological and physiological responses of Indian mustard (Brassica juncea L. Czern.) and rapeseed (Brassica napus L.) roots to Cu treatment were investigated. The possible involvement of redox active molecules (reactive oxygen species and nitric oxide) and modification in cell wall structure associated with Cu-induced morphological responses were also studied. In short- and long-term treatments, B. juncea suffered more pronounced growth inhibition as compared with B. napus. In addition to the shortening of primary and lateral roots, the number and the density of the laterals were also decreased by Cu. Exposure to copper induced nitric oxide generation in the root tips and this event proved to be dependent on the duration of the exposure and on the plant species. In short- and long-term treatments, Indian mustard showed more significant activation of superoxide dismutase (SOD), inhibition of ascorbate peroxidase (APX) and oxidation of ascorbate (AsA) than B. napus. Moreover, H2O2-dependent lignification was also observed in the Cu-exposed plants. In longer term, significant AsA accumulation and callose deposition were observed, reflecting serious oxidative stress in B. juncea. Based on the morphological and physiological results, we conclude that rapeseed tolerates Cu excess better than Indian mustard.

Biological significance of naturally occurring deuterium: the antitumor effect of deuterium depletion

A felszíni vizekben a deutérium (D) koncentrációja több mint 16 mmol/l (150 ppm), az élő szervezetekben 10 mmol/l fölötti. A csökkentett deutériumtartalmú (30±5 ppm) vízzel folyó kutatások során korábban azt tapasztalták, hogy a deutériummegvonás gátolta a sejtosztódást in vitro különböző tumoros sejtvonalakban (PC-3, humán prosztatatumor; MDA, humán emlőtumor; HT-29, humán vastagbéltumor; M14, humán melanoma). A csökkentett deutériumtartalmú víz tumorregressziót idézett elő humán eredetű tumorral xenotranszplantált, immunszuppresszált egerekben (MDA és MCF-7 humán emlőtumor, PC-3 prosztatatumor), és apoptózist indukált in vitro és in vivo . A csökkentett deutériumtartalmú víz (25±5 ppm) részleges vagy teljes tumorregressziót idézett elő spontán tumoros kutyákban és macskákban. A készítményt 1999-ben daganatellenes állatgyógyszerként törzskönyvezték (Vetera-DDW-25 A.U.V., 13/99 FVM). Injekciós változatát klinikai vizsgálatban sikeresen tesztelték. Az Országos Gyógyszerészeti Intézet 5621/40/95 számú engedélye alapján, a GCP-elvek betartásával lefolytatott randomizált, kettős vak elrendezésű humán fázis II klinikai vizsgálat szignifikáns különbséget igazolt a kontroll- és a kezelt csoport között a vizsgált paraméterek vonatkozásában. Egyéves utánkövetés során a csökkentett deutériumtartalmú víz szignifikánsan csökkentette a prosztatatumoros betegek halálozási arányát, miközben a túlélés hosszát szignifikánsan növelte. Az eredmények azt igazolják, hogy a sejtek képesek szabályozni a deutérium/hidrogén (D/H) arányát és ennek változtatásával elindítani bizonyos molekuláris folyamatokat, amelyeknek kulcsszerepük van a sejtciklus szabályozásában. Feltételezzük, hogy nem az intracelluláris pH változása, hanem az azt kísérő D/H arány változása adja meg a sejteknek a jelet az S-fázisba lépéshez. A D-koncentráció csökkenése beavatkozik a szignáltranszdukciós folyamatokba, így idézve elő a tumor regresszióját. A D szerepének felismerése a sejtosztódás szabályozásában új lehetőségeket nyit meg a daganatterápia és a megelőzés területén, hozzájárulva ezzel a jelenlegi daganatellenes terápiák hatékonyságának növeléséhez.

Store-operated Ca2+-channels are sensitive to changes in extracellular pH

The sensitivity of store-operated Ca(2+)-entry to changes in the extra- and intracellular pH (pH(o) and pH(i), respectively) was investigated in SH-SY5Y human neuroblastoma cells. The intracellular Ca(2+)-stores were depleted either with 1 mM carbachol (CCH) or with 2 microM thapsigargin (TG). Extracellular acidification suppressed both the CCH- and TG-mediated Ca(2+)-entry while external alkalinization augmented both the CCH- and the TG-induced Ca(2+)-influx. Mn(2+)-quenching experiments revealed that the rates of Ca(2+)-entry at the thapsigargin- or carbachol-induced plateau were both accelerated at pH(o) 8.2 and slowed down at pH(o) 6.8 with respect to the control at pH(o) 7.4. Alteration of pH(o) between 6.8 and 8.2 did not have any significant prompt effect on pH(i) and changes in pH(i) left the CCH-induced Ca(2+)-entry unaffected. These findings demonstrate that physiologically relevant changes in pH(o) affect the store-operated Ca(2+)-entry in SH-SY5Y cells and suggest that endogenous pH(o) shifts may regulate cell activity in situ via modulating the store-operated Ca(2+)-entry.

In vitro model of neurotoxicity of A? 1?42 and neuroprotection by a pentapeptide: irreversible events during the first hour

The cell biology of Alzheimer's disease (AD) is characterized mainly by the neurodegeneration caused by the beta-amyloid (Abeta) peptides and by the formation of neurofibrillary tangles. The initial events of neurodegeneration in the brain tissue include synaptic dysfunction and axonopathy. Abeta-induced axonopathy and neurite degeneration were studied in vitro on differentiated human-derived neurotypic SH-SY5Y cells. Different methods were used to investigate the mechanism of action of aggregated Abeta on neuroblastoma cells. Abeta 1-42 aggregated for 1 h induced irreversible changes in the neurite morphology. Change of tau hyperphosphorylation and cell viability (cytoplasmic redox state and active membrane uptake) was irreversible during the first hour after the addition of Abeta 1-42 to the cells. These rapid events indicate that Abeta might induce neurodegeneration even at an early stage of Abeta-cell contact. A novel pentapeptide LPYFD-amide, an analog of Soto's LPFFD, significantly decreased neurite degeneration, tau aggregation, and cell viability reduction induced by Abeta 1-42.

[Change of fibroblast calcium levels caused by beta-amyloid peptide in Alzheimer disease]

RATIONALE

beta-amyloid peptides, comprising the major neuropathological lesions of Alzheimer's disease, have been found to form depositions in various peripheral tissues, including the skin. Neurons in the disorder succumb to the altered ionic homeostasis and some other factors caused by this toxic peptide. In line with these findings, our study aimed to find differences in biochemical processes of cultured cutaneous fibroblasts derived from sporadic Alzheimer patients and from age-matched control individuals that may mirror changes in the central nervous system.

METHODS

Intracellular ionic homeostasis of Alzheimer and control fibroblasts was measured in Fura-2AM-loaded human fibroblasts by dual wavelength spectrofluorimetry.

RESULTS

Cells derived from Alzheimer patients exhibited lower intracellular free calcium levels as compared to the control cultures. Exposure of fibroblasts to beta-amyloid resulted in increased calcium concentrations of the control cells, but not of Alzheimer ones.

CONCLUSION

Our findings indicate that Alzheimer's disease is a systemic disorder that, among others, affects the calcium homeostasis of fibroblasts. Even though it is unknown whether the diminished ionic response of Alzheimer fibroblasts is a disease or actual status marker, it could prove to be a useful model for the analysis of Alzheimer specific changes.

Comparative studies on [Ca2+]i-level of fibroblasts from Alzheimer patients and control individuals

The accumulation of the beta-amyloid peptide (betaAP) in the brain, produced from the ubiquitously expressed amyloid precursor protein (APP) is a defining feature of Alzheimer's disease (AD). Consistent with studies demonstrating the importance of skin biopsy in the diagnosis of neurodegenerative disorders, we investigated whether differences in intracellular free calcium levels ([Ca2+]i) of cultured cutaneous fibroblasts derived from sporadic AD patients and from age-matched control individuals might be present. [Ca2+]i was measured in Fura-2AM-loaded human fibroblasts by dual wavelength spectrofluorimetry. AD cells exhibited lower [Ca2+]i as compared to the control cultures. Exposure of fibroblasts to betaAP resulted in increased [Ca2+]i of the control cells, but not of AD fibroblasts. Our test could prove useful in supporting the diagnosis of (sporadic) AD in patients suspected of suffering from the disease.

beta-Amyloid[1-40]-induced early hyperpolarization in M26-1F cells, an immortalized rat striatal cell line

The short-term (20-minute) action of beta[1-40]-amyloid on the resting transmembrane potential was investigated by means of flow-cytofluorimetric studies in M26-1F cells, an immortalized rat striatal cell line, using the potential-sensitive fluorescent probe bis-oxonol. The distribution of the individual cell-associated probe fluorescence was found to be shifted to lower levels in cells treated with beta-amyloid[1-40] for 20 minutes as compared with that of their untreated counterparts. A change in the same direction was caused by valinomycin, a hyperpolarizing ionophore, whereas gramicidin, a depolarizing ionophore, induced a shift to higher fluorescence intensities. These findings, together with the reported behaviour of this particular fluorescent probe at different transmembrane potential levels, indicate that beta-amyloid[1-40] is capable of inducing early hyperpolarization in M26-1F cells. This is one of the earliest cell physiological effect of beta-amyloid peptides that has been reported so far. Moreover, our findings indicate an ionophore-like action of amyloid peptides.

beta-amyloid neurotoxicity is mediated by a glutamate-triggered excitotoxic cascade in rat nucleus basalis

Whereas a cardinal role for beta-amyloid protein (Abeta) has been postulated as a major trigger of neuronal injury in Alzheimer's disease, the pathogenic mechanism by which Abeta deranges nerve cells remains largely elusive. Here we report correlative in vitro and in vivo evidence that an excitotoxic cascade mediates Abeta neurotoxicity in the rat magnocellular nucleus basalis (MBN). In vitro application of Abeta to astrocytes elicits rapid depolarization of astroglial membranes with a concomitant inhibition of glutamate uptake. In vivo Abeta infusion by way of microdialysis in the MBN revealed peak extracellular concentrations of excitatory amino acid neurotransmitters within 20-30 min. Abeta-triggered extracellular elevation of excitatory amino acids coincided with a significantly enhanced intracellular accumulation of Ca2+ in the Abeta injection area, as was demonstrated by 45Ca2+ autoradiography. In consequence of these acute processes delayed cell death in the MBN and persistent loss of cholinergic fibre projections to the neocortex appear as early as 3 days following the Abeta-induced toxic insult. Such a sequence of Abeta toxicity was effectively antagonized by the N-methyl-D-aspartate (NMDA) receptor ligand dizocilpine maleate (MK-801). Moreover, Abeta toxicity in the MBN decreases with advancing age that may be associated with the age-related loss of NMDA receptor expression in rats. In summary, the present results indicate that Abeta compromises neurons of the rat MBN via an excitotoxic pathway including astroglial depolarization, extracellular glutamate accumulation, NMDA receptor activation and an intracellular Ca2+ overload leading to cell death.

Propionyl-IIGL tetrapeptide antagonizes beta-amyloid excitotoxicity in rat nucleus basalis

A putative tetrapeptide beta-amyloid (Abeta) antagonist (propionyl-Ile-Ile-Gly-Leu [Pr-IIGL]) based on the [31-34] sequence of Abeta was previously shown to rescue astrocytes from Abeta-induced membrane depolarization and subsequent long-term elevations of the intracellular Ca2+ concentration in vitro. Here we provide in vivo evidence that the Pr-IIGL tetrapeptide effectively attenuates the excitotoxic action of Abeta(1-42) on cholinergic neurons of the rat magnocellular nucleus basalis (MBN). We also demonstrate by means of microdialysis that administration of Pr-IIGL abolished Abeta(1-42)-induced increases in extracellular aspartate and glutamate concentrations in the MBN, which coincide with a significant preservation of cholinergic MBN neurons and their cortical projections. This neuroprotective effect was associated with preserved exploratory behavior in an open-field paradigm, and improved memory retention in a step-through passive avoidance task. Our data presented here indicate for the first time the efficacy of short, modified functional Abeta antagonists in ameliorating Abeta excitotoxicity in vivo.

A putative tetrapeptide antagonist prevents beta-amyloid-induced long-term elevation of [Ca2+]i in rat astrocytes

Comparative fluorimetric studies on the long-term (8-hour) action of beta[1-42]amyloid and its shorter fragments beta[1-40], beta[25-35] and beta[31-35] on the steady-state intracellular Ca2+ concentration in primary cultures of rat astroglial cells using the Ca2+-sensitive fluorescent probe Fura-2 AM revealed higher 340/380 fluorescence excitation ratios in the treated cells as compared to the untreated controls. All the peptides were found to induce similar cellular effects, suggesting the [31-35] region as the putative active centre of the molecule. No significant alteration was detectable in Fura-2 fluorescence using the Ca2+-insensitive excitation wavelength of 367 nm, indicating that the observed changes reflect a real alteration in the Ca2+ concentration of the cells. Moreover, no considerable difference was observed in the total protein content of treated and untreated cells. Co-treatment of the cells with Pr-Ile-Ile-Gly-Leu-NH2 (Pr-IIGL) peptide, an analogue of the [31-34] region of beta[1-42]-amyloid, was found to effectively antagonize the beta[1-42]-amyloid-induced elevation of the fluorescence excitation ratio, leaving the 367-nm fluorescence unaffected. To the best of the authors' knowledge, this is the first report on an analogue of beta-amyloid peptide capable of blocking one of its physiological effects, thereby raising the possibility that this sequence could prove to be a lead compound for designing effective beta-amyloid antagonists.

Role of interleukin-3 in the regulation of intracellular K+ homeostasis in cultured murine haemopoietic cells

Comparative fluorimetric, flow cytofluorimetric and fluorescence ratiometric determinations of intracellular K+ concentrations in murine haemopoietic cells (FDCP-Mix clone A4) cultured in the presence and absence of the specific growth factor Interleukin-3 were carried out with the fluorescent potassium-binding benzofuran-isophthalate acetoxymethyl ester probe. Cell suspensions kept in the absence of Interleukin-3 for 5 hours exhibited lower fluorescence intensities and smaller fluorescence ratios than their growth-factor-replete counterparts, an effect found to be reversible by readdition of the growth factor. It is concluded that Interleukin-3 deprivation of these cells leads to loss of intracellular K+. It is tentatively suggested that this deprivation-induced K+ loss might be associated with an early event in apoptotic cell death.

Transmembrane potentials in cells: a diS-C3(3) assay for relative potentials as an indicator of real changes

The mechanism by which the fluorescent cationic dye diS-C3(3) reports on cellular transmembrane potential has been investigated in murine haemopoietic cells. Due to the large molar absorbance of diS-C3(3) and its high quantum yield of fluorescence in cells, this dye can be used at very low labelling concentrations (5 x 10(-8) to 2 x 10(-7) M). In contrast to the quenching of fluorescence observed for the most commonly used voltage-sensitive dyes of the carbocyanine class, the fluorescence intensity of diS-C3(3) increases when the dye accumulates in the cells. The method of synchronous emission spectroscopy was used to resolve the intracellular and extracellular components of the diS-C3(3) fluorescence of suspensions of labelled cells. In comparing changes in these signals consequent on changes in transmembrane potential induced by varying the extracellular concentration of potassium ions in the presence of valinomycin, the logarithm of the ratio of intensities of these two components, as predicted theoretically, was found to be a good linear measure of transmembrane potential under these conditions. The dye was also demonstrated to be suitable for flow-cytofluorimetric analysis, the logarithm of the mean population signal similarly being found to provide a good linear measure of the transmembrane potential. The conditions under which such linearity may be expected with respect to possible effects due to changes in the capacity for binding of the dye to proteins and various cytosolic structures are delineated and their validity with respect to the possibly contentious role of mitochondria in such measurements examined in particular. The use of the method in indicating changes in the transmembrane potential and/or changes in the transport numbers of the major ions determining transmembrane potential between different physiological states, the possible extension to determinations of absolute differences in potential between different cell states without calibration or comparison with potassium-ion potentials, and the conditions for validity and limitations of these partially complementary measurements, are discussed.

Interleukin-3-specific modification of cell membrane "fluidity" of haemopoietic cells

The work reported here clearly demonstrates that a specific growth factor, interleukin-3 (IL-3), which acts on multipotent haemopoietic stem cells as well as on committed myeloid progenitor cells of different lineages (Schrader, 1988; Whetton and Dexter, 1986), specifically induces a modification of the physical state ("fluidity") of the cell membranes of two IL-3-responsive and apparently normal haemopoietic cell lines. Furthermore, in a derived IL-3 independent myeloid leukaemic cell line, no such physical response to IL-3 binding was observed. The rapidity of the "normal" response suggests further that it may be associated with, or even constitute per se a critical early effect elicited by IL-3 in sensitive cells, the necessity for which is abrogated in the malignant derivative.

Photosynthetic Properties and Cross-Resistance to Some Urea Herbicides of Triazine-Resistant Conyza canadensis Cronq (L.)

A comparison of the photosynthetic activities, chloroplast ultrastructures and sensitivities to some urea herbicidcs of atrazine-resistant (R) and suspectible (S) biotypes of Conyza canadensis Cronq (L.) (horseweed) in the rosette stage showed that: 1) The light-intensitv dependences of the rates of CO: reduction in intact leaves of the R and S plants are very similar. 2) The rate of the Hill reaction of the R chloroplasts at 25 °C is 15 - 20% lower at all light intensities than that of the S chloroplasts. 3) The rates of the Hill reactions of the R and S chloroplasts exhibit different temperature-dependences. The activation energy for the S chloroplasts in the temperature range 10-40 °C was found to be 15.3 kJ mol-1. For the R chloroplasts. the discontinuity in the Arrhenius plot was found at around 20 °C; the activation energy was 20.1 kJ mol-1 at below 20 °C. and decreased to 8.2 kJ mol-1 at higher temperatures. 4) The R plants have a better adaptive capacity than the S plants at low temperatures. 5) The chloroplast ultrastructure in the R plants was not reminiscent of that of plants grown under low light intensity. 6) The R biotvpe exhibited cross-resistance to chlorbromuron and metobromuron. and tolerance to linuron. The R and S biotypes, however, were equally sensitive to diuron. The results permitted conclusions on the properties of the triazine-resistance and urea cross-resistance.

Photosynthetic Properties and Cross-Resistance to Some Urea Herbicides of Triazine-Resistant Conyza canadensis Cronq (L.)

A comparison of the photosynthetic activities, chloroplast ultrastructures and sensitivities to some urea herbicides of atrazine-resistant (R) and suspectible (S) biotypes of Conyza canadensis Cronq (L.) (horseweed) in the rosette stage showed that: I) The light-intensitv dependences of the rates of CO2 reduction in intact leaves of the R and S plants are very similar. 2) The rate of the Hill reaction of the R chloroplasts at 25 0C is 15 - 20% lower at all light intensities than that of the S chloroplasts. 3) The rates of the Hill reactions of the R and S chloroplasts exhibit different temperature-dependences. The activation energy for the S chloroplasts in the temperature range 10-40 0C was found to be 15.3 kJ mol-1. For the R chloroplasts. the discontinuity in the Arrhenius plot was found at around 20 °C: the activation energy was 20.1 kJ mol-1 at below 20 0C. and decreased to 8.2 kJ mol-1 at higher temperatures. 4) The R plants have a better adaptive capacity than the S plants at low temperatures. 5) The chloroplast ultrastructure in the R plants was not reminiscent of that of plants grown under low light intensity. 6) The R biotype exhibited cross- resistance to chlorbromuron and metobromuron. and tolerance to linuron. The R and S biotypes, however, were equally sensitive to diuron. The results permitted conclusions on the properties of the triazine-resistance and urea cross-resistance.

Effects of Pyridazinone Herbicides during Chloroplast Development in Detached Barley Leaves III. Effects of SAN 6706 on Photosynthetic Activity and Chlorophyll-Protein Complexes

The photosynthetic activities of barley leaves in vivo and of thylakoids, isolated from the leaves, in vitro were studied during greening in the presence or absence of 2 × 10-4 м SAN 6706. The degree of chlorophyll bleaching increased from 32% at 24 h of greening to 60% at the final stage. Treated leaves were unable to carry out 14CO2-fixation, their fluorescence induction properties showed very limited, if any, photosystem II-activity, and the thylakoids isolated from the leaves were also inactive in mediating ferricyanide Hill reaction. The leaves, however, exhibited lightinduced quenching of fluorescence revealed by slow fluorescence induction measurements; and the thylakoids were active in mediating photosystem I-specific in vitro Mehler reaction. Thylakoid membranes of the chloroplasts isolated from treated leaves contained CP 1 and LHCP3 bands as revealed by polyacrylamide gel electrophoresis. From these results it is concluded that i) greening in the presence of SAN 6706 leads to the formation of inactive photosystem -II units; that ii) photosystem-I per se is active in vitro, and can, possibly, mediate cyclic electron transport in vivo coupled to the formation of ATP; and that iii) the presence of xanthophyll pigments is required for the assembly of the light-harvesting complex.

The experiments were repeated with the application of SAN 9789, another pyridazinone compound, and yielded practically the same results as those obtained with SAN 6706. For practical reasons, only the results obtained with SAN 6706 are demonstrated throughout this communication.

Photosynthetic characteristics of detached barley leaves during greening in the presence of SAN 9785

The effects of the pyridazinone compound SAN 9785 on the photosynthetic competence of leaves, on the photochemical activity of isolated thylakoids and on the formation and spectral properties of chlorophyll-protein complexes were studied during a 72-h greening period of detached etiolated leaves of barley (Hordeum vulgare L. cv. Horpácsi kétsoros). It was established that i) the photosynthetic capacity of the leaves decreased considerably (by 80 and 90%, as determined by(14)CO2 fixation and fast fluorescence induction measurements, respectively); ii) the photochemical activity of isolated thylakoids from water to potassium ferricyanide and from dichlorophenol indophenol/ascorbate to methylviologen exhibited only slight reductions when expressed on a chlorophyll basis compared with the control; iii) the slow fluorescence induction curves of the treated leaves demonstrated the presence of a peculiar fluorescence component interrupting the quenching of fluorescence at around 1 min illumination; iv) a shortage of the chlorophyll-protein complex of photosystem I (CPI) occurred with a higher content of the monomer of the light harvesting complex in the thylakoids of treated leaves; and v) the fluorescence spectrum of the CPI band present in treated leaves indicates the destruction of the structural integrity of this complex during isolation from the membrane.