Disturbance of the secretory pathway inMicrasterias denticulata by tunicamycin and cyclopiazonic acid

Summary Both tunicamycin, an inhibitor of N-linked glycosylation of proteins, and cyclopiazonic acid, which inhibits the Ca²⁺-dependent ATPase in the ER, influence the secretory pathway at the ER level and lead to a cessation of cell growth inMicrasterias. Electron microscopical investigations reveal that the mode of action of the two inhibitors differs. While tunicamycin treatment results in a disintegration of the Golgi bodies into small vesicles, cyclopiazonic acid prevents products being supplied from the ER, resulting in the dilatation of ER cisternae and a reduction in the number of Golgi cisternae, combined with a loss of dictyosomal activity. The disturbed cell wall formation under tunicamycin indicates that N-linked glycosylation of proteins is required for normal cell growth inMicrasterias. Moreover, our studies reveal that changes in cytoplasmic free calcium concentration, as a consequence of ATPase inhibition in the ER by cyclopiazonic acid, may inhibit wall material secretion by interrupting the normal ER-dictyosome association.Abbreviations CPA cyclopiazonic acid - ER endoplasmic reticulum - TM tunicamycin     

Endocytosis in maize root cap cells

Summary Primary roots of maize seedlings have been treated with solutions of lanthanum and lead salts in an attempt to demonstrate endocytosis. Subsurface cells in the root cap reveal deposits of these heavy metals in coated pits in the plasma membrane and in coated vesicles. In addition lead deposits were observed in coated evaginations (pits) on large (secretory) vesicles present at the trans-pole of the Golgi apparatus and on small vacuoles. Lead was also found in the peripheral regions of individual cisternae throughout the dictyosomal stack. We interpret our results as providing evidence for coated pit/coated vesicle-mediated endocytosis and for the direct recycling of plasma membrane to the Golgi apparatus.     

Acid phosphatase activity during spore differentiation of the red algaeGigartina teedii andChondria tenuissima

The acid phosphatase activity during carposporogenesis inGigartina and tetrasporogenesis inChondria was studied using the Gomori technique. During the first steps of gonimoblast maturation ofGigartina, portions of cytoplasm are ensheathed by ER cisternae with acid phosphatase activity, giving rise to autolysosomal concentric membrane bodies. In a similar way large mucilage sacs are severed. They extrude their contents in a kind of exocytosis. Multivesicular bodies, concentrically arranged cisternae and extracytoplasmic compartments, each with acid phosphatase activity, remain in young carpospores for some time, probably as remnants of the autophagocytotic and exocytotic events. The Golgi apparatus is poorly developed in gonimoblast cells and young carpospores. It becomes a prominent cell component in maturing carpospores and then participates in cell wall formation. Only some of the dictyosomal cisternae contain acid phosphatase; these are irregularly distributed in the dictyosome. — In pre- and postmeiotic tetraspore mother cells ofChondria massive lead deposits are found in the dictyosomes and in adjacent Golgi vesicles. Finer lead precipitates occur in ER cisternae, especially in those which are sequestering starch-grain-containing portions of the cytoplasm to give rise to autolysosomes. During cell cleavage, the dictyosomes aggregate. They become devoid of acid phosphatase activity with the exception of vesicles at the trans face. Later, Golgi stacks associate and have common, Gomori positively reacting, narrow cisternae at the cis face. The Golgi apparatus derived cored vesicles do not contain lead precipitates whereas the Golgi cisternae in the final stage of tetrasporogenesis show acid phosphatase activity. Variations in acid phosphatase distribution are explained in the light of current models of membrane flow.Dedicated to Univ.-Prof. DrO. Härtel on the occasion of his 80th birthday.     

A Fragrant Solution to Soil Remediation

The ability of scented geraniums (Pelargonium sp. ‘Frensham’) plants to tolerate, uptake, and accumulate lead was assessed compared with two well-established metal accumulators, Indian mustard (Brassica juncea) and sunflower (Helianthus annuus), under greenhouse conditions. The efficiency of the photosynthetic apparatus and the number and size of active photosynthetic reaction centers (expressed as chlorophyll a fluorescence ratios of variable fluorescence to maximal fluorescence [Fv/Fm] and variable fluorescence to unquenchable portion of fluorescence [Fv/Fo], respectively) were affected to varying degrees at all metal concentrations in all the plants tested. Lead exposure did not significantly affect the efficiency of photosystem II activity or the number and size of the photosynthetic reaction centers in scented geraniums, but the ratios decreased significantly in Indian mustard and sunflower plants following lead exposure. In addition to tolerating high levels of lead, the scented geraniums accumulated in excess of 3000 mg of lead per kg DW of shoot and above 60,000 mg of lead per kg DW of root tissue. Additionally, scented geraniums exposed to a mixture of metals (lead + cadmium + nickel) had the ability to uptake in excess of 4.72% Pb + 0.44% Cd + 0.52% Ni per kg of root DW, as well as 0.17% Pb + 0.07% Cd + 0.14% Ni per kg of shoot DW within 14 d, indicated the potential for existence of more than one functional tolerance and metal uptake mechanism(s). The cellular localization of lead was assessed using transmission electron microscopy coupled with an X-ray microanalyzer. Lead accumulation was observed in the apoplasm and in the cytoplasm, vacuoles, and as distinct globules (potentially as lead-lignin or lead-phosphate complexes) on the cell membrane and cell wall. We conclude that the ability of scented geraniums to tolerate high lead accumulation in its biomass is due, in part, to limiting damage to photosynthetic apparatus and metal detoxification by formation of metal complexes.     

Induction of gravity-dependent plasmatic responses in root statocytes by short time contact between amyloplasts and the distal endoplasmic reticulum complex

Statocytes from roots of Lepidium sativum L., which developed after a 2-min soaking on a horizontal clinostat (2 rotations per min) for 44 h, exhibit the same polarity as in vertically grown roots, as indicated by a complex of endoplasmic reticulum (ER) cisternae at the distal cell pole. Amyloplasts are distributed randomly. The kinetics of graviresponse (=curvature) of such roots are identical to those of normally grown roots. Ten-minute exposure of the root, after 24 h development on the clinostat with gravity acting towards the root's basis (inversion), induces no changes in statocyte ultrastructure. However, corresponding exposure in normal orientation leads to subsequent disintegration of the distal ER complex, loss of amyloplast starch, confluence of lipid droplets, and an increase of the lytic compartment. These ultrastructural events thus appear to be induced by a physical contact — however short — between amyloplasts and the distal ER complex.Abbreviation ER endoplasmic reticulum Dedicated to Professor Dr. W. Haupt on the occasion of his 60th birthday     

Restitution of polarity in statocytes from centrifuged roots*

Abstract The structural polarity of statocytes from cress roots is changed by centrifugation. Upon low- dose centrifugation (3000 g min), the extent of stratification depends on statocyte position, i.e., central statocytes are affected more than lateral ones. Upon higher doses of centrifugation (60,000 and 360,000 g min), a uniform density gradient is established in all statocytes. If, after centrifugation, the roots are exposed to gravity again, the endoplasmic reticulum (ER) cisternae are relocated parallel to the periclinal cell walls within a few minutes; this relocation is independent of the direction of gravity in relation to the root axis, and independent of the previously applied centrifugation dose. This supports the notion that polarity is determined genetically. Cytochalasin B treatment, before and during centrifugation, totally inhibits the relocation of ER. After removing the drug by rinsing the roots, the statocytes restore cell polarity and relocate ER. These results indicate that relocation of ER cisternae may be mediated by microfilaments. When centrifuged roots are exposed to 1 g in the horizontal position, the latent period of gravitropism increases by 8–10 min relative to controls, regardless of the previously applied centrifugation doses. The kinetics of curvature are virtually identical. Since the increase in the latent period coincides with the time needed for most statocytes to restore the distal cell pole, it is evident that perception of gravity is correlated to the integrity of the distal cell pole.     

The golgi-mediated scale production in the marine haptophycean alga Ochrosphaera neapolitana Schussnig

Abstract

Some ultrastructural features of cells of the marine haptophycean alga, Ochrosphaera neapolitana Schussnig in the palmelloid stage were examined. Chloroplasts which are contained in a compartment isolated from the cytoplasm by ER profiles and nuclear envelope, display trilamellated thylakoids running along the major axis. The stalked pyrenoid with inner bilamellated thylakoids, protrudes in a large membrane-bounded vacuole. Other structures, as the haptonematic and flagellar bases, autophagic vacuoles and mitochondria, are typical of the chrysophycean and haptophycean genera so far investigated.

The Golgi apparatus is represented by a single dictyosome composed of stacked cisternae fonctioning in a way that they form organic scales which constitute the main part of the cell covering. The scales, build up of microfibrils disposed parallel each to other, lie in cisternal lumina of the dictyosomal maturing face; scaly cisternae are numerous in the peripheral cytoplasm and are observed merging in the plasma membrane and discharging the content outside the protoplast.

Dictyosomal activity is evidenced morphologically by massive vesicle production. Three kinds of membrane-bounded vesicles were identified in the present material: i) inner-granulated vesicles, arising from the maturation face; ii) coated vesicles, scattered in the cytoplasm or at the periphery of the golgi body, and iii) dense-cored vesicles, present in the proximity of the maturation face. The possible functional relationships related to scale production and assembly outside the protoplast, and between the nucleus and dictyosome are discussed.     

Correlation of growth inhibition with accumulation of Pb in cell wall and changes in response to oxidative stress in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> seedlings

Uptake of the non-essential element, lead (Pb), by 7-days-old Arabidopsis thaliana seedlings caused inhibition of root growth. Pb accumulated mainly in the root and only a small proportion of the total uptake was transported to the shoot. At the ultrastructural level, Pb was localized mainly in the cell walls, intercellular spaces and vacuoles, which may serve to minimize Pb toxicity to vital functions of the cytosol. Pb exposure induced the generation of reactive oxygen species (ROS) and increased the level of lipid hydroperoxide. These changes were accompanied by up-regulation of the activities of antioxidative enzymes in a dose-dependent manner. Although no major destructive changes to the cytoplasm and vital organelles were observed, it is postulated that at least part of the cost of Pb exposure to A. thaliana seedlings is reflected in reduced root growth associated with increased free radical production by cell wall-accumulated Pb.     

Endocytosis in nonciliated epithelial cells of the ductuli efferentes in the rat

The nonciliated cells lining the ductuli efferentes presented three distinct cytoplasmic regions. The apical region contained, in addition to cisternae of endoplasmic reticulum and mitochondria, two distinct membranous elements. The tubulovesicular system consisted of dilated tubules connected to the apical plasma membrane and subjacent distended vesicular profiles. The apical tubules, not connected to the cell surface, consisted of numerous densely stained tubules of small size which contain a compact, finely granulated material. The supranuclear region, in addition to a Golgi apparatus and ER cisternae, contained dilated vacuoles, pale and dense multivesicular bodies, as well as numerous dense granules identified cytochemically as lysosomes. The basal region contained the nucleus and many lipid droplets. The endocytic activity of these cells was investigated using cationic ferritin (CF) and concanavalin-A-ferritin (Con-A-ferritin) as markers of adsorptive endocytosis; and native ferritin (NF), concanavalin-A-ferritin in the presence of alpha-methyl mannoside, and horseradish peroxidase or albumin bound to colloidal gold for demonstrating fluid-phase endocytosis. These tracers were injected separately into the rete testis, and animals were sacrificed at various time intervals after injection. At 1 min, CF or Con-A-ferritin were seen bound to the apical plasma membrane, to the membrane of microvilli, and to the membrane delimiting elements of the tubulovesicular system. Between 2 and 5 min, these tracers accumulated in the densely stained apical tubules and at 15 min in the dilated vacuoles. Between 30 min and 1 hr, the tracers appeared in multivesicular bodies of progressively increasing density, whereas at 2 hr and later time intervals, many dense lysosomal elements became labeled. The tracers for fluid-phase endocytosis showed a distribution similar to that for CF or Con-A-ferritin except that they did not bind to the apical plasma membrane, microvilli, or membrane delimiting the tubulovesicular system. At no time interval were any of the tracers observed in the abluminal spaces. Thus, the nonciliated epithelial cells of the ductuli efferentes are actively involved in fluid-phase and adsorptive endocytosis, both of which result in the sequestration of endocytosed material within the lysosomal apparatus of the cell.     

The morphology,occurrence, and distribution of dilated cisternae of the endoplasmic reticulum in tissues of plants of theCruciferae

Summary Morphology, occurrence, and distribution of dilated cisternae of the endoplasmic reticulum (ER) were studied by electron microscopy. The cisternae which contained an electron-dense matrix were intimately associated with the granular ER membranes appearing as tubular necks at the edges of the ER profiles. After budding off from the ER the cisternae still had ribosomes attached to the outside of the bounding membranes. The accumulations were variable in shape, being 0.4 to 1.5 in width and 4 to 5 in length.The cisternae were found to be unique for plants of theCruciferae and could not be observed in species from related families such asPapaveraceae andResedaceae.The dilated cisternae were a common component of the cytoplasm in root tips, stems, and leaves. In meristematic cells the number of accumulations was small but increased in older differentiating cells of the root cap. The similarity to microbodies described by previous authors from other plants is discussed.     

Cellular compartments in mitotic cells: ultrahistochemical identification of Golgi elements in PtK-1 cells

This investigation focuses on the identification, distribution, and transport of intracellular membrane systems during mitosis. The membranes of the Golgi apparatus can be identified cytochemically by staining for acid phosphatase (acPase) and thiamine pyrophosphatase (TPPase) activity. Using this approach we are able to study the disintegration of the Golgi apparatus during mitosis and to follow the dislocation as well as the organized reappearance of Golgi elements after the completion of mitosis. We are able to demonstrate that during mitosis the activity of both enzymes is strong enough to react with the substrate applied during the staining procedure. Furthermore, we observe a characteristic pattern of membrane distribution in mitotic cells. During interphase the TPPase reaction is characteristically limited to one or two cisternae of a dictyosomal stack. The acPase reaction stains the membranes of the total stack, of the GERL, of some vesicles and cisternae near the dictyosomes and lysosomes. After the mitotic breakdown of the dictyosomal stacks the forming vesicles still stain positively and are distributed over the entire cytoplasm. At late anaphase and early telophase the enzyme activity occurs not only in the reconstituting dictyosomes but also in the nuclear envelope and in some ER cisternae. The extended spectrum of membrane structures indicating Golgi enzyme activity becomes obvious. This phenomenon favors the idea that at least some functions of the Golgi apparatus persist during mitosis.     

Membrane traffic from the endoplasmic reticulum to the Golgi apparatus is disturbed by an inhibitor of the Ca2+-ATPase in the ER

Summary An electron microscopic study of cress (Lepidium sativum L.) roots treated with cyclopiazonic acid (CPA), an inhibitor of the Ca²⁺-ATPase in the endoplasmic reticulum (ER) has been carried out. Drastic changes in the endomembrane system of the secretory root cap cells were observed. After treatment with CPA dense spherical or elliptoidal aggregates of ER (diameter 2–4 m) were formed in addition to the randomly distributed ER cisternae characteristic for control cells. The formation of ER aggregates indicates that in spite of an inhibition of the Ca²⁺ -ATPase in the ER by CPA, membrane synthesis in the ER continued. The ER aggregates are interpreted as a reservoir of ER membrane material newly synthesized during the 2 h CPA-treatment. Hypertrophied Golgi cisternae and secretory vesicles, which are characteristic for secretory cells under control conditions, were completely absent. Additionally the shape of the Golgi stacks was flat and the diameter of the cisternae was shortened by about one third. These phenomena are indicative of an inactive state of the Golgi apparatus. The cellular organization of both other cell types of the root cap, meristematic cells and statocytes, was not visibly affected by CPA, both having a relatively low secretory activity. The formation of ER aggregates as well as the reduction of Golgi compartments are indications for the existence of a unidirectional transport of membrane material from the ER to the Golgi. It is suggested that the membrane traffic from the ER to the Golgi apparatus is regulated by the cytosolic and/or luminal calcium concentration in secretory cells of the root cap.Abbreviations CPA cyclopiazonic acid - ER endoplasmic reticulum     

Gravitropic bending of cress roots without contact between amyloplasts and complexes of endoplasmic reticulum

The polar arrangement of cell organelles in Lepidium root statocytes is persistently converted to a physical stratification during lateral centrifugation (the centrifugal force acts perpendicular to the root long axis) or by apically directed centrifugation combined with cytochalasin-treatment. Lateral centrifugation (10 min, 60 min at 10\g or 50\g) causes displacement of amylplasts to the centrifugal anticlinal cell wall and shifting of the endoplasmic reticulum (ER) complex to the centripetal distal cell edge. After 60 min of lateral centrifugation at 10\g or 50\g all roots show a clear gravitropic curvature. The average angle of curvature is about 40° and corresponds to that of roots stimulated gravitropically in the horizontal position at 1\g in spite of the fact that the gravistimulus is 10-or 50-fold higher. Apically directed centrifugation combined with cytochalasin B (25 g\ml^-1) or cytochalasin D (2.5 g\ml^-1) incubation yields statocytes with the amyloplasts sedimented close to the centrifugal periclinal cell wall and ER cisternae accumulated at the proximal cell pole. Gravitropic stimulation for 30 min in the horizontal position at 1\g and additional 3 h rotation on a clinostat result in gravicurvature of cytochalasin B-treated centrifuged (1 h at 50\g) roots, but because of retarded root growth the angle of curvature is lower than in control roots. Cytochalasin D-treatment during centrifugation (20 min at 50\g) does not affect either root growth or gravicurvature during 3 h horizontal exposure to 1\g relative to untreated roots. As lateral centrifugation enables only short-term contact between the amyloplasts and the distal ER complex at the onset of centrifugation and apically directed centrifugation combined with cytochalasin-treatment even exclude any contact the integrity of the distal cell pole need not necessarily be a prerequisite for graviperception in Lepidium root statocytes.Abbreviations CB cytochalasin B - CD cytochalasin D - ER endoplasmic reticulum - g gravitational acceleration     

ABSCISIC ACID EFFECTS ON FRONDS AND ROOTS OF LEMNA MINOR L.

Plants of Lemna minor L. were grown in axenic culture in order to investigate the direct effect of abscisic acid (ABA) on individual fronds and roots. Both frond and root growth rates were inhibited by 60%, and total growth of both organs was reduced by 30% with ABA concentrations of 2 mg/l. Abscisic acid inhibited frond reproduction, and treated fronds tended to remain attached to parents. Reduction of root elongation and frond expansion occurred within 1–4 hr. Prolonged exposure to ABA inhibited both cell enlargement and cell division in the roots. The results are discussed in the light of current views on the control of growth with endogenous levels of promoter and inhibitor hormones.     

Cytodifferentiation of polar plant cells: Formation and turnover of endoplasmic reticulum in root statocytes

By application of cytochalasin D (10 micrograms/ml) the distribution and turnover of endoplasmic reticulum (ER) in root statocytes of cress (Lepidium sativum L.) was studied. After 7 min of incubation, the distal ER complex, in 20-h-old control statocytes consisting of stacked cisternae, was disintegrated and redistributed. The amyloplasts sedimented into the most distal part of the cell. When the incubation time was increased up to 4 h, ER was formed near the nucleus and accumulated at the proximal cell pole. Thus microfilaments are suggested to be involved in (i) stabilization of the distal ER complex and (ii) the ER translocation from the forming site into the distal cell pole. By morphometric measurements the volume of story II (story III) statocytes was calculated to be 2400 microns3 (3000 microns3), containing an ER area of 1824 microns2 (2400 microns2). From the net ER formation rate of 5.2 microns2/min (story II) and 4.6 microns2/min (story III) and the net decrease rate of 23 microns2/min (story II) and 39.2 microns2/min (story III), a total ER formation rate of about 27 microns2/min (story II) and 43 microns2/min (story III) was estimated.     

Movement of Cell Organelles and the Geotropic Curvature in Roots of Norway Spruce (Picea abies)

The geotropic development in roots of Norway spruce [(Picea abies (L.)] H. Karst, has been followed by light and electron microscopy and compared with the movement of cell organelles (statoliths) in the root cap cells. The geotropic curvature develops in two phases: (a) an initial curvature in the root cap region, which results in an asymmetry in the extreme root tip and which appears after about 3 h stimulation in the horizontal position; and (b) the geotropic curvature in the basal parts of the root tip, which after 8 h is distributed over the entire elongation zone. A graphic extrapolation, based on measurements of the root curvatures after various stimulation periods, indicates a presentation time in the range of 8 to 10 min. The root anatomy and ultrastructure have been examined in detail in order to obtain information as to which organelles may act as gravity receptors. The root cap consists of a central core (columella) distinct from the peripheral part. The core contains three to four rows of parenchymatic cells each consisting of 15 to 18 storeys of statocyte cells with possibly mobile cell organelles. Amyloplasts and nuclei have been found to be mobile in the root cap cells, and the movement of both types of organelles has been followed after inversion of the seedlings and stimulation in the horizontal position for various periods of time at 4°C and 21°C. Three-dimensional reconstructions of spruce root cap cells based on serial sectioning and electron microscopy have been performed. These demonstrate that the endoplasmic reticulum (ER)-system and the vacuoles occupy a considerable part of the statocyte cell. For this reason the space available for free movement of single statolith particles is highly restricted.     

Pectinous cell wall thickenings formation—A response of moss protonemata cells to lead

Lead poisoning constitutes one of most detrimental environmental hazards to all living organisms. Plants developed a variety of avoidance and tolerance mechanisms that are activated in response to lead exposure. Plant cell walls were suggested to play important role in these reactions by creating an efficient barrier to lead entry to the protoplasts, but the molecular mechanisms involved in such shielding reaction have not been elucidated. Tip growing protomemata of Funaria hygrometrica (Hedw.) were used as model for studying effects of lead exposure on plant cell walls (CWs). Forty-eight hour-treatment 4 μM PbCl₂ resulted in the appearance of cell wall thickenings (CWTs) at the tip of the apical cell, which is the lead entry site to the cell protoplast [Krzes?owska, M., Wo?ny, A., 1996. Lead uptake localization and changes in cell ultrastructure of Funaria hygrometrica protonemata. Biol. Plant. 38, 253–259]. The nature of these thickenings differed from the one of cell wall in unexposed plants as revealed by immunolabelling with monoclonal antibodies and histochemical analyses. The most striking difference was the appearance high amount of low-esterified (JIM5 epitope) and unesterified (PAM1 epitope) homogalacturonan, which were absent from the tip cell wall of control protonemata and are known as the compounds able to bind and immobilise Pb²⁺. Furthermore, the cell wall thickenings commonly contained callose and at least two kinds of lipid compounds known as the substances preventing metal ions entry to the protoplast.Observations in transmission electron microscope (TEM) showed that CWTs contained a few distinct, varied structurally regions. The dominant one was the region of a granular structure—never found in the control CW. This region contained both the highest amount of JIM5 pectins—and the most numerous lead deposits. In many cases gold particles, identifying JIM5 pectins, appeared to be bound to lead deposits. It indicated that JIM5 pectins which accumulated in CWTs were involved in immobilisation of high amounts of Pb²⁺. Because the region of lead accumulation occupied the largest volume of the CWTs, we concluded that CWTs appear to be a very important repository for Pb²⁺ in protonemata cells. Thus, we postulate that, CWTs localized at the tip of the apical cell—the main region of lead uptake [Krzes?owska, M., Wo?ny, A., 1996. Lead uptake localization and changes in cell ultrastructure of Funaria hygrometrica protonemata. Biol. Plant. 38, 253–259] rich in JIM5 pectins, callose and lipids function as the effective barrier against lead ions penetration into the protonema protoplast.The findings substantiate previous hypotheses that lead ions can be sequestered in cell walls and point to the possibility that capacity for lead binding might increase in cell response to lead.     

ULTRASTRUCTURE AND ACID PHOSPHATASE IN PEDICEL ABSCISSION OF HIBISCUS

Pedicel abscission in Hibiscus rosa-sinensis was investigated by light and electron microscopy. During the pre-abscission period endoplasmic reticulum declined somewhat, dictyosomes increased in number and apparent activity, and mitochondria maintained their numbers. The observations suggested that dictyosomal vesicles were migrating to and fusing with the plasma membrane. The enzyme acid phosphatase was associated with dictyosomes and dictyosomal saccules, with small vacuoles and invaginations of the plasma membrane, and in the paramural region between the plasma membrane and the cell wall. Our interpretation is that acid phosphatase, (and probably also the enzymes involved in cell wall dissolution) are transported via an endoplasmic reticulum-dictyosome-vesicle carrier system to the paramural regions of the cell. In more general terms, our observations support the view that the enzymes involved in the cell wall hydrolysis of abscission are synthesized within a compartmentalized, lysosomal system prior to their release and action.     

N-acetylcysteine exposure on lead-induced lipid peroxidative damage and oxidative defense system in brain regions of rats

Lead (Pb) is known to disrupt the pro-oxidant/antioxidant balance of tissues, which leads to biochemical and physiological dysfunction. Oxidative stress is considered a possible molecular mechanism involved in Pb neurotoxicity. Considering the vulnerability of the brain to oxidative stress under Pb neurotoxicity, this study investigated the effects of exposure of the thiol antioxidant N-acetylcysteine (NAC) on lead-induced oxidative damage and lipid peroxidation in brain regions of the rat. Wister strain rats were exposed to lead in the form of lead acetate (20 mg/kg body wt/d) for a period of 2 wk and the effects of NAC on lead-induced neurotoxicity in rat brain regions were assessed by postadministration of NAC (160 mg/kg body wt/d) for a period of 3 wk. The lipid peroxidation byproduct, malondialdehyde (MDA) increased following lead exposure in both of the regions, and the antioxidant capacities of the cell in terms of the activity of antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) was diminished. Following NAC treatment, lead-induced lipid peroxidation decreased and antioxidant enzyme activities improved, with CAT showing enhancement in the cerebral region only and SOD showing enhancements in the cerebellar region. Our result suggests that thiol-antioxidant supplementation following Pb exposure might enhance the reductive status of brain regions by arresting the lipid peroxidative damage in brain regions.