Mechanism Of Membrane Damage Research Articles

3,6-O-[N-(2-Aminoethyl)-acetamide-yl]-chitosan exerts antibacterial activity by a membrane damage mechanism

A novel chitosan derivative, 3,6-O-[N-(2-aminoethyl)-acetamide-yl]-chitosan (AACS), was successfully prepared to improve water solubility and antibacterial activity of chitosan. AACS had good antibacterial activity, with minimum inhibitory concentrations of 0.25mg/mL, against Escherichia coli and Staphylococcus aureus. Cell membrane integrity, electric conductivity and NPN uptake tests showed that AACS caused quickly increasing the release of intracellular nucleic acids, the uptake of NPN, and the electric conductivity by damaging membrane integrity. On the other hand, hydrophobicity, cell viability and SDS-PAGE experiments indicated that AACS was able to reduce the surface hydrophobicity, the cell viability and the intracellular proteins through increasing membrane permeability. SEM observation further confirmed that AACS could kill bacteria via disrupting their membranes. All results above verified that AACS mainly exerted antibacterial activity by a membrane damage mechanism, and it was expected to be a new food preservative.

Ascorbate anti‐cancer activity is increased by Mn(III)N‐alkylpyridylporphyrins through production of reactive oxygen species

Ascorbate (Asc) has shown potential for cancer therapy, and cancer cells typically accumulate porphyrins and display aberrant redox homeostasis. Mn(III)N‐alkylpyridylporphyrins (MnPs) are redox‐active superoxide dismutase mimetics with many prospective therapeutic applications. This study examined how structural modifications of MnPs might affect their anticancer activity through selective cellular targeting of production of reactive oxygen species (ROS) produced by redox‐cycling with ascorbate.MethodsPII/MDA ER‐negative human breast cancer and non‐tumorigenic HBL100 human breast epithelial cell lines were used as model systems. Uptake of MnPs and ascorbate oxidation rates were determined spectrophotometrically. MTT/SRB assays were used to investigate cytotoxic and anti‐proliferative actions of MnPs and Asc, and combinations thereof. Membrane damage and cell death mechanisms were investigated by flow cytometry.ResultsAscorbate and MnPs redox‐cycle to generate cytotoxic ROS, mainly H2O2. Anticancer efficiency of MnPs correlated with ability to oxidize ascorbate; differences in cellular uptake and subcellular distribution had only minor effect.ConclusionsThe major factor determining MnPs’ anticancer activity in cell culture models is redox potentialSupport or Funding InformationSupport: College of Graduate Studies, Kuwait University and Research Sector, Kuwait University; Research Grant YM04/14 and University Grant SRUL02/13

Antifungal Activity of Isoliquiritin and Its Inhibitory Effect against Peronophythora litchi Chen through a Membrane Damage Mechanism.

This study investigated the antifungal activity and potential antifungal mechanism(s) of isoliquiritin against P. litchi Chen, one of the main litchi pathogens. The antifungal activity of isoliquiritin against P. litchi Chen had been proven in a dose-dependent manner through in vitro (mycelial growth and sporangia germination) and in vivo (detached leaf) tests. Results revealed that isoliquiritin exhibited significant antifungal activity against the tested pathogens, especially, P. litchi Chen, with a minimum inhibitory concentration of 27.33 mg/L. The morphology of P. litchi Chen was apparently changed by isoliquiritin through cytoplasm leakage and distortion of mycelia. The cell membrane permeability of the P. litchi Chen increased with the increasing concentration of isoliquiritin, as evidenced by a rise in relative electric conductivity and a decrease in reducing sugar contents. These results indicated that the antifungal effects of isoliquiritin could be explained by a membrane lesion mechanism causing damage to the cell membrane integrity leading to the death of mycelial cells. Taken together, isoliquiritin may be used as a natural alternative to commercial fungicides or a lead compound to develop new fungicides for the control of litchi downy blight.

Mechanism of Inhibition of Human Islet Amyloid Polypeptide-Induced Membrane Damage by a Small Organic Fluorogen.

Human islet amyloid polypeptide (hIAPP) is believed to be responsible for the death of insulin-producing β-cells. However, the mechanism of membrane damage at the molecular level has not been fully elucidated. In this article, we employ coarse- grained dissipative particle dynamics simulations to study the interactions between a lipid bilayer membrane composed of 70% zwitterionic lipids and 30% anionic lipids and hIAPPs with α-helical structures. We demonstrated that the key factor controlling pore formation is the combination of peptide charge-induced electroporation and peptide hydrophobicity-induced lipid disordering and membrane thinning. According to these mechanisms, we suggest that a water-miscible tetraphenylethene BSPOTPE is a potent inhibitor to rescue hIAPP-induced cytotoxicity. Our simulations predict that BSPOTPE molecules can bind directly to the helical regions of hIAPP and form oligomers with separated hydrophobic cores and hydrophilic shells. The micelle-like hIAPP-BSPOTPE clusters tend to be retained in the water/membrane interface and aggregate therein rather than penetrate into the membrane. Electrostatic attraction between BSPOTPE and hIAPP also reduces the extent of hIAPP binding to the anionic lipid bilayer. These two modes work together and efficiently prevent membrane poration.

Antimicrobial Activity of Gallic Acid-Grafted-Chitosan Against Fish Pathogens

GRAPHICAL ABSTRACTThe objective of this study is to evaluate the antibacterial activity of the gallic acid-grafted-chitosan (GA-g-chitosan) against important fish pathogens. The antibacterial assay revealed that the GA-g-chitosan was most active against Streptococcus parauberis 12046 but had relatively weak activity against Streptococcus iniae and Vibrio anguillarum. The minimum inhibitory concentrations (MICs) of the GA-g-chitosan against five S. parauberis strains were 96 to 128 μg/mL. The cell integrity and microscopic observation indicated that the GA-g-chitosan exerted the antibacterial activity against S. parauberis through a membrane damage mechanism.

Antibacterial activity of new peptides from barbel protein hydrolysates and mode of action via a membrane damage mechanism against Listeria monocytogenes

There is great interest in the development of antimicrobial peptides as a potentially novel class of antimicrobial agents. In this study we evaluated the mode of action of new peptides (Gly-Val-His, Trp-His-Arg, Trp-His-Phe, Pro-Pro-Ser-Ser, Ala-Ala-Ala-Leu, Ala-Ala-Gly-Gly-Val, Ala-Ala-Val-Lys-Met, Ala-Ser-Ser-Ser), previously characterized, from barbel protein hydrolysates against Listeria monocytogenes via a membrane damage mechanism. The minimum inhibitory concentrations (MIC) of these peptides toward six strains and their hemolytic activity toward bovine erythrocytes were determined.Prediction of peptide secondary structure indicated that these peptides should have random coil structures and high content of hydrophobic amino acids. In addition, results of the determination of extracellular potassium, which is considered a good marker of membrane permeability, revealed that treatment with pure barbel peptides could cause morphological changes of L. monocytogenes and destruction of the cell integrity via irreversible membrane damage. The results could provide information for investigating the antibacterial model of antibacterial peptides derived from fish protein hydrolysates.

Chitosan antimicrobial and eliciting properties for pest control in agriculture: a review

In agriculture, current control of pathogens relies mainly on chemical fertilizers and pesticides. However, alternative solutions are needed due to concerns for public health, environmental protection, and development of resistant pests. Chitosan is a nontoxic, biodegradable biopolymer showing antimicrobial and plant-immunity eliciting properties. Here, we review chitosan antimicrobial activities, modes of action, and the elicitation of plant defense responses. The major points are the following: (1) Chitosan exhibits various inhibitory efficiency against bacteria, fungi, and viruses; (2) the five main modes of action of chitosan are electrostatic interactions, plasma membrane damage mechanism, chitosan-DNA/RNA interactions, metal chelation capacity of chitosan, and deposition onto the microbial surface; (3) the elicitation of plant defense responses by chitosan may be related to various pathogenesis-related proteins, defense-related enzymes, and secondary metabolites accumulation, as well as the complex signal transduction network. The facing problems and strategies for antimicrobial mechanism research and agricultural application of chitosan are also discussed.

Lipophilic organic pollutants induce changes in phospholipid and membrane protein composition leading to Vero cell morphological change

Membrane damage related to morphological change in Vero cells is a sensitive index of the composite biotoxicity of trace lipophilic chemicals. However, judging whether the morphological change in Vero cells happens and its ratio are difficult because it is not a quantitative characteristic. To find biomarkers of cell morphological change for quantitatively representing the ratio of morphological changed cell, the mechanism of cell membrane damage driven by typical lipophilic chemicals, such as trichlorophenol (TCP) and perfluorooctanesulphonate (PFOS), was explored. The ratio of morphologically changed cells generally increased with increased TCP or PFOS concentrations, and the level of four major components of phospholipids varied with concentrations of TCP or PFOS, but only the ratio of phosphatidylcholine (PC)/phosphatidylethanolamine (PE) decreased regularly as TCP or PFOS concentrations increased. Analysis of membrane proteins showed that the level of vimentin in normal cell membranes is high, while it decreases or vanishes after TCP exposure. These variations in phospholipid and membrane protein components may result in membrane leakage and variation in rigid structure, which leads to changes in cell morphology. Therefore, the ratio of PC/PE and amount of vimentin may be potential biomarkers for representing the ratio of morphological changed Vero cell introduced by trace lipophilic compounds, thus their composite bio-toxicity.

The Perforin Pore Facilitates the Delivery of Cationic Cargos

Cytotoxic lymphocytes eliminate virally infected or neoplastic cells through the action of cytotoxic proteases (granzymes). The pore-forming protein perforin is essential for delivery of granzymes into the cytoplasm of target cells; however the mechanism of this delivery is incompletely understood. Perforin contains a membrane attack complex/perforin (MACPF) domain and oligomerizes to form an aqueous pore in the plasma membrane; therefore the simplest (and best supported) model suggests that granzymes passively diffuse through the perforin pore into the cytoplasm of the target cell. Here we demonstrate that perforin preferentially delivers cationic molecules while anionic and neutral cargoes are delivered inefficiently. Furthermore, another distantly related pore-forming MACPF protein, pleurotolysin (from the oyster mushroom), also favors the delivery of cationic molecules, and efficiently delivers human granzyme B. We propose that this facilitated diffusion is due to conserved features of oligomerized MACPF proteins, which may include an anionic lumen.

Citral inhibits mycelial growth of Penicillium italicum by a membrane damage mechanism

This study investigated the anti-fungal activity and potential anti-fungal mechanisms of citral against Penicillium italicum, one of the main citrus postharvest pathogens. Results showed that citral exhibited strong anti-fungal activity against the test pathogen, with minimum inhibitory concentration and minimum fungicidal concentration of 0.50 and 1.00 μL/mL, respectively. Citral could evidently alter the morphology of P. italicum hyphae by causing loss of cytoplasm and distortion of mycelia. The membrane permeability of the P. italicum increased with increasing concentrations of citral, as evidenced by the release of cell constituents, extracellular pH, and leakage of potassium ions. Moreover, citral could induce a decrease in total lipid and ergosterol contents of P. italicum cells, indicating the disruption of membrane integrity. These results suggest that the anti-fungal activity of citral against P. italicum can be attributed to the disruption of the cell membrane integrity and membrane permeability.

Ballet dancers cardiorespiratory, oxidative and muscle damage responses to classes and rehearsals

This study aimed to describe and compare ballet dancers' cardiorespiratory responses, muscle damage and oxidative stress levels during a ballet class (practice of isolated ballet exercises performed with barre/hand-rail support and across-the-floor movements to improve technical skills) and rehearsal (practice of ballet choreography involving technical-artistic skills to improve dancers' performance for shows). The 12 advanced female ballet dancers undertook three exercise sessions: maximum effort test, class and rehearsal. Heart rate (HR) and oxygen consumption (V̇O2) were continuously measured. Lactate was determined before 15 min and after class and rehearsal. Blood was sampled pre, post and 48 h after class and rehearsal for creatine kinase (CK), lipid peroxides (LPO) and glutathione analysis (GSSG/GSH). Class was of lower intensity than rehearsal as shown by V̇O2, HR and lactate values: V̇O2 (mL.kg−1.min−1): 14.5±2.1 vs 19.1±1.7 (p < 0.001); HR (bpm.min−1): 145.7±17.9 vs 174.5±13.8 (p < 0.001); lactate (mmol.L−1): 4.2±1.1 vs 5.5±2.7 (p = 0.049). CK (IU) increased following class and rehearsal, remaining high 48 h after: class (pre = 109.3±48.5; post = 144±60; 48 h = 117.2±64.6); rehearsal (pre = 78.6±52.1; post = 122±70.7; 48 h = 104.9±89.5). LPO (µM) increased from pre-class (1.27±0.19) to post-class (1.41±0.19) and went down after 48 h (1.20±0.22). No LPO time-course changes followed the rehearsal. GSSG/GSH decreased 48 h after class and rehearsal. Greater increases in LPO post-class suggest it promotes CK release by an oxidative membrane-damage mechanism. Physiological increases of LPO and CK in class indicate it prepares the dancers for exercise-induced oxidative stress and muscle damage during rehearsals. Ballet dancers' muscle damage and oxidative stress responses seem not to be dependent on exercise intensity based on V̇O2 responses.

Cations as Switches of Amyloid-Mediated Membrane Disruption Mechanisms: Calcium and IAPP

Disruption of the integrity of the plasma membrane by amyloidogenic proteins is linked to the pathogenesis of a number of common age-related diseases. Although accumulating evidence suggests that adverse environmental stressors such as unbalanced levels of metal ions may trigger amyloid-mediated membrane damage, many features of the molecular mechanisms underlying these events are unknown. Using human islet amyloid polypeptide (hIAPP, aka amylin), an amyloidogenic peptide associated with β-cell death in type 2 diabetes, we demonstrate that the presence of Ca2+ ions inhibits membrane damage occurring immediately after the interaction of freshly dissolved hIAPP with the membrane, but significantly enhances fiber-dependent membrane disruption. In particular, dye leakage, quartz crystal microbalance, atomic force microscopy, and NMR experiments show that Ca2+ ions promote a shallow membrane insertion of hIAPP, which leads to the removal of lipids from the bilayer through a detergent-like mechanism triggered by fiber growth. Because both types of membrane-damage mechanisms are common to amyloid toxicity by most amyloidogenic proteins, it is likely that unregulated ion homeostasis, amyloid aggregation, and membrane disruption are all parts of a self-perpetuating cycle that fuels amyloid cytotoxicity.

Selectivity for and destruction of Salmonella typhimurium via a membrane damage mechanism of a cell-penetrating peptide ppTG20 analogue

P7, an analogue of the cell-penetrating peptide (CPP) ppTG20, was derived by replacing Phe and Trp with Arg based on the structure–activity relationships of CPPs and antimicrobial peptides (AMPs). P7 showed antimicrobial activity against Salmonella typhimurium at 4μM and possessed broad antimicrobial activity greater than its parent peptide. P7 displayed good selectivity, with low haemolysis below its minimum inhibitory concentration range, but displayed cytotoxic activity against the HT29 and MDA-MB231 mammalian cell lines. Studies of calcein leakage from egg yolk l-α-phosphatidylcholine/egg yolk l-α-phosphatidyl-dl-glycerol (EYPC/EYPG) (bacterial membrane mimic) and EYPC/cholesterol (eukaryotic membrane mimic) vesicles also demonstrated that P7 exhibited high selectivity and caused pore formation in the bacterial membrane. Circular dichroism experiments suggested that the conformation of P7 underwent transitions from a random coil in sodium phosphate buffer to an α-helical conformation in bacterial model membranes. P7 induced influx of the membrane fluorescent probe 1-N-phenylnaphthylamine (NPN) and the nucleic acid fluorescent probe SYTOX® Green by increasing live S. typhimurium cell outer membrane and plasma membrane permeability, respectively. P7 also induced ion channel formation in the cell plasma membrane causing leakage of potassium ions. Flow cytometric analysis demonstrated that S. typhimurium cell membrane integrity was destroyed following incubation with P7. These results indicated that P7 exhibited good bacterial selectivity and exerted its antibacterial activity by a membrane damage mechanism. Furthermore, these results suggested that CPPs may represent a source of templates for AMP design.

Level of 8-OHdG in drained dialysate appears to be a marker of peritoneal damage in peritoneal dialysis

PurposePeritoneal dialysis (PD) is a successful renal replacement therapy; however, long-term PD leads to structural and functional peritoneal damage. Therefore, the monitoring and estimation of peritoneal function are important in PD patients. Oxidative stress has been implicated as one possible mechanism of peritoneal membrane damage. The aim of this study was to evaluate the association between an oxidative stress marker, 8-hydroxydeoxyguanosine (8-OHdG), and peritoneal damage in PD patients.MethodsThe authors evaluated 8-OHdG in drained dialysate by enzyme immunoassay to investigate the association between 8-OHdG and solute transport rate estimated by peritoneal equilibration test and matrix metalloproteinase-2 (MMP-2) level in 45 samples from 28 PD patients.ResultsThe 8-OHdG level was significantly correlated with dialysate:plasma creatine ratio (r = 0.463, P < 0.05) and significantly inversely correlated with D/D0 glucose (where D is the glucose level of peritoneal effluents obtained 4 hours after the injection and D0 is the glucose level obtained immediately after the injection) (r = −0.474, P < 0.05). The 8-OHdG level was also significantly correlated with MMP-2 level (r = 0.551, P < 0.05), but it was not correlated with the age of subjects, the duration of PD, or blood pressure.ConclusionThe level of 8-OHdG in drained dialysate may be a useful novel marker of peritoneal damage in PD.

Mechanism of Membrane Interaction and Disruption by α-Synuclein

Parkinson's disease is a common progressive neurodegenerative condition, characterized by the deposition of amyloid fibrils as Lewy bodies in the substantia nigra of affected individuals. These insoluble aggregates predominantly consist of the protein α-synuclein. There is increasing evidence suggesting that the aggregation of α-synuclein is influenced by lipid membranes and, vice versa, the membrane integrity is severely affected by the presence of bound aggregates. Here, using the surface-sensitive imaging technique supercritical angle fluorescence microscopy and Förster resonance energy transfer, we report the direct observation of α-synuclein aggregation on supported lipid bilayers. Both the wild-type and the two mutant forms of α-synuclein studied, namely, the familiar variant A53T and the designed highly toxic variant E57K, were found to follow the same mechanism of polymerization and membrane damage. This mechanism involved the extraction of lipids from the bilayer and their clustering around growing α-synuclein aggregates. Despite all three isoforms following the same pathway, the extent of aggregation and their effect on the bilayers was seen to be variant and concentration dependent. Both A53T and E57K formed cross-β-sheet aggregates and damaged the membrane at submicromolar concentrations. The wild-type also formed aggregates in this range; however, the extent of membrane disruption was greatly reduced. The process of membrane damage could resemble part of the yet poorly understood cellular toxicity phenomenon in vivo.

Antimicrobial Proteins from Snake Venoms: Direct Bacterial Damage and Activation of Innate Immunity Against Staphylococcus aureus Skin Infection

The innate immune system is the first line of defense against microbial diseases. Antimicrobial proteins produced by snake venoms have recently attracted significant attention due to their relevance to bacterial infection and potential development into new therapeutic agents. Staphylococcus aureus is one of the major human pathogens causing a variety of infections involving pneumonia, toxic shock syndrome, and skin lesions. With the recent emergence of methicillin (MRSA) and vancomycin (VRSA) resistance, S. aureus infection is a serious clinical problem that will have a grave socio-economic impact in the near future. Although S. aureus susceptibility to innate antimicrobial peptides has been reported recently, the protective effect of snake venom phospholipase A₂ (svPLA₂) proteins on the skin from S. aureus infection has been understudied. This review details the protective function of svPLA₂s derived from venoms against skin infections caused by S. aureus. We have demonstrated in vivo that local application of svPLA₂ provides complete clearance of S. aureus within 2 weeks after treatment compared to fusidic acid ointment (FAO). In vitro experiments also demonstrate that svPLA₂ proteins have inhibitory (bacteriostatic) and killing (bactericidal) effects on S. aureus in a dose-dependant manner. The mechanism of bacterial membrane damage and perturbation was clearly evidenced by electron microscopic studies. In summary, svPLA₂s from Viperidae and Elapidae snakes are novel molecules that can activate important mechanisms of innate immunity in animals to endow them with protection against skin infection caused by S. aureus.

Membrane-active host defense peptides – Challenges and perspectives for the development of novel anticancer drugs

Although much progress has been achieved in the development of cancer therapies in recent decades, problems continue to arise particularly with respect to chemotherapy due to resistance to and low specificity of currently available drugs. Host defense peptides as effector molecules of innate immunity represent a novel strategy for the development of alternative anticancer drug molecules. These cationic amphipathic peptides are able to discriminate between neoplastic and non-neoplastic cells interacting specifically with negatively charged membrane components such as phosphatidylserine (PS), sialic acid or heparan sulfate, which differ between cancer and non-cancer cells. Furthermore, an increased number of microvilli has been found on cancer cells leading to an increase in cell surface area, which may in turn enhance their susceptibility to anticancer peptides. Thus, part of this review will be devoted to the differences in membrane composition of non-cancer and cancer cells with a focus on the exposure of PS on the outer membrane. Normally, surface exposed PS triggers apoptosis, which can however be circumvented by cancer cells by various means.Host defense peptides, which selectively target differences between cancer and non-cancer cell membranes, have excellent tumor tissue penetration and can thus reach the site of both primary tumor and distant metastasis. Since these molecules kill their target cells rapidly and mainly by perturbing the integrity of the plasma membrane, resistance is less likely to occur. Hence, a chapter will also describe studies related to the molecular mechanisms of membrane damage as well as alternative non-membrane related mechanisms. In vivo studies have demonstrated that host defense peptides display anticancer activity against a number of cancers such as e.g. leukemia, prostate, ascite and ovarian tumors, yet so far none of these peptides has made it on the market. Nevertheless, optimization of host defense peptides using various strategies to enhance further selectivity and serum stability is expected to yield novel anticancer drugs with improved properties in respect of cancer cell toxicity as well as reduced development of drug resistance.

Molecular Modeling of Amyloid Oligomers and their Interactions with Membranes

The aggregation of monomeric proteins/peptides to form ordered amyloid oligomers/fibrils is a pathogenic feature of many degenerative diseases including Alzheimer's, Parkinson's, and prion diseases. Despite of significant progress, oligomeric structures and associated toxicity at the very early stage of aggregation remain unclear. Structural knowledge of these oligomers is essential for understanding the pathology of amyloidoses and for rationally designing drugs against amyloid diseases. In this work, we model and identify a series of stable oligomeric structures with different structural morphologies (micelles, annulars, triangulars, globulomers, and linears) for various amyloid peptides (Abeta, hIAPP, GNNQQNY, and K3). Some common structural characteristics and underlying driving force stabilizing these oligomers are delineated. More importantly, we further examine the interactions of these stable oligomers with lipid bilayers to illustrate two postulated mechanisms of membrane damage (membrane thinning vs. ion channel) associated with amyloid toxicity.

Studies on Effect of TiO2 Nanoparticles on Growth and Membrane Permeability of Escherichia coli, Pseudomonas aeruginosa, and Bacillus subtilis

Metal oxide nanoparticles are known to possess strong antimicrobial properties. Titanium dioxide (titania) nanoparticles have wide range antimicrobial as well biomedical applications. In the present work the antimicrobial properties of Titanium dioxide- anatase nanoparticles were investigated in the concentration range 10-100 ppm using Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa. The average size of the nanoparticles used was measured to be below 25 nm. The concentration dependent growth inhibitory effect of titania nanoparticles on the three bacterial strains were compared based on batch growth kinetic data (by dynamic growth rate). Bacterial sensitivity to nanoparticles was found to vary depending on the microbial species. The mode of antibacterial action was investigated by assaying extracellular proteins, the integrity of the cell membranes and the permeability of the inner membrane (IM) of the microbial strains. The results suggested that titania caused the antibacterial effect through membrane damage mechanisms. FT-IR studies revealed that most of amide-I, amide – II groups were absent in the nanoparticles treated cells when compared with that of control, corroborating the cell damage mode of action. The antimicrobial effects of the nanoparticles essentially differed between the microbial strains due to structural differences in the cell membranes.

Effect of light irradiations on photosynthetic machinery and antioxidative enzymes during ex vitro acclimatization of Tylophora indica plantlets

In the present communication, we studied the effect of light stress on pigment contents, net photosynthetic rate, electrolyte leakage, malondialdehyde concentration and various antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and ascorbate peroxidase (APX) during acclimatization of micropropagated Tylophora indica plantlets. Pigment (Chlorophyll a, b and carotenoids) contents in ex vitro formed leaves were found significantly higher compared to the in vitro formed ones. In vitro plantlets (day 0) exhibited a low photosynthetic activity, but with the emergence of new leaves a significant increase in net photosynthetic rates was observed. Changes in the activity of the antioxidant enzymes system were also observed during the critical days of acclimatization. Plantlets showed increased levels of SOD production, indicating its preventive mechanism of membrane oxidation and damage to biological molecules in high light (HL) acclimatized plantlets. The CAT activity increased at both low lights (LL) and HL during the whole period of acclimatization. Likewise, photoexposure of plantlets at LL and HL showed elevated activity of GR and APX against 0 day plantlets.