Introduction: Parkinson"s disease (PD) is a human neurodegenerative disorder which is associated with a massive and progressive degeneration of dopaminergic neurons in subistantia nigra (SN). There is a strong evidence of an oxidative stress participates in the etiology of PD. Materials and Methods: The rats were divided into sham-operated, experimental and vitamin E-treated groups. For anesthesia, a mixture of ketamine and xylazine was used (i.p.). The experimental group received 5ml of 0.9% saline containing 6-hydroxydoppamine (6-OHDA) and 2% ascorbic acid in addition to 0.8 ml/kg of propylene glycol (PG, i.m.), and sham-operated group received and identical volume of saline- ascorbate in left side of striatum. The vitamin E-treated group received D-a-tocopheryl acid succinate (24 I.U./Kg, i.m.) dissolved in PG, one hour before the surgery and three times a week for a month after the surgery. Tyrosine hydroxylase (TH) immunohistochemistry in SN and striatum was used as an index for the tratment efficacy. Results: The results, showed than an over all reduction (47%) in the number of TH immunoreactive (IR) neurons in the left SN-cell was observed in 6-OHDA lesioned group (P<0.005). However, the cell loss had attenuated to 18% in vitamin E-treated animals (P<0.05) compared with the right side. A non-significant difference in the number of TH-positive neurons between the sham-operated and the vitamin E-treated groups was noticed. A microscopic inspection of the injection site in the striatum revealed that in all treated animal, there was a dense halo of TH-IR fiber around the needle track. A grater loss of TH-IR fiber has been observed around the injection site in the experimental group. Conclusion: Vitamin E-treatment can enhance the resistance and longitivity of dopaminergic nigral neurons against the oxidative stress induced by 6-OHDA. The results may prompt an interest in the use of vitamin E as a neuroprotective agent in the treatment of PD.

In the persence of heavy metals in soils, plants responses are various. Cadmium as a heavy metal induced seriour symptoms in plants such as growth retardation, root damahes, alternation in plasma membrane properties, changing enzyme activities and the amount of antioxidant compounds. In this study the effects of various concentrations of cadmium chloride on growth parameters and physiological processes of canola seedlings were investigated. Seeds were germinated-on filter paper in Petri dishes containing various concentration of Cd2+. After a week identical seedlings selected and then analyzed. The obtained results show significant decrease in root growth, root elongation and total chlorophyll contents, especially in higher cadmium ion concentration. It seems that chlorophyll decreasing could be from direct effect of cadmium ions on chlorophyll synthesis. Cd2+ absorption by root and Cd2+transport in xylem and its accumulation in leaves caused significant increased lipid peroxidation in root and leaf. It happened because of high susceptibility of double bounds of lipids in memberane ehich is reactive to oxygen species (ROS) and increasing activeity of peroxidase. The seedlings sublected to high level 06 Cd2-showed decrease in ascorbate (ASe) / dehydroascorbate (DHA) ratio while total ascorbate concentration did not show remarkable changes in comparison to controls. The results suggested that growth retadation is because of direct effect of cadmium ion on cell growth and cell division. This is because of high tedency of cadmium ion to solfhydry groups or the indirect effect of cadmium ion via reactive oxygen species (ROS) formation. Red-brown coloration of merlstemic and elongation zone could possibly be the increase activation of peroxidase enzymes. In the other hand, it seems that growth retardation may caused because of impaired ascorbate - glutathion .cycle activity in high cadmium concentation . Decrease in ascorbate content is caused from glu tathion (GSH) impotring to GSH pool for phytochelation synthesis and decreased ascorbate as reduction substrate. However, synthesis of ascorbate, ascorbate peroxidase, monodehydroascorbate reductase and glutathion reductase is stimulated in lower concentration of cadmium ion which inceases in GSH cycle activity and detoxification of ROS.

Salicylic acid (SA) is a compound that has a basic role in increasing cold tolerance in plants. When two-day old radish seedlings were pretreated with different concentra-tions of SA (0, 0.5, 1, 1.5 and 2 mM) for 24 hours and then imposed to cold stress at 2.5°C for 48 hours, cold resistance is increased in them. This phenomenon is shown by reduced efflux of K+ ions and soluble sugars and increased root length of seedlings especially at 0.5 mM, SA concentration. This finding shows that there is a straight correlation between SA concentration and reduced cold injury. Measuring the activity of three antioxidant enzymes, ascorbate peroxidase (APX), guaiacol peroxidase (GPX) and catalase (CAT) in shoot and roots of radish seedlings, revealed that SA induced cold resistance is accompanied by increased activity of these antioxidant enzymes.

It has been reported that ascorbate reduces morphine-induced dependence and tolerance in humans and rodents. Since most drugs of abuse increase, release and metabolism of dopamine in the shell area of nucleus accumbens, therefore, this study was conducted to evaluate the effect of ascorbate on dopamnie metabolism in this nucleus in naive rats and those acutely treated with morphine using in vivo microdialysis method. For this purpose, dialysate level of dihydroxyphenylacetic acid (DOPAC) as a dopamine metabolite was measured by high performance liquid chromatography with electrochemical detection (HPLC-ECD). The results showed that acute morphine treatment (20 mg/kg; i.p.) increased DOPAC level in the nucleus accumbens by 170% of the basal level. Meanwhile, although acute ascorbate treatment (500 mg/kg; i.p.) alone did not alter DOPAC level in this nucleus, but ascorbate pretreatment (500 mg/kg; i.p.) 30 min before morphine administration attenuated the effect of acute morphine on dopamine metabolism.

In the present research, we studied the effects of ascorbic acid (AsA) to act as a highly effective antioxidant in soybean (Glycine max L. cv. Union x Elf) plants undergoing oxidantive stress caused by nickel (Ni). One-week-old hydroponically-grown seedlings were exposed to variable concentrations of NiCl2, 6H2O (0, 0.5, 1mM) and AsA (0.1 mM). Ni was more accumulated in roots than in shoots. Surprisingly, root-to-shoot translocation of Ni depressed by ASA. In the absence of ASA, excess Ni suppressed biomass production of both roots and shoots and reduced chlorophyll content in leaves, while ASA removed these effects. The existence of Ni induced oxidative stress can be demonstrated by an increasing in malondialdehyde (MDA) production. This rise could be explained by activation of the enzyme lipoxygenase (LOX, EC.1.13.11.12). Addition of ASA together with Ni ions, almost completely restored LOX activity and reduced MDA production. In the other hand, ascorbate peroxidase (APX, EC 1.11.1.11) and catalase (CAT, EC 1.11.1.6) activities in both roots and leaves were strongly reduced by Ni stress. While ASA highly increased APX and CAT activities in Ni-stressed plants. Consequently, ascorbic acid by sequestration of Ni in roots and with an altogether increases in the activities of antioxidant enzymes reduces Ni induced oxidative damage in a certain extent.

Effects of toxic concentrations (up to 100µM) of copper (Cu) and manganese (Mn) on growth and oxidative defense system of rice (Oryza sativa L.) and sunflower (Helianthus annuus L.) were studied under three light intensities in hydroponic medium. Rice expressed higher susceptibility to both Cu and Mn toxicity than sunflower. Higher light intensity strengthened the effect of toxicity of Cu while ameliorated that of Mn. Activity of ascorbate peroxidase and glutathione reductase responded to Cu and Mn differently in rice. Cu toxicity increased their activity but Mn did not change or rather decreased it. Activity of catalase was induced in response to both Cu and Mn particularly under higher light intensities. Activity of peroxidase, in contrast to other tested enzymes, was correlated with growth response of plants. Copper was not effective in induction of malondialdehyde accumulation. Mn, in concentrations causing no growth inhibition (100µM), resulted in a significant increase of malondialdehyde. Changes in the tissue content of proline, similar with peroxidase activity, was mainly associated with stress conditions as judged by growth data. On the other word, activity of peroxidase and accumulation of proline monitored the stress conditions without any protecting role and any effect on adaptation of plants. Our results suggested that the antioxidant capacity of plants is not independently correlated with the growth response of plants without regarding the other physiological responses to metal exposure.