ASCORBATE as a strong antioxidant has a considerable bio effect on growth of plants, such as increase in their tolerance against environment stresses. In this investigation, the effect of salt stress and its interaction with ASCORBATE on amount of proline, catalase and ASCORBATE PEROXIDASE enzymes and MDA in a medicinal plant ofCuminum cyminum L. was randomly studied in the green house conditions with three replications. Plants were treated by different concentrations of NaCl (0, 25, 50, 75, 100, 125 mmolar) and ASCORBATE (9 mmolar). In the plants treated with salt, the amount of proline, antioxidant enzymes activity and MDA were increased with increasing NaCl concentrations. The plants treated with NaCl and ASCORBATE at the same time in a same NaCl concentration, the amount of proline, catalase activity, ASCORBATE PEROXIDASE and MDA were increased. The results indicated that the ASCORBATE was one of the antioxidants that caused an increase in resistance of Cuminum cyminum L. to salt stress.

Background and purpose: As one of the antioxidant enzymes, ASCORBATE PEROXIDASE (APX) has an important role in the defense system of plants against environmental stresses and is effective in regulating the concentration of hydrogen peroxide (H2O2) in plant cells. APX decomposes hydrogen peroxide in order to prevent plant damage. During various environmental stresses, antioxidant enzymes such as APX increase in different plant parts such as fruit. Of course, the rate of biosynthesis of this antioxidant enzyme depends on the intensity and duration of stress in the plant. Considering the importance of the presence of this enzyme in plant structures, this study was conducted to investigate the maximum activity of ASCORBATE PEROXIDASE enzyme at different levels of surfactants and chaotropes.Materials and methods: This research was carried out in the research laboratory of Payam Noor University of Kurdistan. In order to prepare the extract from strawberries and blackberries, in the presence of 0.1 M citrate-phosphate buffer with pH 7 and 0.02 phenylmethanesulfonylfluoride solution as a protease inhibitor, the fruits were homogenized separately. Results: Based on the results of this research, for the ASCORBATE substrate used in the APX measurement in the extracts prepared from strawberry (ST.APX) and blackberry (BM.APX), the optimal pH is 6.7 and the catalytic efficiency of BM.APX, is about 1.6 times higher than ST.APX was obtained. With the increase of ASCORBATE concentration in constant concentration of H2O2, the activity of BM.APX and ST.APX increases, so that the highest level of activity of both plant 0. 5 units per mg of protein. A further increase in substrate concentration was associated with substrate inhibition of BM.APX and ST.APX. The activity curve of APX in both plant species is hyperbolic, which follows the Michaelis-Menten kinetics, which indicates the high tendency of the enzyme to consume ASCORBATE. The activity of ST.APX and BM.APX is inhibited by kojic acid and it is non-competitive in both. Among the used chaotropes and surfactants, only SDS activated the activity of ST.APX and BM.APX, and the activities of ST.APX and BM.APX showed different sensitivities to the surfactants, chaotropes and kojic acid. Despite the fact that BM.APX showed higher activity than ST.APX in the presence of ASCORBATE and SDS, in the presence of other factors, the rate of inhibition of BM.APX was higher than ST.APX and showed higher percentages of inhibition. Urea and guanidine hydrochloride as reducing agents showed an inhibitory role on ST.APX and BM.APX. The activity of APX The results also showed that the activity of ST.APX and BM.APX was inhibited by kojic acid and it was non-competitive in both. Among the chaotropes and surfactants used, only SDS activated the activity of ST.APX and BM.APX and its maximum effect occurred at a concentration of 0.2 mM. On the other hand, in other factors, the rate of inhibition and reduction of BM.APX activity was higher than ST.APX, and with the exception of ASCORBATE PEROXIDASE response to kojic acid and sodium calate in strawberry, the enzyme response followed a monophasic decreasing exponentialConclusion: In this research, ASCORBATE PEROXIDASE takes a more active form by following Michaelis Menten's kinetics and binding the substrate to the active site of the enzyme, and by performing enzyme catalysis, it causes ASCORBATE consumption in strawberries and blackberries. Ionic surfactants with an activation mechanism such as SDS and an inhibitory mechanism such as sarkosyl and sodium cholate have different effects on ASCORBATE PEROXIDASE. Non-ionic surfactants such as kojic acid and chaotrope agents reduce the activity of ASCORBATE PEROXIDASE in both plant species. The position of kojic acid is different from the position of ASCORBATE due to the non-competitive type of inhibition.

In this investigation the effects of Zinc excess and it’s interaction with ascorbic acid on photosynthetic pigments and antioxidant enzymes activity of Catalase, PEROXIDASE and ASCORBATE PEROXIDASE in Brassica napus (cv.Hyola) were studied. Seedlings were treated with Hougland nutrient solution (control), excess Zn concentration (50, 100, 250, 500, 700 mm) and also same concentration with 1mm ascorbic for two weeks. According to the results with Zn, increase photosynthetic pigments (chlorophyll a, b and carotenoids) decreased significantly in comparison to control plants. Enzymes activity of catalase, PEROXIDASE and ASCORBATE PEROXIDASE in shoots increased. In roots the increase of catalase activity was only evident. In the presence of ascorbic acid decreasing amount of photosynthetic pigments and increasing level of antioxidant enzymes activity were decreased. In Zn concentration of 250, 500, 700 mm chlorosis signs observed especially on apical leaves. In 700 mm from 8th day of treatment apical leaves started necrosis. But in the presence of ascorbic acid, Brassica napus tolerate zinc excess concentration. On the other hand ascorbic acid decreased Zn toxicity and promoted the plant resistance.

Dunaliella salina was isolated from Maharlu salt lake in Shiraz, Iran, and was analyzed for the effects of salinity stress on its growth, pigment content and ASCORBATE PEROXIDASE activity. Growth, expressed as number of cells ml-1, which was most rapid at 2 M NaCl, was reduced at salinity extremes. During the exponential phase of growth, increasing salinity from 0.5 to 4 M NaCl increased Chl a from 0.3 to 0.9 pg cell-1, while b-carotene was decreased from 3.6 to 2.4 pg cell-1 and Chl b remained unchanged. At stationary phase, increasing salinity increased the pigment content of cells. b-carotene content per cell reached its highest value of 10.1 pg at 4 M NaCl. Maximum b-carotene to total Chl ratio of 7.4 was obtained at 2 M NaCl. The TLC chromatogram of pigments extracted from cells at the exponential phase of growth resembled that of spinach leaves while the chromatogram of pigments extracted from cells at the stationary phase resembled that of carrot and commercial b-carotene. A significant increase in ASCORBATE PEROXIDASE activity was observed with increasing salinity from 1 to 4 MNaCl. It is suggested that increased capacity to scavenge ROS may help to optimize algal biomass and b- carotene production.

ROS detoxification is an essential process in protecting plant cells and their organelles, which is caused by ROS generated in stress condition. PEROXIDASE (POD) isozyme, Malondialdehyde (MDA) content, and ASCORBATE PEROXIDASE (APX) activity are the indicators of plants for measuring pollution effects. The purpose of the present study was to investigate Cd-induced stress on POD isozymes, MDA content, and APX activity in seedlings of Berberis integerrima and Cercis siliquastrum.100 seedlings were treated with cadmium chloride separately at concentrations of 0, 1000, 2000, 4000, 6000 mg/kg three times at intervals of 15 days. POD activity varied at different levels of Cd stress Cercis siliquastrum, while this was not the case with Berberis integerrima. MDA was slightly increased up to 6000 mg/kg from 5% to 27%, but a sharp increase (41%) was found at 6000 mg/kg compared with 4000 mg/kg Cd treatment in Cercis siliquastrum. The highest MDA content (10.5 mM/ g FW) was recorded at 6000 mg/kg trearment in Berberis integerrima, while the lowest value (2.3 mM/ g FW) was found in control Cercis siliquastrum plants. The maximum and minimum APX activity were found in the treatments of 6000 mg/kg (0.13 unit/mg protein) and control (0.02 unit/mg protein), respectively, for both Cercis siliquastrum and Berberis integerrima. In control Berberis integerrima, APX activity (0.02 unit/mg protein) was higher than that of Cercis siliquastrum (0.006 unit/mg protein) (p˂0.05). Overall, the findings suggest that Berberis integerrima is less tolerant than Cercis siliquastrum under Cd-induced stress.