Iranian Journal of Plant Physiology
Volume:3 Issue: 3, Spring 2013

Polyphenol oxidase (PPO) was extracted from three segments of Solanum melongenas and Musa sapietum fruits and partially purified. The specific activity of PPO was measured at each purification step to ascertain level of enzyme purity. In all cases, PPO conformed to Michaelis-Menten kinetics, showing different values of kinetics parameters. Michaelis-Menten constant (PPOKm) of S. melongenas mid-section and anterior segments showed no significant difference (p < 0.05), whereas the posterior gave PPOKm = 4.6±0.49 mM (p > 0.05). Maximum PPO activity (PPOVmax) was highest in the posterior segment: PPOVmax = 0.602±0.09 U. Mid-section of M. sapietum exhibited the highest Km value (PPOKm = 5.8±0.69 mM) compared with the anterior (PPOKm = 3.9±0.69 mM) (p > 0.05) and posterior PPOKm = 4.9±0.11 mM segments (p < 0.05). Overall, M. sapietum PPOKm values were relatively higher than those of S. melongenas. Posterior S. melongenas exhibited the highest PPOVmax = 0.602±0.09 U, whereas the lowest value was registered in the anterior segment of M. sapietum PPOVmax = 0.234±0.09 U. Substrate specificity for PPO (PPOVmax/Km) extracted from various segments of S. melongenas was in the increasing order of Mid-section > Posterior > Anterior, whereas that of M. sapietum was Mid-section > Anterior > Posterior. PPOVmax/Km between the two fruits showed strong positive correlation (r = 0.862339). Catechol was a better substrate for PPOS. melongenas than PPOM. sapietum. The experimentally observed kinetic parameters of S. melongenas and M. sapietum signified the presence of PPO isoenzymes and non-uniform distribution of PPO in the two fruits.

In recent years, many research studies have been conducted on the effects of magnetic field on plants. But certain mechanisms regarding magnetic influences have not been defined yet. In this study, effects of magnetic fields (MF) on the growth parameters and enzyme activities of Helianthus annuus L. were investigated. Sterilized seeds in sterile conditions were exposed to 0, 0.5, 1 and 1.5 mT of MF. One day after the treatments percentage of seed germination was increased at 0.5 mT. Different MF densities had no significant effects on root length and fresh weight of leaves. The highest level of shoot length was gained at 1 mT. In this treatment the activity of auxin oxidase was significantly decreased compared with that of the control samples. The activity of the catalase and peroxidase were decreased by MF. The minimum level of protein content and catalase and peroxidase activity were observed in the samples exposed to 1 mT of MF while there were no significant differences in the ascorbate peroxidase activity of different treatments. MF caused a reduction in chlorophyll a, b in all treatments compared to the control. The Results confirmed that the intensity of the MF had different effects on the growth parameters and enzyme activity.

A field experiment was carried out to study the response of presoaked faba bean seeds (Vicia faba cv. Misr 2) in freshly prepared ascorbic acid (50 ppm) or distilled water (control) for 4 hrs at natural environmental conditions, to salinity stress. NaCl treatments caused a reduction in all productivity and yield parameters as compared with control, particularly at high NaCl level (150 mM), whereas the number of pods per plant, fresh weight of pods per plant, number of seeds per pod and fresh weight of seeds per pod were reduced. In the mean time, ascorbic acid had no effect on the yield parameters. Salinity stress increased the protein content of seeds to some extent. Ascorbic acid treatment to salinized plants remarkably increased the protein content. Also, seed alkaloids were increased with salinity stress, but the response was more pronounced at 100 mM NaCl whether alone or combined with ascorbic acid. The results revealed that protein pattern showed considerable effects of salinity stress on the protein bands. Application of ascorbic acid induced the synthesis and increased the intensity of the original protein bands and caused the appearance of additional new bands.

The present investigation assessed the effects of a metalloid (arsenic) and two heavy metals (cadmium and mercury), on the growth and metal accumulation in two medicinal plant species, artichoke (Cynara scolymus L.) and Savory (Satureja hortensis L.). The experiment was conducted hydroponically in spiked solution with different concentrations of arsenic (0, 20, 100, and 500 μM), cadmium (0, 10, 50, 250, and 500 μM) and mercury (0, 5, 25, and 50 μM) for four weeks. Under elevated arsenic and heavy metal stresses, root and shoot biomass of artichoke and savory were reduced. Shoot dry weight was significantly (p<0.05) decreased at arsenic supply levels of 20-500 μM, cadmium levels of 10-500 μM and mercury levels of 5-50 μM compared to the control plants. Similar response patterns to arsenic, cadmium and mercury supply levels were noted for root dry weight in the two plant species. Arsenic and heavy metal accumulated by the plants root and shoot linearly increased with increasing their supply levels. More accumulation of arsenic, cadmium and mercury was observed in roots than shoots in artichoke and savory. Artichoke had higher metalloid and heavy metal uptake, bioaccumulation factor, and root-to-shoot translocation efficiencies than those of savory. This can be attributed to a greater accumulating capacity in artichoke. Overall results indicated that metal phytoextraction using the artichoke can be applied to clean up soils moderately contaminated by arsenic, cadmium and mercury in polluted lands.

About 10 percen of lands around the world under crops planting are affected by salinity. Therefore, comprehensive researches have been conducted to minimize the harmful effects of salinity in agriculture. The purpose of this study is examination of the Mmethyl jasmonate effect on reducing the effects of salinity in germination and vegetative stages of the basil plant.For the methyl jasmonate treatment, seeds were soaked in methyl jasmonate (0,0/1 and 0/01 μM) and then seeds were placed on filter papers wet using NaCl (50, 100, 200 mM). Then, the morphological parameters examined. The results indicated that high concentration of salinity cause to decrease in germination percentage and Methyl jasmonate cause increase in germination percentage, and this indicated the positive effect of methyl jasmonate on improvement of stress conditions in plant. Furthermore, salinity increases the growth of root and shoot, and methyl jasmonate offsets this reduction.

The effects of exogenous abscisic acid (ABA) and its two agonists, Sulfacetamide (Sa) and Sulfasalazine (SS) on tolerance of tomato (Lycopersicon esculentum Mill. Cv. Super chief) under drought stress were studied. Eight-week plants were treated with ABA (25 and 50 mg/L), Sulfacetamide (Sa) (25, 50 and 100 mg/L) and Sulfasalazine (SS) (25, 50 and 100 mg/L). Solutions were sprayed daily and sampling was done at 48 h, 96 h, 144 h and 48 h after re-watering (recovery phase). Treated plants showed relatively greater drought tolerance. This indicates that, Sulfacetamide and Sulfasalazine improved resistance in tomato, like ABA, increasing activity of antioxidant enzymes, i.e., catalasthise (CAT), ascorbate peroxidase (APX)and guaiacol peroxidase (GPX). On the other hand, abscisic acid, Sulfacetamide and Sulfasalazine reduced H2O2 and MDA contents in the plants under study. Daily application of these agonists during moisture stress period was effective in increasing tomato plants tolerance to drought as was ABA.

Borage is an important medicinal plant which must be cultivated commercially in order to meet the ever-increasing demand for pharmaceutical industry. This study was done under hydroponics condition. Seeds of Borage were obtained from Neka Research Center (North of Iran). After applying Benomyl fungicide, the seeds were rinsed with distilled water and planted in vermiculite. After germination and appearance of two leaves, the plants were nourished by 0.5 Longshtein solutions. At 4-leaf stage, the plants were divided into two groups: control and salinity. Proline and soluble sugars contents were regularly studied under saline condition. While the content of proline increased, soluble sugars experienced a decrease under salinity. It was concluded that Borage was able to resist against stress due to change of contents of these compounds under salinity.