سید کریم تهامی

Basil (Ocimum basilicum), as an annual plant, belongs to the family Lamiaceae, native to Asia (Iran, India, Pakistan, Thailand, etc.) and grows in warm and semi-warm regions. Arsenic (As) is a highly dangerous heavy metal for plants and human. This quasi-metal is widely distributed in the earth's crust, and also is the twentieth most abundant element in the earth's crust. Selenium (Se) is a non-metallic chemical element and also has similarities to arsenic. Global interest in the biological effects of selenium on the environment and the food chain is growing because selenium is essential as a micronutrient for many organisms, including humans and other animals (although it is toxic in high concentrations). Given that arsenic is one of the most important factors limiting crop production in the agricultural sector, it seems necessary to conduct researches in this field to eliminate or reduce the toxic effects of these element on agricultural plants.           

In this study, the effect of selenium on increasing the tolerance rate of basil plant against arsenic heavy metal stress was investigated as a factorial experiment based on completely randomized design under greenhouse condition. The first factor included arsenic-contaminated soil (4576 mg kg-1) and non-contaminated soil, and the second factor included different concentrations of selenium treatment (0, 5 and 10 mg L-1 selenium sodium). Foliar application of selenium was conducted at two stages. The first stage of foliar application was carried out at 4-leaf stage and the second stage of foliar application was done two weeks after the first stage. Leaf number, leaf area, stem height, fresh and dry weight of leaf and stem, chlorophyll and carotenoid content, free proline content, phenol, flavonoid and anthocyanin content, electrolyte leakage and antioxidant enzymes activity were evaluated at the end of the experiment.

The results showed that arsenic stress negatively affected the morphological traits such as leaf number and area, fresh and dry weight of leaf, fresh and dry weight of stem and plant height, but selenium treatment alleviated the toxicity of arsenic and increased the values of these traits, so that treated plants had higher values of morphological characteristics comparing to control plants under arsenic heavy metal stress. The highest values of morphological traits were observed in plants treated with the highest concentration of selenium (10 mg L-1). In terms of physiological traits, arsenic heavy metal stress reduced the values of some of these traits, so that the lowest amounts of chlorophyll a, chlorophyll b and total chlorophyll, anthocyanin, phenol, and flavonoids were recorded in plants grown in arsenic-contaminated soil without foliar application of selenium. On the other hand, the lowest activity rates of guaiacol peroxidase, catalase and ascorbate peroxidase were observed in plants grown in non-contaminated soil and without selenium foliar application. Also, the both arsenic stress and selenium treatment increased proline accumulation and soluble sugars content of treated plants comparing to control plants. Heavy metal stress increases the production and accumulation of reactive oxygen species (ROS) and damages the membrane structure resulting in more electrolyte leakage. Selenium application led to increasing plant resistance rate against arsenic stress, mainly by enhancing cells antioxidant capacity and osmotic potential.

Considering basil is one of the most important aromatic vegetables which has fresh consumption, crispness and wateriness of its leaves and young shoots is one of the most important commercially traits which directly affect crop marketability. Considering arsenic stress has a negative effect on leaf morphological traits (number, area, fresh weight and dry weight) and stem characteristics (fresh weight, dry weight and height), it is recommended to use selenium foliar application as an efficient technique to overcome adverse effects of arsenic stress on basil production in regions with contaminated soils.

Mentha spicata is one of main cultivated crops in temperate, Mediterranean and sub-tropical regions. This plant is an enriched source of vitamins and mineral nutrients. Also, it is used for various medicinal purposes such as treatment of gastrointestinal and respiratory diseases. Nowadays, among the plant stresses, heavy metals toxicity is considered as dominant and global issue damaginh the environment. Heavy metals toxicity is mainly caused by human activities such as mining, irrigation with wastewater and using the products with high content of heavy metals. Heavy metals can negatively affect soil and water quality and human health even in low concentrations. Copper (Cu) is one of most dangerous heavy metals which threatens the human health and reduces the crops quality. Pseudomonas putida and Pseudomonas fluorescens bacteria are plant growth-promoting bacteria. They can stimulate growth and enhance plant resistance to different environmental stresses such as heavy metals toxicity. The aime of this study was to alleviate the adverse effects of Cu heavy metal toxicity on some of most important characteristics of Mentha spicata through the application of bacterial treatments.

In order to evaluate the influence of bacterial treatments including Pseudomonas putida, Pseudomonas fluorescens and putida + P. fluorescens on copper chloride toxicity stress at three levels including 0 (control), 100 and 200 mg kg-1 soil, a factorial experiment was carried out based on completely randomized design with four replications, at Department of Horticultural Science and Engineering of Maragheh University, during 2019. Some of most important characteristics of Mentha spicata such as plant height, aerial part fresh weight, root fresh weigh, photosynthetic pigments content, malondialdehyde (MDA) content, free proline content and antioxidant enzymes activity were measured under stress conditions.

The results of the current study showed that copper chloride toxicity stress had a negative effect on plant growth parameters such as plant height, fresh weight of aerial parts and root as well as photosynthetic pigments content, while the use of Pseudomonas putida and Pseudomonas fluorescens bacteria significantly alleviated these negative effects through increasing the activity of antioxidant enzymes and proline content. The highest fresh weight of aerial part (5.65 g) was recorded in plants treated with putida + P. fluorescens under control condition. The lowest weight of aerial part (2.95 g) was measured in plants treated with P. fluorescens under stress level of 200 mg kg-1 copper chloride. According to reports, the growth-promoting bacteria improve plant growth parameters by reduction of ethylene concentration in plant tissues under heavy metals stress conditions. Also these bacteria, directly increase plants growth rate through the increasing solubility of nutrients such as N and P in soil and biosynthesis of plant growth regulators and phytohormones. The highest SOD activity (35.55 U g-1 min-1) was measured in plants treated with P. putida + P. fluorescens under stress level of 100 mg kg-1 copper chloride.

Based on the results of the present study, copper chloride stress decreased stem height, fresh weight of aerial parts, fresh weigh of roots and the leaf photosyntheyic pigments content (chlorophyll a and b), and increased malondialdehyde and proline content in Mentha spicata plants. However, the use of P. putida and P. fluorescens bacteria alleviated the negative effects of heavy metal stress by increasing the activity of antioxidant enzymes (SOD and GPX) and proline content and reducing the amount of MDA (MDA is considered as indicator for cell membrane damages rate). Therefore, using P. putida and P. fluorescens bacteria treatment could be introduced as efficient and widely used technique to enhance tolerance rate of Mentha spicata against copper chloride toxicity stress.

The synthetic seeds strategy is an effective method for conservation, germplasm exchange, and distribution of Rosmarinus officinalis. R. officinalis is one of the plants of the Lamiaceae family that originates from the Mediterranean region. According to our knowledge, there is no report on the production of synthetic seeds from somatic embryos obtained from shoots of R. officinalis. In this study, a method for synthetic seed production and regeneration was investigated from shoot explants of R. officinalis. Shoots of R. officinalis were cultured on the MS medium containing various concentrations of NAA and 2,4-D. The best callus induction (41.66%) was obtained on the MS medium fortified with 1 mg/L 2,4-D. The friable embryogenic calli were transferred to a half-strength MS medium with various concentrations of BAP and 2,4-D. Somatic embryos were obtained after 45 days. The highest somatic embryogenesis was obtained on the MS medium containing 1 mg/L 2,4-D and 0.5 mg/L BAP. Somatic embryos at the torpedo stage were encapsulated in sodium alginate and synthetic seeds were obtained. The highest growth ability of synthetic seeds (80.55%) was obtained in the MS medium supplemented with 1.5 mg/L kinetin and 0.5 mg/L BAP. Moreover, the germination percentage of synthetic seeds decreased with increasing storage period and temperature. However, a higher reduction in the synthetic seed germination was recorded at 20±2 °C. The highest germination percentage of the synthetic seeds (85%) was obtained 30 days after storage at 4±1 °C.

Anthurium is belonging to the Araceae family. The effect of hydrogen peroxidase on vase life and postharvest quality of cut Oriental Trumpet hybrid lily “Manissa” was investigated. The results showed that the lower concentrations of H2O2 increased the vase life of a treated flower from 9.8 days (in control flowers) to 12.8 days in treated flowers. It’s reported that BA application delayed senescence in Roses, Irises and Tulips and prevent leaf yellowing in stocks and Gladiolus. The goal of this study was to investigate the effects and the best concentrations of H2O2 and BA on vase life of Anthurium andraenum.

In order to study the effects of various concentration of benzyladenin (1, 50, 100, 150, 200, 400 and 1000 ppm), hydrogen peroxide (5, 10, 15, 25, 35, 50 and 100 µM) on physicochemical characteristics of cut Anthurium andraenum flowers, three separated experiment were conducted based on completely randomized design with 5 replications. Some traits such as vase life, flower fresh weight, solution uptake rate, soluble sugar content and ion leakage were tested.

The results of each 3 experiments showed that benzyladenin at rate 100 ppm significantly (p < 0.05) increased flower vase life (from 15 days in control to 19.6 days in 100 ppm BA) compared to control. In the 1st experiment, 25 µM of hydrogen peroxide had significant (p < 0.05) effect on vase life, solution uptake and fresh weight. Whereas, the higher concentration of H2O2 (50 and 100 µM) had no effect on measured traits. In the 2nd experiment, 5, 15 and 25 µM of H2O2 and in the 3rd experiment, all tested concentration of H2O2 had significant (p < 0.05) effect of evaluated traits. However, in the 3rd experiment, the effects of all treatments on soluble sugar content and ion leakage were significant (p < 0.05). In all 3 experiments, the effects of different concentration of hydrogen peroxide on vase life were better than control.

With the considering of the positive effects of the BA and H2O2 on solution uptake, using of these compounds can lead to preventing the water loss of the cut Anthurium flowers. Therefore, both compounds can positively affect the freshness and vase life of cut Anthurium flowers. Moreover, treatment of cut Anthurium flowers by various concentrations of BA and H2O2 showed a considerable increase in soluble carbohydrates and decrease in ion leakage. It’s found that application of 100 ppm BA and some rates of H2O2 (5, 10, 15 and 25 µM) are helpful to increase the freshness and vase life of the cut Anthurium flowers.