Maryam Haghighi

Effect of silicon nutrition on lipid peroxidation and antioxidant response of cucumber plants exposed to salinity stress

The effect of silicon (Si) on salinity-induced oxidative damages of cucumber was investigated in a greenhouse experiment. Two cucumber cultivars (Cucumis sativus L. cvs. Negin and Super Dominus) were exposed to two salinity levels (0 and 50 mM NaCl) and two Si levels (0 and 1 µM). Silicon stimulated shoot growth of cucumber particularly under saline conditions. Leaf malondialdehyde (MDA) content was increased in ‘Super Dominus’ while it remained unchanged in ‘Negin’ by salt stress. MDA content in cucumber leaves was reduced by Si. The effect of salinity on activity of catalase (CAT) and ascorbate peroxidase (APX) was dependent on enzyme type and cultivar. Silicon increased activity of  CAT, APX, and guaiacol peroxidase (GPX) in the leaves. Silicon nutrition could alleviate salt-oxidative stress on cucumber plants by increasing activity of antioxidant enzymes. Higher activity of CAT, APX, and GPX in ‘Negin’ might be associated with its greater tolerance to salinity.

Photosynthetic Activity and N Metabolism of Lettuce as Affected by Humic Acid

The mechanism by which humic substances stimulate plant biological activities is not clear. To study effects of humic acid on N metabolism and growth of lettuce (Lactuca sativa L.) a hydroponic experiment was conducted under greenhouse conditions. Humic acid (HA) at 0, 100, or 1000 mg·L−1 was added with a nutrient solution to plants. HA accelerated uptake of N and NO3 and accelerated N metabolism by enhancing nitrate reductase activity, which resulted in production of protein. HA did not affect P absorption and proline content of leaves. The photosynthetic activity of lettuce increased with all levels of HA due to enhancement of chlorophyll content and mesophyll conductance. HA can stimulate N metabolism and photosynthesis activity of lettuce to improve yield.

The effect of carbon nanotubes on the seed germination and seedling growth of four vegetable species

Carbon nanotubes (CNTs) can change the morphological and physiological characteristics of plant cells. Laboratory and greenhouse studies were conducted to study the effect of CNTs on the germination and seedling growth of tomato (Lycopersicum esculentum Mill. cv. ‘Falcato’), onion (Allium cepa L. cv. ‘Yellow Sweet Spanish’), turnip (Brassica rapa L. cv. ‘Toria’) and radish (Raphanus sativus L. cv. ‘Small radish’). Seeds were germinated in four concentrations of CNTs (0, 10, 20 and 40 mg L-1) in Petri dishes under laboratory conditions. The same concentrations were used in a greenhouse to study the response of seedling growth to CNTs. To evaluate the effect of CNTs on germination and growth, germination percentage (GP), germination rate (GR), seedling length, seedling fresh and dry weight and mean germination time (MGT) were measured. Scanning electron microscopy (SEM) was used to confirm the presence of CNTs. CNTs at 10–40 mg L-1 improved tomato and onion germination more than for radish and turnip, the highest GP in tomato and onion being 8 and 95%, respectively. In radish, the control showed the highest GP (96%) under laboratory conditions. CNTs at 40 mg L-1 had a deleterious and toxic effect on onion and radish seed germination. In the greenhouse experiment, the fresh weight of radish seedlings decreased as the CNT concentration increased. The dry weight of tomato and radish shoots increased following the application of all concentrations (10–40 mg L-1) of CNTs. CNTs did not alter turnip germination and growth. SEM revealed that the effectiveness of CNTs may depend on the plant species and on the distribution of CNTs on the testa and root surface. CNTs thus provide a viable and important new technique to improve seed germination and selective seedling growth-related characteristics, although the benefit-toxic balance needs to be tested for other horticultural crops and other (higher) concentrations of CNTs.

The effect of N-TiO2 on tomato, onion, and radish seed germination

The effects of nano-size titanium dioxide (N-TiO2) on the germination of tomato (Lycopersicum esculentum L.), onion (Allium cepa L.), and radish (Raphanus sativus L.) seeds were assessed in laboratory and greenhouse trials. Seeds were germinated in Petri dishes in a laboratory and in peat:perlite (1:1, v/v) in a greenhouse containing four concentrations of N-TiO2 (0, 100, 200, and 400 mg L-1). N-TiO2 at 100 and 200 mg L-1 had the most positive effect on germination. In the laboratory, the highest germination percentage of tomato and onion was observed at 100 mg L-1 (100 and 30%, respectively), and in radish, 100% germination was obtained with 400 mg L-1. In the greenhouse, seedlings were tallest after exposure to 400 and 200 mg L-1 for tomato and onion, respectively, and 400 and 100 mg L-1 for radish. N-TiO2 may serve as a seed-priming agent for horticultural crops.

The Alleviation Effect of Silicon on Seed Germination and Seedling Growth of Tomato Under Salinity Stress

The Alleviation Effect of Silicon on Seed Germination and Seedling Growth of Tomato Under Salinity Stress This study was conducted to evaluate the effectiveness of silicon (Si) application under salinity levels on seed germination and growth characteristics of tomato seeds. A laboratory experiment was performed on completely randomized design with two levels of salinity (25 and 50 mM NaCl) and 2 concentration of Si (1 and 2 mM) with 4 replications. Germination percentage, germination rate, seedling shoot and root length, fresh and dry weight of seedling and mean germination time was measured. Seed germination of Lycopersicon esculentum L. was significantly affected by salinity levels, Si and their interaction. Germination characteristics of tomato seeds decreased drastically by increasing NaCl concentrations. However, 1 mM Si had positive effects on seed germination characteristics and improved germination percentage, germination rate and mean germination time. Si alleviated the harmful effect of salinity stress on tomato seed germination at almost all germination characteristics. Pozytywny Wpływ Krzemu Na Kiełkowanie Nasion I Wzrost Siewek Pomidora W Warunkach Stresu Zasolenia Badania przeprowadzono w celu oceny skuteczności stosowania krzemu (Si) w warunkach zasolenia na kiełkowanie nasion i cechy wzrostu siewek pomidora. Wykonano doświadczenie laboratoryjne w układzie kompletnie losowym z dwoma poziomami zasolenia (25 i 50 mM NaCl) i dwoma stężeniami Si (1 i 2 mM) w 4 powtórzeniach. Określano procent kiełkowania, zdolność kiełkowania, długość pędu i korzenia siewek, świeżą i suchą masę siewek oraz średni czas kiełkowania. Na kiełkowanie nasion Lycopersicon esculentum L. w istotny sposób oddziaływały poziomy zasolenia, krzem i ich interakcja. Kiełkowanie nasion pomidora zmniejszało się znacznie w miarę zwiększania stężenia NaCl. Dodatek 1 mM Si miał pozytywny wpływ na kiełkowanie, zwiększając procent skiełkowanych nasion, zdolność kiełkowania i średni czas kiełkowania. Si łagodził szkodliwy wpływ stresu zasolenia na kiełkowanie nasion pomidora pod względem niemal wszystkich parametrów związanych z kiełkowaniem.

The effect of humic and glutamic acids in nutrient solution on the N metabolism in lettuce

BACKGROUND This paper reports for the first time the influence of partially replacing the nitrogen (N) source of a nutrient solution with amino acids and humic acid on the physiological and antioxidant activities and N metabolism in lettuce. A hydroponic experiment was designed to replace 25 and 50% of the N in nutrient solutions (NSs) with glutamic acid (GA) and humic acid (HA) and evaluate the effects on growth, nitrate (NO(3)) assimilation, protein content, nitrate reductase (NR) activity and antioxidant changes in lettuce. RESULTS The results showed that, when a portion of the N was replaced with GA and HA, the fresh and dry weights of lettuce shoots did not change significantly compared with the full NO(3) treatment. The titratable acidity was not affected by adding HA and/or GA to the NS. The nitrite concentration and NR activity decreased with reductions in the N concentration of the NS and improved with the addition of GA and HA. GA enhanced the NO(3) uptake and protein content more than HA. Changes in the superoxide dismutase (SOD) and peroxidase (POD) activities and malondialdehyde content were inconclusive: SOD and POD activities decreased with decreasing N content of the NS, and HA addition improved the SOD and POD activities. CONCLUSION When HA and GA were substituted for NO(3) in an NS, the acids effectively adjusted the N metabolism and growth in lettuce and decreased the N consumption of the NS.

Effects of selenium as a beneficial element on growth and photosynthetic attributes of greenhouse cucumber

ABSTRACT Selenium (Se) is an essential element for human and livestock with antioxidant and anticancer characteristics. Although Se is not an essential element for plants, it has been reported that it can improve plant growth. This experiment was conducted at the Isfahan University of Technology in winter 2010. The experiment was factorial based on a completely randomized design (CRD) with four replications. Se was added to nutrient solution in four concentrations 2, 4, and 6 mg/L sodium selenite (Na2SeO3). Root volume, fresh and dry weights of shoots and roots, number and weight of fruits, chlorophyll content, and photosynthesis traits [photosynthesis rate, stomata internal carbon dioxide (CO2) concentration, stomata conductance] were measured. Results showed that Se increased root dry weight. Fresh and dry weights of shoot increased in the 2 mg/L Se treatment and decreased at the higher level of Se. Chlorophyll content and photosynthesis rate were not affected by Se. Stomata internal CO2 concentration and stomata conductance decreased by Se addition. Overall, Se at 2 mg/L application rate was effective in some physiological characteristics of cucumber.

Influence of Selenium on Cadmium Toxicity in Cucumber (Cucumis sativus cv. 4200) at an Early Growth Stage in a Hydroponic System

ABSTRACT An experiment was established to assess the ability of selenium (Se) to reduce cadmium (Cd) toxicity when tomato was grown hydroponically. A factorial experiment was arranged in a completely randomized design with six replicates in cucumber (Cucumis sativus cv. 4200). The Se was applied at four levels [0 mg L–1 (Se0), 2 mg L–1 Se (Se1), 4 mg L–1 Se (Se2), and 6 mg L–1 Se (Se3)], whereas Cd was applied at three levels [0 µM Cd (Cd0), 5 µM Cd (Cd1), and 7 µM Cd (Cd2)]. The Se improved the dry weight of roots even when plants were exposed to Cd. Treatment Se1 improved the dry weight of shoots in Cd1 and Cd2. Treatments Se1 and Se2 improved photosynthesis in Cd1. Treatment Se1 significantly improved stomatal conductance in Cd2 at all levels of Se relative to Cd2. The greatest Cd concentration in leaves was observed in Cd2 × Se0 and while Se concentration in solution increased in response to Se1, Se2, and Se3. The greatest Se level reduced Cd uptake the most. Growth and photosynthetic attributes can be negatively affected by Cd, but Se has the ability to buffer, or improve, several attributes.

Influence of Humic Acid in Diluted Nutrient Solution on Growth, Nutrient Efficiency, and Postharvest Attributes of Gerbera

A hydroponics experiment was conducted to study the effect of humic acid (HA) on gerbera (Gerbera jamesonii L.) cv. Malibu in different diluted nutrient solutions. The HA (500 mgL−1) was added to a nutrient solution (NS) of gerbera with two dilution levels of NS, ½ NS and ¼ NS, and full-strength nutrient solution (NSc). The HA application compensated for nitrogen, magnesium, and iron deficiency in the ½ NS. Nutrient utilization efficiency (NUTE) of nitrogen in shoot decreased and that of Fe increased in the ½ NS compared with the ¼ NS when HA was applied. The number of harvested flowers per plant was the greatest in the NSc and the ½ NS with incorporating HA. Flower vase life improved by increasing NS level (9.33 days). It seems HA could be successfully considered as a compound to decrease nutrients input in gerbera hydroponics production.

EFFECT OF HUMIC ACID APPLICATION ON CADMIUM ACCUMULATION BY LETTUCE LEAVES

Humic acid (HA) is a plant growth stimulator compound that may also reduce cadmium (Cd) concentration in plant tissues. The aim of the present study was to investigate the effect of adding humic acid (HA) to the growth medium on Cd concentration in lettuce leaves. In a soilless experiment, seedlings of lettuce (Lactuca sativa L.) were exposed to three levels of Cd [0, 2 and 4 mg L−1 in the form of cadmium chloride (CdCl2)] and three levels of HA (0, 100 and 1000 mg L−1). Application of HA increased significantly the shoot fresh weight of lettuce while it had no effect on the photosynthetic rate and concentrations of chlorophyll, proline, and phosphorus (P) in lettuce leaves. In contrast, increasing Cd concentration was associated with decreases in the photosynthetic rate, shoot fresh weight, and leaf chlorophyll concentration. A significant reduction in leaf Cd concentration was found by addition of HA to the growth media. It seems that application of HA could be successful for improving plant growth and reducing accumulation of Cd in edible parts of lettuce.