Effect of exogenous melatonin on improvement of chlorophyll content and photochemical efficiency of PSII in mallow plants (Malva parviflora L.) treated with cadmium.

Melatonin is a growth regulator that improves the growth and chlorophyll (chl) content in plants. This study aims to investigate the effect of melatonin pretreatment on chl synthesis and fluorescence parameters in Malva parviflora exposed to cadmium (Cd). The 42-day-old plants were transferred to nutrient solutions containing 50 µM melatonin. After two days, some plants were exposed to 50 µM Cd. Eight days after Cd treatment, some indicators related to chl fluorescence and some biochemical parameters were measured. In this study, melatonin increased chl content and chl a/pheophytin a (pheo a) ratio, chlorophyllide a (chlide a), porphyrin compounds, and 5-aminolevulinic acid (5-ALA) in the presence of Cd. However, it decreased chl a/chlide a ratio under these conditions. Whereas Cd treatment resulted in significant reductions in photochemical activity and electron transfer rate in PSII, melatonin improved photochemical efficiency of PSII by reducing the toxic effect of Cd on the activity of the oxygen evolving complex (OEC) on the electron donor site and reducing non-photochemical quenching (NPQ). Based on the results, it appears that melatonin can maintain the chl content of plants exposed to Cd by increasing the precursors of the chl biosynthesis pathway and reducing its degradation rate. These results may, at least in our experimental conditions, partly explain the reason for the improved yield and growth of Cd-exposed plants when pretreated with melatonin.

Modulation of the toxic effects of zinc oxide nanoparticles by exogenous salicylic acid pretreatment in Chenopodium murale L.

Due to many uses of zinc oxide nanoparticles (ZnO NPs) in various industries, the release of these particles in the environment and their effects on living organisms is inevitable. In this study, the role of salicylic acid (SA) pretreatments in modulating the toxicity of ZnO NPs was investigated using a hydroponic system. After pretreatment with different concentrations of SA (0, 25, 75, and 150 µM), Chenopodium murale plants were exposed to ZnO NPs (50 mg L-1). The results showed that exogenous SA increased the length, weight, chlorophyll, proline, starch, and soluble sugars in the plants. Besides, SA pretreatments improved water status in the plants treated with ZnO NPs. In SA-pretreated plants, increased activity of catalase (CAT), guaiacol peroxidase (GPX), and superoxide dismutase (SOD) was associated with a decline in electrolyte leakage (EL %) and membrane peroxidation. Under NPs stress, SA pretreatments increased the content of phenolic compounds by increasing the activity of phenylalanine ammonia-lyase (PAL). Exogenous SA reduced the translocation of larger amounts of Zn to the shoots, with more accumulation in the roots. This result can be used to produce healthy food from plants grown in environments contaminated with nanoparticles. It seems that all concentrations of SA reduced the symptoms of ZnO NPs toxicity in the plant by strengthening the function of the antioxidant system and increasing the content of some metabolites. Findings also suggest that SA pretreatment can compensate for the growth reduction caused by ZnO NPs.

Alleviation of cadmium-induced phytotoxicity and growth improvement by exogenous melatonin pretreatment in mallow (Malva parviflora) plants.

The present work was aimed to study the effect of melatonin pretreatments on growth, oxidative stress modulation, cadmium (Cd) accumulation, and tolerance in mallow (Malva parviflora, Malvaceae) plants under the hydroponic system. Application of substances that can modulate the harmful effects of Cd on plant yield and reduce its accumulation in the edible parts is of particular importance. Therefore, the mallow plants pretreated with 15, 50, and 100 µM of melatonin were exposed to 50 µM Cd. Our results showed that melatonin, especially at 15 and 50 µM, led to positive effects on Cd tolerance, including a significant increase in growth, photosynthetic pigments, and soluble protein content. Exogenous melatonin could improve relative water content (RWC) and stomatal conductance in the plants treated with Cd, probably through an increase in proline. Further, lower concentrations of melatonin led to a decrease in Cd translocation to the shoots. Based on the results, melatonin considerably increased catalase (CAT), superoxide dismutase (SOD), and guaiacol peroxidase (GPX) activities as well as the production of phenols. The increased activity of antioxidant enzymes led to a decrease in electrolyte leakage (EL), lipid peroxidation, and H2O2 content in the plants exposed to Cd stress. Under Cd stress, the increased phenols content in melatonin-pretreated plants could be due to the induction of phenylalanine ammonia-lyase (PAL) activity and an increase in shoot soluble carbohydrates. The results showed that the use of melatonin could reduce oxidative stress and improve biomass in the plants exposed to Cd. At least in our experimental conditions, this information appears to be useful for healthy food production.

ZnO nanoparticles-induced oxidative stress in Chenopodium murale L, Zn uptake, and accumulation under hydroponic culture.

To understand toxic effect of Zn oxide nanoparticles (ZnO NPs) on Chenopodium murale, 40-day-old plants were exposed to 10, 50, and 250 mg L-1 of NPs using hydroponic system under controlled light and temperature conditions. Aboveground parts and roots were harvested 3 and 6 days after treatments and evaluated for some growth and biochemical indices. By increasing the concentration of ZnO NPs, the content of Zn increased in the roots more than the shoots. Our findings showed that all ZnO NPs treatments resulted in a decrease in growth, total chlorophyll content and soluble proteins, while the content of carotenoids, lipid peroxidation, leaf hydrogen peroxide (H2O2), and leaf electrolyte leakage increased significantly compared with the control. These changes, along with increased proline content and catalase (CAT), guaiacol peroxidase (GPX), and superoxide dismutase (SOD) activities in the treated plants, suggest that all concentrations of ZnO NPs used in this study strongly induced oxidative stress. A decline in growth-related indicators can be considered as an indicator of ZnO NPs phytoxicity in C. murale. Based on the concentration of Zn dissolved in the solution, the effects of Zn released into the nutrient solution may be greatly involved in induction of toxicity and retardation of growth at least under our experimental conditions. The results of this study suggest that an important mechanism of ZnO NPs phytotoxicity may be the exacerbation of oxidative stress and damage to biomembranes.

Modification of oxidative stress through changes in some indicators related to phenolic metabolism in Malva parviflora exposed to cadmium.

This study was conducted to investigate the role of phenolic compounds in the antioxidant defense system in Malva parviflora L. plants treated with cadmium (Cd). After surface sterilization, the seeds were sown on seedling trays. Forty-day-old plants were then transferred to hydroponic cultures with Cd (40 µM) or without Cd (control). Some biochemical and physiological parameters were assayed on the sixth day after Cd treatment. Based on the results, the plants showed an increase in leaf soluble carbohydrates, total phenolic compounds, total flavonoids, and phenylalanine ammonia-lyase (PAL) activity at the end of the exposure period. However, length, fresh weight, chlorophyll (Chl) b, total Chl, stomatal conductance and starch content decreased under Cd treatment. There was no significant difference between the plants exposed to Cd and the control group for Chl a, SPAD index, carotenoids, and anthocyanins as well as the H2O2 content six days after treatment. The Cd content in the roots was considerably higher than that in the shoots. In assessing the antioxidant capacity of plant extracts, different results were observed using 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) test and beta-carotene/linoleic acid bleaching assay. According to the results of this study, it seems that increased activity of PAL enzyme leads to an increase in biosynthesis of phenolic compounds in M. parviflora. This mechanism probably increases the antioxidant capacity of the plant to suppress Cd-induced toxicity and oxidative stress.

Evaluation of antioxidant bioindicators and growth responses in Malva parviflora L. exposed to cadmium.

In this study, the effect of cadmium (Cd) uptake and concentration on some growth and biochemical responses were investigated in Malva parviflora under Cd treatments including 0, 10, 50 and 100 µM. The shoots and roots were able to accumulate Cd. However, increased Cd dose led to a considerable Cd content in the roots. Cd stress decreased growth, increased lipid peroxidation and also enhanced proline and ascorbic acid contents in both shoots and roots. Chlorophyll and carotenoid contents decreased in the plants with the increasing Cd concentration. While the activities of catalase (CAT) and superoxide dismutase (SOD) increased in the shoots under different Cd doses, these activities decreased in the roots as compared to the control. Both shoots and roots demonstrated a significant increase in guaiacol peroxidase activity in response to Cd stress. Contrary to the aboveground parts, the roots subjected to Cd doses showed a rise in protein content. Despite higher Cd content in the roots, it seems that CAT and SOD do not play a key role in detoxification of Cd-induced oxidative stress. These findings confirm that reduced biomass and growth under Cd stress can be due to an increase in oxidative stress and a decrease in photosynthetic pigment content. The present study clearly indicates that the shoots and roots exploit different tolerance behaviors to alleviate Cd-induced oxidative stress in M. parviflora.

Oxidative Damage and Antioxidant Response in Chenopodium murale L. Exposed to Elevated Levels of Zn

ABSTRACT Present study was carried out to investigate the effects of different Zn concentrations on growth and some antioxidant responses in Chenopodium murale L. The seeds were sown on the pots. 45-day plants were transferred to hydroponic solution containing 0.2 (control), 150, 300 and 600 µM Zn. The plants were harvested at 6 days after applying Zn treatments and some parameters were evaluated including plant length, fresh weight, photosynthetic pigments, malondialdehyde (MDA), ascorbate, proline and enzymatic antioxidants such as catalase (CAT), guaiacol peroxidase (GPX) and superoxide dismutase (SOD). Zn concentration showed a considerable increase in the shoot and root as the concentration of Zn increased in the medium, meanwhile the roots were characterized by higher Zn accumulation. At 150 µM Zn, the length and fresh weight did not show important changes compared to the control, but these parameters decreased at 300 and 600 µM Zn. With increasing Zn doses, the content of total chlorophyll declined, and also the content of carotenoids elevated. Excess Zn led to an increase in lipid peroxidation, free proline and ascorbate pool. Moreover, elevated Zn levels enhanced the activities of CAT, GPX and SOD. C. murale probably tolerates Zn concentrations up to 150 µM using the production of carotenoid, proline and ascorbate as well as enhanced activity of enzymatic antioxidants. Higher Zn treatments seem to be toxic due to a severe decline in growth.

The Arabidopsis nitrate transporter NRT2.5 plays a role in nitrate acquisition and remobilization in nitrogen-starved plants.

Nitrogen is a key mineral nutrient playing a crucial role in plant growth and development. Understanding the mechanisms of nitrate uptake from the soil and distribution through the plant in response to nitrogen starvation is an important step on the way to improve nitrogen uptake and utilization efficiency for better growth and productivity of plants, and to prevent negative effects of nitrogen fertilizers on the environment and human health. In this study, we show that Arabidopsis NITRATE TRANSPORTER 2.5 (NRT2.5) is a plasma membrane-localized high-affinity nitrate transporter playing an essential role in adult plants under severe nitrogen starvation. NRT2.5 expression is induced under nitrogen starvation and NRT2.5 becomes the most abundant transcript amongst the seven NRT2 family members in shoots and roots of adult plants after long-term starvation. GUS reporter analyses showed that NRT2.5 is expressed in the epidermis and the cortex of roots at the root hair zone and in minor veins of mature leaves. Reduction of NRT2.5 expression resulted in a decrease in high-affinity nitrate uptake without impacting low-affinity uptake. In the background of the high-affinity nitrate transporter mutant nrt2.4, an nrt2.5 mutation reduced nitrate levels in the phloem of N-starved plants further than in the single nrt2.4 mutants. Growth analyses of multiple mutants between NRT2.1, NRT2.2, NRT2.4, and NRT2.5 revealed that NRT2.5 is required to support growth of nitrogen-starved adult plants by ensuring the efficient uptake of nitrate collectively with NRT2.1, NRT2.2 and NRT2.4 and by taking part in nitrate loading into the phloem during nitrate remobilization.