Iranian Journal of Plant Physiology
Volume:9 Issue: 4, Summer 2019

Heavy metal (HMs) pollution is currently one of the serious issues for the environment and agriculture as it has a direct impact on the production yield. This situation has gained a rapid momentum in the present era due to the population pressure, industrialization, and various anthropogenic activities which in turn lead to oxidative stress in plants and thus disturbs the redox homeostasis and ultimately affects the crop yield. However, plants possess a different regulatory system that work in a synergetic manner to combat stress and thus adapt themselves in such contaminated soils. These act as sinks to neutralize the toxic effects of these heavy metals by chelation, sequestration, and intensification of enzyme system. Excessive stress induces a cascade, MAPK (mitogen-activated protein kinase) pathway and biosynthesis of metal detoxifying ligands. The understanding of detoxification mechanism of metal ions through MAPK cascade and biosynthesis of metal-detoxifying ligands is an interesting way for searching insights and outlook in the field of plant biotechnology. Here, we discuss the impact of heavy metals on plants and the role of different regulatory elements that play a prominent role in metal detoxification.

Aglaonema widuri is an evergreen and indoor ornamental plant. This study aimed to investigate the effect of some plant growth regulators on micropropagation of A. widuri. A protocol was developed for high frequency in vitro multiplication of A. widuri on the same medium for both shoots and roots induction. This condition decreases time duration and cost of micropropagation. Apical buds as explants were obtained from greenhouse-grown A. widuri and were established on Murashige and Skoog (MS) medium. Three cytokinins including N6-benzyladenine (BA; 0.00, 3.00, 3.50, and 4.00 mg l-1), 1-phenyl-3-(1,2,3-thiaiazol-5-yl), urea (TDZ; 0.00, 0.50, and 1.00 mg l-1), and N6-(2-isopentenyl) adenine (2-iP; 0.00 and 7.00 mg l-1), along with one auxin [α-naphtalene acetic acid (NAA; 0.00, 0.10, 0.20, 0.30, and 0.40 mg l-1) were studied for their effect on micropropagation of A. widuri. The plantlets were transferred to pots and grown in the greenhouse with a success rate of 95%. BA and NAA treatments as 3.00 mg l-1+ 0.2 mg l-1 recorded the highest shoot proliferation rate (number: 6.00 shoots and length: 7.75 cm per explant). Treatment of 4.00 mg l-1 BA + 0.10 mg l-1 NAA + 0.50 mg l-1 TDZ produced maximum nodes (13.25 per explant). The largest number of leaves (4.25 per explant) was produced in the medium containing 3.50 mg l-1 BA + 0.20 mg l-1 NAA. Maximum root initiation and development (14.25 per explant) was obtained on the medium containing 3.00 mg l-1 BA + 0.20 mg l-1 NAA. The combination of 3.50 mg l-1 BA + 0.20 mg l-1 NAA was found to be the most suitable growth regulator for obtaining the highest root length (8.25 cm per explant).

Drought stress causes severe metabolic dysfunctions by formation of oxidative stress that may lead to damage in DNA, inactivation of enzymes, and lipid peroxidation. Plants have developed different morphological, physiological, and biochemical mechanisms to withstand the drought stress. Plant growth regulators (PGRs) are one of the most important endogenous substances involved in the amelioration of tolerance in various plant species. In this study, the possible recovery ability of Verbascum nudicuale plants from drought stress conditions was assessed using methyl jasmonate (MJA), titanium dioxide nanoparticles (TiO2NPs), and their interactions as the PGRs in liquid culture media. Results showed that the growth parameters and photosynthetic pigment content markedly decreased due to polyethylene glycol (PEG)-induced drought stress. The treatment of V. nudicuale plants with TiO2NPs showed a considerably improving effect on pigments synthesis and biomass production during the treatment. However, cultures containing MJA negatively affected the growth parameters and increased the content of hydrogen peroxide (H2O2) and malondialdehyde (MDA). Treatment of plants with PGRs showed a considerable improvement in increasing the synthesis of the phenolic compounds and proline accumulation. Alteration in the activity of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), and polyphenol oxidase (PPO) significantly varied in different treatments. These findings suggest that the recovery treatment with PGRs proved to be very effective in alleviating the adverse effects of drought stress.

Previous studies have confirmed that the growth and development of plants are entirely dependent on the gravitational acceleration of the Earth. So far, most of the studies on the plant response to the Earth gravity have focused on the geotropism of root tip of higher plants. Under space and clinorotation conditions, however, plant growth and development are supposed to be modified. The aim of the present study was to evaluate the growth and metabolism of cultured tobacco (Nicotiana tabacum L. cv. Burley 21) cells after 1 week continuous treatment with 2-D clinorotation. In these cells, the sensing of gravity and response to it occur in single cells without the involvement of specialized organs or tissues. The contents of phenolic compounds and phytohormones were evaluated by HPLC. Growth parameters i.e., fresh and dry weight of 2-D clinorotation-exposed tobacco cells significantly increased and it was accompanied by a significant increase in the contents of Indole-3-acetic acid and brassinosteroids, compared to the control group. Exposure to clinorotation also increased the content of antioxidant phenolics but significantly decreased the content of lignin producing phenolic acids. Altogether, these metabolic alterations prevented membrane damage and maintained wall loosening and growth potential of tobacco cells.

Evening primrose (Oenothera biennis L.) is native to North America, belongs to Onagraceae family, and is a biennial plant. This experiment was performed as factorial based on a completely randomized design in three replications. The main purpose of the study was to evaluate the effect of moist-chilling and GA3 on seed germination and flower induction of evening primrose. The seeds were soaked in distilled water for 30 min, and treated with seven levels of moist-chilling period (0,10, 20, 30, 40, 50, and 60 days) and were kept in 2-4 °C in refrigerator conditions. At the end of day 60 half of the seeds were treated with 500 ppm GA3 solution for 24 hours. After that, both groups were planted in pots with three replications to see the plant reproductive responses. Simultaneously, the same seeds were planted in Petri dishes with three replications for seed germination. Germination was controlled every three days and seed germination test was done for 15 days. Seedling characteristics were measured at the end of germination test. Results showed that moist-chilling and GA3 significantly influenced the seed germination percentage. The highest germination percentage was observed in a combination of 20 days moist-chilling conditions and 500 ppm GA3. Rootlet length increased while moist-chilling was increased from 10 to 30 days. By increasing moist-chilling to 40 - 60 days, rootlet length decreased unexpectedly. Combination of moist-chilling and GA3 did not influence flower stem production and seed yield significantly. On the other hand, the earliest flower stem production was observed in seeds treated with moist chilling for 40 and 60 days. To guaranty flower stem production of spring sowing evening primrose in the areas with warm winter, seeds are strongly recommended to be treated with moist chilling for 40 days at 4 °C.

Investigation of different irrigation methods on plants is necessary due to limited water resources and the increasing need for food products. The purpose of this study was to evaluate the effect of sprinkler and drip irrigation systems and hormones on morphological and physiological characteristics of potato. Treatments included sprinkler and drip irrigation systems and hormones (gibberellic acid, acetylsalicylic acid, epi-brassinolide, and no use of growth regulators) as split plot based on randomized complete block design with three replications during 2015 and 2016 growing seasons at a research farm located in Malayer. Results showed that the highest level of tuber dry matter (TDM) was related to epi-brassinolide hormone + drip irrigation after using 80% of the field capacity(FC) in 2015 and epi-brassinolide hormone + drip irrigation after using 70% of the FC in 2016. The lowest amount of water use efficiency (WUE) was seen in sprinkler irrigation + no use of regulators in both years. The highest value of WUE was seen in epi-brassinolide hormone along with drip irrigation after using 80% the FC and drip irrigation after using 70% of the FC in 2015 and also in epi-brassinolide hormone + drip irrigation after using 70% of the FC in 2016. There were high and significant correlations between water use efficiency and relative water content with morphological characteristics. In order to increase the production and potato water use efficiency in cold dry climate, drip irrigation along with epi-brassinolide hormone is recommended.

In this study, the effects of different concentrations of silica nanoparticles (NPs) were studied on growth, membrane stability, and antioxidant properties of Matricaria chamomilla in vitro. The sterilized seeds were incubated in different concentrations of silica NPs (0, 2, 4, 6 g L-1) for one hour and then were cultured on Murashing and Skoog medium. Silica NPs application enhanced relative water content and fresh and dry weight of leaf and root. The highest growth was observed at 4 g L-1 silica NPs. Hydrogen peroxide and malondialdehyde significantly reduced at 4 g L-1 silica NPs. Total phenol and flavonoid contents increased by silica NPs treatment, and induction effect of silica NPs was more prominent at 6 g L-1 silica NPs. Low level of IC50 was detected at 6 g L-1 silica NPs. Overall, application of silica NPs at proper concentration can improve growth and induces the production of metabolites in M. chamomilla.

Plants are generally subjected to a combination of different conditions such as magnetic field and soil bacteria in their life. The present investigation tried to compare the effects and interactions of magnetic field and rhizobial inoculant in alfalfa. A pot experiment was performed under a natural condition by a factorial design to investigate the influences of magnetic field with 0.75 and 1.5 mT intensities on treated and untreated alfalfa seed with Sinorhizobium meliloti. Results showed that 1.5 mT magnetic intensity reduces growth parameters, protein content, catalase, ascorbate peroxidase, and peroxidase activity as a stress factor while superoxide dismutase activity, malondialdehyde, and reducing sugars content increased. Interaction of rhizobial inoculant and 1.5 mT intensity can reduce the damage caused by magnetic field generated in the plant. Application of 0.75 mT intensity and rhizobial inoculant (individual and together) led to a significant increase in growth parameters, protein content, catalase, ascorbate peroxidase, peroxidase, and superoxide dismutase enzyme activity while malondialdehyde and reducing sugars content reduced. Therefore, as an eco-friendly technique in agriculture, the application of 0.75 mT and rhizobial inoculant might improve the plant quality. This method could be used as a biofertilizer for vegetable production which reduces the environmental pollution caused by the application of biochemical fertilizers.