Root Metabolite Differences in Two Maize Varieties Under Lead (Pb) Stress

To assess root metabolic differences of maize varieties in their response to lead (Pb) stress, the lead-tolerant variety Huidan No. 4 and the lead-sensitive variety Ludan No. 8 were tested under Pb-free and Pb-stressed conditions. Changes in metabolites were measured using ultra-performance liquid chromatography–mass spectrometry. Pb stress changed the levels of the amino acids proline, glutamine, lysine, and arginine in both varieties, whereas glutamate and phenylalanine levels changed only in Huidan No. 4. Pb stress altered cystine, valine, methionine, and tryptophan levels only in Ludan No. 8. Therefore, the synthesis and decomposition of amino acids may affect the response of maize to Pb stress. The degree of change in differential metabolites for Huidan No. 4 was greater than that for Ludan No. 8. In cell wall subcellular components, increases in superoxide dismutase (SOD), peroxidases (PODs), and Pb concentrations were greater in Huidan No. 4 than in Ludan No. 8. Therefore, the greater Pb tolerance of Huidan No. 4 could be due to better sequestration of Pb in cell walls and more effective removal of reactive oxygen species (ROS) from the plant. The levels of certain metabolites only increased in Ludan No. 8, indicating that Pb-sensitive varieties may use different metabolic pathways to cope with Pb stress. Both varieties showed increased levels of some metabolites related to antioxidant protection and osmotic regulation. This study provides an understanding of maize Pb tolerance mechanisms and a basis for further development of tools for use in maize breeding.

Alleviating Role of Gibberellic Acid in Enhancing Plant Growth and Stimulating Phenolic Compounds in Carrot (Daucus carota L.) under Lead Stress

Toxicity of heavy-metals in soil is a major constraint for the production of carrots (Daucus carota L.). Different plant growth regulators are being used to overcome this problem. It has been found that plant growth regulators induce stress tolerance in plants. In this study, the role of exogenously applied plant growth regulator, gibberellic acid (GA3) was examined in soil grown two carrot cultivars under four different levels of lead (0, 50, 100, and 150 mg/kg) with one level of gibberellic acid (50 ppm). Results showed that Pb stress retarded the plant growth and reduced chlorophyll contents in the leaves of both carrot cultivars. A significant decrease was observed in photosynthetic attributes by Pb addition alone. However, exogenously applied GA3 ameliorated the plant growth and chlorophyll contents in the leaves of both carrot cultivars under Pb stressed conditions. Moreover, GA3 also decreased the uptake of Pb concentration in carrot leaves and roots. In addition, GA3 significantly regulated the phenolic compounds concentration in both carrot cultivars under Pb stress. In this study, cultivar T-29 was found to be more tolerant to Pb stress, however, cultivar Mevarick experienced higher damage regarding plant growth under Pb stress.

Antioxidant Enzyme Activities as Biomarkers of Cu and Pb Stress in Centella asiatica

The present study investigated the antioxidant enzyme activities (AEA) of ascorbate peroxidase (APX), catalase (CAT), guaiacol peroxidase (GPX), and superoxide dismutase (SOD) as biomarkers of Cu and Pb stress by using Centella asiatica grown in an experimental hydroponic condition. The results showed (i) higher accumulations of Cu and Pb in the roots of C. asiatica than those in the leaves, (ii) synergistic effects of Cu and Pb stress at higher metal-level exposures, and (iii) Cu and Pb stress triggered the increment of APX, CAT, GPX, and SOD levels in both the leaves and roots of C. asiatica. The increment of four AEA indicated that C. asiatica underwent oxidative stress caused by the production of reactive oxygen species when the plant was exposed to Cu and Pb. In order to prevent damages caused by Cu and Pb stress, the AEA system was heightened in C. asiatica, in which APX, CAT, GPX, and SOD can be used as biomarkers of Pb and Cu stress in the plant.

Alleviation of Lead Stress on Sage Plant by 5-Aminolevulinic Acid (ALA)

Oxidative stress is imparted by a varying range of environmental factors involving heavy metal stress. Thus, the mechanisms of antioxidant resistance may advance a policy to improve metal tolerance. Lead as a toxic heavy metal negatively affects the metabolic activities and growth of medicinal and aromatic plants. This investigation aimed to assess the function of 5-aminolevulinic acid (ALA) in the alleviation of Pb stress in sage plants (Salvia officinalis L.) grown either hydroponically or in pots. Various concentrations of Pb (0, 100, 200, and 400 µM) and different concentrations of ALA (0, 10, and 20 mg L−1) were tested. This investigation showed that Pb altered the physiological parameters. Pb stress differentially reduced germination percentage and protein content compared to control plants. However, lead stress promoted malondialdehyde (MDA) and H2O2 contents in the treated plants. Also, lead stress enhanced the anti-oxidative enzyme activities; ascorbate peroxidase superoxide, dismutase, glutathione peroxidase, and glutathione reductase in Salvia plants. ALA application enhanced the germination percentage and protein content compared to their corresponding controls. Whereas, under ALA application MDA and H2O2 contents, as well as the activities of SOD, APX, GPX, and GR, were lowered. These findings suggest that ALA at the 20 mgL−1 level protects the Salvia plant from Pb stress. Therefore, the results recommend ALA application to alleviate Pb stress.

Liquiritoside Alleviated Pb Induced Stress in Brassica rapa subsp. Parachinensis: Modulations in Glucosinolate Content and Some Physiochemical Attributes

Current research was conducted to explore the effects of liquiritoside on the growth and physiochemical features of Chinese flowering cabbage (Brassica rapa subsp. parachinensis) under lead (Pb) stress. Lead stressed B. rapa plants exhibited decreased growth parameters, chlorophyll, and carotenoid contents. Moreover, Pb toxicity escalated the synthesis of malondialdehyde (MDA), hydrogen peroxide (H2O2), flavonoids, phenolics, and proline in treated plants. Nevertheless, foliar application of liquiritoside mitigated Pb toxicity by decreasing oxidative stress by reducing cysteine, H2O2, and MDA contents in applied plants. Liquiritoside significantly increased plant height, shoot fresh weight and dry weight, number of leaves, and marketable value of Chinese flowering cabbage plants exposed to Pb toxicity. This biotic elicitor also enhanced the proline, glutathione, total phenolics, and flavonoid contents in Chinese flowering cabbage plants exposed to Pb stress compared with the control. Additionally, total glucosinolate content, phytochelatins (PCs), and non-protein thiols were effectively increased in plants grown under Pb regimes compared with the control plants. Overall, foliar application of liquiritoside can markedly alleviate Pb stress by restricting Pb translocation in Chinese flowering cabbage.

Genotypic screening of wheat and their physiological responses under lead toxicity

Lead (Pb) is the second most harmful heavy metal contaminant in the environment and toxic for plant growth and development. Therefore, the identification and selection of plant genotypes tolerant to Pb stress are of great significance. In this study, twenty-six wheat lines (Triticum aestivum) were screened for Pb tolerance based on their morpho-physiological variations at the seedling stage with a rapid hydroponic technique using lead nitrate (Pb(NO3)2) at two concentrations (500 ?M and 1 mM) along with control. Wheat genotypes showed distinct variations in plant height, plant biomass and chlorophyll concentration in response to different concentrations of Pb. Considering all parameters, Akbar was found most tolerant (T) with minimum RS (2.97) to Pb stress, followed by BARI Gom-31 (3.45), Barkat (3.54) and Sufi (3.65), while BARI Gom-26 (10.14) was most sensitive (S) followed by Khude Gom (9.69), BARI Gom-30 (8.79), LalGom (8.76) and BARI Gom-32 respectively. More scores were seen in the remaining genotypes and were graded as moderately tolerant/resistant (MT) to Pb stress. Results showed that the resistant line had less damage to root and shoot characteristics along with chlorophyll score, thereby providing a hint about the Pb tolerance capacity of wheat genotypes at the seedling stage. Furthermore, findings indicate that Pb susceptibility in wheat is predominantly associated with a decrease in the Pb components of the root and shoot. We suggest Akbar as an elite genotype to cultivate or use in downstream studies on the basis of our findings to ensure an improved crop production relative to other varieties evaluated. These findings provide the necessary background for Pb cleansing and Pb-free wheat development for environment and health safety.

Indole Acetic Acid (IAA) Mediated Amelioration of Lead (Pb) Stress- Physiological Indices of Mung Bean [Vigna radiata (L.) Wilczek]

Background: Heavy metals have their adverse effects on growth and physiology of plant. Plant growth regulators help in improving the growth and physiological phenomenon in plants. A pot culture experiment was devised to explore the ameliorative potential of Indole Acetic Acid (IAA) for toxicity of rhizospheric lead (Pb) on two varieties of Mung bean [Vigna radiate (L.) Wickzek]. Methods: Seeds of two varieties i.e., M- 8 and MN-92 were grown in earthen pots filled with sandy loam soil and were arranged under complete randomization. Fifteen days after germination, the lead (Pb) was added @ 10mg/kg and 20mg/kg soil as solution Pb NO3. Indole Acetic Acid @100.0mM was foliarly sprayed twice at 15 and 30 days of plants emergence. Physiological parameters i.e., Photosynthetic Rate, Transpiration Rate, Stomatal conductance, Sub Stomatal CO2 Concentration and biomass production in the form of stem, root and leaf dry weights were determined at the age of physiological maturity for three replicates. Result: By application of IAA, photostnthetic rate reduction was declined from 24.61% to 17.78% under 10mg Pb stress and from 55.54% to 27.35% under 20mg Pb stress. Stomatal conductance reduction was declined from 0.56% to 0.28% under 10mg Pb stress and from 3.37% to 1.68% under 20mg Pb stress. Alleviation of Pb stress by IAA for transpiration rate was non significant. Similarly, the role of IAA for alleviation of Pb stress in term of dry weights of stem,root and leaves were non significant statistically.