The Exogenous Application of 24-Epibrassinolide (24-EBL) Increases the Cd and Pb Resilience in Zea mays (L.) by Regulating the Growth and Physiological Mechanism

Heavy metals (HMs) at a concentration above the threshold level act as environmental pollutants and very often threaten the agricultural productivity globally. Finding affordable and environmentally sustainable deliverables to address this issue is therefore a top focus. Phytohormones alleviate the HMs-induced toxicity and positively influence the plant growth. Considering the importance of phytohormones, the present study aimed to assess the effect of 24-epibrassinolide (24-EBL; 10 µM) as seed soaking treatment on growth performance of Zea mays (L.) contaminated separately with increasing concentrations (50-400 mg.kg-1) of lead (Pb) and cadmium (Cd). With increasing metal concentrations, growth and plant biometric criteria were reduced. For instance, Cd at 400 mg.kg-1 soil reduced the germination efficiency (56%), root (77%) and shoot (69%) dry weight, total chlorophyll (64%), and carotenoid content (45%). Contrarily, both HMs caused increase in stress biomarkers and antioxidant enzymes in seedling. However, exogenous administration of 24-EBL significantly enhanced the growth attributes, photosynthetic pigments, proline, MDA, and antioxidant enzyme activity while reducing the harmful effects of HMs stress on Z. mays. For instance, 24-EBL (10 µM) improved the germination percentage, root biomass, chl a, chl b, total chlorophyll, and carotenoid content by 16, 21, 17, 34, 18, and 15%, respectively, in 50 mg.Pb.kg-1 soil-treated Z. mays plants. Furthermore, the amounts of proline, MDA, and antioxidant enzymes in foliage of Z. mays were interestingly and dramatically lowered by 24-EBL application. Uptake of metals in plant organs was significantly reduced when 24-EBL was applied to Pb- and Cd-treated Z. mays. The recent findings help us better understand how 24-EBL regulates growth and development of Z. mays as well as how it boosts HMs' resilience, which could increase the possibility of employing 24-EBL to increase Z. mays productivity. Thus, the present findings confirmed the potentiality of pre-soaking the seed in 24-EBL solution that neutralizes the toxic effects of heavy metals in Z. mays plants. Therefore, it is suggested that applying phytohormones including 24-EBL in removal of heavy metal stress in plants is the best possible solution in sustainable agriculture.

Cu-tolerant Klebsiella variicola SRB-4 increased the nanoparticle (NP) stress resilience in garden peas (Pisum sativum L.) raised in soil polluted with varying doses of copper oxide (CuO)-NP

Utilizing metal/nanoparticle (NP)- tolerant plant growth-promoting rhizobacteria (PGPR) is a sustainable and eco-friendly approach for remediation of NP-induced phytotoxicity. Here, Pisum sativum (L.) plants co-cultivated with different CuO-NP concentrations exhibited reduced growth, leaf pigments, yield attributes, and increased oxidative stress levels. Cu-tolerant (800 µM) Klebsiella variicola strain SRB-4 (Accession no. OR715781.1) recovered from metal-contaminated soils produced various PGP traits, including IAA, EPS, siderophore, HCN, ammonia, and solubilized insoluble P. The PGP substances were marginally increased with increasing CuO-NP concentrations. When applied, Cu-tolerant SRB-4 strain increased root length (18%), root biomass (15.3%), total chlorophyll (29%), carotenoids (30%), root N (21%), root P (23%), total soluble protein (20%) nodule number (32%), nodule biomass (39%) and leghaemoglobin content (18%) in 50 µM CuO-NP-exposed peas. Furthermore, proline, malondialdehyde (MDA), superoxide radical, hydrogen peroxide (H2O2) content, and membrane injury in K. variicola-inoculated and 50 µM CuO-NP-treated plants were maximally and significantly (p ≤ 0.05) reduced by 70.6, 26.8, 60.8, and 71.6%, respectively, over uninoculated but treated with similar NP doses. Moreover, K. variicola inoculation caused a significant (p ≤ 0.05) decline in Cu uptake in roots (71%), shoots (65.5%), and grains (76.4%) of peas grown in soil contaminated with 50 µM CuO-NP. The multivariate i.e. heat map and pearson correlation analyses between the NP-treated and PGPR inoculated parameters revealed a significant and strong positive corelation. The NP-tolerant indigenous beneficial K. variicola could be applied as an alternative to enhance the production of P. sativum cultivated in nano-polluted soil systems. Additionally, more investigation is required to ascertain the seed/soil inoculation effect of K. variicola SRB-4 on soil biological activities and different crops under various experimental setups.

Boosting disease resistance in Solanum melongena L. (eggplant) against Alternaria solani: the synergistic effect of biocontrol Acinetobacter sp. and indole-3-acetic acid (IAA)

Alternaria solani causes early blight disease in eggplants, threatening production and leading to significant economic losses. Fungicides are used to control fungal diseases, but their overuse raises resistance concerns. Finding novel, eco-friendly biocontrol agents is therefore a solution for the future. The coordination between antagonistic bacterial agents and plant growth hormones in defense responses against fungal pathogens are crucial. This study assessed biocontrol potential of Acinetobacter sp. SCR-11 (Accession no. OR751536.1) and indole-3-acetic acid (IAA; 100 µM), singly and in combination, against A. solani in eggplants. Strain SCR-11 produced hydrogen cyanide (HCN; 5.7 µg mL⁻1), siderophore i.e. salicylic acid (14.7 µg mL⁻1), 2,3-dihydroxybenzoic acid (23.1 µg mL⁻1) and various extracellular lytic enzymes. Strain SCR-11 exhibited antagonistic activity by strongly inhibiting (82%) A. solani. Acinetobacter sp. inoculation and IAA treatment enhanced growth, biomass, and leaf pigments of A. solani-diseased eggplants, with effectiveness in order: SCR-11 + IAA > SCR-11 > IAA >. The combined treatments (SCR-11 + IAA) most effectively increased total soluble protein (62.5%), carbohydrate (60%), total soluble sugar (81%), and phenol (74%) in A. solani-infected eggplant. Biocontrol agent and IAA application significantly (p ≤ 0.05) reduced proline and malondialdehyde (MDA) levels, alleviating oxidative stress in A. solani-diseased eggplant. The SCR-11 + IAA treatment significantly reduced the percent disease index (71%) and increased protection (69%) in diseased eggplant. The Acinetobacter sp. and IAA coordination enhanced disease resistance in A. solani-infected eggplants by boosting defense enzyme activities (SOD, POD, PAL, and β-1, 3 glucanase), significantly protecting plants from pathogen attack. At harvest, soil populations of A. solani decreased, while SCR-11 populations increased significantly. Acinetobacter sp. and IAA work synergistically through pathogen suppression, plant growth promotion, and induction of plant defense responses. Thus, applying antagonistic PGPR strain with exogenous IAA enhances eggplant resistance to A. solani, providing an environmentally friendly agricultural solution.

Production of biodegradable food packaging from mango peel via enzymatic hydrolysis and polyhydroxyalkanoates synthesis: A review on microbial intervention

The rising environmental problem of plastic packaging waste has led to the development of sustainable alternatives, particularly for food packaging. Polyhydroxyalkanoates (PHAs) are biodegradable, thermoplastic polyesters. They are employed in the production of various products, including packaging films. The bio-based nature and appropriate features of PHAs, similar to conventional synthetic plastics, have garnered significant attention from researchers and industries. The current study aimed to produce biodegradable food packaging using mango peel (a major agricultural waste) with enzymatic hydrolysis and PHAs synthesis. Mango peel is the hub for macro-and micronutrients, including phytochemicals. The process includes an enzymatic hydrolysis step that converts complex carbohydrates into simple sugars using mango peel as a substrate. The produced sugars are used as raw materials for bacteria to synthesize PHAs, which are a class of biodegradable polymers produced by these microorganisms that can serve as packaging materials in the food industry. To solve environmental problems and increase the utilization of agricultural by-products, this review presents a practical method for producing food packaging that is environmentally friendly.

Colonization potential of endophytes from halophytic plants growing in the "Runn of Kutch" salt marshes and their contribution to mitigating salt stress in tomato cultivation

Increasing soil salinity depreciates the quantity of the crop produce. Looking at the tremendous potential of plant-associated microorganisms in salinity stress mitigation, it would be very useful in exploring and deciphering salt-tolerant microorganisms from halophytic plants and their utilization in cultivated plants. With this aim, in the present study, four halophytic plants were taken from Rann of Kutch, and bacterial endophytes were isolated from different plant organs. These endophytes were characterized by plant growth and health promotion features. The molecular identification was done based on 16 s rRNA sequence similarity. It was found that the endophytic bacteria isolated from 4 different halophytes found sharing phylogenetic relatedness. Four potential endophytes Alkalihalobacillus gibsonii 2H2, Achromobacter insuavis 2H18, Terribacillus halophilus 2H20, and Bacillus siamensis 4H1 were tested in tomato for salinity stress alleviation. Changes in the levels of antioxidants were analyzed. Total chlorophyll, total phenolics, malondialdehyde, and proline content indicated reduced damage in the plant system due to salinity by the application of endophytes. All the treatments exhibited low levels of electrolyte leakage. The accumulation of enzymatic reactive oxygen species scavengers was assessed from the levels of peroxidase, catalase, superoxide dismutase, phenylalanine ammonia-lyase, ascorbate peroxidase, and guiacol peroxidase. The NBT and DAB staining confirmed the findings. The reduction in the accumulation of Na+ ions in tomato leaves was visualized using Sodium Green probes under CSLM and found to be lowest in Terribacillus halophilus 2H20 and Bacillus siamensis 4H1 inoculated plants. The endophyte Terribacillus halophilus 2H20 was the most promising isolate. The colonization in tomato roots was confirmed using a cell tracker system. Results showed that the endophytes were found to have salinity stress mitigation traits. The efficiency could be further improved with the combination of other endophytes tested earlier.

NO and melatonin interplay augment Cd-tolerance mechanism in eggplants: ROS detoxification and regulation of gene expression

Global crop productivity is consistently threatened by cadmium (Cd) soil contamination. Crosstalk between nitric oxide (NO) and melatonin (MT) in enhancing crop resilience to heavy metal stress has gained significant attention. Here, we evaluated the joint effect of sodium nitroprusside (SNP; 200 μM as NO donor) and MT (100 μM) on Cd-stressed eggplant (Solanum melongena L.). Cd stress significantly reduced plant growth, biomass yield, leaf pigments, and biochemical properties. Conversely, SNP, MT, and particularly their combined (SNP + MT) application reduced Cd toxicity and enhanced growth and physio-biochemical traits of eggplants. For instance, at 50 mg Cd kg-1 soil, SNP, MT, and SNP + MT increased root biomass (41.6, 30, and 47%), total chlorophyll (30.7, 26.3, and 46%), soluble protein (20.5, 17.6 and 37%) and RLWC (23, 17.5, and 29%) over their respective control. Furthermore, SNP + MT significantly (p ≤ 0.05) reduced levels of EL, H2O2, proline, and MDA by 54.5, 66, 61 and 70%, respectively, in Cd-stressed eggplants. SNP + MT interplay enhanced antioxidant defense responses in leaf tissues under Cd stress. Besides, SNP and MT upregulated transcript levels of POD, SOD, CAT, and GPX genes in eggplants under Cd stress. SNP and MT applications improved essential nutrient cation homeostasis in Cd-stressed shoot tissues of eggplants. Moreover, SNP + MT lessens metal-induced toxicity by decreasing Cd uptake, translocation (TF) and bioconcentration (BCF) factors. Conclusively, these findings validated the beneficial defensive interaction between SNP and MT in regulating Cd tolerance in eggplants. However, further research is needed to uncover the underlying defensive mechanisms of these synergistic effects.

Trichoderma Inoculation Alleviates Cd and Pb-Induced Toxicity and Improves Growth and Physiology of Vigna radiata (L.)

Heavy metals (HMs) pose a serious threat to agricultural productivity. Therefore, there is a need to find sustainable approaches to combat HM stressors in agriculture. In this study, we isolated Trichoderma sp. TF-13 from metal-polluted rhizospheric soil, which has the ability to resist 1600 and 1200 μg mL-1 cadmium (Cd) and lead (Pb), respectively. Owing to its remarkable metal tolerance, this fungal strain was applied for bioremediation of HMs in Vigna radiata (L.). Strain TF-13 produced siderophore, salicylic acid (SA; 43.4 μg mL-1) and 2,3-DHBA (21.0 μg mL-1), indole-3-acetic acid, ammonia, and ACC deaminase under HM stressed conditions. Increasing concentrations of tested HM ions caused severe reduction in overall growth of plants; however, Trichoderma sp. TF-13 inoculation significantly (p ≤ 0.05) increased the growth and physiological traits of HM-treated V. radiata. Interestingly, Trichoderma sp. TF-13 improved germination rate (10%), root length (26%), root biomass (32%), and vigor index (12%) of V. radiata grown under 25 μg Cd kg-1 soil. Additionally, Trichoderma inoculation showed a significant (p ≤ 0.05) increase in total chlorophyll, chl a, chl b, carotenoid content, root nitrogen (N), and root phosphorus (P) of 100 μg Cd kg-1 soil-treated plants over uninoculated treatment. Furthermore, enzymatic and nonenzymatic antioxidant activities of Trichoderma inoculated in metal-treated plants were improved. For instance, strain TF-13 increased proline (37%), lipid peroxidation (56%), catalase (35%), peroxidase (42%), superoxide dismutase (27%), and glutathione reductase (39%) activities in 100 μg Pb kg-1 soil-treated plants. The uptake of Pb and Cd in root/shoot tissues was decreased by 34/39 and 47/38% in fungal-inoculated and 25 μg kg-1 soil-treated plants. Thus, this study demonstrates that stabilizing metal mobility in the rhizosphere through Trichoderma inoculation significantly reduced the detrimental effects of Cd and Pb toxicity in V. radiata and also enhanced development under HM stress conditions.