Impact of galactoglucomannan oligosaccharides and Cd stress on maize root growth parameters, morphology, and structure

Differences of cadmium uptake and accumulation in roots of two maize varieties (Zea mays L.)

Different maize varieties respond differentially to cadmium (Cd) stress. As the first organ in contact with the soil, the response of the root is particularly important. However, the physiological mechanisms that determine the response are not well defined. Here, we compared the differences in Cd-induced related gene expression, ionic homeostasis, and ultrastructural changes in roots of Cd-tolerant maize variety (XR57) and Cd-sensitive maize variety (LY296), and assessed their effects on Cd uptake and accumulation. Our findings indicate that XR57 absorbed a significantly lower Cd than LY296 did, and that the expression levels of genes related to Cd uptake (ZmNRAMP5 and ZmZIP4) and efflux (ZmABCG4) in the root were consistent with the Cd absorption at the physiological levels. Compared with LY296, the lower Cd concentration in the roots of XR57 caused less interference with the ion balance. Transmission electron microscope images revealed that the roots from XR57 exposed to Cd had developed thicker cell walls than LY296. In addition, the large increase ZmABCC1 and ZmABCC2 expression levels in XR57 mediated the appearance of numerous electron-dense granules in the vacuoles present in the roots. As a result, the high Cd tolerance of XR57 is the result of a multi-level response that involves increased resistance to Cd uptake, a stronger capacity for vacuolar regionalization, and the formation of thicker cell walls. These findings may provide a theoretical basis for maize cultivation in Cd-contaminated areas.

Galactoglucomannan oligosaccharides mitigate cadmium toxicity in maize protoplasts by improving viability and cell wall regeneration

To avoid human health endangerment via the food chain, the investigation of Cd's effects on plant growth and development, and the discovery of various compounds that would mitigate the toxic effects of Cd, are essential. Galactoglucomannan oligosaccharides (GGMOs) are biologically active compounds, which improve the growth and development of plants. Therefore, the impact of GGMOs on the mitigation of Cd toxicity on maize (Zea mays L.) protoplasts was the main objective of this research. Here, protoplast viability, de novo cell wall regeneration on protoplasts' surface and Cd-uptake by protoplasts were studied. To study the influence of different treatments over time, the protoplasts were sampled on various days during the 14-day-long cultivation. The medium containing 2,4-dichlorophenoxyacetic acid, 6-benzylaminopurine, and GGMOs in a 10-9 M concentration with a pH of 3.8 was found to be optimal for protoplast cultivation. The toxic effect of Cd2+, which was evident already on the 2nd day of cultivation, resulted in decreased protoplast viability, the de novo cell wall regeneration, and in increased Cd-uptake. However, the application of GGMOs on Cd-stressed protoplasts increased cell wall regeneration. Fully or partly regenerated cell walls decreased the uptake of Cd2+ through the plasma membrane and improved protoplast viability. This is the first study that confirmed that biologically active oligosaccharides promote cell wall regeneration on the protoplast surface in both non-stress and Cd-stress conditions.

Galactoglucomannan oligosaccharides alleviate cadmium toxicity by improving physiological processes in maize

Phosphate fertilisers and past mining activity are significant source of cadmium (Cd) pollution; thus, the concentration of Cd in agricultural soils has been substantially rising. Various substances have been tested for their potential to alleviate the toxicity of Cd and stimulate the accumulation of Cd in plant organs. This study brought new insight of the impact of galactoglucomannan oligosaccharides (GGMOs) on the maize plants grown under/in Cd stress. The application of GGMOs reduced concentration of Cd in the maize leaves and thus GGMOs increased their growth (by 24%), concentration of photosynthetic pigments (up to 39.4%), effective quantum yield of photosystem II (up to 29.6%), and net photosynthetic rate (up to 19.6%). The concentrations of stress markers increased in the Cd and Cd + GGMOs treatment; however, significantly lower concentration was detected in the Cd + GGMOs treatment (malondialdehyde by 21.7%, hydrogen peroxide by 13%). The concentration of auxin increased almost by two-fold in the Cd + GGMOs treatment compared to the Cd treatment. The recovered auxin level and enhanced nutrient uptake are proposed mechanisms of GGMOs' action during stress. GGMOs are molecules with biostimulant potential that could support vitality of maize plants in Cd stress.

Heterologous expression of MirMAN enhances root development and salt tolerance in Arabidopsis

Introduction

β-Mannanase is a plant cell wall remodeling enzyme involved in the breakdown of hemicellulose and plays an important role in growth by hydrolyzing the mannan-like polysaccharide, but its function in adaptation to salt stress has been less studied.

Methods

Based on cloned the mannanase (MAN) gene from Mirabilis jalapa L., the study was carried out by heterologously expressing the gene in Arabidopsis thaliana, and then observing the plant phenotypes and measuring relevant physiological and biochemical indicators under 150 mM salt treatment.

Results and discussion

The results indicate that MirMAN is a protein with a glycohydrolase-specific structural domain located in the cell wall. We first found that MirMAN reduced the susceptibility of transgenic Arabidopsis thaliana to high salt stress and increased the survival rate of plants by 38%. This was corroborated by the following significant changes, including the reduction in reactive oxygen species (ROS) levels, increase in antioxidant enzyme activity, accumulation of soluble sugars and increase of the expression level of RD29 in transgenic plants. We also found thatthe heterologous expression of MirMAN promoted root growth mainly by elongating the primary roots and increasing the density of lateral roots. Meanwhile, the expression of ARF7, ARF19, LBD16 and LBD29 was up-regulated in the transgenic plants, and the concentration of IAA in the roots was increased. Those results indicate that MirMAN is involved in the initiation of lateral root primordia in transgenic plants through the IAA-ARF signalling pathway. In conclusion, MirMAN improves plant salt tolerance not only by regulating ROS homeostasis, but also by promoting the development of lateral roots. Reflecting the potential of the MirMAN to promote root plastic development in adaptation to salt stress adversity.

Exogenous Hemin alleviates cadmium stress in maize by enhancing sucrose and nitrogen metabolism and regulating endogenous hormones

Cadmium (Cd) stress restricts maize growth and productivity severely. We aimed to investigate the effects of Hemin on the metabolism of sucrose and nitrogen and endogenous hormones in maize under cadmium stress. Maize varieties 'Tiannong 9' (cadmium tolerant) and 'Fenghe 6' (cadmium sensitive) were grown in nutrient solutions to study the effects of Hemin on maize physiological and ecological mechanisms under cadmium stress. The results showed that Hemin mediated the increase of sucrose content and the activities of key enzymes sucrose phosphate synthase (SPS) and sucrose synthase (SS) in maize leaves under cadmium stress. Soluble acid invertase (SAInv) and basic/neutral invertase (A/N-Inv) enzyme activities in leaves were decreased significantly, and sucrose accumulation in leaves was increased. Hemin also mediated the increase of NO₃^- content in leaves, the decrease of NH₄⁺ content and the increase of nitrate reductase (NR), glutamine synthetase (GS), glutamate synthase activity (GOGAT) and glutamate dehydrogenase (GDH) enzyme activities under cadmium stress. The contents of IAA, ZR, and GA in leaves and roots increased, ABA, MeJA, and SA decreased, and IAA/ABA, ZR/ABA, and GA/ABA increased under cadmium stress. Our study showed Hemin can alleviate cadmium stress in maize by enhancing sucrose and nitrogen metabolism and regulating endogenous hormones.

Identification of low grain cadmium accumulation genotypes and its physiological mechanism in maize (Zea mays L.)

Soil cadmium (Cd) contamination poses adverse impacts on crop yield and quality. Maize is a widely cultivated cereal throughout the world. In this study, field and hydroponic experiments were conducted to investigate the genotypic difference in Cd accumulation and tolerance in maize. There were significant genotypic differences in grain Cd concentrations among 95 genotypes. From these 95 genotypes, L42 which showed a higher grain Cd concentration and L63 which showed a lower grain Cd concentration was selected for further study. Under Cd stress, L63 showed much less reduction in plant growth than L42 compared with the control. Seedlings of L63 recorded higher Cd concentration in roots, but lower in shoots L42, indicating that the low grain Cd concentration in L63 is mainly due to the low rate of transportation of Cd from roots to shoots. Most Cd accumulated in epidermis and xylem vessels of L63, while the green fluorescent was found across almost the entire cross-section of root in L42. Obvious ultrastructural damage was observed in L42 under Cd stress, especially in mesophyll cells, while L63 was less affected. These findings could contribute to developing low Cd accumulation and high tolerance maize cultivars.

Recent advances in physiological and molecular mechanisms of heavy metal accumulation in plants

Among abiotic stress, the toxicity of metals impacts negatively on plants' growth and productivity. This toxicity promotes various perturbations in plants at different levels. To withstand stress, plants involve efficient mechanisms through the implication of various signaling pathways. These pathways enhance the expression of many target genes among them gene coding for metal transporters. Various metal transporters which are localized at the plasma membrane and/or at the tonoplast are crucial in metal stress response. Furthermore, metal detoxification is provided by metal-binding proteins like phytochelatins and metallothioneins. The understanding of the molecular basis of metal toxicities signaling pathways and tolerance mechanisms is crucial for genetic engineering to produce transgenic plants that enhance phytoremediation. This review presents an overview of the recent advances in our understanding of metal stress response. Firstly, we described the effect of metal stress on plants. Then, we highlight the mechanisms involved in metal detoxification and the importance of the regulation in the response to heavy metal stress. Finally, we mentioned the importance of genetic engineering for enhancing the phytoremediation technique. In the end, the response to heavy metal stress is complex and implicates various components. Thus, further studies are needed to better understand the mechanisms involved in response to this abiotic stress.

Loci and natural alleles for cadmium-mediated growth responses revealed by a genome wide association study and transcriptome analysis in rice

BACKGROUND

Cadmium (Cd) is a toxic heavy metal that is harmful to the environment and human health. Cd pollution threatens the cultivation of rice (Oryza sativa L.) in many countries. Improving rice performance under Cd stress could potentially improve rice productivity.

RESULTS

In this study, 9 growth traits of 188 different cultivated rice accessions under normal and Cd stress conditions were found to be highly variable during the seedling stage. Based on ~3.3 million single nucleotide polymorphisms (SNPs), 119 Cd-mediated growth response (CGR) quantitative trait loci (QTL) were identified by a genome-wide association study (GWAS), 55 of which have been validated by previously reported QTL and 64 were new CGR loci. Combined with the data from the GWAS, transcriptome analysis, gene annotations from the gene ontology (GO) Slim database, and annotations and functions of homologous genes, 148 CGR candidate genes were obtained. Additionally, several reported genes have been found to play certain roles in CGRs. Seven Cd-related cloned genes were found among the CGR genes. Natural elite haplotypes/alleles in these genes that increased Cd tolerance were identified by a haplotype analysis of a diverse mini core collection. More importantly, this study was the first to uncover the natural variations of 5 GST genes that play important roles in CGRs.

CONCLUSION

The exploration of Cd-resistant rice germplasm resources and the identification of elite natural variations related to Cd-resistance will help improve the tolerance of current major rice varieties to Cd, as well as provide raw materials and new genes for breeding Cd-resistant varieties.

Loci and natural alleles for cadmium-mediated growth responses revealed by a genome wide association study and transcriptome analysis in rice

BACKGROUND

Cadmium (Cd) is a toxic heavy metal that is harmful to the environment and human health. Cd pollution threatens the cultivation of rice (Oryza sativa L.) in many countries. Improving rice performance under Cd stress could potentially improve rice productivity.

RESULTS

In this study, 9 growth traits of 188 different cultivated rice accessions under normal and Cd stress conditions were found to be highly variable during the seedling stage. Based on ~3.3 million single nucleotide polymorphisms (SNPs), 119 Cd-mediated growth response (CGR) quantitative trait loci (QTL) were identified by a genome-wide association study (GWAS), 55 of which have been validated by previously reported QTL and 64 were new CGR loci. Combined with the data from the GWAS, transcriptome analysis, gene annotations from the gene ontology (GO) Slim database, and annotations and functions of homologous genes, 148 CGR candidate genes were obtained. Additionally, several reported genes have been found to play certain roles in CGRs. Seven Cd-related cloned genes were found among the CGR genes. Natural elite haplotypes/alleles in these genes that increased Cd tolerance were identified by a haplotype analysis of a diverse mini core collection. More importantly, this study was the first to uncover the natural variations of 5 GST genes that play important roles in CGRs.

CONCLUSION

The exploration of Cd-resistant rice germplasm resources and the identification of elite natural variations related to Cd-resistance will help improve the tolerance of current major rice varieties to Cd, as well as provide raw materials and new genes for breeding Cd-resistant varieties.

Data-independent acquisition proteomic analysis of biochemical factors in rice seedlings following treatment with chitosan oligosaccharides

Chitosan oligosaccharides (COS) can elicit plant immunity and defence responses in rice plants, but exactly how this promotes plant growth remains largely unknown. Herein, we explored the effects of 0.5 mg/L COS on plant growth promotion in rice seedlings by measuring root and stem length, investigating biochemical factors in whole plants via proteomic analysis, and confirming upregulated and downregulated genes by real-time quantitative PCR. Pathway enrichment results showed that COS promoted root and stem growth, and stimulated metabolic (biosynthetic and catabolic processes) and photosynthesis in rice plants during the seedling stage. Expression levels of genes related to chlorophyll a-b binding, RNA binding, catabolic processes and calcium ion binding were upregulated following COS treatment. Furthermore, comparative analysis indicated that numerous proteins involved in the biosynthesis, metabolic (catabolic) processes and photosynthesis pathways were upregulated. The findings indicate that COS may upregulate calcium ion binding, photosynthesis, RNA binding, and catabolism proteins associated with plant growth during the rice seedling stage.

Recent advances in the knowledge of wine oligosaccharides

Oligosaccharides are carbohydrates with a low polymerization degree containing between three and fifteen monosaccharide residues covalently linked through glycosidic bonds. Oligosaccharides are related to plant defense responses and possess beneficial attributes for human health. Research has focused in wine oligosaccharides only in the last decade. In this paper, a summary of these works is provided. They include: (i) wine oligosaccharides origins, (ii) techniques for isolating oligosaccharide fraction and determining their content, composition and structure, (iii) their dependence on the grape origin and cultivar and winemaking process, and (iv) the connection between oligosaccharides and wine sensorial attributes. Further research is required regarding the impact of agricultural aspects and winemaking techniques on wine oligosaccharides. The knowledge concerning their influence on sensorial and physicochemical properties of wines and on human health should also be improved. The implementation of laboratory methods will provide better understanding of these compounds and their performance within wine's matrix.

Combination of rhamnolipid and biochar in assisting phytoremediation of petroleum hydrocarbon contaminated soil using Spartina anglica

Biochar (BC) and rhamnolipid (RL) is used in bioremediation of petroleum hydrocarbons, however, the combined effect of BC and RL in phytoremediation has not been studied until now. In this paper, the phytoremediation of petroleum hydrocarbon-contaminated soil using novel plant Spartina anglica was enhanced by the combination of biochar (BC) and rhamnolipid (RL). Samples of petroleum-contaminated soil (10, 30 and 50 g/kg) were amended by BC, BC+ RL and rhamnolipid modified biochar (RMB), respectively. After 60 day's cultivation, the removal rate of total petroleum hydrocarbons (TPHs) for unplanted soil (UP), planted soil (P), planted soil with BC addition (P-BC), planted soil with BC and RL addition (P-BC + RL) and planted soil with addition of RMB (P-RMB) were 8.6%, 19.1%, 27.7%, 32.4% and 35.1% in soil with TPHs concentration of 30 g/kg, respectively. Compared with UP, the plantation of Spartina anglica significantly decreased the concentration of C_8-14 and tricyclic PAHs. Furthermore, the application of BC and RMB alleviated the toxicity of petroleum hydrocarbons to Spartina anglica via improving plant growth with increasing plant height, root vitality and total chlorophyll content. High-throughput sequencing result indicated that rhizosphere microbial community of Spartina anglica was regulated by the application of BC and RMB, with increase of bacteria and plant mycorrhizal symbiotic fungus in biochar and RMB amended soil.