Genotypic variation in the tolerance to moderate cadmium toxicity among 20 maize genotypes with contrasting root systems

Accumulation Potential of Lead and Cadmium Metals in Maize (Zea mays L.) and Effects on Physiological-Morphological Characteristics

Phytoremediation stands at the forefront of modern environmental science, offering an innovative and cost-effective solution for the remediation of heavy-metal-contaminated soils through the natural capabilities of plants. This study aims to investigate the effects of lead (Pb) and cadmium (Cd) metals on plant growth (e.g., seedling height, stem diameter, fresh and dry weight), physiological properties (e.g., tissue relative water content, tissue electrical conductivity), and biochemical parameters (e.g., chlorophyll content, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) enzyme activities) of maize compared to the control group under greenhouse conditions at the Atatürk University Plant Production Application and Research Center. The results show that plant height decreased by 20% in the lead (Pb3000) application and by 42% in the cadmium (Cd300) application compared to the control group. The highest Pb dose (Pb3000) caused a 15% weight loss compared to the control, while the highest Cd dose (Cd300) caused a weight loss of 63%. The accumulation rates of heavy metals in soil, roots, and aboveground parts of plants indicated that maize absorbed and accumulated more Cd compared to Pb.

Full-length transcriptome assembly and RNA-Seq integration of diploid and tetraploid ryegrass to investigate differences in cd uptake and accumulation among ryegrass with different ploidy levels

BACKGROUND

The accumulation of cadmium (Cd) in ryegrass (Lolium multiflorum Lamk.) as a widely used pasture plant poses a serious risk to food safety. This study aimed to investigate the differences in phenotypes, physiology, and expression of metal transporters between four ryegrass genotypes (diploid/tetraploid and Cd-tolerant/sensitive).

RESULTS

The diploid/Cd-sensitive genotypes were found to uptake, accumulate, and translocate more Cd compared to the tetraploid/Cd-tolerant genotypes. Cd with more soluble components facilitated the transfer of Cd from root to shoot in the sensitive genotypes. Tetraploid and Cd-tolerant Chuansi No.1 accumulated less Cd in shoots but higher ratio in root cell wall, making it a promising model for studying the mechanisms of plant resistance to Cd stress. The complex regulatory system and dilution effect contributed to the lower uptake and accumulation of Cd in tetraploid genotypes. Moreover, tetraploid genotypes exhibited higher expression of genes that promoted Cd efflux, which could contribute to their lower Cd accumulation.

CONCLUSIONS

Overall, this study sheds light on the physiological and transcriptional mechanisms of Cd uptake and accumulation by different polyploids, providing guidance for ryegrass breeding and soil improvement.

Arbuscular mycorrhizal fungi mitigate cadmium stress in maize

Soil cadmium (Cd) pollution poses a significant environmental threat, impacting global food security and human health. Recent studies have highlighted the potential of arbuscular mycorrhizal (AM) fungi to protect crops from various heavy metal stresses, including Cd toxicity. To elucidate the tolerance mechanisms of maize in response to Cd toxicity under AM symbiosis, this study used two maize genotypes with contrasting Cd tolerance: Zhengdan958 (Cd-tolerant) and Zhongke11 (Cd-sensitive). Rhizobox experiments were conducted with and without AM inoculation, alongside Cd treatment. The results revealed that Cd stress severely impaired growth and root development in both genotypes. However, AM symbiosis significantly improved plant height, stem diameter, biomass, root morphology, photosynthetic capacity, nutrient uptake, antioxidant enzyme activity, root Cd content, and concentration, while also reducing lipid peroxidation and shoot Cd accumulation in both genotypes. Notably, AM symbiosis had a more pronounced effect on stem diameter (increased 55 %), root dry weight (118 %), root superoxide dismutase (42 %), and peroxidase activity (209 %), as well as shoot translocation factor (77 %) in Zhongke11 compared to Zhengdan958. Overall, AM symbiosis alleviated Cd toxicity in maize through multiple mechanisms, including enhanced photosynthesis, nutrient uptake, antioxidant defenses, and modulation of Cd transport and accumulation. This study provides valuable insights into the potential application of Cd-tolerant maize genotypes and AM symbiosis for managing Cd-contaminated soils.

Agronomic and ionomics indicators of high-yield, mineral-dense, and low-Cd grains of wheat (Triticum aestivum L.) cultivars

The accumulation of toxic and essential nutrient elements in wheat grain influences wheat yield, grain nutritional quality, and human health. Here, we assessed the potential for breeding wheat cultivars to combine high yield with low cadmium and high iron and/or zinc concentrations in grains, and we screened appropriate cultivars. A pot experiment was conducted to explore differences in grain cadmium, iron, and zinc concentrations among 68 wheat cultivars, as well as their relationships with other nutrient elements and agronomic characters. The results showed 2.04-, 1.71-, and 1.64-fold differences in grain cadmium, iron, and zinc concentrations, respectively, among the 68 cultivars. Grain cadmium concentration was positively correlated with grain zinc, iron, magnesium, phosphorus, and manganese concentrations. Grain copper concentration was positively correlated with grain zinc and iron concentrations, but not with grain cadmium concentration. Therefore, copper has a potential role in regulating grain iron and zinc accumulation without influencing cadmium concentration in wheat grain. There were no significant relationships between grain cadmium concentration and four important wheat agronomic characters (i.e., grain yield, straw yield, thousand kernel weight, and plant height), indicating that the breeding of low-cadmium-accumulating cultivars with dwarfism and high yield characteristics is possible. On cluster analysis, four cultivars (Ningmai11, Xumai35, Baomai6, and Aikang58) exhibited low-cadmium and high-yield characteristics. Among them, Aikang58 contained moderate iron and zinc concentrations, while Ningmai11 had relatively high iron but low zinc concentrations in the grain. These results imply that it is feasible to breed high-yield dwarf wheat with low cadmium and moderate iron and zinc concentrations in the grain.

Subcellular distribution, chemical forms of cadmium and rhizosphere microbial community in the process of cadmium hyperaccumulation in duckweed

Duckweed is a newly reported Cd hyperaccumulator that grow rapidly; however, little is known about its tolerance and detoxification mechanisms. In this study, we investigated the tissue, subcellular, and chemical form distribution of the Cd in duckweed and studied the influences of Cd on duckweed growth, ultrastructure, and rhizosphere microbial community. The results showed that Cd could negatively affect the growth of duckweed and shorten the root length. More Cd accumulated in the roots than in the leaves, and Cd was transferred from the roots to the leaves with time. During 12-24 h, Cd mainly existed in the cell wall fraction (2.05 %-95.52 %) and the organelle fraction (5.03 %-97.80 %), followed the soluble fraction (0.14 %-16.98 %). Over time, the proportion of Cd in the organelles increased (46.64 %-92.83 %), exceeding that in the cell wall (6.79 %-66.23 %), which indicated that duckweed detoxification mechanism may be related to the retention of cell wall and vacuole. The main chemical form of Cd was the NaCl-extracted state (30.15 %-88.66 %), which was integrated with pectate and protein. With increasing stress concentration and time, the proportion of the HCl-extracted state and HAc-extracted state increased, and they were low-toxic Cd oxalate and Cd phosphate, respectively. Cd damaged the ultrastructure of cells such as chloroplasts and mitochondria and inhibited the diversity of microbial communities in the duckweed rhizosphere; however, the dominant populations that could tolerate heavy metals increased. It was speculated that duckweed distributed Cd in a less toxic chemical form in a less active location, mainly through retention in the root cell wall and sequestration in the leaf vacuoles, and is dynamically adjusted. The rhizosphere microbial communities tolerate heavy metals may also be one of the mechanisms by which duckweed can tolerate Cd. This study revealed the mechanism of duckweed tolerance and detoxification of Cd at the molecular level and provides a theoretical basis for further development of duckweed.