Screening Arabidopsis mutants in genes useful for phytoremediation

Recent advances in phyto-combined remediation of heavy metal pollution in soil

The global industrialization and modernization have witnessed a rapid progress made in agricultural production, along with the issue of soil heavy metal (HM) pollution, which has posed severe threats to soil quality, crop yield, and human health. Phytoremediation, as an alternative to physical and chemical methods, offers a more cost-effective, eco-friendly, and aesthetically appealing means for in-situ remediation. Despite its advantages, traditional phytoremediation faces challenges, including variable soil physicochemical properties, the bioavailability of HMs, and the slow growth and limited biomass of plants used for remediation. This study presents a critical overview of the predominant plant-based HM remediation strategies. It expounds upon the mechanisms of plant absorption, translocation, accumulation, and detoxification of HMs. Moreover, the advancements and practical applications of phyto-combined remediation strategies, such as the addition of exogenous substances, genetic modification of plants, enhancement by rhizosphere microorganisms, and intensification of agricultural technologies, are synthesized. In addition, this paper also emphasizes the economic and practical feasibility of some strategies, proposing solutions to extant challenges in traditional phytoremediation. It advocates for the development of cost-effective, minimally polluting, and biocompatible exogenous substances, along with the careful selection and application of hyperaccumulating plants. We further delineate specific future research avenues, such as refining genetic engineering techniques to avoid adverse impacts on plant growth and the ecosystem, and tailoring phyto-combined strategies to diverse soil types and HM pollutants. These proposed directions aim to enhance the practical application of phytoremediation and its integration into a broader remediation framework, thereby addressing the urgent need for sustainable soil decontamination and protection of ecological and human health.

Natural resistance-associated macrophage proteins are involved in tolerance to heavy metal Cd2+ toxicity and resistance to bacterial wilt of peanut (Arachis hypogaea L.)

Peanut (Arachis hypogaea L.) is one of the most important oil and industrial crops. However, heavy-metal pollution and frequent soil diseases, poses a significant threat to the production of green and healthy peanuts. Herein, we investigated the effects of heavy metal Cd2+ toxicity to the peanuts, and screened out two peanut cultivars H108 and YZ 9102 with higher Cd2+-tolerance. RNA-seq revealed that Natural resistance-associated macrophage proteins (NRAMP)-like genes were involved in the Cd2+ stress tolerance in H108. Genome-wide identification revealed that 28, 13 and 9 Nramp-like genes existing in the A. hypogaea, A. duranensis and A. ipaensis, respectively. The 50 peanut NRAMP genes share conserved architectural characters, and they were classified into two groups. Expressions of AhNramps, particularly AhNramp4, AhNramp12, AhNramp19, and AhNramp25 could be greatly induced by not only cadmium toxicity, but also copper and zinc stresses. The expression profiles of AhNramp14, AhNramp16 and AhNramp25 showed significant differences in the H108 (resistance) and H107 (susceptible) under the infection of bacterial wilt. In addition, we found that the expression profiles of AhNramp14, AhNramp16, and AhNramp25 were greatly up- or down-regulated by the application of exogenous salicylic acid, methyl jasmonate, and abscisic acid. The AhNramp25, of which expression was affected by both heavy metal toxicity and bacterial wilt infection, were selected as strong candidate genes for peanut stress breeding. Our findings will provide an additional information required for further analysis of AhNramps involved in tolerance to heavy metal toxicity and resistance to bacterial wilt of peanut.

Progress in phytoremediation of chromium from the environment

As chromium (Cr) in ecosystems affects human health through food chain exposure, phytoremediation is an environmentally friendly and efficient way to reduce chromium pollution in the environment. Here, we review the mechanism of absorption, translocation, storage, detoxification, and regulation of Cr in plants. The Cr(VI) form is more soluble, mobile, and toxic than Cr(III), reflecting how various valence states of Cr affect environmental risk characteristics, physicochemical properties, toxicity, and plant uptake. Plant root's response to Cr exposure leads to reactive oxygen species (ROS) generation and apoptosis. Cell wall immobilization, vacuole compartmentation, interaction of defense proteins and organic ligand with Cr, and removal of reactive oxygen species by antioxidants continue plant life. In addition, the combined application of microorganisms, genetic engineering, and the addition of organic acids, nanoparticles, fertilization, soil amendments, and other metals could accelerate the phytoremediation process. This review provides efficient methods to investigate and understand the complex changes of Cr metabolism in plants. Preferably, fast-growing, abundantly available biomass species should be modified to mitigate Cr pollution in the environment as these green and efficient remediation technologies are necessary for the protection of soil and water ecology.

Biological and green remediation of heavy metal contaminated water and soils: A state-of-the-art review

Contamination of the natural ecosystem by heavy metals, organic pollutants, and hazardous waste severely impacts on health and survival of humans, animals, plants, and microorganisms. Diverse chemical and physical treatments are employed in many countries, however, the acceptance of these treatments are usually poor because of taking longer time, high cost, and ineffectiveness in contaminated areas with a very high level of metal contents. Bioremediation is an eco-friendly and efficient method of reclaiming contaminated soils and waters with heavy metals through biological mechanisms using potential microorganisms and plant species. Considering the high efficacy, low cost, and abundant availability of biological materials, particularly bacteria, algae, yeasts, and fungi, either in natural or genetically engineered (GE) form, bioremediation is receiving high attention for heavy metal removal. This report comprehensively reviews and critically discusses the biological and green remediation tactics, contemporary technological advances, and their principal applications either in-situ or ex-situ for the remediation of heavy metal contamination in soil and water. A modified PRISMA review protocol is adapted to critically assess the existing research gaps in heavy metals remediation using green and biological drivers. This study pioneers a schematic illustration of the underlying mechanisms of heavy metal bioremediation. Precisely, it pinpoints the research bottleneck during its real-world application as a low-cost and sustainable technology.

Mini-review: Lipid flippases as putative targets for biotechnological crop improvement

An increasing world population and drastic changes in weather conditions are challenging agricultural production. To face these challenges and ensure sustainable food production in the future, crop plants need to be improved to withstand several different biotic and abiotic stresses. Commonly, breeders select varieties that can tolerate a specific type of stress and then cross these varieties to stack beneficial traits. This strategy is time-consuming and strictly dependent on the stacked traits been genetically unlinked. Here, we revise the role of plant lipid flippases of the P4 ATPase family in stress-related responses with a special focus on the pleiotropic nature of their functions and discuss their suitability as biotechnological targets for crop improvement.

The effects of different electrode materials on seed germination of Solanum nigrum L. and its Cd accumulation in soil

The effects of different electrode on Solanum nigrum L. seed germination were determined. The result showed that germination percentage (GP) of seeds in treatment T2 (titanium electrode) was 26.6% higher than in control (CK, without electric field). High potassium and calcium concentrations were beneficial for seed enzymatic activity in treatment T2, which could partly explain the increase in GP. Cd accumulation (μg/pot) in S. nigrum treated with any electric field was significantly higher (p<0.05) than in CK without electric field. Specifically, Cd accumulation under the treatment T3 (stainless steel electrode) was the highest both in roots and shoots; this accumulation in shoots and roots were 74.7 % and 67.4 % higher for stainless steel than in CK. This increase must have been associated with a higher Cd concentration in plants and did not exert a significant effect on the biomass. In particular, Cd concentrations in roots and shoots under stainless steel treatment were both significantly higher than in CK (p<0.05), which had to be related to the higher available Cd concentration in the soil in the middle region. Furthermore, it could be attributed to altered soil pH and other soil properties. Moreover, none of the biomasses were significantly affected (p<0.05) by different electrode materials compared to CK.

Soil Remediation: Towards a Resilient and Adaptive Approach to Deal with the Ever-Changing Environmental Challenges

Pollution from numerous contaminants due to many anthropogenic activities affects soils quality. Industrialized countries have many contaminated sites; their remediation is a priority in environmental legislation. The aim of this overview is to consider the evolution of soil remediation from consolidated invasive technologies to environmentally friendly green strategies. The selection of technology is no longer exclusively based on eliminating the source of pollution but aims at remediation, which includes the recovery of soil quality. “Green remediation” appears to be the key to addressing the issue of remediation of contaminated sites as it focuses on environmental quality, including the preservation of the environment. Further developments in green remediation reflect the aim of promoting clean-up strategies that also address the effects of climate change. Sustainable and resilient remediation faces the environmental challenge of achieving targets while reducing the environmental damage caused by clean-up interventions and must involve an awareness that social systems and environmental systems are closely connected.

Arabidopsis P4 ATPase-mediated cell detoxification confers resistance to Fusarium graminearum and Verticillium dahliae

Many toxic secondary metabolites produced by phytopathogens can subvert host immunity, and some of them are recognized as pathogenicity factors. Fusarium head blight and Verticillium wilt are destructive plant diseases worldwide. Using toxins produced by the causal fungi Fusarium graminearum and Verticillium dahliae as screening agents, here we show that the Arabidopsis P4 ATPases AtALA1 and AtALA7 are responsible for cellular detoxification of mycotoxins. Through AtALA1-/AtALA7-mediated vesicle transport, toxins are sequestered in vacuoles for degradation. Overexpression of AtALA1 and AtALA7 significantly increases the resistance of transgenic plants to F. graminearum and V. dahliae, respectively. Notably, the concentration of deoxynivalenol, a mycotoxin harmful to the health of humans and animals, was decreased in transgenic Arabidopsis siliques and maize seeds. This vesicle-mediated cell detoxification process provides a strategy to increase plant resistance against different toxin-associated diseases and to reduce the mycotoxin contamination in food and feed.

Molecular Mechanisms of Nitric Oxide (NO) Signaling and Reactive Oxygen Species (ROS) Homeostasis during Abiotic Stresses in Plants

Abiotic stressors, such as drought, heavy metals, and high salinity, are causing huge crop losses worldwide. These abiotic stressors are expected to become more extreme, less predictable, and more widespread in the near future. With the rapidly growing human population and changing global climate conditions, it is critical to prevent global crop losses to meet the increasing demand for food and other crop products. The reactive gaseous signaling molecule nitric oxide (NO) is involved in numerous plant developmental processes as well as plant responses to various abiotic stresses through its interactions with various molecules. Together, these interactions lead to the homeostasis of reactive oxygen species (ROS), proline and glutathione biosynthesis, post-translational modifications such as S-nitrosylation, and modulation of gene and protein expression. Exogenous application of various NO donors positively mitigates the negative effects of various abiotic stressors. In view of the multidimensional role of this signaling molecule, research over the past decade has investigated its potential in alleviating the deleterious effects of various abiotic stressors, particularly in ROS homeostasis. In this review, we highlight the recent molecular and physiological advances that provide insights into the functional role of NO in mediating various abiotic stress responses in plants.

Characterization of the biochemical basis for copper homeostasis and tolerance in Biscutella auriculata L

Biscutella auriculata L. is a plant that belongs to the Brassicaceae family and it has been found growing in a metal-contaminated area of the San Quíntín mine (Ciudad Real, Spain). The purpose of this work was to evaluate the mechanisms that allow this plant to tolerate high concentrations of copper. Seedlings were grown in a semi-hydroponic system for 15 days under 125 μM of Cu (NO₃ )₂ . Exposure to copper resulted in growth inhibition and reduction in the photosynthetic parameters. Copper was mainly accumulated in vascular tissue and vacuoles of the roots and only a minor proportion was transferred to the shoot. Biothiol analysis showed a greater enhancement of reduced glutathione in leaves and increases of phytochelatins (PC2 and PC3) in both leaves and roots. Copper treatment induced oxidative stress, which triggered a response of the enzymatic and non-enzymatic antioxidant mechanisms. The results show that B. auriculata is able to tolerate high metal levels through the activation of specific mechanisms to neutralize the oxidative stress produced and also by metal sequestration through phytochelatins. The preferential accumulation of copper in roots provides clues for further studies on the use of this plant for phytostabilization and environmental recovery purposes in Cu-contaminated areas.

Role of potassium transporter KUP8 in plant responses to heavy metals

Heavy metal concentrations, which have been increasing over the last 200 years, affect soil quality and crop yields. These elements are difficult to eliminate from soils and may constitute a human health hazard by entering the food chain. Recently, we obtained a selection of mutants with different degrees of tolerance to a mixture of heavy metals (HMmix) in order to gain a deeper insight into the underlying mechanism regulating plant responses to these elements. In this study, we characterized the mutant obtained Atkup8 (in this work, Atkup8-2), which showed one of the most resistant phenotypes, as determined by seedling root length. Atkup8-2 is affected in the potassium transporter KUP8, a member of the high-affinity K⁺ uptake family KUP/HAK/KT. Atkup8-2 mutants, which are less affected as measured by seedling root length under HMmix conditions, showed a resistant phenotype with respect to WT seedlings which, despite their delayed growth, are able to develop true leaves at levels similar to those under control conditions. Adult Atkup8-2 plants had a higher fresh weight than WT plants, a resistant phenotype under HMmix stress conditions and lower levels of oxidative damage. KUP8 did not appear to be involved in heavy metal or macro- and micro-nutrient uptake and translocation from roots to leaves, as total concentrations of these elements were similar in both Atkup8-2 and WT plants. However, alterations in cellular K⁺ homeostasis in this mutant cannot be ruled out.

Lipid flippases as key players in plant adaptation to their environment

Lipid flippases (P4 ATPases) are active transporters that catalyse the translocation of lipids between the two sides of the biological membranes in the secretory pathway. This activity modulates biological membrane properties, contributes to vesicle formation, and is the trigger for lipid signalling events, which makes P4 ATPases essential for eukaryotic cell survival. Plant P4 ATPases (also known as aminophospholipid ATPases (ALAs)) are crucial for plant fertility and proper development, and are involved in key adaptive responses to biotic and abiotic stress, including chilling tolerance, heat adaptation, nutrient deficiency responses and pathogen defence. While ALAs present many analogies to mammalian and yeast P4 ATPases, they also show characteristic features as the result of their independent evolution. In this Review, the main properties, roles, regulation and mechanisms of action of ALA proteins are discussed.

Enhancing phytoremediation of hazardous metal(loid)s using genome engineering CRISPR-Cas9 technology

Rapid and drastic changes in the global climate today have given a strong impetus to developing newer climate-resilient phytoremediation approaches. These methods are of great public and scientific importance given the urgency of this environmental crisis. Climate change has adverse effects on the growth, outputs, phenology, and overall productivity of plants. Contamination of soil with metal(loid)s is a major worldwide problem. Some metal(loids) are carcinogenic pollutants that have a long half-life and are non-degradable in the environment. There are many instances of the potential link between chronic heavy metal exposure and human disease. The adaptation of plants in the changing environment is, however, a major concern in phytoremediation practice. The creation of climate-resistant metal hyperaccumulation plants using molecular techniques could provide new opportunities to mitigate these problems. Consequently, advancements in molecular science would accelerate our knowledge of adaptive plant remediation/resistance and plant production in the context of global warming. Genome modification using artificial nucleases has the potential to enhance phytoremediation by modifying genomes for a sustainable future. This review focuses on biotechnology to boost climate change tolerant metallicolous plants and the future prospects of such technology, particularly the CRISPR-Cas9 genome editing system, for enhancing phytoremediation of hazardous pollutants.

Abandoned Mine Lands Reclamation by Plant Remediation Technologies

Abandoned mine lands (AMLs), which are considered some of the most dangerous anthropogenic activities in the world, are a source of hazards relating to potentially toxic elements (PTEs). Traditional reclamation techniques, which are expensive, time-consuming and not well accepted by the general public, cannot be used on a large scale. However, plant-based techniques have gained acceptance as an environmentally friendly alternative over the last 20 years. Plants can be used in AMLs for PTE phytoextraction, phytostabilization, and phytovolatilization. We reviewed these phytoremediation techniques, paying particular attention to the selection of appropriate plants in each case. In order to assess the suitability of plants for phytoremediation purposes, the accumulation capacity and tolerance mechanisms of PTEs was described. We also compiled a collection of interesting actual examples of AML phytoremediation. On-site studies have shown positive results in terms of soil quality improvement, reduced PTE bioavailability, and increased biodiversity. However, phytoremediation strategies need to better characterize potential plant candidates in order to improve PTE extraction and to reduce the negative impact on AMLs.

The transport mechanism of P4 ATPase lipid flippases

P4 ATPase lipid flippases are ATP-driven transporters that translocate specific lipids from the exoplasmic to the cytosolic leaflet of biological membranes, thus establishing a lipid gradient between the two leaflets that is essential for many cellular processes. While substrate specificity, subcellular and tissue-specific expression, and physiological functions have been assigned to a number of these transporters in several organisms, the mechanism of lipid transport has been a topic of intense debate in the field. The recent publication of a series of structural models based on X-ray crystallography and cryo-EM studies has provided the first glimpse into how P4 ATPases have adapted the transport mechanism used by the cation-pumping family members to accommodate a substrate that is at least an order of magnitude larger than cations.

Deciphering lead tolerance mechanisms in a population of the plant species Biscutella auriculata L. from a mining area: Accumulation strategies and antioxidant defenses

The uptake and distribution of Pb and the mechanisms involved in the metal tolerance have been investigated in a mine population of Biscutella auriculata. Seedlings were exposed to 125 μM Pb(NO₃)₂ for 15 days under semihydroponic conditions. The results showed an increase in the size of Pb-treated seedlings and symptoms of toxicity were not observed. ICP-OES analyses showed that Pb accumulation was restricted to root tissue. Imaging of Pb accumulation by dithizone histochemistry revealed the presence of the metal in vacuoles and cell wall in root cells. The accumulation of Pb in vacuoles could be stimulated by an increase in phytochelatin PC2 content. Pb did not promote oxidative damage and this is probably due the increase of antioxidative defenses. In the leaves, Pb produced a significant increase in superoxide dismutase activity, while in roots an increase in catalase and components of the Foyer- Halliwell-Asada cycle were observed. The results indicated that Biscutella auriculata has a high capacity to tolerate Pb and this is mainly due to a very efficient mechanism to sequester the metal in roots and a capacity to avoid oxidative stress. This species could therefore be very useful for phytostabilization and repopulation of areas contaminated with Pb.

Characterization of mechanisms involved in tolerance and accumulation of Cd in Biscutella auriculata L

Biscutella auriculata L. is one of the rare species that is able to grow in a very contaminated mining area in Villamayor de Calatrava (Ciudad Real, Spain). In an effort to understand the mechanisms involved in the tolerance of this plant to high metal concentrations, we grew B. auriculata in the presence of 125 μM Cd(NO₃)₂ for 15 days and analysed different parameters associated with plant growth, nitric oxide and reactive oxygen species metabolism, metal uptake and translocation, photosynthesis rate and biothiol (glutathione and phytochelatins) content. Treatment with Cd led to growth inhibition in both the leaves and the roots, as well as a reduction of photosynthetic parameters, transpiration and stomatal conductance. The metal was mainly accumulated in the roots and in the vascular tissue, although most Cd was detected in areas surrounding their epidermal cells, while in the leaves the metal accumulated mainly in spongy mesophyll, stomata and trichrome. Based on the Cd bioaccumulation (5.93) and translocation (0.15) factors, this species denoted enrichment of the metal in the roots and its low translocation to the upper tissues. Biothiol analysis showed a Cd-dependent increase of reduced glutathione (GSH) as well as the phytochelatins (PC2 and PC3) in both roots and leaves. Cd-promoted oxidative damage occurred mainly in the leaves due to disturbances in enzymatic and nonenzymatic antioxidants, while the roots did not show significant damage as a result of induction of antioxidant defences. It can be concluded that B. auriculata is a new Cd-tolerant plant with an ability to activate efficient metal-sequestering mechanisms in the root surface and leaves and to induce PCs, as well as antioxidative defences in roots.

The front-heavy and back-light nitrogen application mode to increase stem and leaf biomass significantly improved cadmium accumulation in Solanum nigrum L

Differently from the goal of fertilization in agricultural production to enhance the yield of seeds, the aim of present work focused on cadmium (Cd) phytoremediation is to increase the stem and leaf biomasses as much as possible due to they are the main organs of a hyperaccumulator extracting risk elements from soil. This experiment compared the effects of different nitrogen (N) application modes on Cd accumulation from soil by Solanum nigrum L. The results showed that stem and leaf biomasses of S. nigrum reached the maximum values with the N fertilizer application at Mode 4 (50 %: 40 %: 10 %, i.e. the front-heavy and back-light application of nitrogen fertilizer). In particular, application of N as (NH₄)₂SO₄ and CH₄N₂O produced the greatest increases in S. nigrum biomasses compared to the control (CK₂) with no N fertilizer. N concentration of S. nigrum and N fertilizer productivity under its different treatments were consistent with the above results. Similarly, Cd capacities were the highest in shoots of S. nigrum in Mode 4 either due to their Cd concentration without affected by N fertilizers. Thus, Mode 4 N application showed very important scientific merit for effective Cd phytoextraction in the real conditions.

Genome-wide association study (GWAS) reveals genetic loci of lead (Pb) tolerance during seedling establishment in rapeseed (Brassica napus L.)

BACKGROUND

Lead (Pb) pollution in soil has become one of the major environmental threats to plant growth and human health. Safe utilization of Pb contaminated soil by phytoremediation require Pb-tolerant rapeseed (Brassica napus L.) accessions. However, breeding of new B. napus cultivars tolerance to Pb stress has been restricted by limited knowledge on molecular mechanisms involved in Pb tolerance. This work was carried out to identify genetic loci related to Pb tolerance during seedling establishment in rapeseed.

RESULTS

Pb tolerance, which was assessed by quantifying radicle length (RL) under 0 or 100 mg/L Pb stress condition, shown an extensive variation in 472 worldwide-collected rapeseed accessions. Based on the criterion of relative RL > 80%, six Pb-tolerant genotypes were selected. Four quantitative trait loci (QTLs) associated with Pb tolerance were identified by Genome-wide association study. The expression level of nine promising candidate genes, including GSTUs, BCATs, UBP13, TBR and HIPP01, located in these four QTL regions, were significantly higher or induced by Pb in Pb-tolerant accessions in comparison to Pb-sensitive accessions.

CONCLUSION

To our knowledge, this is the first study on Pb-tolerant germplasms and genomic loci in B. napus. The findings can provide valuable genetic resources for the breeding of Pb-tolerant B. napus cultivars and understanding of Pb tolerance mechanism in Brassica species.

Strontium uptake and antioxidant capacity comparisons of low accumulator and high accumulator oat (Avena sativa L.) genotypes

The main object of the present study is to investigate genotypic differences in strontium (Sr) resistance of two oat varieties, including Neimengkeyi-1 (high accumulator) and Bayou-3 (low accumulator). The growth and antioxidant enzyme responses to five Sr concentrations (0, 25, 100, 500, and 1000 mg kg^-1) were compared after 30-day Sr treatment. The shoot-Sr concentrations of Neimengkeyi-1 were higher than those of Bayou-3 in all treatments. The translocation factors of Neimengkeyi-1 in all treatments were greater than 1 and significantly higher than those of Bayou-3. Sr ions did not affect the growth of Neimengkeyi-1. The H₂O₂ contents and the leaf malondialdehyde contents of Neimengkeyi-1 were lower than those of Bayou-3. The activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase of Neimengkeyi-1 were significantly higher than those of Bayou-3. Significant negative correlations were found between H₂O₂ contents and SOD and CAT activities in Neimengkeyi-1. The results of this study suggest that Sr accumulation patterns have significant genotypic differences, and SOD and CAT may play a pivotal role in the detoxification mechanism of Sr.

Role of nitric oxide in plant responses to heavy metal stress: exogenous application versus endogenous production

Anthropogenic activities, such as industrial processes, mining, and agriculture, lead to an increase in heavy metal concentrations in soil, water, and air. Given their stability in the environment, heavy metals are difficult to eliminate and can constitute a human health risk by entering the food chain through uptake by crop plants. An excess of heavy metals is toxic for plants, which have various mechanisms to prevent their accumulation. However, once metals enter the plant, oxidative damage sometimes occurs, which can lead to plant death. Initial production of nitric oxide (NO), which may play a role in plant perception, signalling, and stress acclimation, has been shown to protect against heavy metals. Very little is known about NO-dependent mechanisms downstream from signalling pathways in plant responses to heavy metal stress. In this review, using bioinformatic techniques, we analyse studies of the involvement of NO in plant responses to heavy metal stress, its possible role as a cytoprotective molecule, and its relationship with reactive oxygen species. Some conclusions are drawn and future research perspectives are outlined to further elucidate the signalling mechanisms underlying the role of NO in plant responses to heavy metal stress.

Differences of Cd uptake and expression of OAS and IRT genes in two varieties of ryegrasses

Pot experiment was conducted to study the difference of cadmium uptake and OAS and IRT genes' expression between the two ryegrass varieties under cadmium stress. The results showed that with the increase of cadmium levels, the dry weights of roots of the two ryegrass varieties, and the dry weights of shoots and plants of Abbott first increased and then decreased. When exposed to 75 mg kg^-1 Cd, the dry weights of shoot and plant of Abbott reached the maximum, which increased by 11.13 and 10.67% compared with the control. At 75 mg kg^-1 Cd, cadmium concentrations in shoot of the two ryegrass varieties were higher than the critical value of Cd hyperaccumulator (100 mg kg^-1), 111.19 mg kg^-1 (Bond), and 133.69 mg kg^-1 (Abbott), respectively. The OAS gene expression in the leaves of the two ryegrass varieties showed a unimodal curve, which was up to the highest at the cadmium level of 150 mg kg^-1, but fell back at high cadmium levels of 300 and 600 mg kg^-1. The OAS gene expression in Bond and Abbott roots showed a bimodal curve. The OAS gene expression in Bond root and Abbott stem mainly showed a unimodal curve. The expression of IRT genes family in the leaves of ryegrass varieties was basically in line with the characteristics of unimodal curve, which was up to the highest at cadmium level of 75 or 150 mg kg^-1, respectively. The IRT expression in the ryegrass stems showed characteristics of bimodal and unimodal curves, while that in the roots was mainly unimodal. The expression of OAS and IRT genes was higher in Bond than that in Abbott due to genotype difference between the two varieties. The expression of OAS and IRT was greater in leaves than that in roots and stems. Ryegrass tolerance to cadmium can be increased by increasing the expression of OAS and IRT genes in roots and stems, and transfer of cadmium from roots and stems to the leaves can be enhanced by increasing expression OAS and IRT in leaves.

Catch You on the Flip Side: A Critical Review of Flippase Mutant Phenotypes

Lipid flippases are integral membrane proteins that use ATP hydrolysis to power the generation of phospholipid asymmetry between the two leaflets of biological membranes, a process essential for cell survival. Although the first report of a plant lipid flippase was published in 2000, progress in the field has been slow, partially due to the high level of redundancy in this gene family. However, recently an increasing number of reports have examined the physiological function of lipid flippases, mainly in Arabidopsis thaliana. In this review we aim to summarize recent findings on the physiological relevance of lipid flippases in plant adaptation to a changing environment and caution against misinterpretation of pleiotropic effects in genetic studies of flippases.

Differences of Cd uptake and expression of MT family genes and NRAMP2 in two varieties of ryegrasses

In order to understand the mechanism of the difference of Cd absorption and Cd enrichment in different ryegrass varieties, pot experiment was conducted to study on the response of two varieties of ryegrass (Bond and Abbott) to Cd stress as well as the differences of Cd uptake and expression of MT family genes and NRAMP2. Results showed that root dry weights of two varieties and shoot dry weights of Abbott increased first and then decreased with the increase of Cd level in soil. When exposed to 75 mg kg^-1 Cd, shoot dry weight and plant dry weight of Abbott both reached maximum values (10.92 and 12.03 g pot^-1), which increased by 11.09 and 10.67% compared with the control, respectively. Shoot dry weight and plant dry weight of Bond decreased with the increase of Cd level in soil. When the Cd level in soil was 75 mg kg^-1, shoot Cd concentrations of the two varieties were 111.19 mg kg^-1 (Bond) and 133.69 mg kg^-1 (Abbott), respectively, both of which exceeded the critical value of Cd hyperaccumulator (100 mg kg^-1). The expression of MT gene family and NRAMP2 in the leaf of Bond variety significantly increased at the Cd level of 75 mg kg^-1 and reached maximum value (except MT2C) at Cd level of 150 mg kg^-1. The expression of MT gene family in the stem of Bond variety showed a double-peak pattern, while the expression of NRAMP2 was a single-peak pattern. The expression of MT gene family and NRAMP2 in Abbott variety was consistent with single-peak pattern. The expression of MT gene family and NRAMP2 in leaf both significantly increased at Cd level of 150 mg kg^-1, while that in stem and root significantly increased at Cd level of 75 mg kg^-1. For both varieties of ryegrass, the expression amount of MT family genes and Nramp2 in leaf was higher than that in root and stem, indicating the Cd tolerance of ryegrass can be improved by increasing the expression levels of MT family genes and Nramp2 in stem and root. There was significant genotypic difference in the expression of MT gene family and NRAMP2 between the two varieties of ryegrass, and the expression of MT gene family and NRAMP2 in leaves and stems of Bond variety was higher than that in Abbott variety, while the expression of MT gene family and NRAMP2 in roots of Abbott variety was higher than that in Bond variety. The two gene families investigated in this study may be closely related to Cd uptake, but not related to Cd transport from root to leaf and Cd enrichment in shoot.

Cytokinin at the Crossroads of Abiotic Stress Signalling Pathways

Cytokinin is a multifaceted plant hormone that plays major roles not only in diverse plant growth and development processes, but also stress responses. We summarize knowledge of the roles of its metabolism, transport, and signalling in responses to changes in levels of both macronutrients (nitrogen, phosphorus, potassium, sulphur) and micronutrients (boron, iron, silicon, selenium). We comment on cytokinin's effects on plants' xenobiotic resistance, and its interactions with light, temperature, drought, and salinity signals. Further, we have compiled a list of abiotic stress-related genes and demonstrate that their expression patterns overlap with those of cytokinin metabolism and signalling genes.