Brassinosteroids and Plant Responses to Heavy Metal Stress. An Overview

Soil contamination with heavy metals has become a world-wide problem, leading to the loss in agricultural productivity. Plants have a remarkable ability to take up and accumulate heavy metals from their external environment and it is well known that high levels of heavy metals affect different physiological and metabolic processes. Brassinosteroids are considered as the sixth class of plant hormones and they are essential for plant growth and development. These compounds are able of inducing abiotic stress tolerance in plants. In this paper, information about brassinosteroids and plant responses to heavy metal stress is reviewed.

Effect of Heavy Metal Stress on Seed Germination of Albizia julibrissin

[Objectives]This study was conducted to investigate the effects of different heavy metal stresses on seed germination,in order to provide a theoretical basis for phytoremediation of soil heavy metal pollution.[Methods]With the seeds of A.julibrissin as an experimental material,the germination test of A.julibrissin seeds under different concentrations of Cu^(2+),Zn^(2+) and Pb^(2+) was carried out.The germination potential,germination rate,germination index,radicle length,embryo length and other indexes were measured.[Results]①Different heavy metals had different effects on the germination of A.julibrissin seeds.Low concentrations of Cu^(2+),Zn^(2+) and Pb^(2+) stresses had certain promotion effects on the germination of A.julibrissin seeds,but high concentrations of Cu^(2+),Zn^(2+),Pb^(2+) stresses had obvious inhibitory effects on the germination of A.julibrissin seeds.②There were obvious differences in the tolerance of A.julibrissin seeds to different metal ion stresses.According to the comparison of the average values of membership functions,the order of their tolerance to different heavy metal ions was:Zn^(2+)>Cu^(2+)>Pb^(2+).[Conclusions]In the case of light pollution,the germination of A.julibrissin seeds was not inhibited,and the use of this plant for the remediation of lightly contaminated soil with heavy metals can also be considered.

Accumulation behavior of heavy metals by Bidens pilosa L.from metallurgical slag:effects on plant physiology and absorption characteristics

Many of the abandoned mining and industrial land in villages and towns are seriously polluted by heavy metals in China,it is necessary for sustainable development to adopt efficient and economical ways to restore the ecology of abandoned mining and industrial land.Pollution level of topsoil contaminated with metallurgical slag from nonferrous metal smelting waste site in Baoding,North China and the heavy metals(HMs)accumulation behavior of Bidens pilosa L.(B.pilosa,native pioneer plant)were studied.Two selected study sites were mainly contaminated by As(270~434 mg/kg),Cd(63~95 mg/kg),Pb(5496~24504 mg/kg)and Zn(4500~21300 mg/kg),which exceed the national standard severely.Investigation of multi-metal accumulation in different parts of B.pilosa indicated that the absorption of toxic metals varied by types,concentration and species of HMs under stress conditions,soil property and plant tissues.The results showed that B.pilosa had excellent ability to accumulate HMs under different HMs stress condition,with the highest accumulation concentration of 85 mg/kg for As,380 mg/kg for Cd,4000 mg/kg for Pb,and 7500 mg/kg for Zn in roots under experimental conditions,respectively.The growth trend of B.pilosa declined with the increase of HMs stress concentration in tested soils.HMs stress led to different degrees of plant toxicity and obstruction of physiological metabolism.Among the plant physiological index,Chla and ChlT decreased 28.0%and 28.1%,37.3%and 35.5%under different stress treatments,respectively.Indicators related to physiological metabolic strength and stress resistance of plant,such as MDA(Malondiadehyde),CAT(catalase),SOD(superoxide dismutase)and SP(soluble protein),all increased with the increase of HMs stress concentration.

Advances in Research on Effect of Heavy Metals Cd and Pb on Wheat and Mitigation Effect of Conditioners

In this article,the effect of heavy metals Cd and Pb on seed germination,seedling growth and yield of wheat is investigated,and the effect of related conditioners on improving soil and alleviating Cd and Pb stress is explored.

Cd and Hg Mediated Oxidative Stress,Antioxidative Metabolism and Molecular Changes in Soybean(Glycine max L.)

Cadmium(Cd)and Mercury(Hg)is among the heavy metals most hazardous for plant and human health.Known to induce oxidative stress in plants and disbalance equilibrium in the antioxidant defence system,these metals alter plant growth and cause damage at the cellular and molecular levels.Soybean is an important oilseed crop that is raised in soils often contaminated by Cd and Hg.The comparative studies on the deleterious effect of Cd and Hg and the defence system of antioxidants were not studied earlier in soybean plant.In this study,soybean plants were exposed to Cd(100μM CdCl_(2))and Hg(100μM HgCl_(2))and studied for physiological,biochemical and molecular responses.Both Cd and Hg treatment increased the magnitude of oxidative stress.Activities of antioxidant enzymes were significantly upregulated in response to Cd and Hg stress.Quantitative and qualitative assessment of isolated RNA showed significant differences in RNA under stress.Integrity values of RNA confirmed alterations.Transcript level of the Actin gene,involved in the morphogenesis of plants and also used as referenced gene in expression studies was analyzed using qRT-PCR just to check its stability and response under heavy metal stress.Results showed significant upregulation of the gene in the presence of Cd.It can be concluded that both Cd and Hg caused oxidative damage to plants,and adversely affected the quality of RNA.However,soybean tried to limit the adverse impacts of Cd and Hg stress by elevating the antioxidant system and upregulating Actin gene.

Genomics,transcriptomics,and peptidomics of the greater wax moth Galleria mellonella neuropeptides and their expression in response to lead stress

Neuropeptides are crucial in regulation of a rich variety of developmental,physiological,and behavioral functions throughout the life cycle of insects.Using an integrated approach of multiomics,we identified neuropeptide precursors in the greater wax moth Galleria mellonella,which is a harmful pest of honeybee hives with a worldwide distribution.Here,a total of 63 and 67 neuropeptide precursors were predicted and annotated in the G.mellonella genome and transcriptome,in which 40 neuropeptide precursors were confirmed in the G.mellonella peptidome.Interestingly,we identified 12 neuropeptide precursor genes present in G.mellonella but absent in honeybees,which may be potential novel pesticide target sites.Honeybee hives were contaminated with heavy metals such as lead,enabling its bioaccumulation in G.mellonella bodies through the food chain,we performed transcriptome sequencing to analyze the effects of Pb stress on the mRNA expression level of G.mellonella neuropeptide precursors.After treatment by Pb,the expression of neuropeptide F1 was found to be significantly downregulated,implying that this neuropeptide might be associated with responding to the heavy metal stress in G.mellonella.This study comprehensively identified neuropeptide precursors in G.mellonella,and discussed the effects of heavy metals on insect neuropeptides,with the example of G.mellonella.The results are valuable for future elucidation of how neuropeptides regulate physiological functions in G.mellonella and contribute to our understanding of the insect's environmental plasticity and identify potential new biomarkers to assess heavy metal toxicity in insects.

Research Progress of Maternal Environmental Effects in Resource-based Regions

Heavy metal pollution is common in resource-based regions.However,the morphological,physiological and biochemical mechanisms of plants transmitting environmental information to their offspring in environments polluted by heavy metals have not been studied yet.Taking soybean,an annual self-pollinated plant in Huang-Huai-Hai region,as the research object,the morphological,physiological and biochemical indexes and heavy metal enrichment and distribution characteristics of plants under heavy metal stress were monitored continuously for about three generations,and the trans-generational differences of soybean reproduction,vegetative growth,stress resistance and life cycle in heavy metal stress environment were elucidated.The results will be helpful to better understand the long-term adaptive strategy of plants to heavy metal stress and provide the theory basis for ecological security of soybean and other crops under heavy metal stress.

Effects of Cadmium on Polar Lipid Composition and Unsaturation in Maize(Zea mays) in Hydroponic Culture

This study aimed to evaluate the effect of Cd exposure （100 μmol/L） on polar lipid composition, and to examine the level of fatty acid unsaturation in maize （Zea mays L.）. In roots, the level of 16：0 and monounsaturated fatty acids （16：1 ＋ 18：1） decreased in phosphatidylcholine （PC） and phosphatidylethanolamine （PE）. In contrast, the proportion of unsaturated 18-C fatty acid species showed an opposite response to Cd. The content, on the other hand, of PC, PE, digalactosyldiacylglycerol （DGDG）, and steryl lipids increased in roots （2.9-, 1.6-, 5.3-, and 1.7-fold increase, respectively）. These results suggest that a more unsaturated fatty acid composition than found in control plants with a concomitant increase in polar lipids may favor seedling growth during Cd exposure. However, the observed increase in the steryl lipid （SL） ： phospholipid （PL） ratio （twofold）, the decrease in monogalactosyldiacylglycerol （MGDG） ： DGDG ratio, as well as the induction of lipid peroxidation in roots may represent symptoms of membrane injury. In shoots, the unsaturation level was markedly decreased in PC and phosphatidylglycerol （PG） after Cd exposure, but showed a significant increase in sulfoquinovosyldiacylglycerol （SQDG）, MGDG and DGDG. The content of PG and MGDG was decreased by about 65%, while PC accumulated to higher levels （4.4-fold increase）. Taken together, these changes in the polar lipid unsaturation and composition are likely to be due to alterations in the glycerolipid pathway. These results also support the idea that the increase in overall unsaturation plays some role in enabling the plant to withstand the metal exposure.

Mutualistic fungus Piriformospora indica modulates cadmium phytoremediation properties of host plant via concerted action of enzymatic and non-enzymatic biochemicals

Soils and ecosystems contaminated with cadmium (Cd) threaten human health and adversely affect morphological,physiological,and biochemical parameters of plants.The symbiotic association of endophytic fungi with their host plants is the best strategy to improve various plant characteristics and remediate soils polluted with heavy metal(loid)s (HMs).Being a well-known plant growth-promoting fungus,Piriformospora indica confers resistance against a number of abiotic stresses,including HM stress.This pot experiment explored the potential and ameliorative effects of P.indica on Artemisia annua L.plants treated with different concentrations (0,40,80,and 120 mg kg-1) of Cd.Inoculation with P.indica significantly increased plant performance,especially by enhancing chlorophyll concentration and water potential and by decreasing electrolytic leakage,when compared with un-inoculated plants,despite the high Cd levels.Similarly,P.indica enhanced antioxidant enzyme activities,thereby reducing the drastic effects of Cd in inoculated plants.In addition,P.indica accumulated Cd in the roots of colonized plants,as revealed by atomic absorption spectroscopy,and restricted Cd translocation to aerial parts.Furthermore,P.indica showed in vitro resistance (up to a certain level) to Cd stress;however,fungus growth was inhibited at very high Cd concentrations,proving it an excellent candidate for use as a potential phytoremediator in fields affected by Cd contamination.The transcriptional analysis showed that the signaling genes and artemisinin and flavonoid biosynthetic pathway genes were significantly upregulated in P.indica-co-cultivated plants when compared with un-inoculated plants,suggesting a fine collaboration between primary and secondary metabolisms to modulate resistance capacity and to enhance the phytoremediation capability of A.annua against Cd toxicity.