Advances in Understanding Cadmium Stress and Breeding of Cadmium-Tolerant Crops

Cadmium(Cd) pollution has emerged as a critical global environmental concern, due to its significant toxicity, environmental persistence, and the pervasiveness of contamination. Significantly, the bioaccumulation of Cd in agricultural crops constitutes a primary vector for its entry into the human diet. This issue warrants urgent attention from both the scientific community and policymakers to develop and implement effective mitigation strategies. This review delves into the physiological impacts of Cd stress on plants, including the suppression of photosynthetic activity, amplification of oxidative stress, and disruptions in mineral nutrient homeostasis. Additionally, the resistance mechanisms deployed by plants in response to Cd stress have been explored, and the prospective contributions of molecular breeding strategies in augmenting crop tolerance to Cd and minimizing its bioaccumulation have been assessed. By integrating and analyzing these findings, we seek to inform future research trajectories and proffer strategic approaches to enhance agricultural sustainability, safeguard human health, and protect environmental integrity.

Cloning of PsMYB62 and analysis of cadmium resistant in Potentilla sericea

Potentilla sericea is a heavy metal hyperaccumulator landscaping plant.MYB transcription factors play an important role in regulating plant stress response to adversity.However,there are few studies on MYB transcription factors in stress tolerance in Potentilla sericea.In this study,the PsMYB62 gene was successfully cloned from Potentilla sericea.Methods:Bioinformatic analysis and real-time quantitative PCR(qPCR)methods were used to evaluate this gene.The transgenic A.thaliana were obtained by flower dipping and the gene function was identified by determining physiological indicators under cadmium stress.Results:The open reading frame of PsMYB62 is 942 bp,which encodes 313 amino acids(aa)and belongs to the R2R3 MYB transcription factor.The plant overexpression vector PBI121-PsMYB62-GFP was constructed and successfully transferred into A.thaliana.The relative expression level of PsMYB62 was significantly increased by CdCl_(2),NaCl,ABA,and mannitol treatments.The germination rate of transgenic seeds was higher than those of wild type(WT)and empty vector(EV)under different concentrations of cadmium treatment.Upon treatment with 100μmol·L^(−1)of CdCl_(2)·2.5H_(2)O,the activities of superoxide dismutase(SOD),peroxidase(POD),and catalase(CAT)in the transgenic plants were significantly higher than those in the WT and EV.The contents of H_(2)O_(2),O_(2)·−and malondialdehyde(MDA)in transgenic lines were increased,but lower than those in WT and EV.The expression levels of AtGSH,AtPCS,and AtNAS4 that were related to the regulation of cadmium were increased,but the expression levels of transgenic lines were higher than those of WT and EV.Conclusion:The above results showed that PsMYB62 could be induced by cadmium and could improve the cadmium resistance of plants.

Effects of Cadmium Stress on Key Enzymes Involved in Nitrogen Metabolism and Nitrogen,Phosphorus, Potassium Accumulation of Different Varieties of Rice

In this study, the pot experiment was used to explore the differences of activity of key enzymes involved in N metabolism and NPK accumulation under Cd stress during the til iering stage of differen varieties of rice. The results showed that：Cd stress could increase the NPK concentration of different rice type in the til ering stage, while Shen-Liangyou 5867,Yongyou 5550 and Wu-Yunjing 27 showed the highest amplification respectively. Morever, Cd stress can also contribute to the ac-tivity of NR,GS,GOGAT increasing.A s for NR,the Cd stress significantly contribute to NR activity increasing of Huang-Huazhan and Yongyou 538 but is not significant for Wu-Yunjing 27, Shen-Liangyou 5867 and Yongyou 5550, however, the difference among them is not obvious.However, for the activity of GS , Cd stress promote the GS activity. Huang-Huazhan and Wu-Yunjing 27 with low activity in Cd normal level are the most sensitive. Meanwhile the difference between two treatment is the most significant. To the contrary, restrain the GS activity of Shen-Liangyou 5867, Yongy-ou 5550 and the difference is not significant. And under Cd stress, either difference reached significant in GS activity. Cd stress also improve the activity of GOGAT, Wu-Yunjing 27 showed the highest inprovement which showed the lowest GOGAT activity under Cd normal level. Cd stress on rice growth and development of ad-verse, make its lower seed setting rate, 1 000 grain weight decreased, resulting in different degrees of reduction of output of rice.

Effects of Different Kinds of Exogenous Auxin on the Growth of Rice Roots under Cadmium Stress

[Objective] The aim was to study the effect of different kinds of exogenous auxin on the growth of rice roots under cadmium stress.[Method] Oryza sativa L.cv Zhonghua No.11 was used as experimental materials to detect the effect of different kinds of exogenous auxin on the growth of rice roots.[Result] The results showed that 0.1 mmol/L Cd treatment could not only increase primary,adventitious and lateral root length but also lateral root number,whereas the shoot growth was inhibited.When supplemented with different concentrations of NAA,IAA,IBA and 2,4-D,the growth of root system varied and similar change trend had been found.At the auxin concentration of 10^-9-10^-7 mol/L in particular 10^-8 mol/L,all four kinds of auxin promoted the elongation growth of primary and adventitious roots,but inhibition was observed when auxin was higher than 10^-7 mol/L.The decreased shoot growth caused by Cd could not be counteracted by supplementing with the four kinds of auxin.However,at the auxin concentration of 10^-9-10^-8 mol/L,NAA could improve rice growth under Cd stress condition.The formation and development of lateral roots on primary and adventitious roots was not only similar but also different after applying the same concentration of four auxins.[Conclusion] The addition of suitable amount of auxin under cadmium stress （such as 10^-9-10^-8 mol/L of NAA and so on） could ease the damage of cadmium on plants to a certain extent.

Effect of Cadmium Stress on the Growth, Antioxidative Enzymes and Lipid Peroxidation in Two Kenaf (Hibiscus cannabinus L.) Plant Seedlings

The effects of cadmium stress on the growth, antioxidative enzymes and lipid peroxidation in two kenaf plants, Fuhong 991 and ZM412, were analysed under control （0.5-strength Hoagland＇s nutrient solution） or five levels of cadmium stress （0.5- strength Hoagland＇s nutrient solution containing different concentrations of Cd2＋）. The leaves and roots of control and cadmium-stressed plants were harvested after 3 wk. At the same Cd concentration, the Cd tolerance index of Fuhong 991 was higher than that of ZM412, indicating that Fuhong 991 may be more tolerant to Cd than ZM412. The superoxide dismutase （SOD）, catalase activity （CAT） and peroxidase （POD） activities fluctuated in the leaves of the Cd-stressed plants compared to the control, whereas the glutathione reductase activity （GR） was much larger than the control for Fuhong 991, ensuring that sufficient quantities of GSH were available to respond to the cadmium stress. In comparison to the control, the dynamic tendency of the SOD, CAT and POD activities in roots of the Cd-stressed plants all increased and then declined, but the POD activity of Fuhong 991 remained nearly unchanged at all of the stress levels. The increase in the enzyme activities demonstrated that Fuhong 991 was more tolerant to cadmium than ZM 412. The lipid peroxidation was enhanced only in the leaves of Cd-stressed ZM 412. These findings indicated that antioxidative activities may play important roles in Cd-stressed Fuhong 991 and ZM 412 and that the leaf and root cell membranes of Fuhong 991 have a greater stability than those of ZM 412. For pollution monitoring purposes, the GR activity in the roots and leaves may serve as a biomarker of Cd for Fuhong 991, whereas lipid peroxidation may serve as biomarker for ZM 412.

Response of Glutathione and Glutathione S-transferase in Rice Seedlings Exposed to Cadmium Stress

A hydroponic culture experiment was done to investigate the effect of Cd stress on glutathione content （GSH） and glutathione S-transferase （GST, EC 2.5.1,18） activity in rice seedlings. The rice growth was severely inhibited when Cd level in the solution was higher than 10 mg/L. In rice shoots, GSH content and GST activity increased with the increasing Cd level, while in roots, GST was obviously inhibited by Cd treatments, Compared with shoots, the rice roots had higher GSH content and GST activity, indicating the ability of Cd detoxification was much higher in roots than in shoots. There was a significant correlation between Cd level and GSH content or GST activity, suggesting that both parameters may be used as biomarkers of Cd stress in rice.

Molecular cloning, sequence analysis, and cadmium stress-rated expression changes of BTG1 in freshwater pearl mussel(Hyriopsis schlegelii)

The B cells translocation gene 1 （BTG1） is a member of the BTG/TOB family of anti-proliferative genes, which have recently emerged as important regulators of cell growth and differentiation among vertebrates. Here, for the first time we cloned the full-length eDNA sequence of Hyriopsis schlegelii （Hs-BTG1）, an economically important freshwater shellfish and potential indicator of environmental heavy metal pollution, for the first time. Using rapid amplification of eDNA ends （RACE） together with splicing the EST sequence from a haemocyte eDNA library, we found that Hs-BTG1 contains a 525 bp open reading frame （ORF） encoding a 174 amino-acid polypeptide, a 306 bp 5＇ untranslated region （5＇ UTR）, and a 571 bp 3＇ UTR with a Poly（A） tail as well as a transcription termination signal （AATAAA）. Homologne searching against GenBank revealed that Hs-BTG1 was closest to Crassostrea gigas BTG1, sharing 50.57% of protein identities. Hs-BTG1 also shares some typical features of the BTG/TOB family, possessing two well-conserved A and B boxes. Clustering analysis of Hs-BTG1 and other known BTGs showed that Hs-BTG1 was also closely related to BTG1 of C. gigas from the invertebrate BTG1 clade. Function prediction via homology modeling showed that both Hs-BTG1 and C. gigas BTG1 share a similar three-dimensional structure with Homo sapiens BTG1. Tissue-specific expression analysis of the Hs-BTG1 via real-time PCR showed that the transcripts were constitutively expressed, with the highest levels in the hepatopancreas and gills, and the lowest in both haemocyte and muscle tissue. Expression levels of Hs-BTG1 in hepatopancreas （2.03-fold）, mantle （2.07-fold）, kidney （2.2-fold） and haemocyte （2.5-fold） were enhanced by cadmium （Cd2＋） stress, suggesting that Hs-BTG 1 may have played a significant role in H, schlegelii adaptation to adverse environmental conditions.

Effect of Biochar on Relieving Cadmium Stress and Reducing Accumulation in Super japonica Rice

It is of great importance to solve the threats induced by cadmium pollution on crops. This paper examined the effect of biochar on cadmium accumulation in japonica rice and revealed the mechanism underlying the response of protective enzyme system to cadmium stress. Biochar derived from rice straw was applied at two application rates under three cadmium concentrations. Shennong 265, super japonica rice variety, was selected as the test crop. The results indicated that cadmium content in above-ground biomass of rice increased with increasing soil cadmium concentrations, but the biochar application could suppress the accumulation of cadmium to some extent. Under high concentrations of cadmium, content of free proline and MDA （malondialdehyde） were high, so did the SOD （superoxide dismutase）, POD （peroxidase） and CAT （catalase） activity in the flag leaf of rice. However, the protective enzyme activities remained at low level when biochar was added.

Effects of Melatonin on Growth,Physiology and Gene Expression in Rice Seedlings Under Cadmium Stress

Melatonin(MLT)is a hormonal substance found in many organisms and can improve plant stress resistance.In this study,the japonica rice variety Y32 and indica rice variety NJ6 were cultivated in hydroponics under different concentrations of CdCl2 at the two-leaf stage.The growth,physiological and biochemical responses of the seedlings and the expression of cadmium(Cd)-related genes under exogenous melatonin(MLT)treatment were assessed.The results indicated that Cd stress destroyed the dynamic balance between reactive oxygen species(ROS)production and removal,resulting in ROS accumulation,membrane lipid peroxidation,and impaired growth and development.Following the application of exogenous MLT to rice seedlings,increases in plant biomass including both underground and above-ground areas were observed.MLT also scavenged the inhibition of superoxide dismutase(SOD)and peroxidase(POD)in a concentration dependent manner in response to Cd stress.Catalase(CAT)activity and malondialdehyde(MDA)expression also decreased following MLT treatment.Amongst the six Cd-related genes assessed,five genes were downregulated and one was up-regulated in response to MLT treatment.Taken together,these data demonstrate that MLT improves the resilience of rice seedlings at the biochemical,physiological,and molecular levels,and diminishes the damage caused by Cd stress.

Effects of Waterlogging Time on Rice Cd Absorption and Accumulation under Cadmium Stress

A pot experiment with exogenous cadmium was utilized to study the effects of waterlogging time on rice yield and Cd accumulationin different growth stages including top tillering stage and filling stage.The results showed that the rice yields of all flooding treatments were lower than the CK(CI).The WI,T1,T2,T3 and T4 decreased significantly by 23.7%,16.0%,15.5%,20.2%and 18.6%respectively.The Cd content of brown rice decreased with the extension of waterlogging time.And WF was the lowest,at only 3.4%of the wet irrigation of the whole growth period(WI).Under the same waterlogging condition,the Cd content in brown rice with 1 to 4 weeks of flooding treatment at the top tillering stage decreased by 27.1%(P﹤0.05),46.6%(P﹤0.05),56.0%(P﹤0.05)and 35.2%(P﹥0.05)respectively,compared with the treatment at the filling stage.And the average decrease was 41.2%.The variation tendency of Cd content in stems and leaves was similar to brown rice.The translocation efficiency of Cd from stems and leaves to rice seeds decreased with the extension of waterlogging time.The Cd enrichment factor of stems and leaves,as well as brown rice,varied greatly with different treatments.Specifically,the Cd enrichment factors in brown rice and in stems and leaves under WI were 28.0 and 17.8 times higher respectively than those under WF.The findings of this study demonstrated that flooding could inhibit the uptake and accumulation of Cd in rice,with significant positive correlation between them.The inhibition effect of flooding treatment on Cd accumulation in rice at the top tillering stage was superior to that at the filling stage.

Effects of Cadmium Stress on the Growth of Rice Seedlings

The seedlings of 6 rice varieties were treated with Cd concentrations of 25,50 and 100μmol/L for 5 d.The results showed that the longest root length,seedling height,fresh weight per plant and dry weight per plant of 6 rice varieties were significantly inhibited.The inhibiting effects showed a trend as the following:the longest root length>fresh weight per plant>dry weight per plant>seedling height,and the inhibiting effect increased with the increase of Cd stress concentration.It is more economical and reasonable to use 50μmol/L Cd stress concentration to identify Cd tolerance of rice seedlings.And it is more scienti fic to evaluate the Cd tolerance of rice seedling comprehensively by using the 4 indexes of longest root length,fresh weight per plant,dry weight per plant and seedling height.

Purification and Identification of Glutathione S-transferase in Rice Root under Cadmium Stress

Cadmium （Cd） contamination in paddy soils poses a serious threat to the production and quality of rice. Among various biochemical processes related to Cd detoxification in rice, glutathione S-transferase （GST） plays an important role, catalyzing Cd complexation with glutathione （GSH） and scavenging reactive oxygen species （ROS） in cells. In this study, a hydroponic experiment was conducted to investigate the response of GST isozymes in rice roots upon Cd exposure. Results showed that the GST activity in rice roots was clearly enhanced by 50 pmol/L Cd treatment for 7 d. The GST isozymes were purified by ammonium sulphate precipitation, gel filtration chromatography and affinity chromatography. After being separated by SDS-PAGE and visualized by silver staining, GSTU6 was identified by in-gel digestion, MALDI-TOF-MS analysis and peptide mass fingerprint. The results confirm the vital function of tau class rice GST in Cd detoxification.

Transcriptome Sequencing and Analysis of Agaricus blazei Mycelia Under Cadmium Stress

To explore the mechanism of Agaricus blazei Murrill enrichment of the heavy metal cadmium,we employed Illumina high-throughput sequencing to analyze the transcriptomes of A.blazei mycelia treated with and without exogenous cadmium addition,and then the differentially expressed genes(DEGs)of the strains with high and low cadmium enrichment between the control and cadmium treatment were screened out.The results showed that the DEGs were mainly involved in steroid biosynthesis,antibiotic biosynthesis,protein processing in endoplasmic reticulum,glutathione metabolism and other pathways.Carbon metabolism and glutathione metabolism may play an important role in the response of A.blazei mycelium to cadmium stress.

Alterations of Antioxidative Enzymes Activities and Induction of Lipid Peroxidation in Germinating Wheat Seeds Subjected to Cadmium Stress

Germinating wheat （Triticum aestivum L.） seeds were exposed to CdCI2 （50, 100 and 200 μM） for 48 h and some aspects of oxidative metabolism was assessed in the embryonic tissues. The germination percentage and the soluble protein content of the embryonic tissues were found to decrease with increasing of Cd concentration. There was elevation in superoxide dismutase （SOD） and decline in catalase （CAT） and peroxidase （POX） activities. The increasing of lipid peroxidation levels indicated the prevalence of oxidative stress in the tissues which was probably due to the alteration of antioxidative enzymes activities. The adding of ascorbate, along with CdCl2, has resulted in restoration of the Cd induced decline in CAT activity. Weakening in H2O2 detoxification system seems to be the principal reason behind Cd induced oxidative stress in germinating seeds. Thus, imposition of oxidative stress might be the consequence of cadmium stress and this finding may help in elucidating the mechanisms underlying cadmium mediated toxicity in germinating seeds.

Oxidative stress responses to cadmium in the seedlings of a commercial seaweed Sargassum fusiforme

Cadmium(Cd)is a common heavy metal pollutant in the aquatic environment,generally toxic to plant growth and leading to growth inhibition and biomass reduction.To study the oxidation resistance in Sargassum fusiforme seedlings in response to inorganic Cd stress,we cultured the seedlings under two different Cd levels:natural seawater and high Cd stress.High Cd stress significantly inhibited the seedlings growth,and darkened the thalli color.Additionally,the pigment contents,growth rate,peroxidase(POD)activity,dehydroascorbic acid(DHA)content,and glutathione reductase(GR)activity in S.fusiforme were significantly reduced by high Cd treatment.Contrarily,the Cd accumulation,Cd2+absorption rate,dark respiration/net photosynthetic rate(Rd/Pn),ascorbic acid(Vc)content,soluble protein(SP)content,glutathione(GSH),and the activities of superoxide dismutase(SOD)and catalase(CAT)of S.fusiforme under Cd treatment significantly increased compared to the control group.The decrease of malondialdehyde(MDA)was not significant.Although S.fusiforme seedlings increased the antioxidant activities of POD,SOD,Vc,and the AsA-GSH cycle to disseminate H2O2 and maintain healthy metabolism,high Cd stress caused Cd accumulation in the stem and leaves of S.fusiforme seedlings.The excessive Cd significantly restricted photosynthesis and reduced photosynthetic pigments in the seedlings,resulting in growth inhibition and deep morphological color,especially of the stems.High levels of Cd in seawater had toxic effects on commercial S.fusiforme seedlings,and risked this edible seaweed for human food.

Physiological Response of Hydrilla verticillata （I.f.） Royle Exposed to Cadmium Stress

Hydrilla verticillata （I.f.） Royle twigs were exposed to CdCI2 （50, 100, 200 and 500 BM） under continuous light for 48 hrs and the physiological parameters like photosynthetic pigment （chlorophylls a, b and carotenoids） contents, activities of antioxidative enzymes like superoxide dismutase （SOD）, catalase （CAT） and peroxidase （POX） along with lipid peroxidation level were determined. With respect to increase in Cd concentration in the medium and exposure duration, decrease in pigment contents, and decrease in the activities of SOD, CAT and POX were found. The increased levels of lipid peroxidation indicated the prevalence of oxidative stress situation in the tissues which might be one of the reasons behind Cd induced toxicity in Hydrilla verticillata. Since there was significant decrease in the activities of key antioxidative ezymes, the study suggests that Hydrilla verticillata may not be effective for phytoremediation of cadmium in these concentration ranges.

Role of phosphorus on the biogeochemical behavior of cadmium in the contaminated soil under leaching and pot experiments

Phosphorus(P)is involved in various biochemical reactions in plant growth,so it is beneficial to plants growing in soils contaminated by metals,including cadmium(Cd).However,few studies have reported on the mechanistic roles of P in mitigating Cd toxicity to ryegrass root,and especially in alleviating the disruption of the mitochondrial function of living cells.In this study,the physiological and biochemical mechanisms associated with ryegrass growth under various Cd and P treatments were investigated using leaching and pot systems.The concentration of Cd in soil leachates showed a significantly positive relationship with redox potential(P<0.05),but negative relationship(P<0.05)with leachate pH values and dissolved organic carbon(DOC),indicating that exogenous P addition(as H_(2)PO_(4)*)may decrease Cd leaching from contaminated soil.Compared to the control(without P addition),the cumulative Cd content was reduced by 53.3%and 64.5%in the soil leachate with exogenous P application(20 mg/L and 80 mg/L),respectively.Notably,application of P decreased the Cd concentrations in the symplastic fractions and increased the Cd concentrations in the apoplastic fractions in root tips,which may help to alleviate Cd stress to the protoplast.Moreover,exogenous P was found to play a positive role in mitochondrial function and Ca^(2+)variation in root cells under Cd stress,which provides novel insights into the mechanisms of exogenous P in alleviating plant Cd injury.

Cadmium induced a non-coding RNA microRNA535 mediates Cd accumulation in rice

Identifying key regulators related to cadmium(Cd)tolerance and accumulation is the main factor for genetic engineering to improve plants for bioremediation and ensure crop food safety.MicroRNAs(miRNAs),as fine-tuning regulators of genes,participate in various abiotic stress processes.MiR535 is an ancient conserved non-coding small RNA in land plants,positively responding to Cd stress.We investigated the effects of knocking out(mir535)and overexpressing miR535(mir535 and OE535)under Cd stress in rice plants in this study.The mir535 plants showed better Cd tolerance than wild type(WT),whereas the OE535 showed the opposite effect.Cd accumulated approximately 71.9%and 127%in the roots of mir535 and OE535 plants,respectively,compared to WT,after exposure to 2μmol/L Cd.In brown rice,the total Cd accumulation of OE535 and mir535 was about 78%greater and 35%lower than WT.When growing in 2 mg/kg Cd of soil,the Cd concentration was significantly lower in mir535 and higher in OE535 than in the WT;afterward,we further revealed the most possible target gene SQUAMOSA promoter binding-like transcription factor 7(SPL7)and it negatively regulates Nramp5 expression,which in turn regulates Cd metabolism.Therefore,the CRISPR/Cas9 technology may be a valuable strategy for creating new rice varieties to ensure food safety.

The transcription factor NAC102 confers cadmium tolerance by regulating WAKL11 expression and cell wall pectin metabolism in Arabidopsis

Cadmium(Cd) toxicity severely limits plant growth and development. Moreover, Cd accumulation in vegetables, fruits, and food crops poses health risks to animals and humans. Although the root cell wall has been implicated in Cd stress in plants, whether Cd binding by cell wall polysaccharides contributes to tolerance remains controversial, and the mechanism underlying transcriptional regulation of cell wall polysaccharide biosynthesis in response to Cd stress is unknown. Here, we functionally characterized an Arabidopsis thaliana NAC-type transcription factor, NAC102, revealing its role in Cd stress responses. Cd stress rapidly induced accumulation of NAC102.1, the major transcript encoding functional NAC102, especially in the root apex. Compared to wild type(WT) plants, a nac102 mutant exhibited enhanced Cd sensitivity, whereas NAC102.1-overexpressing plants displayed the opposite phenotype. Furthermore, NAC102 localizes to the nucleus, binds directly to the promoter of WALL-ASSOCIATED KINASE-LIKE PROTEIN11(WAKL11), and induces transcription, thereby facilitating pectin degradation and decreasing Cd binding by pectin. Moreover, WAKL11 overexpression restored Cd tolerance in nac102mutants to the WT levels, which was correlated with a lower pectin content and lower levels of pectin-bound Cd. Taken together, our work shows that the NAC102-WAKL11 module regulates cell wall pectin metabolism and Cd binding, thus conferring Cd tolerance in Arabidopsis.

Hydrogen Peroxide-Mediated Growth of the Root System Occurs via Auxin Signaling Modification and Variations in the Expression of Cell-Cycle Genes in Rice Seedlings Exposed to Cadmium Stress

The link between root growth, H2O2, auxin signaling, and the ceil cycle in cadmium （Cd）-stressed rice （Oryza sativa L. cv. Zhonghua No. 11） was analyzed in this study. Exposure to Cd induced a significant accumulation of Cd, but caused a decrease in zinc （Zn） content which resulted from the decreased expression of OsHMA9 and OsZIP. Analysis using a Cd-specific probe showed that Cd was mainly localized in the meristematic zone and vascular tissues. Formation and elongation of the root system were significantly promoted by 3-amino-l,2,4-triazole （AT）, but were markedly inhibited by N,N＇. dimethylthiourea （DMTU） under Cd stress. The effect of H2O2 on Cd-stressed root growth was further confirmed by examining a gain-of-function rice mutant （carrying catalasel and glutathione-S-transferase） in the presence or absence of diphenylene iodonium. DR5-GUS staining revealed close associations between H2O2 and the concentration and distribution of auxin. H2O2 affected the expression of key genes, including OsYUCCA, OsPIN, OsARF, and OslAA, in the auxin signaling pathway in Cd-treated plants. These results suggest that H2O2 functions upstream of the auxin signaling pathway. Furthermore, H2O2 modified the expression of cell-cycle genes in Cd-treated roots. The effects of H2O2 on root system growth are therefore linked to auxin signal modification and to variations in the expression of cell-cycle genes in Cd-stressed rice. A working model for the effects of H2O2 on Cd-stressed root system growth is thus proposed and discussed in this paper.