Does the different proteomic profile found in apical and basal leaves of spinach reveal a strategy of this plant toward cadmium pollution response?

Phytotoxic effects of polyethylene microplastics combined with cadmium on the photosynthetic performance of maize (Zea mays L.)

Microplastics (MPs) and cadmium (Cd) has attracted increasing attention due to their combined toxicity to terrestrial vegetation. Photosynthesis which utilizes light energy to synthesize organic substances is crucial for crop production. However, the plant photosynthetic response to the joint toxicity of MPs and Cd is still unknown. Here, we studied the effects of polyethylene (PE) MPs on the photosynthetic performance of two maize cultivars Xianyu 335 (XY) and Zhengdan 958 (ZD) grown in a Cd contaminated soil. Results showed that the leaf Cd concentration in XY and ZD reached 26.1 and 31.9 μg g-1, respectively. PE-MPs did not influence the leaf Cd content, but posed direct and negative effects on photosynthesis by increasing the malondialdehyde content, reducing the chlorophyll content, inhibiting photosynthetic capacity, disrupting the PSII donor side, blocking electron transfer in different photosystems, and suppressing the oxidation and reduction states of PSI. Transcriptomic analysis revealed that the inhibitory effect of combined PE-MPs and Cd on maize photosynthesis was attributed to suppressed expression of the genes encoding PSII, PSI, F-type ATPase, cytochrome b6/f complex, and electron transport between PSII and PSI. Using WGCNA, we identified a MEturquoise module highly correlated with photosynthetic traits. Hub genes bridging carbohydrate metabolism, amino acid metabolism, lipid metabolism, and translation provided the molecular mechanisms of PE-MPs and Cd tolerance in maize plants. The comprehensive information on the phytotoxicity mechanisms of Cd stress in the presence or absence of PE-MPs on the photosynthesis of maize is helpful for cloning Cd and PE-MP resistance genes in the future.

Comparative transcriptome analysis of the hyperaccumulator plant Phytolacca americana in response to cadmium stress

To study the molecular mechanism of the hyperaccumulator plant Phytolacca americana against cadmium (Cd) stress, the leaves of P. americana treated with 400 μM Cd for 0, 2, 12, and 24 h were harvested for comparative transcriptome analysis. In total, 110.07 Gb of clean data were obtained, and 63,957 unigenes were acquired after being assembled. Due to the lack of P. americana genome information, only 24,517 unigenes were annotated by public databases. After Cd treatment, 5054 differentially expressed genes (DEGs) were identified. KEGG pathway enrichment analysis of DEGs showed that genes involved in the flavonoid biosynthesis and antenna proteins of photosynthesis were significantly down-regulated, while genes related to the lignin biosynthesis pathway were remarkably up-regulated, indicating that P. americana could synthesize more lignin to cope with Cd stress. Moreover, genes related to heavy metal accumulation, sulfur metabolism and glutathione metabolism were also significantly up-regulated. The gene expression pattern of several key genes related to distinct metabolic pathways was verified by qRT-PCR. The results indicated that the immobilization of lignin in cell wall, chelation, vacuolar compartmentalization, as well as the increase of thiol compounds content may be the important mechanisms of Cd detoxification in hyperaccumulator plant P. americana. Accession numbers: the raw data of P. americana transcriptome presented in this study are openly available in NCBI SRA database, under the BioProject of PRJNA649785.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02865-x.

Selection and Validation of Reference Genes for RT-qPCR Analysis in Spinacia oleracea under Abiotic Stress

Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) is an accurate and convenient method for mRNA quantification. Selection of optimal reference gene(s) is an important step in RT-qPCR experiments. However, the stability of housekeeping genes in spinach (Spinacia oleracea) under various abiotic stresses is unclear. Evaluating the stability of candidate genes and determining the optimal gene(s) for normalization of gene expression in spinach are necessary to investigate the gene expression patterns during development and stress response. In this study, ten housekeeping genes, 18S ribosomal RNA (18S rRNA), actin, ADP ribosylation factor (ARF), cytochrome c oxidase subunit 5C (COX), cyclophilin (CYP), elongation factor 1-alpha (EF1α), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), histone H3 (H3), 50S ribosomal protein L2 (RPL2), and tubulin alpha chain (TUBα) from spinach, were selected as candidates in roots, stems, leaves, flowers, and seedlings in response to high temperature, CdCl₂, NaCl, NaHCO₃, and Na₂CO₃ stresses. The expression of these genes was quantified by RT-qPCR and evaluated by NormFinder, BestKeeper, and geNorm. 18S rRNA, actin, ARF, COX, CYP, EF1α, GAPDH, H3, and RPL2 were detected as optimal reference genes for gene expression analysis of different organs and stress responses. The results were further confirmed by the expression pattern normalized with different reference genes of two heat-responsive genes. Here, we optimized the detection method of the gene expression pattern in spinach. Our results provide the optimal candidate reference genes which were crucial for RT-qPCR analysis.

Overexpression of Trx CDSP32 gene promotes chlorophyll synthesis and photosynthetic electron transfer and alleviates cadmium-induced photoinhibition of PSII and PSI in tobacco leaves

Cadmium stress causes a decrease in chlorophyll content and inhibits photosynthesis in tobacco leaves. The role of thioredoxin-like protein CDSP32 expressed in plant chloroplasts is to alleviates the reduced enzymes expression involved in chlorophyll synthesis of tobacco leaves due to Cd exposure, effectively preventing chlorophyll degradation and promoting increased tobacco biomass. Overexpression of Trx CDSP32 can protect the oxygen-evolving complex on the PSII donor side and promote electron transfer on the PSII acceptor side of tobacco leaves under Cd stress. Trx CDSP32 not only significantly increase the PSI activity of tobacco leaves, but also alleviate cadmium-induced PSI photoinhibition. Although Trx CDSP32 has no significant effect on the expression of PC and FNR proteins in tobacco leaves under Cd stress, it can alleviate the decreased expression of protein subunits involved in photosynthetic electron transfer such as Cyt b6/f complex subunits, Fd, and ATP synthase subunits. Trx CDSP32 can promote the synthesis of chlorophyll, stabilize the electron transfer chain, and promote ATP synthase activity to alleviate cadmium-induced photoinhibition of PSII and PSI in tobacco leaves.

Toxic effects of heavy metal Cd and Zn on chlorophyll, carotenoid metabolism and photosynthetic function in tobacco leaves revealed by physiological and proteomics analysis

To explore the mechanisms underlying the action of the heavy metals Cd and Zn on the photosynthetic function of plant leaves, the effects of 100 μmol L-1 Cd and 200 μmol L-1 Zn stress (the exposure concentrations of Cd and Zn in the culture medium were 2.24 mg kg-1 and 5.36 mg kg-1) on the chlorophyll and carotenoid contents as well as the photosynthetic function of tobacco leaves (Long Jiang 911) were studied. The key proteins in these physiological processes were quantitatively analyzed using a TMT-based proteomics approach. Cd stress was found to inhibit the expression of key enzymes during chlorophyll synthesis in leaves, resulting in a decrease of the Chl content. However, Zn stress did not significantly influence the chlorophyll content. Leaves adapted to Zn stress by upregulating CAO expression and increase the Chl b content. Although the Car content in leaves did not significantly change under either Cd or Zn stress, the expressions of ZE and VDE during Car metabolism decreased significantly under Cd stress. This was accompanied by damages to the xanthophyll cycle and the NPQ-dependent energy dissipation mechanism. In contrast, under Zn stress, leaves adapted to Zn stress by increasing the expression of VDE, thus improving NPQ. Under Cd stress, the expressions of three sets of proteins were significantly down-regulated, including PSII donor-side proteins (PPD3, PPD6, OEE1, OEE2-1, OEE2-2, OEE2-3, and OEE3-2), receptor-side proteins (D1, D2, CP43, CP47, Cyt b559α, Cyt b559β, PsbL, PsbQ, PsbR, Psb27-H1, and Psb28), and core proteins of the PSI reaction center (psaA, psaB, psaC, psaD, psaE-A, PsaE-B, psaF, psaG, psaH-1, psaK, psaL, psaN, and psaOL). In comparison, only eight of the above proteins (PPD6, OEE3-2, PsbL, PsbQ, Psb27-H1, psaL, and psaOL) were significantly down-regulated by Zn stress. Under Cd stress, both the donor side and the receptor side of PSII were damaged, and PSII and PSI experienced severe photoinhibition. However, Zn stress did not decrease either PSII or PSI activities in tobacco leaves. In addition, the expression of electron transport-related proteins (cytb6/f complex, PC, Fd, and FNR), ATPase subunits, Rubisco subunits, and RCA decreased significantly in leaves under Cd stress. However, no significant changes were observed in any of these proteins under Zn stress. Although Cd stress was found to up-regulate the expressions of PGRL1A and PGRL1B and induce an increase of PGR5/PGRL1-CEF in tobacco leaves, NDH-CEF was significantly inhibited. Under Zn stress, the expressions of ndhH and PGRL1A in leaves were significantly up-regulated, but there were no significant changes in either NDH-CEF or PGR5/PGRL-CEF. Under Cd stress, the expressions of proteins related to Fd-dependent nitrogen metabolism and reactive oxygen species (ROS) scavenging processes (e.g., FTR, Fd-NiR, and Fd-GOGAT) were significantly down-regulated in leaves. However, no significant changes of any of the above proteins were identified under Zn stress. In summary, Cd stress could inhibit the synthesis of chlorophyll in tobacco leaves, significantly down-regulate the expressions of photosynthesis-related proteins or subunits, and suppress both the xanthophyll cycle and NDH-CEF process. The expressions of proteins related to the Fd-dependent nitrogen metabolism and ROS scavenging were also significantly down-regulated, which blocked the photosynthetic electron transport, thus resulting in severe photoinhibition of both PSII and PSI. However, Zn stress had little effect on the photosynthetic function of tobacco leaves.

Morpho-Physiological and Proteome Level Responses to Cadmium Stress in Sorghum

Cadmium (Cd) stress may cause serious morphological and physiological abnormalities in addition to altering the proteome in plants. The present study was performed to explore Cd-induced morpho-physiological alterations and their potential associated mechanisms in Sorghum bicolor leaves at the protein level. Ten-day-old sorghum seedlings were exposed to different concentrations (0, 100, and 150 μM) of CdCl2, and different morpho-physiological responses were recorded. The effects of Cd exposure on protein expression patterns in S. bicolor were investigated using two-dimensional gel electrophoresis (2-DE) in samples derived from the leaves of both control and Cd-treated seedlings. The observed morphological changes revealed that the plants treated with Cd displayed dramatically altered shoot lengths, fresh weights and relative water content. In addition, the concentration of Cd was markedly increased by treatment with Cd, and the amount of Cd taken up by the shoots was significantly and directly correlated with the applied concentration of Cd. Using the 2-DE method, a total of 33 differentially expressed protein spots were analyzed using MALDI-TOF/TOF MS. Of these, treatment with Cd resulted in significant increases in 15 proteins and decreases in 18 proteins. Major changes were absorbed in the levels of proteins known to be involved in carbohydrate metabolism, transcriptional regulation, translation and stress responses. Proteomic results revealed that Cd stress had an inhibitory effect on carbon fixation, ATP production and the regulation of protein synthesis. Our study provides insights into the integrated molecular mechanisms involved in responses to Cd and the effects of Cd on the growth and physiological characteristics of sorghum seedlings. We have aimed to provide a reference describing the mechanisms involved in heavy metal damage to plants.

Comparative proteomic analysis provides insight into cadmium stress responses in brown algae Sargassum fusiforme

Sargassum fusiforme is one of the most widely consumed seaweeds in China, Korea and Japan. In this work, we performed growth analysis and comparative proteomics to investigate the molecular mechanisms of the response to 1 day and 5 days Cd stress in S. fusiforme. Our results showed a significant decrease in growth rate and an increase in Cd ion content in S. fusiforme in response to Cd treatment. Comparative proteomic analysis revealed 25 and 51 differentially expressed protein spots in S. fusiforme under 1 day and 5 days Cd stress, respectively. A great number of these proteins was metabolic enzymes involved in carbohydrate metabolism and energy metabolism. Many proteins involved in the processing of genetic information showed a decrease in abundance under 1 day Cd stress. In contrast, 9 of the identified protein spots primarily involved in genetic information processing and carbohydrate metabolism were greatly enriched under 5 days Cd stress. Overall, our investigation indicated that Cd stress negatively affects the metabolic activity of S. fusiforme through the down-regulation of key metabolic enzymes. In addition, S. fusiforme may adapt to 5 days Cd stress by promoting consumption of photoassimilates through the up-regulation of glycolysis and the citrate cycle to supply energy for survival.

Comparative proteomic analysis of two tobacco (Nicotiana tabacum) genotypes differing in Cd tolerance

Tobacco can easily accumulate cadmium (Cd) in leaves and thus poses a potential threat to human health. Cd-stress-hydroponic-experiments were performed, and the proteomic and transcriptional features of two contrasting tobacco genotypes Yun-yan2 (Cd-tolerant) and Guiyan1 (Cd-sensitive) were compared. We identified 18 Cd-tolerance-associated proteins in leaves, using 2-dimensional gel electrophoresis coupled with mass spectrometry, whose expression were significantly induced in Yunyan2 leaves but down-regulated/unchanged in Guiyan1, or unchanged in Yunyan2 but down-regulated in Guiyan1 under 50 µM Cd stress. They are including epoxide hydrolase, enoyl-acyl-carrier-protein reductase, NPALDP1, chlorophyll a-b binding protein 25, heat shock protein 70 and 14-3-3 proteins. They categorized as 8 groups of their functions: metabolism, photosynthesis, stress response, signal transduction, protein synthesis, protein processing, transport and cell structure. Furthermore, the expression patterns of three Cd-responsive proteins were validated by quantitative real-time PCR. Our findings provide an insight into proteomic basis for Cd-detoxification in tobacco which offers molecular resource for Cd-tolerance.

Cadmium induces two waves of reactive oxygen species in Glycine max (L.) roots

Cadmium (Cd) is a non-essential heavy metal that may be toxic or even lethal to plants as it can be easily taken up by the roots and loaded into the xylem to the leaves. Using soybean roots (Glycine max L.) DM 4800, we have analysed various parameters related to reactive oxygen metabolism and nitric oxide (NO) during a 6 day Cd exposure. A rise in H(2)O(2) and NO, and to a lesser extent O(2)(·-) content was observed after 6 h exposure with a concomitant increase in lipid peroxidation and carbonyl group content. Both oxidative markers were significantly reduced after 24 h. A second, higher wave of O(2)(·-) production was also observed after 72 h of exposure followed by a reduction until the end of the treatment. NOX and glicolate oxidase activity might be involved in the initial Cd-induced reactive oxygen species (ROS) production and it appears that other sources may also participate. The analysis of antioxidative enzymes showed an increase in glutathione-S-transferase activity and in transcript levels and activity of enzymes involved in the ascorbate-glutathione cycle and the NADPH-generating enzymes. These results suggest that soybean is able to respond rapidly to oxidative stress imposed by Cd by improving the availability of NADPH necessary for the ascorbate-glutathione cycle.

Problems inherent to a meta-analysis of proteomics data: a case study on the plants' response to Cd in different cultivation conditions

This meta-analysis focuses on plant-proteome responses to cadmium (Cd) stress. Initially, some general topics related to a proteomics meta-analysis are discussed: (1) obstacles encountered during data analysis, (2) a consensus in proteomic research, (3) validation and good reporting practices for protein identification and (4) guidelines for statistical analysis of differentially abundant proteins. In a second part, the Cd responses in leaves and roots obtained from a proteomics meta-analysis are discussed in (1) a time comparison (short versus long term exposure), and (2) a culture comparison (hydroponics versus soil cultivation). Data of the meta-analysis confirmed the existence of an initial alarm phase upon Cd exposure. Whereas no metabolic equilibrium is established in hydroponically exposed plants, an equilibrium seems to be manifested in roots of plants grown in Cd-contaminated soil after long term exposure. In leaves, the carbohydrate metabolism is primarily affected independent of the exposure time and the cultivation method. In addition, a metabolic shift from CO2-fixation towards respiration is manifested, independent of the cultivation system. Finally, some ideas for the improvement of proteomics setups and for comparisons between studies are discussed.

BIOLOGICAL SIGNIFICANCE

This meta-analysis focuses on the plant responses to Cd stress in leaves and roots at the proteome level. This meta-analysis points out the encountered obstacles when performing a proteomics meta-analysis related to inherent technologies, but also related to experimental setups. Furthermore, the question is addressed whether an extrapolation of results obtained in hydroponic cultivation towards soil-grown plants is possible.

Cadmium stress responses in Brassica juncea: hints from proteomics and metabolomics

Among heavy metal stressors, cadmium (Cd) pollution is one leading threat to the environment. In this view, research efforts have been increasingly put forward to promote the individuation of phytoextractor plants that are capable of accumulating and withstanding the toxic metals, including Cd, in the aerial parts. We hereby adopted the hyperaccumulator B. juncea (Indian mustard) as a model to investigate plant responses to Cd stress at low (25 μM) and high (100 μM) doses. Analytical strategies included mass-spectrometry-based determination of Cd and the assessment of its effect on the leaf proteome and metabolome. Results were thus integrated with routine physiological data. Taken together, physiology results highlighted the deregulation of photosynthesis efficiency, ATP synthesis, reduced transpiration, and the impairment of light-independent carbon fixation reactions. These results were supported at the proteomics level by the observed Cd-dependent alteration of photosystem components and the alteration of metabolic enzymes, including ATP synthase subunits, carbonic anhydrase, and enzymes involved in antioxidant responses (especially glutathione and phytochelatin homeostasis) and the Calvin cycle. Metabolomics results confirmed the alterations of energy-generating metabolic pathways, sulfur-compound metabolism (GSH and PCs), and Calvin cycle. Besides, metabolomics results highlighted the up-regulation of phosphoglycolate, a byproduct of the photorespiration metabolism. This was suggestive of the likely increased photorespiration rate as a means to cope with Cd-induced unbalance in stomatal conductance and deregulation of CO2 homeostasis, which would, in turn, promote CO2 depletion and O2 (and thus oxidative stress) accumulation under prolonged photosynthesis in the leaves from plants exposed to high doses of CdCl2. Overall, it emerges that Cd-stressed B. juncea might rely on photorespiration, an adaptation that would prevent the over-reduction of the photosynthetic electron transport chain and photoinhibition.

Differential responses of microsomal proteins and metabolites in two contrasting cadmium (Cd)-accumulating soybean cultivars under Cd stress

While there are significant genotypic differences in cadmium (Cd) uptake and distribution in soybean cultivars, little attention has been paid to the underlying molecular mechanisms. We adopted a comparative proteomic approach coupled with metabolite analysis to examine Cd uptake and translocation in two contrasting Cd-accumulating soybean cultivars, Enrei and Harosoy, which accumulate higher amount of Cd in the roots and aerial parts, respectively. Proteins extracted from the root microsomal fraction were evaluated by immunoblot analysis using different subcellular marker proteins. Analysis of control and Cd-exposed samples by two-dimensional gel electrophoresis coupled with mass spectrometry revealed a total of 13 and 11 differentially expressed proteins in the Enrei and Harosoy cultivars, respectively. Metabolome profiling identified a total of 32 metabolites, the expression of 18 of which was significantly altered in at least in one cultivar in response to Cd stress. Analysis of the combined proteomic and metabolomic results revealed that proteins and amino acids associate with Cd-chelating pathways are highly active in the Enrei cultivar. In addition, proteins associated with lignin biosynthesis are significantly upregulated in the Enrei cultivar under Cd stress. Our results indicate that in the Enrei cultivar, Cd-chelating agents may bind excess free Cd ion and that translocation of Cd from the roots to the aerial parts might be prevented by increased xylem lignification.

Cd-induced changes in leaf proteome of the hyperaccumulator plant Phytolacca americana

Cadmium (Cd) is highly toxic to all organisms. Soil contamination by Cd has become an increasing problem worldwide due to the intensive use of Cd-containing phosphate fertilizers and industrial zinc mining. Phytolacca americana L. is a Cd hyperaccumulator plant that can grow in Cd-polluted areas. However, the molecular basis for its remarkable Cd resistance is not known. In this study, the effects of Cd exposure on protein expression patterns in P.americana was investigated by 2-dimensional gel electrophoresis (2-DE). 2-DE profiles of leaf proteins from both control and Cd-treated (400μM, 48h) seedlings were compared quantitatively using ImageMaster software. In total, 32 differentially expressed protein spots were identified using MALDI-TOF/TOF mass spectrometry coupled to protein database search, corresponding to 25 unique gene products. Of those 14 were enhanced/induced while 11 reduced under Cd treatment. The alteration pattern of protein expression was verified for several key proteins involved in distinct metabolic pathways by immuno-blot analysis. Major changes were found for the proteins involved in photosynthetic pathways as well as in the sulfur- and GSH-related metabolisms. One-third of the up-regulated proteins were attributed to transcription, translation and molecular chaperones including a protein belonging to the calreticulin family. Other proteins include antioxidative enzymes such as 2-cys-peroxidase and oxidoreductases. The results of this proteomic analysis provide the first and primary information regarding the molecular basis of Cd hypertolerance in P. americana.

Investigating the plant response to cadmium exposure by proteomic and metabolomic approaches

Monitoring molecular dynamics of an organism upon stress is probably the best approach to decipher physiological mechanisms involved in the stress response. Quantitative analysis of proteins and metabolites is able to provide accurate information about molecular changes allowing the establishment of a range of more or less specific mechanisms, leading to the identification of major players in the considered pathways. Such tools have been successfully used to analyze the plant response to cadmium (Cd), a major pollutant capable of causing severe health issues as it accumulates in the food chain. We present a summary of proteomics and metabolomics works that contributed to a better understanding of the molecular aspects involved in the plant response to Cd. This work allowed us to provide a finer picture of general signaling, regulatory and metabolic pathways that appeared to be affected upon Cd stress. In particular, we conclude on the advantage of employing different approaches of global proteome- and metabolome-wide techniques, combined with more targeted analysis to answer molecular questions and unravel biological networks. Finally, we propose possible directions and methodologies for future prospectives in this field, as many aspects of the plant-Cd interaction remain to be discovered.

Popeye strikes again: The deep proteome of spinach leaves

The cytoplasmic proteome of spinach leaves (Spinacia oleracea L) has been investigated with the help of commercially available (ProteoMiner) combinatorial peptide ligand libraries and with home-made ligand beads as prepared in our laboratory. The protein capture had been performed at three pH values (4.0, 7.0 and 9.3) and elution performed in 4% boiling SDS, 20mM DTT. The total number of unique gene products identified amounts to 322 proteins, of which 114 are in common with the control, untreated sample, 18 are present only in the control and 190 represent the new species detected with the help of all combined eluates and likely represent low-abundance species. This is the first in depth exploration of the spinach cytoplasmic proteome and might enable further studies on interaction, regulation and expression of proteins biological processes in combination or not with transcriptomics data.

Changes induced by two levels of cadmium toxicity in the 2-DE protein profile of tomato roots

Tomato is an important crop from nutritional and economical points of view, and it is grown in greenhouses, where special substrates and the use of recycled water imply an increased risk of Cd accumulation. We investigated tomato root responses to low (10 microM) and high (100 microM) Cd concentrations at the root proteome level. Root extract proteome maps were obtained by 2-DE, and an average of 121, 145 and 93 spots were detected in the 0, 10 and 100 microM Cd treatments, respectively. The low Cd treatment (10 microM) resulted in significant and higher than 2-fold changes in the relative amounts of 36 polypeptides, with 27 of them identified by mass spectrometry, whereas the 100 microM Cd treatment resulted in changes in the relative amounts of 41 polypeptides, with 33 of them being identified. The 2-DE based proteomic approach allowed assessing the main metabolic pathways affected by Cd toxicity. Our results suggests that the 10 microM Cd treatment elicits proteomic responses similar to those observed in Fe deficiency, including activation of the glycolytic pathway, TCA cycle and respiration, whereas the 100 microM Cd treatment responses are more likely due to true Cd toxicity, with a general shutdown of carbon metabolism and increases in stress related and detoxification proteins.

Acute metal stress in Populus tremula x P. alba (717-1B4 genotype): leaf and cambial proteome changes induced by cadmium 2+

The comprehension of metal homeostasis in plants requires the identification of molecular markers linked to stress tolerance. Proteomic changes in leaves and cambial zone of Populus tremula x P. alba (717-1B4 genotype) were analyzed after 61 days of exposure to cadmium (Cd) 360 mg/kg soil dry weight in pot-soil cultures. The treatment led to an acute Cd stress with a reduction of growth and photosynthesis. Cd stress induced changes in the display of 120 spots for leaf tissue and 153 spots for the cambial zone. It involved a reduced photosynthesis, resulting in a profound reorganisation of carbon and carbohydrate metabolisms in both tissues. Cambial cells underwent stress from the Cd actually present inside the tissue but also a deprivation of photosynthates caused by leaf stress. An important tissue specificity of the response was observed, according to the differences in cell structures and functions.