Nickel and zinc accumulation capacities and tolerance to these metals in the excluder Thlaspi arvense and the hyperaccumulator Noccaea caerulescens

Representatives of Brassicaceae species—the hyperaccumulator Noccaea caerulescens F.K. Mey and the metal excluder Thlaspi arvense L.—were compared in terms of their ability to accumulate nickel (Ni) and zinc (Zn) and their tolerance to these metals. Four ecotypes of N. caerulescens were used: the ecotypes La Calamine (LC, Belgium) and Saint Felix de Palliéres (SF, France) grow naturally on calamine soils rich in Zn, Cd, and Pb; the ecotype Monte Prinzera (MP, Italy) originates from serpentine soils rich in Ni, Co, and Cr; and the ecotype Lellingen (LE, Luxembourg) inhabits non-metalliferous soils. The plants of N. caerulescens were grown for 8 weeks in a half-strength Hoagland solution supplemented with 25, 100, 200, 300, and 400 μM Ni(NO₃)₂ (ecotypes LC, SF, MP, LE) or 100, 200, 400, 800, and 1000 μM Zn(NO₃)₂ (ecotypes LC, SF, LE); the plants of T. arvense were grown in the presence of 10, 20, 25, and 30 μM Ni(NO₃)₂ or 40, 50, 60, 70, 80 μM Zn(NO₃)₂. The toxic effect of Ni and Zn was assessed from changes in dry matter of roots and shoots of treated plants compared to untreated. The content of metals in roots and shoots was determined by means of atomic absorption spectrophotometry. The Ni-accumulating capacity of N. caerulescens ecotypes increased in the order: LC < SF < LE < MP, and the Zn-accumulating capacity increased in the row: LC < SF < LE. In the hyperaccumulating plant N. caerulescens, the increments of biomass started to decrease at a lower metal content in roots than in shoots, whereas the opposite pattern was observed in the metal excluder T. arvense. Since T. arvense plants accumulated Ni and Zn in roots, whereas N. caerulescens accumulated these metals in shoots, one may assume that the greater sensitivity of root growth compared with shoots in N. caerulescens was determined by more effective mechanisms of metal detoxification in shoots. Conversely, the higher sensitivity of shoot growth compared to root growth in T. arvense was determined by more effective mechanisms of metal detoxification in roots. Being more tolerant to Ni and Zn than T. arvense plants, the N. caerulescens ecotypes differed substantially in terms of metal-accumulating capacity and their tolerance to heavy metals. The ecotype originating from non-metalliferous soils (LE) accumulated larger amounts of Zn, but was less tolerant compared with ecotypes growing naturally on calamine soils (SF and LC), whereas the ecotype occurring on serpentine soils (MP) exhibited a markedly greater tolerance to Ni, compared with other ecotypes examined, as well as the largest accumulation of this metal. The results indicate the existence of different mechanisms responsible for plant tolerance to Ni and Zn; the study of these mechanisms is a promising direction for future research.     

MAPKs as a cross point in H2O2 and auxin signaling under combined cadmium and zinc stress in rice roots

Previously, we have reported the role of MAPKs (mitogen-activated protein kinases) under cadmium stress. This work continue to explore the relationship between MAPKs, H₂O₂, auxin signaling, and OsHMA and OsZIP gene expression in rice (Oryza sativa L.) roots under combined cadmium (Cd) and zinc (Zn) stress. Compared with Cd, Cd+Zn reduced Cd levels but increased Zn accumulation in the roots. Three OsMAPK genes were negatively regulated, while two OsHMA and two OsZIP genes were positively regulated by MAPK pathways under Cd+Zn stress. Transgenic rice expressing DR5-GUS exhibited enhanced GUS activity in H₂O₂-, PD (MAPKK inhibitor PD98059)-, or (Cd+Zn)-treated roots, which also exhibited increased H₂O₂ concentrations, whereas GUS staining decreased in roots in response to Cd+Zn+PD, DMTU (N,N′-dimethylthiourea, a H₂O₂ scavenger), or Cd+Zn+DMTU treatment, with reduced H₂O₂ levels. GUS levels were consistent with H₂O₂ levels, suggesting that MAPK pathway-mediated auxin redistribution occurs via H₂O₂, and H₂O₂ functions downstream of MAPK but upstream of auxin signaling pathways. Furthermore, MAPK pathways serve specific functions in regulating the expression of some key genes of auxin signaling (OsYUCCA, OsPIN, OsARF, and OsIAA) under Cd+Zn stress. Overall, MAPK cascades function in the integration of metal transport, H₂O₂ generation, and auxin signaling in rice seedlings grown under Cd+Zn stress.     

Isolated Thellungiella shoots do not require roots to survive NaCl and Na2SO4 salt stresses

Shoots of Thellungiella derived by micropropagation were used to estimate the plants'' salt tolerance and ability to regulate Na⁺ uptake. Two species with differing salt tolerances were studied: Thellungiella salsuginea (halophilla), which is less tolerant, and Thellungiella botschantzevii, which is more tolerant. Although the shoots of neither ecotype survived at 700 mM NaCl or 200 mM Na₂SO₄, micropropagated shoots of T. botschantzevii were more tolerant to Na₂SO₄ (10–100 mM) and NaCl (100–300 mM). In the absence of roots, Na₂SO₄ salinity reduced shoot growth more dramatically than NaCl salinity. Plantlets of both species were able to adapt to salt stress even when they did not form roots. First, there was no significant correlation between Na⁺ accumulation in shoots and Na⁺ concentration in the growth media. Second, K⁺ concentrations in the shoots exposed to different salt concentrations were maintained at equivalent levels to control plants grown in medium without NaCl or Na₂SO₄. These results suggest that isolated shoots of Thellungiella possess their own mechanisms for enabling salt tolerance, which contribute to salt tolerance in intact plants.Key words: Thellungiella salsuginea, Thellungiella botschantzevii, salt tolerance, isolated shoots, growth, rhizogenesis, ion accumulation     

Localization of Nickel in Tissues of Streptanthus polygaloides Gray (Cruciferae) and Endemic Nickel Hyperaccumulators from California

The genus Streptanthus Nutt. is one of the most important indicators of ultramafic floras in western North America. This genus contains taxa that are endemic or tolerant of ultramafic soils. Streptanthus polygaloides is an annual nickel hyperaccumulator strictly confined to ultramafic soils throughout the Californian Sierra Nevada foothills. Nickel concentration in S. polygaloides populations was evaluated by elemental microanalysis using inductively coupled plasma mass spectrometry (ICP-MS). Representative samples of S. polygaloides roots, stems, leaves, flowers, and fruits were studied by scanning electron microscopy (SEM) coupled to an energy-dispersive X-ray probe (SEM-EDX). Results show Ni accumulation values between 0.09 and 1.18 %, and a distribution pattern similar to that observed in other Ni hyperaccumulator taxa, with the leaf epidermis accumulating the largest concentrations.     

Responses of the Populus × euramericana clone I-214 to excess zinc: Carbon assimilation,structural modifications,metal distribution and cellular localization

Poplar (Populus), the model system in tree research, is a fast-growing and high biomass plant which is promising for energy, paper and pulp production, and for growth in soils contaminated with metals. Contamination of soils and water with heavy metals has become a widespread problem; environmental pollution by excess zinc (Zn), one of the more important contaminants, occurs frequently and yet the responses of Populus to high Zn concentrations are still not clearly understood.We investigated the effects of Zn on the functional and structural parameters in the Populus × euramericana clone I-214 by Zn localization in frozen-hydrated leaves and roots by cryo-scanning electron microscopy (cryo-SEM)/energy-dispersive X-ray microanalysis (EDXMA). The experiment was conducted on cuttings grown in nutrient solutions with an increasing Zn concentration gradient (0.001–10 mM).Biomass partitioning and Zn uptake were affected by the metal treatments, showing organ- and tissue-dependent responses. In particular, Zn accumulated in old leaves and moved from shoot to root as the Zn concentration in the growth medium increased. At the highest treatment concentration (10 mM), Zn was preferentially localized in photosynthetic tissues of shoots, and in epidermis and cortex tissues of roots. Gas exchange and chlorophyll measurements showed impairments in leaf biochemistry rather than in stomatal function. Modifications in foliage area, stomatal density and leaf layer thickness were investigated to reduce and/or compensate the negative effects of excess Zn on CO₂ assimilation.To counteract Zn toxicity, clone I-214 adopted different defense/tolerance mechanisms involving complex structural, physiological and biochemical processes, attributed to both Zn excluders and accumulators. This study demonstrates the advantages of combining cryo-SEM/EDXMA, gas exchange and chemical analyses for studying metal localization and structural as well as physiological responses in plants.     

In vitro breeding of Brassica juncea L. to enhance metal accumulation and extraction properties

In vitro breeding and somaclonal variation were used as tools to improve the potential of Indian mustard (Brassica juncea L.) to extract and accumulate toxic metals. Calli from B. juncea were cultivated on a modified MS medium supplemented with 10–200 μM Cd or Pb. Afterwards, new B. juncea somaclones were regenerated from metal-tolerant callus cells. Three different phenotypes with improved tolerance of Cd, Zn and Pb were observed under hydroponic conditions: enhanced metal accumulation in both shoots and roots; limited metal translocation from roots to shoots; reduced accumulation in shoots and roots. Seven out of thirty individual variants showed a significantly higher metal extraction than the control plants. The improvement of metal shoot accumulation of the best regenerant (3× Cd, 1.6× Zn, 1.8× Pb) and metal extraction (6.2× Cd, 3.2× Zn, 3.8× Pb) indicated a successful breeding and selection of B. juncea, which could be used for phytoremediation purpose.     

Predictability of the Zn and Cd phytoextraction efficiency of a Salix smithiana clone by DGT and conventional bioavailability assays

Aims

Phytomanagement of metal-polluted soils requires information on plant responses to metal availability in soil, but the predictability of metal accumulation in plant shoots and/or roots may be limited by metal toxicity and inherent shortfalls of the bioavailability assays.

Methods

We measured the uptake of Cd and Zn in a Salix smithiana clone grown in a pot experiment on soils with different characteristics and metal availabilities, determined by conventional soil single extractions (0.05 M Na₂-EDTA and 1 M NH₄NO₃), soil solution obtained by centrifugation, and diffusive gradients in thin films (DGT). The Cd and Zn phytoavailability after a 2-year phytoextraction by willow was assessed by metal accumulation in the straw of the following barley culture.

Results

The phytoextraction efficiency was largest on a moderately polluted acid soil. Biomass and shoot Zn concentrations of S. smithiana were better predicted by DGT-measured Zn concentrations in soil solution (C _DGT) than by Zn concentrations in the soil solution and extractable soil fractions. The weaker correlation for Cd in shoots may be related to relative Cd enrichment in the plant tissues. The metal accumulation in barley straw was unaffected or increased after a 2-year phytoextraction.

Conclusions

The shoot Zn and Cd removal of the tested Salix clone can be predicted by C _DGT concentrations and is highest on either calcareous or moderately polluted acid soils. Single extraction with NH₄NO₃ and the C _DGT value of Cd were not able to predict shoot Cd removal on the tested soils. Only shoot removal of Zn was predicted fairly well by the C _DGT value.     

Effect of zinc and cadmium on physiological and production characteristics in <Emphasis Type="Italic">Matricaria recutita</Emphasis>

Effects of zinc (12–180 μM) alone and in mixtures with 12 μM Cd on metal accumulation, dry masses of roots and shoots, root respiration rate, variable to maximum fluorescence ratio (F_V/F_M), and content of photosynthetic pigments were studied in hydroponically cultivated chamomile (Matricaria recutita) plants. The content of Zn in roots and shoots increased with the increasing external Zn concentration and its accumulation in the roots was higher than that in the shoots. While at lower Zn concentrations (12 and 60 μM) the presence of 12 μM Cd decreased Zn accumulation in the roots, treatment with 120 and 180 μM Zn together with 12 μM Cd caused enhancement of Zn content in the root. Presence of Zn (12–120 μM) decreased Cd accumulation in roots. On the other hand, Cd content in the shoots of plants treated with Zn + Cd exceeded that in the plants treated only with 12 μM Cd. Only higher Zn concentrations (120 and 180 μM) and Zn + Cd mixtures negatively influenced dry mass, chlorophyll (Chl) and carotenoid content, F_V/F_M and root respiration rate. Chl b was reduced to a higher extent than Chl a.     

Evaluation of the potential for interspecific hybridization between Camelina sativa and related wild Brassicaceae in anticipation of field trials of GM camelina

Camelina (Camelina sativa (L.) Crantz) is a re-emergent oilseed crop that is also becoming important as a model for applied projects based on studies in Arabidopsis thaliana, since the two species are closely related members of the tribe Camelineae of the Brassicaeae. Since camelina can be transformed genetically by floral dip, genetically modified (GM) camelina is being created in many laboratories, and small-scale field trials are already being conducted in the US and Canada. Although camelina does not cross-fertilize Brassica crop species, such as oilseed rape, nothing was known about its ability to cross with other members of the tribe Camelineae, which in addition to arabidopsis includes the widespread weed, shepherd’s purse (Capsella bursa-pastoris). We have tested the ability of camelina to cross with arabidopsis and C. bursa-pastoris, as well as with the more distantly related Cardamine hirsuta, tribe cardamineae. No seeds were produced in crosses with arabidopsis, and a few seeds were obtained in crosses with C. hirsuta, but the embryos aborted at an early stage of development. A few seeds were also obtained in crosses with C. bursa-pastoris, which germinated to produce plants of a phenotype intermediate to that of the parents, but the hybrids were both male and female sterile. Therefore, the likelihood of pollen-mediated gene flow from camelina to these related species is low.     

Contrasting Effects of Farmyard Manure (FYM) and Compost for Remediation of Metal Contaminated Soil

We investigated effect of farm yard manure (FYM) and compost applied to metal contaminated soil at rate of 1% (FYM-1, compost-1), 2% (FYM-2, compost-2), and 3% (FYM-3, compost-3). FYM significantly (P < 0.001) increased dry weights of shoots and roots while compost increased root dry weight compared to control. Amendments significantly increased nickel (Ni) in shoots and roots of maize except compost applied at 1%. FYM-3 and -1 caused maximum Ni in shoots (11.42 mg kg^?1) and roots (80.92 mg kg^?1), respectively while compost-2 caused maximum Ni (14.08 mg kg^?1) and (163.87 mg kg^?1) in shoots and roots, respectively. Plants grown in pots amended with FYM-2 and compost-1 contained minimum Cu (30.12 and 30.11 mg kg^?1) in shoots, respectively. FYM-2 and compost-2 caused minimum zinc (Zn) (59.08 and 66.0 mg kg^?1) in maize shoots, respectively. FYM-2 caused minimum Mn in maize shoots while compost increased Mn in shoots and roots compared to control. FYM and compost increased the ammonium bicarbonate diethylene triamine penta acetic acid (AB-DTPA) extractable Ni and Mn in the soil and decreased Cu and Zn. Lower remediation factors for all metals with compost indicated that compost was effective to stabilize the metals in soil compared to FYM.     

Monitoring population and gene pool dynamics of the annual species <Emphasis Type="Italic">Capsella bursa</Emphasis>-<Emphasis Type="Italic">pastoris</Emphasis> (Brassicaceae): a review of relevant species traits and the initiation of a long-term genetic monitoring programme

Species that colonise habitats on an annual basis are important for studying and understanding evolutionary changes and adaptations in the course of environmental shifts, caused, for instance, by global change phenomena. These species are characterised by a weedy ecology enabling them to react fast to environmental changes. As a model species, we selected Capsella bursa-pastoris (Brassicaceae, Shepherd’s Purse), which is annual to biennial, predominantly selfing and closely related to the genetic model plant Arabidopsis thaliana. Differentiation and adaptation in C. bursa-pastoris are shortly reviewed. Based on this knowledge, two Botanical Gardens are currently arranging long-term sites characterised by annual ploughing for the genetic monitoring of C. bursa-pastoris. Demographic parameters will be monitored as well, i.e. different life-cycle phases such as flowering, fruiting, and the soil seed bank. Furthermore, seeds of at least 20 individuals will be sampled per year. Isozyme analyses, flow cytometry, AFLPs, SNPs as well as microsatellites will be utilised to characterise changes in genetic diversity patterns over time. In general, the objective of our genetic monitoring of C. bursa-pastoris is to address the following questions: In the light of future research, our objectives are to study whether the genetic structure and diversity of C. bursa-pastoris alter over time, whether a possible invasion of ecotypes/genotypes of Sheperd’s purse is traceable using genetic markers, and whether it is possible to relate variation in reproductive patterns to respective candidate genes, which may be useful for monitoring.     

Patterns of accumulation of selected metals in members of the soft-water macrophyte flora of central Ontario lakes

The patterns of accumulation of Ni, Cu, Zn, Pb, Cd, Fe, Mn and Al in plant species which are members of the flora of soft-water central Ontario (Canada) lakes are presented. The allocation of each metal between roots and shoots varies with the metal and the overall level of metal enrichment of the site. There is interspecific variation in metal accumulation, but the greatest differences are between vascular plants and bryophytes, rather than within these groups. An index of overall metal enrichment of each site is developed using Cu and Ni sediment concentrations. In Eriocaulon septangulare With., plant metal concentrations were uncorrelated to environmental levels of the corresponding metal but did show trends relative to the index. High plant metal concentrations did not correspond to high index levels for Zn, Mn, Cd and Al. It is suggested that in highly metal-enriched environments competitive exclusions by more common metal ions may be occurring at uptake sites within the plant. As a result of this complexity, metal accumulation in E. septangulare has no predictive value as an indicator of environmental metal contamination.     

Chemical Fractionation and Soil-to-Plant Transfer Characteristics of Heavy Metals in a Sludge Deposit Field of the River Ruhr,Germany

The presented study assessed the heavy metal contamination risk in a former sludge deposit field of the River Ruhr in Essen, Germany. Therefore, the temporal and spatial distribution in soils and plants, chemical fractionation, mobilization potential, and transfer characteristics have been investigated. Soil samples, roots and shoots of rushes (Juncus sp.), and stem wood disks of willows (Salix sp.) were analyzed for Zn, Cu, Pb, Ni, Cr, and Cd. Plant available and mobile heavy metal portions have been determined using a sequential extraction procedure. The results show that the soils and the rushes are highly contaminated, although there is a considerable decrease compared to initial concentrations some 20 years ago. The willows show only small heavy metal enrichment. pH induced mobilization potential in soil is high for Cd, Zn and Ni. Additionally, these elements contain high portions of plant-available fractions. High transfer rates from soil to roots and very high rates from roots to shoots of rushes have been determined for Cd and Zn, indicating an accumulation of these elements in shoots of rushes. The rushes reflect the temporal and spatial heavy metal distribution in soil and might thus be used as a bioindicator or for phytoremediation.     

The mobilisation and fate of soil and rock phosphate in the rhizosphere of ectomycorrhizal Pinus radiata seedlings in an Allophanic soil

A pot experiment was conducted to investigate the uptake of Zn from experimentally contaminated calcareous soil of low nutrient status by maize inoculated with the arbuscular mycorrhizal (AM) fungus Glomus caledonium. EDTA was applied to the soil to mobilize Zn and thus maximize plant Zn uptake. The highest plant dry matter (DM) yields were obtained with a moderate Zn addition level of 300 mg kg^?1. Plant growth was enhanced by mycorrhizal colonization when no Zn was added and under the highest Zn addition level of 600 mg kg^?1, while application of EDTA to the soil generally inhibited plant growth. EDTA application also increased plant Zn concentration, and Zn accumulation in the roots increased with increasing EDTA addition level. The effects of inoculation with G. caledonium on plant Zn uptake varied with Zn addition level. When no Zn was added, Zn translocation from roots to shoots was enhanced by mycorrhizal colonization. In contrast, when Zn was added to the soil, mycorrhizal colonization resulted in lower shoot Zn concentrations in mycorrhizal plants. The P nutrition of the maize was greatly affected by AM inoculation, with mycorrhizal plants showing higher P concentrations and P uptake. The results indicate that application of EDTA mobilized soil Zn, leading to increased Zn accumulation by the roots and subsequent plant toxicity and growth inhibition. Mycorrhizal colonization alleviated both Zn deficiency and Zn contamination, and also increased host plant growth by influencing mineral nutrition. However, neither EDTA application nor arbuscular mycorrhiza stimulated Zn translocation from roots to shoots or metal phytoextraction under the experimental conditions. The results are discussed in relation to the environmental risk associated with chelate-enhanced phytoextraction and the potential role of arbuscular mycorrhiza in soil remediation.     

Molecular cloning and characterization of a Brassica juncea yellow stripe-like gene, BjYSL7, whose overexpression increases heavy metal tolerance of tobacco

Key message

BjYSL7 encodes a plasma-localized metal–NA transporter and has transport Fe(II)–NA complexes activity. BjYSL7 is involved in the transport of Cd and Ni from roots to shoots.

Abstract

Heavy metal transporters play a key role in regulating metal accumulation and transport in plants. In this study, we isolated a novel member of the yellow stripe-like (YSL) gene family BjYSL7 from the hyperaccumulator Brassica juncea. BjYSL7 is composed of 688 amino acids with 12 putative transmembrane domains and is over 90 % identical to TcYSL7 and AtYSL7. Real-time PCR analysis revealed that BjYSL7 mRNA was mainly expressed in the stem under normal condition. The expression of BjYSL7 was found to be up-regulated by 127.1-, 12.7-, and 3.4-fold in roots and 6.5-, 4.3-, and 2.8-fold in shoots under FeSO₄, NiCl₂, and CdCl₂ stresses, respectively. We have demonstrated that BjYSL7 is a Fe(II)–NA influx transporter by yeast functional complementation. Moreover, a BjYSL7::enhanced green fluorescent protein (EGFP) fusion localized to the plasma membrane of onion epidermal cells. The BjYSL7-overexpressing transgenic tobacco plants exhibited longer root lengths, lower relative inhibition rate of lengths and superior root hair development compared to that of wild-type (WT) plants in the presence of CdCl₂ and NiCl₂. Furthermore, the concentrations of Cd and Ni in shoots of BjYSL7-overexpressing plants are significantly higher than that of WT plants. Compared with WT plants, BjYSL7-overexpressing plants exhibited Fe concentrations that were higher in the shoots and seeds and lower in the roots. Taken together, these results suggest that BjYSL7 might be involved in the transport of Fe, Cd and Ni to the shoot and improving heavy metal resistance in plants.     

Variation of trace metal accumulation,major nutrient uptake and growth parameters and their correlations in 22 populations of Noccaea caerulescens

Background and aims

Noccaea caerulescens is a model plant for the understanding of trace metal accumulation and a source of cultivars for phytoextraction. The aim of this study was to investigate natural variation for trace metal accumulation, major nutrient uptake and growth parameters in 22 populations. The correlations among these traits were particularly examined to better understand the eco-physiology and the phytoextraction potential of the species.

Methods

Populations from three edaphic groups, i.e. calamine (CAL), serpentine (SERP) and non metalliferous (NMET) sites were grown in hydroponics for seven weeks at moderate trace metal exposure. Growth indicators, element contents and correlations between these variables were compared.

Results

All the phenotypic characteristics showed a wide variability among groups and populations. The SERP populations showed a smaller plant size, higher cation contents and strong correlations between all element concentrations. NMET populations did not differ in plant size from the CAL ones, but had higher Zn and Ni contents. The CAL populations showed higher Cd and Mn accumulations and lower Ca contents. The trade-off between biomass production and Cd, Ni and Zn accumulation was high in SERP populations and low in the CAL and NMET ones.

Conclusions

N. caerulescens is a genetically diverse species, showing specific features depending on the group and the population. These features may reflect the wide adaptive capacities of the species, and also reveal promising potential for phytoextraction of Cd, Ni and Zn.     

CbCBF from Capsella bursa-pastoris enhances cold tolerance and restrains growth in Nicotiana tabacum by antagonizing with gibberellin and affecting cell cycle signaling

Plant cells respond to cold stress via a regulatory mechanism leading to enhanced cold acclimation accompanied by growth retardation. The C-repeat binding factor (CBF) signaling pathway is essential for cold response of flowering plants. Our previously study documented a novel CBF-like gene from the cold-tolerant Capsella bursa-pastoris named CbCBF, which was responsive to chilling temperatures. Here, we show that CbCBF expression is obviously responsive to chilling, freezing, abscisic acid, gibberellic acid (GA), indoleacetic acid or methyl jasmonate treatments and that the CbCBF:GFP fusion protein was localized to the nucleus. In addition, CbCBF overexpression conferred to the cold-sensitive tobacco plants enhanced tolerance to chilling and freezing, as well as dwarfism and delayed flowering. The leaf cells of CbCBF overexpression tobacco lines attained smaller sizes and underwent delayed cell division with reduced expression of cyclin D genes. The dwarfism of CbCBF transformants can be partially restored by GA application. Consistently, CbCBF overexpression reduced the bioactive gibberellin contents and disturbed the expression of gibberellin metabolic genes in tobacco. Meanwhile, cold induced CbCBF expression and cold tolerance in C. bursa-pastoris are reduced by GA. We conclude that CbCBF confers cold resistance and growth inhibition to tobacco cells by interacting with gibberellin and cell cycle pathways, likely through activation of downstream target genes.     

Physiological responses of Plantago algarbiensis and P. almogravensis shoots and plantlets to low pH and aluminum stress

We investigated the impact of low pH and aluminum (Al) stress on the growth, nutrients concentration, chlorophyll a fluorescence, photosynthetic pigment contents, proline and carbohydrate accumulation in shoots and plantlets (leaves and roots) of Plantago almogravensis and P. algarbiensis. Both species accumulated considerable and similar amounts of Al in their tissues, mainly in the roots. The presence of Al caused a significant reduction on root elongation in P. algarbiensis. Low pH and Al induced significant changes on nutrient accumulation, but no significant alterations on the maximum efficiency of PSII (F _v/F _m), quantum yield of PSII photochemistry (?_PSII), quantum yield of regulated energy dissipation (?_NPQ) and quantum yield of non-regulated energy dissipation (?_NO) were detected in both species in response to these stresses. However, Al increased significantly the non-photochemical quenching and the chlorophyll b content and decreased the PSII excitation pressure (1 ? q _p) in P. almogravensis leaves. Both stress treatments induced carbohydrate accumulation in the shoots and roots of this species, but not in leaves. In P. algarbiensis, low pH and Al decreased the photosynthetic pigment contents in the shoots, whereas Al stimulated the carbohydrate accumulation in the leaves. Although our data showed that both species are tolerant to Al³⁺ and H⁺, P. almogravensis appeared to be more adapted to maintain cellular physiology and growth under those conditions.     

Heterogeneity of epidermal cells in relation to nickel accumulation in hyperaccumulator plants belonging to the genus <Emphasis Type="Italic">Alyssum</Emphasis> L.

Epidermal cells of some plants are able to accumulate high levels of heavy metals (Zn, Ni, Cd). We studied this ability in plants in the genus Alyssum L. distinguished by tolerance to nickel (Ni). It was established that the predominant Ni accumulation occurred in epidermis, whereas in other tissues lower concentrations of the metal were revealed. It was also found that epidermal cells were characterized by heterogeneity in relation to Ni accumulation. The highest metal amount was accumulated in ordinary epidermal cells and in trichomes. Species-specific features of Ni distribution in leaf tissues in Alyssum spp. were shown. The reasons for the heterogeneity of epidermal cells in relation to Ni accumulation were discussed. We have attempted to resolve the contradictions encountered in the literature concerning the distribution and accumulation of Ni in the leaf tissues of plants belonging to the genus Alyssum L.