The performance of DGT versus conventional soil phosphorus tests in tropical soils - An isotope dilution study

Aims

The aim of the present study was to compare lead accumulation and tolerance among heavy metal hyperaccumulating and non-hyperaccumulating metallophytes.

Methods

To this purpose, we compared Pb tolerance and accumulation in hydroponics among calamine and non-calamine populations of Silene vulgaris, Noccaea caerulescens, and Matthiola flavida. We established the effects of Ca on Pb tolerance and accumulation in M. flavida, and measured exchangeable soil Pb and Ca at two calamine sites.

Results

Results revealed that calamine populations of S. vulgaris and N. caerulescens were Pb hypertolerant, but the calamine M. flavida population was not. Pb hyperaccumulation capacity was exclusively found in one of the calamine N. caerulescens populations.

Conclusions

1) Pb hypertolerance is sometimes lacking in metallophyte populations from strongly Pb-enriched soil, probably due to a relatively high level of exchangeable soil Ca, 2) Ca effectively counteracts Pb uptake and Pb toxicity, 3) The tendency to hyperaccumulate Pb is a population-specific phenomenon in N. caerulescens, 4) Pb hypertolerance in N. caerulescens is not necessarily associated with a tendency to hyperaccumulate Pb, 5) apparent natural Pb hyperaccumulation in M. flavida is not reproducible in hydroponics, probably due to the absence of air-born contamination in laboratory experiments.     

Effect of wheat phosphorus status on leaf surface properties and permeability to foliar-applied phosphorus

Aims

This study aimed to analyse the effect of phosphorus (P) nutritional status on wheat leaf surface properties, in relation to foliar P absorption and translocation.

Methods

Plants of Triticum aestivum cv. Axe were grown with three rates of root P supply (equivalent to 24, 8 and 0 kg P ha^?1) under controlled conditions. Foliar P treatments were applied and the rate of drop retention, P absorption and translocation was measured. Adaxial and abaxial leaf surfaces were analysed by scanning and transmission electron microscopy. The contact angles, surface free energy and work-of-adhesion for water were determined.

Results

Wheat leaves are markedly non-wettable, the abaxial leaf side having some degree of water drop adhesion versus the strong repulsion of water drops by the adaxial side. The total leaf area, stomatal and trichome densities, cuticle thickness and contact angles decreased with P deficiency, while the work-of-adhesion for water increased. Phosphorous deficient plants failed to absorb the foliar-applied P.

Conclusions

Phosphorous deficiency altered the surface structure and functioning of wheat leaves, which became more wettable and had a higher degree of water drop adhesion, but turned less permeable to foliar-applied P. The results obtained are discussed within an agronomic and eco-physiological context.     

Response characteristics of seed germination and seedling growth of Acorus tatarinowii under diesel stress

Aims

Responses of typical wetland plant Acorus tatarinowii to diesel stress were investigated to provide basis of ecological monitoring system and phytoremediation for diesel-contaminated wetland.

Methods

Greenhouse experiments were established to determine the germinability of seedlings, hydrogen peroxide in leaves, and DNA damage in roots exposed to a range of potentially phytotoxic diesel.

Results

The presence of diesel did not benefit the growth of A. tatarinowii. The germination ratio and germination rate decreased with the increase of diesel concentration, both the lowest value appeared when the concentration of diesel was 10,000 mg?kg^?1. The lowest diesel concentration (2,000 mg?kg^?1) in the soil significantly reduced the length, average diameter, and projected area of root, especially on the stress of the higher diesel concentration (4,000, 8,000, and 10,000 mg?kg^?1). Furthermore, H₂O₂ concentration in leaves rose with the increasing concentration of diesel. However, no DNA oxidative damage to root was observed in our experiment.

Conclusions

Diesel exposure significantly inhabited the seed germination, root elongation, and seedlings growth of A. tatarinowii. Diesel stress caused the accumulation of H₂O₂ in the leaves of A. tatarinowii.     

Boron delays dehydration and stimulates root growth in Eucalyptus urophylla (Blake,S.T.) under osmotic stress

Background

Water and nutritional restrictions are limiting factors for the growth of Eucalyptus trees in tropical climates. In the dry season, boron (B) uptake is severely affected.

Aims

The objectives of this study were to evaluate the phloem mobility of B and whether its deficiency can increase plant sensitivity to osmotic stress. It was also tested to what extent foliar application of B could mitigate the negative effects of drought under low B supply.

Methods

Seedlings of a drought tolerant Eucalyptus urophylla (Blake, S. T.) clone were grown in nutrient solution, subjected to low availability of B for 25 days, and then submitted to a progressive osmotic stress. After imposition of osmotic stress, B was applied to young or mature leaves.

Results

B applications, mainly to mature leaf, stimulated root growth and delayed dehydration under osmotic stress and led to an increased B translocation and carbon isotopic composition. The expression of B transporters and pectin metabolism genes were also increased in water-stressed plants supplied with B by foliar application.

Conclusions

B deficiency led to increased plant dehydration and decreased root growth under osmotic stress. The application of B to mature leaf of water-stressed plants proved effective in mitigating the negative effects of water deficit in root growth.     

Increasing fluctuations of soil salinity affect seedling growth performances and physiology in three Neotropical mangrove species

Background

Micro-tidal wetlands are subject to strong seasonal variations of soil salinity that are likely to increase in amplitude according to climate model predictions for the Caribbean. Whereas the effects of constant salinity levels on the physiology of mangrove species have been widely tested, little is known about acclimation to fluctuations in salinity.

Aims and methods

The aim of this experiment was to characterize the consequences of the rate of increase in salinity (slow versus fast) and salinity fluctuations over time versus constant salt level. Seedling mortality, growth, and leaf gas exchange of three mangrove species, Avicennia germinans, Laguncularia racemosa, and Rhizophora mangle were investigated in semicontrolled conditions at different salt levels (0, 685, 1025, and 1370 mM NaCl).

Results

Slow salinity increase up to 685 mM induced acclimation, improving the salt tolerance of A. germinans and L. racemosa, but had no effect on R. mangle. During fluctuations between 0 and 685 mM, A. germinans and R. mangle were not affected by a salinity drop to zero, whereas L. racemosa took advantage of the brief freshwater episode as shown by the durable improvement of photosynthesis and biomass production.

Conclusions

This study provides new insights into physiological resistance and acclimation to salt stress. We show that seasonal variations of salinity may affect mangrove seedlings’ morphology and physiology as much as annual mean salinity. Moreover, more severe dry seasons due to climate change may impact tree stature and species composition in mangroves through higher mortality rates and physiological disturbance at the seedling stage.     

Phenotypic seedling responses of a metal-tolerant mutant line of sunflower growing on a Cu-contaminated soil series: potential uses for biomonitoring of Cu exposure and phytoremediation

Background and aims

The potential use of a metal-tolerant sunflower mutant line for both biomonitoring and phytoremediating a Cu-contaminated soil series was investigated.

Methods

The soil series (21–1,170 mg Cu kg^?1) was sampled in field plots at control and wood preservation sites. Sunflowers were cultivated 1 month in potted soils under controlled conditions.

Results

pH and dissolved organic matter influenced Cu concentration in the soil pore water. Leaf chlorophyll content and root growth decreased as Cu exposure rose. Their EC₁₀ values corresponded to 104 and 118 μg Cu L^?1 in the soil pore water, 138 and 155 mg Cu kg^?1 for total soil Cu, and 16–18 mg Cu kg^?1 DW shoot. Biomass of plant organs as well as leaf area, length and asymmetry were well correlated with Cu exposure, contrary to the maximum stem height and leaf water content.

Conclusions

Physiological parameters were more sensitive to soil Cu exposure than the morphological ones. Bioconcentration and translocation factors and distribution of mineral masses for Cu highlighted this mutant as a secondary Cu accumulator. Free Cu²⁺ concentration in soil pore water best predicted Cu phytoavailability. The usefulness of this sunflower mutant line for biomonitoring and Cu phytoextraction was discussed.     

Soil silicon amendments increase resistance of sugarcane to stalk borer Eldana saccharina Walker (Lepidoptera: Pyralidae) under field conditions

Background and aims

Soil amendment with silicon (Si) can significantly increase resistance of susceptible sugarcane cultivars grown in pots to stalk borer Eldana saccharina (Lepidoptera: Pyralidae). This study tested the hypothesis that a single application of silicate can increase resistance to E. saccharina and increase yield in field-grown sugarcane.

Methods

Two Si materials (Calmasil® and Slagment® at 4 and 8 t/ha) were applied at planting to a field trial extending over three successive crops and incorporating three sugarcane cultivars varying in borer susceptibility.

Results

Both materials, especially Slagment, significantly increased soil, leaf and stalk Si content, but leaf Si levels seldom exceeded 0.5 %. Silicon treatment significantly reduced percent stalks bored in all three crops and stalk length bored in the second ratoon crop, but did not affect borer numbers per 100 stalks (E/100) or increase cane or sucrose yield. Borer damage and E/100 were significantly and consistently reduced in the resistant cultivar.

Conclusions

We argue that if leaf Si% in field sugarcane can be elevated to or exceed 0.8 %, using materials that release Si slowly, substantial reductions in stalk damage and sucrose loss could be achieved in susceptible cultivars in low-Si soils.     

Soil-mediated local adaptation alters seedling survival and performance

Background and aims

Soils can act as agents of natural selection, causing differential fitness among genotypes and/or families of the same plant species, especially when soils have extreme physical or chemical properties. More subtle changes in soils, such as variation in microbial communities, may also act as agents of selection. We hypothesized that variation in soil properties within a single river drainage can be a selective gradient, driving local adaptation in plants.

Methods

Using seeds collected from individual genotypes of Populus angustifolia James and soils collected from underneath the same trees, we use a reciprocal transplant design to test whether seedlings would be locally adapted to their parental soil type.

Results

We found three patterns: 1. Soils from beneath individual genotypes varied in pH, soil texture, nutrient content, microbial biomass and the physiological status of microorganisms. 2. Seedlings grown in local soils experienced 2.5-fold greater survival than seedlings planted in non-local soils. 3. Using a composite of height, number of leaves and leaf area to measure plant growth, seedlings grew ～17.5% larger in their local soil than in non-local soil.

Conclusions

These data support the hypothesis that variation in soils across subtle gradients can act as an important selective agent, causing differential fitness and local adaptation in plants.     

Species distribution and crown decline are associated with contrasting water relations in four common sympatric eucalypt species in southwestern Australia

Background and aims

Drought-associated vegetation declines are increasingly observed worldwide. We investigated whether differences in water relations can potentially explain the distribution and vulnerability to drought-induced decline of four common tree species in Mediterranean southwestern Australia.

Methods

We compared seasonal and daily water relations of four eucalypt species (i.e. C. calophylla, E. accedens, E. marginata, E. wandoo) when co-occurring as well as on nearby typical sites for each species.

Results

When co-occurring, species generally inhabiting drier regions (i.e. E. accedens, E. wandoo) had lower summer leaf water potentials, osmotic potential, and vulnerability to cavitation and higher stomatal conductance and relative sapflow velocity. Both wetter zone species (e.g. C. calophylla and E. marginata) had remarkably high vulnerabilities to cavitation for Mediterranean woody species but showed greatly improved leaf water status on nearby sites where they dominate. Using local soil moisture retention curves of saprolitic clay layers underlying southwestern Australia we show the large disadvantage that the wetter zone species have in terms of accessing tightly bound water in these layers.

Conclusions

Our work shows that species distribution and local dominance of four dominant overstorey species in southwestern Australia is largely a function of plant water relations interacting with local soil profiles. The observed differences in water relations amongst species are consistent with some of the declines that have been observed in recent decades.     

AtSKIP functions as a mediator between cytokinin and light signaling pathway in Arabidopsis thaliana

Key message

AtSKIP participated in cytokinin-regulated leaf initiation. Putative phosphorylated AtSKIP (AtSKIP ^DD ) displayed the opposite function in the leaf development from AtSKIP transgenic seedlings.

Abstract

AtSKIP, as a multiple protein, is involved in many physiological processes, such as flowering, cell cycle regulator, photomorphogenesis and stress tolerance. However, the mechanism of AtSKIP in these processes is unclear. Here, we identify one gene, AtSKIP, which is associated with cytokinin-regulated leaf growth process in Arabidopsis. The expression of AtSKIP was regulated by cytokinin. Leaf development in AtSKIP overproduced seedlings was independent of light, but promoted by cytokinin, and phosphorylation of AtSKIP (AtSKIP^DD) partially interfered with AtSKIP function as a positive regulator in cytokinin signaling, indicative of true leaf formation, and the defects of AtSKIP^DD in the true leaf formation could be recovered to some extent by the addition of cytokinin. Moreover, different cytokinin-responsive gene Authentic Response Regulator 7 (ARR7) promoter-GUS activity further proved that expression of AtSKIP or AtSKIP^DD altered endogenous cytokinin signaling in plants. Together, these data indicate that AtSKIP participates in cytokinin-regulated promotion of leaf growth in photomorphogenesis, and that phosphorylation interferes with AtSKIP normal function.     

Strong hydraulic segmentation and leaf senescence due to dehydration may trigger die-back in Nothofagus dombeyi under severe droughts: a comparison with the co-occurring Austrocedrus chilensis

Key message

Total leaf hydraulic dysfunction during severe drought could lead to die-back in N. dombeyi , while hydraulic traits of A. chilensis allow it to operate far from the threshold of total hydraulic failure.

Abstract

Die-back was observed in South America temperate forests during one of the most severe droughts of the 20th century (1998–1999). During this drought Austrocedrus chilensis trees survived, whereas trees of the co-occurring species (Nothofagus dombeyi) experienced symptoms of water stress, such as leaf wilting and abscission, before tree die-back occurred. We compared hydraulic traits of these two species (a conifer and an angiosperm species, respectively) in a forest stand located close to the region with records of N. dombeyi mass mortality. We asked whether different hydraulic traits exhibited by the two species could help explain their contrasting survivorship rates. Austrocedrus chilensis had wide leaf safety margins, which appear to be the consequence of relatively high leaf-and-stem capacitance, large stored water use, strong stomatal control and ability to recover from embolism-induced loss of leaf hydraulic capacity. On the other hand, N. dombeyi even though had a stem hydraulic threshold of ?6.7 MPa before reaching substantial hydraulic failure (P₈₈), leaf P₈₈ occurred at leaf water potentials of only ?2 MPa, which probably are reached during anomalous droughts. Massive mortality in N. dombeyi appears to be the result of the total loss of leaf hydraulic conductance leading to leaf dehydration and leaf drop. Drought occurs during the summer and it is highly likely that N. dombeyi cannot recover its photosynthetic surface to produce carbohydrates required to avoid tissue injury in the winter season with subfreezing temperatures. Strong hydraulic segmentation in N. dombeyi does not seem to have an adaptive value to survive severe droughts.     

Endogenous jasmonic and salicylic acids levels in the Cd-hyperaccumulator Noccaea (Thlaspi) praecox exposed to fungal infection and/or mechanical stress

Key message

Sensitivity to Erysiphe in Noccaea praecox with low metal supply is related to the failure in enhancing SA. Cadmium protects against fungal-infection by direct toxicity and/or enhanced fungal-induced JA signaling.

Abstract

Metal-based defense against biotic stress is an attractive hypothesis on evolutionary advantages of plant metal hyperaccumulation. Metals may compensate for a defect in biotic stress signaling in hyperaccumulators (metal-therapy) by either or both direct toxicity to pathogens and by metal-induced alternative signaling pathways. Jasmonic acid (JA) and salicylic acid (SA) are well-established components of stress signaling pathways. However, few studies evaluate the influence of metals on endogenous concentrations of these defense-related hormones. Even less data are available for metal hyperaccumulators. To further test the metal-therapy hypothesis we analyzed endogenous SA and JA concentrations in Noccaea praecox, a cadmium (Cd) hyperaccumulator. Plants treated or not with Cd, were exposed to mechanical wounding, expected to enhance JA signaling, and/or to infection by biotrophic fungus Erysiphe cruciferarum for triggering SA. JA and SA were analyzed in leaf extracts using LC–ESI(?)–MS/MS. Plants without Cd were more susceptible to fungal attack than plants receiving Cd. Cadmium alone tended to increase leaf SA but not JA. Either or both fungal attack and mechanical wounding decreased SA levels and enhanced JA in the Cd-rich leaves of plants exposed to Cd. High leaf Cd in N. praecox seems to hamper biotic-stress-induced SA, while triggering JA signaling in response to fungal attack and wounding. To the best of our knowledge, this is the first report on the endogenous JA and SA levels in a Cd-hyperaccumulator exposed to different biotic and abiotic stresses. Our results support the view of a defect in SA stress signaling in Cd hyperaccumulating N. praecox.     

Effects of antibacterial mineral leachates on the cellular ultrastructure, morphology, and membrane integrity of Escherichia coli and methicillin-resistant Staphylococcus aureus

Background

We have previously identified two mineral mixtures, CB07 and BY07, and their respective aqueous leachates that exhibit in vitro antibacterial activity against a broad spectrum of pathogens. The present study assesses cellular ultrastructure and membrane integrity of methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli after exposure to CB07 and BY07 aqueous leachates.

Methods

We used scanning and transmission electron microscopy to evaluate E. coli and MRSA ultrastructure and morphology following exposure to antibacterial leachates. Additionally, we employed Bac light LIVE/DEAD staining and flow cytometry to investigate the cellular membrane as a possible target for antibacterial activity.

Results

Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging of E. coli and MRSA revealed intact cells following exposure to antibacterial mineral leachates. TEM images of MRSA showed disruption of the cytoplasmic contents, distorted cell shape, irregular membranes, and distorted septa of dividing cells. TEM images of E. coli exposed to leachates exhibited different patterns of cytoplasmic condensation with respect to the controls and no apparent change in cell envelope structure. Although bactericidal activity of the leachates occurs more rapidly in E. coli than in MRSA, LIVE/DEAD staining demonstrated that the membrane of E. coli remains intact, while the MRSA membrane is permeabilized following exposure to the leachates.

Conclusions

These data suggest that the leachate antibacterial mechanism of action differs for Gram-positive and Gram-negative organisms. Upon antibacterial mineral leachate exposure, structural integrity is retained, however, compromised membrane integrity accounts for bactericidal activity in Gram-positive, but not in Gram-negative cells.     

Nutrient partitioning and grain yield of TaNAM-RNAi wheat under abiotic stress

Aims

Decreased expression of TaNAM genes by RNAi results in delayed senescence and decreased grain protein, iron, and zinc concentrations. Here, we determined whether NAM expression level alters onset of senescence under stress conditions, whether delayed senescence in the TaNAM-RNAi line resulted in improved tolerance to post-anthesis abiotic stress, and determined the effects of post-anthesis abiotic stress on N and mineral remobilization and partitioning to grain.

Methods

Greenhouse-grown WT and TaNAM-RNAi wheat were characterized in two studies:three levels of N fertility or water limitation during grain fill. Studies were conducted under both optimal and heat stress temperatures. Senescence onset was determined by monitoring flag leaf chlorophyll.

Results

Under optimal tempertures, TaNAM-RNAi plants had a yield advantage at lower N. TaNAM-RNAi plants had delayed senescence relative to the WT and lower grain protein and mineral concentrations, N remobilization efficiency, and partitioning of N and most minerals to grain.

Conclusions

Nutritional quality of TaNAM-RNAi grain was consistently lower than WT. Delayed senescence of TaNAM-RNAi plants provided a yield advantage under optimal temperatures but not under water or heat stress. Discovery of specific NAM protein targets may allow separation of the delayed senescence and nutrient partitioning traits, which could be used for improvement of wheat.     

Heterologous expression of Arabidopsis C-repeat binding factor 3 (AtCBF3) and cold-regulated 15A (AtCOR15A) enhanced chilling tolerance in transgenic eggplant (Solanum melongena L.)

Key message

Our study shows that the expression of AtCBF3 and AtCOR15A improved the chilling tolerance in transgenic eggplant.

Abstract

In an attempt to improve chilling tolerance of eggplant (Solanum melongena L) plants, Arabidopsis C-repeat binding factor 3 (AtCBF3) and cold-regulated 15A (AtCOR15A) genes both driven by an Arabidopsis RESPONSIVE TO DESSICATION 29A promoter (AtRD29A) were transferred into the plants of eggplant cultivar Sanyueqie. Two independent homozygous transgenic lines were tested for their cold tolerance. The leaves of the transgenic plants in both lines withered much slower and slighter than the wild-type plants after exposure to cold stress treatment at 2 ± 1 °C. The gene expression of AtCBF3 and AtCOR15A was significantly increased as well as the proline content and the levels of catalase and peroxidase activities, while the relative electrical conductivity and the malondialdehyde content were remarkably decreased in the transgenic plants compared with the wild type at 4 ± 0.5 °C. The results showed that the expression of the exogenous AtCBF3 and AtCOR15A could promote the cold adaptation process to protect eggplant plants from chilling stress.