Charlotte Poschenrieder

Fast root growth responses, root exudates, and internal detoxification as clues to the mechanisms of aluminium toxicity and resistance: a review

This review on aluminium stress in plants specifically addresses the dynamism of early root growth responses to Al. Three response models, threshold for toxicity, hormesis, and threshold for tolerance, are related to current knowledge on the mechanisms of Al toxicity and resistance. Aluminium exclusion by the production of root exudates and rhizodepositions, as well as internal detoxification mechanisms are considered. Special attention is paid to the central role of chelation of Al by organic acid anions and flavonoid type phenolics outside and inside plant cells.

A glance into aluminum toxicity and resistance in plants.

Aluminum toxicity is an important stress factor for plants in acidic environments. During the last decade considerable advances have been made in both techniques to assess the potentially toxic Al species in environmental samples, and knowledge about the mechanisms of Al toxicity and resistance in plants. After a short introduction on Al risk assessment, this review aims to give an up-to-date glance into current developments in the field of Al toxicity and resistance in plants, also providing sufficient background information for non-specialists in aluminum research. Special emphasis is paid to root growth and development as primary targets for Al toxicity. Mechanisms of exclusion of Al from sensitive root tips, as well as tolerance of high Al tissue levels are considered.

Arsenic and heavy metal contamination of soil and vegetation around a copper mine in Northern Peru

Abstract At present, very little information is available on either the environmental impact or the biogeochemistry of mine sites in Latin America. Here we present preliminary results on contamination of soils and plants around a copper mine in the Andes of Northern Peru. Plants and soils were sampled at six sites ranging from low (S1) to high phytotoxicity (S6); samples were analysed for concentrations of As and heavy metals. Stepwise multiple regression analysis was used in order to determine the soil factors that significantly influenced As and metal availability. High As and Cu concentrations in soil extracts (ammonium acetate-EDTA), in addition to low pH and high Al availability, seem to be the most important soil factors that limit plant performance around the mice. A high organic matter content favoured Cu and Al extractability. Nevertheless, phytotoxicity was more intense at sites with low organic matter concentrations. Unusually high concentrations of As and metal concentrations were detected in leaves of some species (e.g. in Bidens cynapiifolia up to 1430 μg/g dry wt. As, 437 Zn, 620 Cu, 6510 Al and 5.7% Fe) while others (e.g. Eriochloa ramosa) more effectively restricted metal transport to the shoots. These plant species seem interesting for future investigations on both metal tolerance mechanisms and revegetation of contaminated soils at the numerous mine sites located at high altitudes in equatorial regions.

Zinc hyperaccumulation in Thlaspi caerulescens. II. Influence on organic acids

Abstract The influence of different zinc (Zn) concentrations (1.5 to 1500 μM) on organic acid levels in roots and shoots of the Zn‐hyperaccumulator plant Thlaspi caerulescens was investigated. In shoots, malate was the most abundant organic acid (164 to 248 μmol/g f.w.), followed by citrate, succinate, and oxalate. A significant correlation between soluble Zn and both malate and oxalate was observed in shoots, but not in roots. In shoots, a significant correlation between inorganic cation equivalents and organic acid anion equivalents was found. These observations and the finding, that organic acid concentrations were high even under suboptimal Zn supply (1.5 μM) suggest that in T. caerulescens the high organic acid concentration in shoots is a constitutive property. The variation of the organic acid concentrations seem to be a consequence of the cation‐anion balance rather than a specific Zn tolerance mechanism. The constitutively high organic acid concentration may be responsible for the high Zn and iro...

Water Transport Properties of Roots and Root Cortical Cells in Proton- and Al-Stressed Maize Varieties.

Root and root cell pressure-probe techniques were used to investigate the possible relationship between Al- or H+-induced alterations of the hydraulic conductivity of root cells (LPc) and whole-root water conductivity (LPr) in maize (Zea mays L.) plants. To distinguish between H+ and Al effects two varieties that differ in H+ and Al tolerance were assayed. Based on root elongation rates after 24 h in nutrient solution of pH 6.0, pH 4.5, or pH 4.5 plus 50 [mu]M Al, the variety Adour 250 was found to be H+-sensitive and Al-tolerant, whereas the variety BR 201 F was found to be H+-tolerant but Al-sensitive. No Al-induced decrease of root pressure and root cell turgor was observed in Al-sensitive BR 201 F, indicating that Al toxicity did not cause a general breakdown of membrane integrity and that ion pumping to the stele was maintained. Al reduced LPc more than LPr in Al-sensitive BR 201 F. Proton toxicity in Adour 250 affected LPr more than LPc. In this Al-tolerant variety LPc was increased by Al. Nevertheless, this positive effect on LPc did not render higher LPr values. In conclusion, there were no direct relationships between Al- or H+-induced decreases of LPr and the effects on LPc. To our knowledge, this is the first time that the influence of H+ and Al on root and root cell water relations has been directly measured by pressure-probe techniques.

Different Effects of Aluminum on the Actin Cytoskeleton and Brefeldin A-Sensitive Vesicle Recycling in Root Apex Cells of Two Maize Varieties Differing in Root Elongation Rate and Aluminum Tolerance

A relationship between aluminum (Al) toxicity, endocytosis, endosomes and vesicle recycling in the root transition zone has recently been demonstrated. Here the importance of filamentous actin (F-actin)-based vesicle trafficking for Al tolerance has been investigating in maize varieties differing in their Al sensitivities. More Al was internalized into root tip cells of the Al-sensitive variety 16x36 than in the Al-tolerant variety Cateto. The actin cytoskeleton and vesicle trafficking were primary targets for Al toxicity in the root tips of the sensitive variety. Visualization of boron-cross-linked rhamnogalacturonan II (RGII)-containing brefeldin A (BFA) compartments revealed that Al inhibited the formation of these compartments, especially in variety 16x36. The time sequence of Al effects on pectin recycling matches the growth effects of Al in this sensitive variety. These results support the hypothesis that Al binding to pectin-rich cell walls can contribute to reversible inhibition of root elongation. Al-induced alterations on F-actin were most evident in the central part of the transition zone of Al-sensitive 16x36, where Al was localized inside the nucleoli. In relation to this observation, a role for symplastic Al in both irreversible growth inhibition and amelioration of BFA-induced inhibition of root elongation is discussed.

Copper in plant species in a copper gradient in Catalonia (North East Spain) and their potential for phytoremediation

The accumulation of Cu in roots and shoots of 32 plant species growing on soils with a wide range of Cu concentrations (30–18 500 μg g−1 total soil Cu) located in Collserola Mountain (Barcelona, Spain) was analysed. High Cu availability decreased the species diversity in the Hyparrhenietum hirto-pubescentis, the natural plant association at the study sites. Shoot and root Cu concentrations in relation to extractable soil Cu concentrations were used for the evaluation of the Cu resistance strategy in the different species. Saturation of Cu accumulation in roots was observed in most species. Hyparrhenia hirta was the most efficient shoot excluder, while the linear increase of shoot Cu with the Cu soil concentration exhibited the highest slope in Hirschfeldia incana. Most species accumulated more Cu in roots than in shoots. High shoot/root Cu ratios were only found in the highly Cu-resistant Hirschfeldia incana, in the resistant or moderately resistant Spartium junceum and Reseda sp. (R. lutea and R. phyteuma), and in the much less resistant Ononis natrix. Only two species, Hirschfeldia incana and Sedum sediforme were able to support the extreme Cu-toxicity conditions on soils with 5000–16 800 μg g−1 extractable Cu. Among the grass species tested Hyparrhenia hirta was the most Cu-resistant species (up to 1950 μg g−1 extractable soil Cu). The potential usefulness of these pseudometallophytes for phytoremediation of Cu-contaminated soils is discussed.

Kinetics of xylem loading, membrane potential maintenance, and sensitivity of K+-permeable channels to reactive oxygen species: physiological traits that differentiate salinity tolerance between pea and barley

Salt sensitive (pea) and salt tolerant (barley) species were used to understand the physiological basis of differential salinity tolerance in crops. Pea plants were much more efficient in restoring otherwise depolarized membrane potential thereby effectively decreasing K(+) efflux through depolarization-activated outward rectifying potassium channels. At the same time, pea root apex was 10-fold more sensitive to physiologically relevant H2 O2 concentration and accumulated larger amounts of H2 O2 under saline conditions. This resulted in a rapid loss of cell viability in the pea root apex. Barley plants rapidly loaded Na(+) into the xylem; this increase was only transient, and xylem and leaf Na(+) concentration remained at a steady level for weeks. On the contrary, pea plants restricted xylem Na(+) loading during the first few days of treatment but failed to prevent shoot Na(+) elevation in the long term. It is concluded that superior salinity tolerance of barley plants compared with pea is conferred by at least three different mechanisms: (1) efficient control of xylem Na(+) loading; (2) efficient control of H2 O2 accumulation and reduced sensitivity of non-selective cation channels to H2 O2 in the root apex; and (3) higher energy saving efficiency, with less ATP spent to maintain membrane potential under saline conditions.

Influence of silicon pretreatment on aluminium toxicity in maize roots

The influence of Si pretreatment on Al toxicity in an Al sensitive maize variety (Zea mays L. var. BR 201 F) was investigated using root elongation rates (RER) and hematoxylin staining as stress indicators. Plants pretreated with 1 mt M Si (+ Si) and then exposed for 24 h to Al in nutrient solution without concurrent Si supply in the rooting medium exhibited higher RER than plants that were not pretreated with Si (-Si). The ameliorative effect of Si was due to lower Al uptake and to the exclusion of Al from the root tips in + Si plants. Lower Al uptake in + Si plants was not a consequence of decreased Al availability in the bulk solution. The possible mechanisms of Si-induced increase of Al resistance are discussed

Zinc hyperaccumulation in Thlaspi caerulescens. I. Influence on growth and mineral nutrition

Abstract Thlaspi caerulescens, a metallophyte that is able to accumulate up to 4% zinc (Zn) in leaf dry matter, has attracted much attention for its possible use in phytoremediation of metal contaminated soils. In the present study, the influence of Zn supply on mineral nutrition in T. caerulescens was investigated, in order to establish the extent to which growth stimulation by high Zn supply is related to changes in the levels of other essential nutrients. The plants were exposed to nutrient solutions containing 1.5, 100, 500, 750, 1000, or 1500 μM Zn. Zinc supply significantly influenced root and shoot concentrations of essential nutrients, but excepting Zn, the concentrations stayed within the range considered adequate for optimum growth in Brassicaceae crops. Best performance was achieved with the supply of 500 μM Zn. Growth stimulation by this treatment was accompanied by increased translocation of iron (Fe) from root to shoot and a significant correlation between shoot dry weight and Fe concentrati...