Arabidopsis thaliana | EPFL Graph Search

Arabidopsis thaliana, the thale cress, mouse-ear cress or arabidopsis, is a small plant from the mustard family (Brassicaceae), native to Eurasia and Africa. Commonly found along the shoulders of roads and in disturbed land, it is generally considered a weed. A winter annual with a relatively short lifecycle, A. thaliana is a popular model organism in plant biology and genetics. For a complex multicellular eukaryote, A. thaliana has a relatively small genome of around 135 megabase pairs. It was the first plant to have its genome sequenced, and is an important tool for understanding the molecular biology of many plant traits, including flower development and light sensing. Description Arabidopsis thaliana is an annual (rarely biennial) plant, usually growing to 20–25 cm tall. The leaves form a rosette at the base of the plant, with a few leaves also on the flowering stem. The basal leaves are green to slightly purplish in color, 1.5

Phytoextraction of heavy metals by hyperaccumulating and non hyperaccumulating plants

Claudia Cosio

Although phytoextraction using hyperaccumulating plants is seen as a promising technique, a lack of understanding of the basic physiological, biochemical, and molecular mechanisms involved in heavy metal hyperaccumulation prevents the optimization of the phytoextraction technique and its further commercial application. The best-long term strategy for improving phytoextraction is therefore to understand and exploit the biological processes involved in metal acquisition, transport and shoot accumulation in plants. In order to compare Cd allocation in leaves and the role of the leaf cells in hyperaccumulating and non hyperaccumulating plants, we used a wide range of techniques and approaches on contrasting ecotypes of Thlaspi caerulescens, Arabidopsis halleri, Arabidopsis thaliana and one high biomass crop Salix viminalis. As a first step, the extent of hyperaccumulation and tolerance was studied in different plants. Five Swiss T. caerulescens populations were compared for their tolerance and Cd hyperaccumulation to two well studied populations: T. caerulescens Ganges (France) and T. caerulescens Prayon (Belgium). We showed that the behaviour of the populations in hydroponics was linked to the characteristics of their soil of origin. However, growing plants in hydroponics with 1 μM Cd seemed to be adequate to discriminate the various populations tested for hyperaccumulation. Cadmium effect on morphological parameters and Cd accumulation in S. viminalis leaves was also monitored. Salix viminalis was surprisingly tolerant to Cd and high Cd concentration in shoots. Because it may give an indication of the tolerance mechanisms employed by the different plants, we studied the general Cd allocation in leaves of hyperaccumulating (Ganges) and non-hyperaccumulating plants (Prayon, S. viminalis). Surprinsingly, when grown in hydroponics the only differences found between Prayon and Ganges at the leaf level was concentration of Cd found in the storage sinks. Results also showed similarities between T. caerulescens and S. viminalis in Cd storage, although the Cd concentrations found in leaves differed greatly. Both point-like accumulation and accumulation at the edges of the leaves were observed. A link could be established with visible symptoms (necrosis). At last differences in Cd localization between young and mature leaves were observed. These differences were attributed to physiological differences between leaves. Salix viminalis and T. caerulescens were both able to reduce Cd toxicity by allocating Cd in less sensitive tissues. Cadmium was found inside the cells and in the cell walls of the leaves of T. caerulescens, but mainly in cell walls and to a lesser extent in the symplasm in S. viminalis. Metal allocation in both plants indicated that the plant general growth strategy governed metal accumulation. We further investigated the role of the leaf cells in allocating Cd in leaves of Ganges, A. halleri and Prayon by characterizing Cd uptake in mesophyll protoplasts. Results indicated that differences in metal uptake could not be explained by different constitutive transport capacities at the leaf protoplast level. However, pre-exposure of the plants to Cd induced an increase in Cd accumulation in protoplasts of Ganges, whereas it decreased Cd accumulation in A. halleri protoplasts. The experiment with competitors eventually showed that probably more than one single transport system are carrying Cd in parallel into the cell. Metal allocation indicates that the principle of metal storage in metabolically less sensitive plant parts governs metal accumulation. Vacuolar compartmentalization and cell wall binding in leaves could therefore both play a role in accumulation of heavy metals. Based on these various results, we suggested that metal storage in plant demands the involvement of more than one compartment. Further work is however needed to assess many steps of the trafficking of metals that remain enigmatic.

EPFL2004

The NPR1-dependent salicylic acid signalling pathway is pivotal for enhanced salt and oxidative stress tolerance in Arabidopsis

Amandine Massart

The role of endogenous salicylic acid (SA) signalling cascades in plant responses to salt and oxidative stresses is unclear. Arabidopsis SA signalling mutants, namely npr1-5 (non-expresser of pathogenesis related gene1), which lacks NPR1-dependent SA signalling, and nudt7 (nudix hydrolase7), which has both constitutively expressed NPR1-dependent and NPR1-independent SA signalling pathways, were compared with the wild type (Col-0) during salt or oxidative stresses. Growth and viability staining showed that, compared with wild type, the npr1-5 mutant was sensitive to either salt or oxidative stress, whereas the nudt7 mutant was tolerant. Acute salt stress caused the strongest membrane potential depolarization, highest sodium and proton influx, and potassium loss from npr1-5 roots in comparison with the wild type and nudt7 mutant. Though salt stress-induced hydrogen peroxide production was lowest in the npr1-5 mutant, the reactive oxygen species (ROS) stress (induced by 1 mM of hydroxyl-radical-generating copper-ascorbate mix, or either 1 or 10 mM hydrogen peroxide) caused a higher potassium loss from the roots of the npr1-5 mutant than the wild type and nudt7 mutant. Long-term salt exposure resulted in the highest sodium and the lowest potassium concentration in the shoots of npr1-5 mutant in comparison with the wild type and nudt7 mutant. The above results demonstrate that NPR1-dependent SA signalling is pivotal to (i) controlling Na+ entry into the root tissue and its subsequent long-distance transport into the shoot, and (ii) preventing a potassium loss through depolarization-activated outward-rectifying potassium and ROS-activated non-selective cation channels. In conclusion, NPR1-dependent SA signalling is central to the salt and oxidative stress tolerance in Arabidopsis.

Oxford University Press2015

Over-expression of PHO1 in Arabidopsis leaves reveals its role in mediating phosphate efflux

Michaël Bensimon, Charles Vidoudez

P>Inorganic phosphate (Pi) homeostasis in multi-cellular eukaryotes depends not only on Pi influx into cells, but also on Pi efflux. Examples in plants for which Pi efflux is crucial are transfer of Pi into the xylem of roots and release of Pi at the peri-arbuscular interface of mycorrhizal roots. Despite its importance, no protein has been identified that specifically mediates phosphate efflux either in animals or plants. The Arabidopsis thaliana PHO1 gene is expressed in roots, and was previously shown to be involved in long-distance transfer of Pi from the root to the shoot. Here we show that PHO1 over-expression in the shoot of A. thaliana led to a two- to threefold increase in shoot Pi content and a severe reduction in shoot growth. 31P-NMR in vivo showed a normal initial distribution of intracellular Pi between the cytoplasm and the vacuole in leaves over-expressing PHO1, followed by a large efflux of Pi into the infiltration medium, leading to a rapid reduction of the vacuolar Pi pool. Furthermore, the Pi concentration in leaf xylem exudates from intact plants was more than 100-fold higher in PHO1 over-expressing plants compared to wild-type. Together, these results show that PHO1 over-expression in leaves leads to a dramatic efflux of Pi out of cells and into the xylem vessel, revealing a crucial role for PHO1 in Pi efflux.

Wiley-Blackwell2011