Yazmín Carreón-Abud

Chromate induces adventitious root formation via auxin signalling and SOLITARY-ROOT/IAA14 gene function in Arabidopsis thaliana

Morphological root plasticity optimizes nutrient and water uptake by plants and is a promising target to improve tolerance to metal toxicity. Exposure to sublethal chromate [Cr(VI)] concentrations inhibits root growth, decreases photosynthesis and compromises plant development and productivity. Despite the increasing environmental problem that Cr(VI) represents, to date, the Cr tolerance mechanisms of plants are not well understood, and it remains to be investigated whether root architecture remodelling is important for plant adaptation to Cr(VI) stress. In this report, we analysed the growth response of Arabidopsis thaliana seedlings to concentrations of Cr(VI) that strongly repress primary and lateral root growth. Interestingly, adventitious roots started developing, branched and allowed seedlings to grow under highly growth-repressing Cr(VI) concentrations. Cr(VI) negatively regulates auxin transport and response gene expression in the primary root tip, as evidenced by decreased expression of auxin-related reporters DR5::GFP, DR5::uidA and PIN1::PIN1::GFP, and then, another auxin maximum is established at the site of adventitious root initiation that drives adventitious root organogenesis. Both primary root growth inhibition and adventitious root formation induced by high Cr(VI) levels are blocked by a gain-of-function mutation in the SOLITARY-ROOT/IAA14 gene of Arabidopsis. These data provide evidence that suggests a critical role for auxin transport and signalling via IAA14/SLR1 in the developmental program linking Cr(VI) to root architecture remodelling.

Effect of mineral nutrients on the uptake of Cr(VI) by maize plants

To determine the potential of maize plants for phytoextraction of chromium (Cr), and the effect that some mineral nutrients have on this process, the uptake of this metal was analyzed in vitro. 12-day-old plants were incubated in nutrient solutions with 200 or 250 μM potassium chromate and 3mM supplements of nitrate, phosphate or sulfate. The greatest accumulation of Cr after 48 hours was in plants that were supplemented with nitrate (800 and 350 mg kg(-1) DW for roots and stems, respectively) with bioaccumulation factors of 18 and 7 in the roots and in the foliage, respectively. Moreover, the translocation factor from root to leaves was 0.4 when nitrate was supplemented; thus, the addition of this nutrient is recommended when the crop is to be used for phytoextraction of Cr. Considering the results obtained, the high biomass produced by this crop and the extensive knowledge of agricultural practices for this plant, we believe that maize has the potential to be considered in the phytoextraction of Cr, based on preliminary assays of soil conditions.

Respuestas morfogénicas de las raíces de Arabidopsis thaliana (Magnoliophyta: Brassicales) al estrés de Cr(VI)

La respuesta del crecimiento de las raices ante las condiciones de estres es una estrategia que le permite a la planta ya sea evadir las condiciones adversas o bien adaptarse a estas. Las actividades humanas han ocasionado la acumulacion de algunos metales que a partir de ciertas concentraciones tienen un efecto adverso en el crecimiento de las plantas. Entre estos metales se encuentra el Cromo (Cr), el cual es un serio contaminante generado por industrias de tratamiento de metales y del curtido de pieles. Para entender de manera detallada la respuesta de las raices al estres del Cr(VI), se utilizo un sistema in vitro con Arabidopsis thaliana usando 3 condiciones experimentales. (A) Plantas germinadas y crecidas por 6 dias, sin raices laterales, transferidas a medios con diferentes concentraciones de Cr(VI). Esto permitio evaluar como se afectaba el crecimiento de la raiz primaria al pasar rapidamente del medio MS al medio MS con Cr(VI) y en que medida se estimulaba o inhibia la formacion y crecimiento de nuevas raices laterales. (B) Plantas germinadas y crecidas durante 8 dias, con raices laterales, transferidas a medios con diferentes concentraciones de Cr(VI). Esta condicion permitio evaluar como se afectaba el crecimiento de raices primarias y raices laterales previamente formadas al pasar rapidamente del medio MS a medios suplementados con Cr(VI). Ademas, permitio comparar como se comportaban las raices laterales nuevas con respecto a las ya existentes

Total Chromium Captured by Maize (Zea Mays) Plants is Increased by Phosphate and Iron Supplementation in the Soil

ABSTRACT In this work, a commercial hybrid maize was used, and the effect of selected mineral nutrients [sulfur (S), phosphorus (P), iron (Fe), and nitrogen (N)] on the chromium (Cr) captured by plants was analysed. Seeds were germinated in vitro, and plants were transferred to pots with soil supplemented with a growth inhibitory Cr concentration and different mineral nutrient combinations. Plants were grown for 13 weeks and irrigated with water. In the harvested plants, total Cr was determined considering the Cr concentration in tissues and the biomass as dry weight. The soil supplemented with phosphorus (P) or Fe improved the total Cr captured by plants by a quarter. Bioconcentration values in plant tissues were similar to those of other plants grown in soil with Cr. This information will be useful either for Cr phytoremediation or to protect commercial maize crops cultivated in Cr contaminated soils.