Response of Vicia faba L. to metal toxicity on mine tailing substrate: Geochemical and morphological changes in leaf and root

Abstract

a b s t r a c tVicia faba L. seeds were grown in a pot experiment on soil, mine tailings, and a mixture of both to mimic field situations in cultivated contaminated areas near mining sites. Metals in the substrates and their translocation in root, stem and leaf tissues were investigated, including morphological responses of plants growing on mine tailings. Metal concentration -and generally bioaccumulation -was in the order: roots > leaves > stems, except Pb and Cd. Translocation was most significant for Zn and Cd, but limited for Pb. Metal concentration in root and leaf was not proportional to that in the substrates, unexpectedly the minimum being observed in the mixed substrate whilst plant growth was retarded by 20% (38% on tailings). Calcium, pH, organic matter and phosphorus were the main influencing factors for metal translocation. The ultrastructure of V. faba L. cells changed a lot in the mine tailings group: root cell walls were thickened with electron dense Pb, Zn and C particles; in chloroplasts, the number of plastoglobuli increased, whereas the thylakoids were swollen and their number decreased in grana. Finally, needleshaped crystalline concretions made of Ca and P, with Zn content, were formed in the apoplast of the plants. The stratagems of V. faba L. undergoing high concentrations of toxic metals in carbonate substrate, suggest root cell wall thickening to decrease uptake of toxic metals, a possible control of metal transport from roots to leaves by synthesizing phytochelators-toxic metal complexes, and finally a control of exceeded Ca and metal concentration in leaves by crystal P formation as ultimate response to stress defense. The geochemical factors influencing metal availability, guaranty a reduction of metal content in plant growing on mixed tailing/soil substrate as far as carbon te are not completely dissolved.

Arsenic-induced oxidative stress in the common bean legume, Phaseolus vulgaris L. seedlings and its amelioration by exogenous nitric oxide

“…However, three types of crystal structures, such as druses, prismatic and crystal sand in stems and petioles and druses as well as needle-like deposits in leaves were detected as the unique anatomical feature under As treatment. Crystal formation is recently recognized as an avoidance mechanism of plants under metal stress (Probst et al 2009). It usually occurs through substitution of minerals ions (e.g., Ca 2+ ) by metals and subsequent transportation and precipitation of displaced minerals as crystals in apoplast (Sarret et al 2001;Probst et al 2009).…”

“…Crystal formation is recently recognized as an avoidance mechanism of plants under metal stress (Probst et al 2009). It usually occurs through substitution of minerals ions (e.g., Ca 2+ ) by metals and subsequent transportation and precipitation of displaced minerals as crystals in apoplast (Sarret et al 2001;Probst et al 2009). However, for the first time, it is detected in any plant species under As exposure, presumably, preventing damage to shoot through deposition.…”

“…Substantial increase in cell wall thickness in root epidermis, presumably, was involved in declining level of As concentration in roots and concomitant reduction of As level in the shoots of SNP + As-treated plants. Epidermal thickness is one of the mechanisms that plant can develop to limit metal absorption in roots (Liu et al 2005;Probst et al 2009). The lowering of As-induced toxicity due to priming of exogenous NO was also supported by the normal level of leaf chlorophyll and carotenoids and reduced level of RO, an indicator of higher ROS generation, in the roots of Astreated P. vulgaris seedlings.…”

“…Significant increase in root POX level, as observed in this study, might be responsible for cell wall thickness in SNP + As-treated roots. POX is able to catalyze lignin synthesis and is induced in higher plants exposed to toxic metals or other stresses (Prasad 1996;Probst et al 2009;Talukdar 2012b).…”

Exogenously applied nitrate improves the photosynthetic performance and nitrogen metabolism in tomato (Solanum lycopersicum L. cv Pusa Rohini) under arsenic (V) toxicity

“…This might be due to the low extent of As(V) accumulation in root and shoot as nitrate being a nutrient got preference over As(V). Also, nitrate helps in increasing cell wall thickness of root epidermis which checks uptake of As(V) in roots and its further translocation to shoots (Probst et al 2009). Data are mean ± SD of three independent experiments; one way ANOVA was run to check the significance (P B 0.05) and different lower case letters indicate significant differences as per Duncan's test…”