Cadmium-induced production of phytochelatins and speciation of intracellular cadmium in organs of Linum usitatissimum seedlings

The capacity of most flax (Linum usitatissimum L.) varieties and cultivars to accumulate cadmium (Cd), underlined by their Cd-tolerant phenotype, brought an interest in their use in phytoextraction of soil Cd to aboveground biomass. The aim of this study was to gain an insight into the mechanism of intracellular detoxification of Cd, by exploring the response of flax seedlings, cultivar AGT 952, to 12 days growth at 50–500 μM Cd. The majority of accumulated Cd (67–74%) was retained in roots, which showed reduced elongation (by 50% at 100 μM Cd) and 3.5 (at 50 μM Cd) to 9.6 (at 500 μM Cd) times higher concentration of Cd than in shoots. Labeling of roots with Leadmium fluorescent marker visualized intracellular localization of Cd. High-performance liquid chromatography of extracts from Cd-treated seedlings revealed induced synthesis of phytochelatins, small intracellular peptides binding Cd through cysteine of their repeating (γ-Glu-Cys)n motives (PCn). Regardless the treatment, PC3 was dominant in all organs and PC2 was restricted to cotyledons. Larger PC4 and PC5 accumulated only in roots grown at 500 μM Cd. Size exclusion chromatography of the organ extracts from seedlings exposed to 100 μM revealed the presence of 2-kDa complexes equated to low-molecular weight (LMW) Cd–PC complexes. In roots, the majority of Cd was stored in ≥9-kDa complex corresponding in apparent molecular mass to stable high-molecular weight (HMW) CdS–PC complexes of yeasts and plants. Data demonstrate that, like in most other plants, the response of flax to Cd involved phytochelatins and suggested that the deposition of Cd in HMW complex should be considered the intrinsic feature reducing translocation of Cd to shoots.

► This study was conducted to better characterize intracellular detoxification of Cd in flax.
► Organs of Cd-treated seedlings accumulated phytochelatins, described for the first time in Linum spp.
► Cotyledons stored intracellular Cd in low-molecular weight (LMW) 2-kDa complexes.
► The majority of intracellular root Cd was stored in ∼9-kDa high-molecular weight (HMW) complexes.
► Pronounced accumulation of Cd in root cells confirmed by Cd fluorescence labeling and its storage in HMW complexes may represent intrinsic feature reducing translocation of Cd to shoots.