Abstract

Dose-dependent changes in cadmium (Cd) tolerance, non-protein thiol (NP-SH) production and their relationship were investigated in sixteen-day-old flax (Linum usitatissimum L.) seedlings derived from seeds pre-soaked with various salicylic acid (SA) doses and grown hydroponically under increased Cd concentrations (0, 50 and 100 µM CdCl₂). The results show that single Cd subjection decreased root elongation as expressed by tolerance index (TI). Moreover, an overproduction of NP-SH was detected in both roots and shoots. These Cd toxicity effects were directly related to the high levels of Cd amounts in flax tissues as expressed by root and shoot Cd bioaccumulation factors (BAF). In addition, Cd-tolerance of roots TI was negatively correlated with changes in root BAF but positively correlated with shoot BAF. However, positive correlation was illustrated between root TI and NP-SH contents. SA considerably reversed the Cd-induced decrease in root growth parameters and TI. Moreover, in Cd-treated plants, SA pre-soaking prevented Cd accumulation in the shoot as consequence of significant decreases in BAF of roots, Cd transport estimated by the translocation factor (TF) and shoot BAF, respectively. Interestingly, SA pre-treatment reduced BAF of roots and shoots, enhanced NP-SH production in roots and decreased it in leaves. These results suggest that SA might play a preventive role in Cd uptake, sequestration and translocation processes based primarily in roots where SA-enhanced NP-SH contribute to the improvement of flax tolerance to Cd stress.

Key words: Cadmium, salicylic acid, bioaccumulation, growth, non-protein thiols,Linum usitatissimum.

Abbreviation

Cd, Cadmium; NP-SH, non-protein thiol; SA, salicylic acid; TI, tolerance index; BAF, bioaccumulation factors; TF, translocation factor; MBP, metal binding proteins; MBC, metal binding complexes; FW, fresh weight; DW, dry weight; EDTA, ethylenediaminetetraacetic acid; PCs, phytochelatins; DTNB, 5, 5’-dithiobis-2-nitrobenzoic acid; APS, adenosine-5'-phosphosulfate; GSH, glutathione.