Page 55 - Plant-Based Remediation Processes

3 Metal/Metalloid Phytoremediation: Ideas and Future 43

genetically and by exogenous feeding, enhanced post-translationally the specific
activity of Ser acetyltransferase (SAT), leading to elevated glutathione (GSH)
biosynthesis and, in consequence, increased resistance to nickel. The authors
presume that in Thlaspi hyperaccumulators, the GSH-mediated Ni tolerance is
signalled by the constitutively elevated levels of salicylic acid, and the increased
GSH pool allows Thlaspi to resist the Ni-induced oxidative stress (Freeman et al.
2004). Furthermore, according to Pa ´l et al. (2002), salicylic acid potentially blocks
the activity of phytochelatin synthase to maintain the efficient GSH level to act as
an antioxidant. Relatively numerous studies have been conducted to assess the
influence of seed priming with SA or its addition to the cultivation medium on
metal uptake and plant resistance parameters. Choudhury and Panda (2004) exam-
ined the influence of salicylic acid on cadmium tolerance of Oryza sativa L.
seedlings. Rice seeds were soaked in salicylic acid solution (100 μM) for 16 h
before germination and then treated with CdCl 2 at concentration of 0, 10, 100 and
1,000 μM in a hydroponic culture. After 24 h of cultivation, cadmium accumulation
in roots was greatly (~50 %) lowered for SA primed seeds at the highest Cd
concentration in the cultivation medium. Increasing Cd concentration resulted in
the gradual decrease of root length and dry mass. However, seed treatment with
salicylic acid reduced the negative effect of cadmium on growth parameters,
especially on the dry mass of the roots, which was markedly (as much as twice)
higher for SA-treated seedlings at each Cd concentration. Simultaneously, seed
treatment with SA depleted the membrane damage in roots resulting from lowered
generation of excessive H 2 O 2 . Thus, the content of malondialdehyde (MDA) from
lipid peroxidation was greatly lowered by SA down to ~65 % of SA-untreated seeds
(at 1,000 μM Cd) and was accompanied by the reduction of catalase, guaiacol
peroxidase and glutathione reductase activity. In a study of Belkadhi et al. (2012),
salicylic acid pre-treatment of flax (Linum usitatissimum L.) seeds markedly
alleviated cadmium toxicity to developed seedlings. After 10 days of cultivation,
exogenous SA in concentrations of 250 and 1,000 μM lowered cadmium
bioaccumulation factor (BAF) in roots and shoots, as well as translocation factor
(TF) to the photosynthetic tissue. Furthermore, the total (mainly shoot) dry weight,
shoot-to-root ratio and leaf area significantly increased as an effect of seed priming
with salicylic acid. Enhanced non-protein thiol (NP-SH) production was observed
in flax roots, and decreased in leaves, suggesting a preventative role of salicylic acid
in Cd uptake, sequestration and translocation processes. Popova et al. (2008)
investigated the effect of SA pre-treatment on cadmium toxicity to pea plants
(Pisum sativum L.). Pea seeds were soaked in 500 μM SA for 6 h before germina-
tion and then cultivated for 12 days in medium containing CdCl 2 at 0, 0.5, 1, 2 and
5 μM. SA treatment significantly lowered cadmium accumulation in pea roots in
comparison to SA-untreated seedlings, i.e. from ~480 down to 130 mg kg 1 DW at
5 μM Cd, and reduced the inhibitory effect of cadmium on growth parameters (roots
and shoots fresh weight). Simultaneously, SA alleviated the negative impact of Cd
on photosynthesis and carboxylation reactions and showed a stabilising effect on
thermo luminescence characteristics of pea leaves. In addition, at moderate Cd
concentrations (1 and 2 μM), SA treatment lowered by about half the metal-induced