Page 225 - Plant-Based Remediation Processes

11 Flax (Linum usitatissimum L.) and Hemp (Cannabis sativa L.)... 217

(Tejklova ´ et al. 2007;Smy ´kalova ´ et al. 2010; Bjelkova ´ et al. 2011a,b)
enabled the study of proteome changes as well as the phytochelatin induction by
Cd stress, in order to better understand mechanisms of HMs tolerance in flax/linseed.
Hradilova ´ et al. (2010) compared proteomic changes of two contrasting genotypes
(Jitka—tolerant/high Cd accumulation; Ta ´bor—low tolerant to sensitive/high Cd
accumulation) in suspension cultures upon Cd exposure (10, 50 and 100 μMCd
(NO 3 ) 2 ). Significant changes in the expression of 14 proteins (2-DE followed by
MALDI-TOF/TOF MS) were detected (proteins related to disease/defence, metabo-
lism, protein destination and storage, signal transduction, energy and cell structure).
Two proteins, ferritin and glutamine synthetase (a key enzyme in glutathione biosyn-
thesis) were only up-regulated by Cd in cv. Jitka, indicating that Cd tolerance
mechanisms in this cultivar may include maintenance of low Cd levels at sensitive
sites by ferritin and low-molecular weight thiol peptides binding Cd. Vrbova ´ et al.
(2009) studied phytochelatins (PCs) induction by Cd treatment in the same experi-
mental design of suspension cultures of cv. Jitka and Ta ´bor. Samples were collected
after 3, 12, 24 and 48 h after Cd treatment and analysed using the adsorptive transfer
stripping (AdTS) linear sweep voltammetry at HMDE. Results show remarkable Cd
concentration- and time of cultivation-dependent changes in the PCs levels. In both
cultivars, 10 μMCd(NO 3 ) 2 appeared to induce PC accumulation without affecting
the cells viability. Lower PC levels observed for cv. Ta ´bor cultivated in the
presence of 50 μMCd(NO 3 ) 2 for 3–24 h can be attributed to inhibition of cell
growth and/or dying of certain population of the cells at this Cd level, while the
intense signal observed after 48 h to accumulation of high PC levels in surviving
cells. In the more tolerant cv. Jitka, much lower PC levels were observed during
cultivation in 50 μMCd(NO 3 ) 2 , which may be in agreement with the speculation
(Fojta et al. 2006) that extremely high amounts of the induced PCs may contribute
to the heavy metal lethality. The prevailing lethal effect of 100 μMCd(NO 3 ) 2 ,in
agreement with no or only relative small increase of the induced PC amounts, was
detected in both flax cvs. The results indicate that the upper limit of Cd tolerance in L.
usitatissimum cell suspension is 50 μM (depending also on cultivar) and higher
concentrations cause toxicity to the cells. PCs changes were significantly enhanced
with increasing concentrations of Cd in the medium. Najmanova et al. (2012)studied
Cd-induced PCs induction and intracellular Cd localisation in 12-days-old linseed
seedlings (line AGT 952) grown on agar medium supplemented with 50–1,000 μM
CdCl 2 . Majority of accumulated Cd was retained in roots, which showed reduced
elongation as related to Cd concentration in the medium. Several classes of PCs
(PC2, PC3, PC4, PC5) were detected by HPLC in seedlings organs. 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. In roots,
the majority of Cd was stored in 9 kDa complex corresponding by molecular mass
to stable high-molecular weight (HMW) CdS–PC complexes of yeasts and plants.
Data of both studies demonstrate that response of flax to Cd involves phytochelatins
and suggest the deposition of Cd in HMW complex in root should be considered
as a mechanism preventing Cd translocation to shoot. Nevertheless, there is necessary
to study these processes in complete flax plants differing in HMs (Cd) uptake,