Page 224 - Plant-Based Remediation Processes

216 M. Griga and M. Bjelkova ´

Indian linseed cultivars (Garima, Gaurav and Kiran). Cv. Kiran appeared to be least
affected by the presence of Cd. Total protein and proline content increased due to
Cd treatment in callus lines, but there were no differences between cultivars tested.
The plantlets of cv. Garima tolerant to Cd 2+ and Zn 2+ were selected on medium
with equimolar concentrations of both elements. Cd was retained mainly in roots (in
cytoplasm), while Zn was translocated to shoot and accumulated in the cell wall.
Peroxidase activity was lower in the Cd/Zn tolerant plantlets as compared to
sensitive controls.
Tejklova ´ et al. (2007) screened 23 flax and linseed varieties, registered in the
Czech Republic (the same set as reported by Soudek et al. 2010), in vitro on a Cd-
supplemented culture medium. Hypocotyl segments (5–10 mm) from aseptically
germinated seedlings were cultured on MS medium (0.005 μM NAA, 1 μM BAP)
1
with increasing concentrations of Cd(NO 3 ) 2 —0 (control), 5, 10, 50 mg L
medium. After 7 weeks, the following parameters were recorded in proliferating
multiple shoot culture: number of viable and necrotic explants, callus formation,
number of buds, shoots and roots per explant and Cd-content in explants and agar
medium. The investigation of selective Cd concentration showed that 5 and
10 mg L 1 Cd(NO 3 ) 2 caused only weak growth/regeneration reduction in vitro,
while 50 mg was completely lethal. Thus, sublethal concentration 40 mg L 1 Cd
(NO 3 ) 2 was used in further experiments. Significant differences in Cd tolerance
(based on explant viability and growth parameters) were recorded among flax/
linseed varieties (the most tolerant ones: Ilona, Lola, Atalante, Jitka; the most
sensitive ones: Ta ´bor, Marylin, Merkur, Super). AAS analysis showed the content
of Cd differs both among varieties (Jitka, Biltstar, Lola—maximum accumulation;
Atalante, Ilona—minimum accumulation) and among explant parts (callus with
buds absorbed more Cd than shoots). More recently (Smy ´kalova ´ et al. 2010), these
2+
data were extended also to Zn . 25 flax/linseed varieties were screened on suble-
2+
2+
thal Cd (19 mg L 1 Cd ) and Zn (33 mg L 1 Zn ) concentrations using two
regeneration approaches from cultured hypocotyl segments. Both growth
parameters in vitro (number of organogenic points; dry matter) and Cd/Zn accumu-
lation were evaluated. Five flax (Ilona, Jitka, Merkur, Ta ´bor, Venica) and three
linseed cvs (Atalante, Biltstar, Lola) were selected as the best Cd/Zn accumulating
ones and this set was further studied in detail. Flax variety Jitka showed superior Cd
tolerance (¼ explants stayed green onto Cd medium, they produced buds, shoots
and roots) and highest Cd/Zn accumulation capacity. In contrast, cv. Merkur while
being tolerant based on growth parameters in vitro, showed the lowest Cd accumu-
lation. Thus, two different mechanisms of Cd tolerance were proposed in the group
of tolerant cvs (1) the first type is connected with a restricted uptake of Cd ions and
low Cd accumulation in tissues, (2) the second represents easy uptake of Cd ions
and their high accumulation in tissues, where Cd ions are detoxified and deposited
in cytoplasm or vacuole (thus protecting cells and tissues from Cd toxicity). The
main output of extensive in vitro and field experiments of our laboratory is that flax
cv. Jitka represents a genotype with high tolerance to Cd/Zn with good root-to-shoot
transport of HMs and high accumulation of HMs in above-ground biomass. The
determination of contrasting flax genotypes as related to Cd tolerance/accumulation