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11 Flax (Linum usitatissimum L.) and Hemp (Cannabis sativa L.)... 219

be a cost and success of such approach. Thus, the more logical next step will be to
engineer transgenic fibre crops with genes responsible for HMs transport or accu-
mulation from wild plant species (hyperaccumulators) or from organisms other than
plants (e.g. mammalian metallothionein—Vrbova ´ et al. 2012).

11.5.2 Organ Distribution of Heavy Metals

There are two opposite requests for HMs accumulation (1) hygienic or food aspect
prefers high retention of toxic metals in the roots with minimum transport to edible
parts (seeds), while (2) phytoremediation aspect stresses the easy transport of HMs
to above-ground biomass. Studies of heavy metal accumulation in flax plants
mostly exhibited maximum concentrations in roots. Common concentration gradi-
ent for Cd is following: root > shoot > capsule seed (Bo ¨hm et al. 1992;Bo ¨hm
and Marquard 1993a, b; Baraniecki et al. 2001; Jiao et al. 2004; Angelova et al.
2004). Nevertheless, the concentrations overcoming hygienic limit in seeds (0.3 mg
Cd kg 1 DW) were very often observed, sometimes exceeding also stem concen-
tration (Gaudchau and Marquard 1990; Heyn and Janssen 1991). Grabowska and
Baraniecki (1997) and Baraniecki et al. (2001) found the highest Pb and Cu
concentrations in capsules and Zn in seeds. Grzebisz et al. (1997a) found in Pb
following concentration gradient: root > shoot > seed > capsule, in Cu: capsule >
root > seed > shoot (see also Mankowski et al. 1994). In contrast, Straczynski
and Andruszczak (1996) reported the highest accumulation of Pb in capsules and
Cd in shoot of flax irrespective of various degree of Cu and Pb pollution of tested
soils. As related to produced biomass of flax/linseed, the total Cd accumulation
(concentration biomass) in particular organs may exhibit following gradients:
shoot > seed > capsule ¼ root (Bo ¨hm and Marquard 1993a, b; Schneider et al.
1996), shoot > root > seed > capsule (Cieslinski et al. 1996; Bjelkova et al. 2001).
Artificial increase of soil Cd (above natural levels) resulted in higher Cd accumula-
tion in roots (Bjelkova et al. 2001) and in the shift of distribution between plant
parts—seeds accumulated more Cd, while shoots less Cd (Bo ¨hm and Marquard
1993a, b). Hocking and McLaughlin (2000) found—by comparison of Cd distribu-
tion in several crops, namely linseed, canola, Indian mustard, two lupin species and
wheat—that physiological mechanisms preventing Cd translocation from the fruit
to seeds are much less effective in linseed than in all other studied crops. Also
Becher et al. (1997) considered differences in Cd translocation from fruit to seeds of
linseed as the main feature of genotype variability of Cd accumulation in the seed.
As mentioned before, majority of published reports on Cd uptake by flax/linseed
was dealing with natural (geogenic) or slightly increased soil Cd concentrations
(usually less than 0.5 mg Cd kg –1 soil), which may be categorised as non Cd-
contaminated soils. Unfortunately, in such soil (which is probably true also for
other metal elements and other culture crops) the varietal differences in tolerance/
accumulation as well as differences in organ distribution of HMs are not clearly
evident. These differences are better visible on soils with HMs concentrations