Results and discussion
Regeneration
In order to induce callus a young rosette leaves of the
A. thaliana ecotype Columbia were used as explants. After
2 weeks of culture on callus-inducing medium some of the
calli were transferred onto a shoot-inducing medium, and
the rest was cultured on callus-inducing medium until the
sixth week of culture, after which they were also transferred
on to shoot-inducing media. The efficiency of the
callus induction, estimated after 2 weeks, was 90 %. In
both cases the first shoots were observed 8 weeks after the
transfer of the calli and after 12 weeks of culture on shootinducing
medium about 90 % of them showed signs of
regeneration. A higher number of shoots per callus was
observed in the 2-week old calli (average 1.55 shoots per
callus) than in the 6-week-old ones (1.0 shoot per callus).
In both cultures about 80 % of the regenerated rosettes
developed roots after transferring them onto a root-inducing
medium. The system of indirect organogenesis of A.
thaliana, which is based on callus, shoot and root induction
with the use of specific media allows for a high efficiency
of regeneration; although it depends on the ecotype, the
type of explant, the culture conditions and the medium and
hormones employed (Negrutiu 1976; Akama et al. 1992;
Candela et al. 2001). The composition of callus and shoot
inducing media used here is recommended as efficient for
induction of A. thaliana regeneration from leaf explants
(Feldmann and Marks 1986, Fras and Maluszynska 2003).
The time of preculture on callus inducing media is one of
the crucial steps in the regeneration process. The short time
of preculture has been shown to induce a generally higher
capacity to produce shoots, but the feasibility of organogenesis
is also dependent on the explant and ecotype used
(Valvekens et al. 1988; Akama et al. 1992). The efficiency
of the shoot production was slightly higher in the 2-weekold
calli where more than one shoot per callus was
observed.