layer were resuspended in 4 ml of the CPPD medium and
plated in 1 ml aliquots on filter paper placed on the
solidified R medium. About 2–3 weeks later small rooted
plantlets were transferred to a fresh R medium for further
growth. During plant regeneration the cultures were
maintained in a climate room at 26 ± 2C under 16 h
photoperiod and light intensity 55 lmol m-2
s
-1
.
If not mentioned otherwise, all media and solutions were
adjusted to pH 5.8 and autoclaved.
Rooted plants of cv. Dolanka with 3–4 leaves were
transplanted to the moss-coconut fiber substrate (Ceres
International) and acclimatized to ex vitro conditions for
2 weeks in a climate chamber at 20 ± 1C under 16 h
photoperiod and light intensity 30 lmol m-2
s
-1
. In the first
week the relative humidity was adjusted to 90% while in the
second week humidity was reduced by 2% every day. During
acclimatization, the plants were watered moderately.
Characterization of regenerants
Ploidy level of acclimatized plants was determined by flow
cytometry according to Kielkowska and Adamus (2010).
Potted plants were grown in the greenhouse for about
4 months and then they were vernalized for the next
3 months at 10 ± 2C to induce flowering. Pollen viability
was evaluated according to the Alexander’s procedure
(1969) based on differential staining of aborted (colored as
light green) and non-aborted grains (colored as magentared)
(Fig. 1p). When the stigma was receptive the flowers
were self-pollinated and seed set was scored.
Data collection and statistical analysis
Protoplast isolation efficiency was recorded using hemocytometer
and was expressed as protoplast number per
gram of fresh weight (fw) source tissue. Protoplast viability
was assessed by staining with fluorescein diacetate (FDA)
according to Anthony et al. (1999) on the first, second,
third, and sixth day of culture for cv. Dolanka and only on
the first day for the remaining accessions. Briefly, 60 ll of
0.3% filter-sterilized FDA acetone stock solution was
dissolved in 4 ml of culture medium to prepare FDA
working solution. 100 ll of that solution was added to the
Petri dish with culture of immobilized protoplasts. Applegreen
fluorescence of live cells (Fig. 1e) was examined
under Zeiss Axiovert S100 microscope equipped with
the appropriate filter set (kEx = 485 nm, kEm = 515 nm).
The percentage of cell colonies formation (number of cell
colonies/total number of observed protoplasts 9 100) was
determined and expressed as plating efficiency. Additionally,
in the first experiments with Dolanka the number of
two-, four-, and multi-cell colonies was determined at the
same time points.
The treatments were set up in three replicates, 3–4
independent experiments were carried out. For protoplast
viability and colony formation, counting was carried out in
five microscopic fields on 100–300 cells per Petri dish.
The mean values and standard errors were calculated.
The overall effect of treatments was assessed using analysis
of variance (ANOVA) and Tukey’s honestly signifi-
cant difference (HSD) test in Statistica 8.0 (Stat Soft. Inc.).
R