Liquid Culture Systems for in vitro Plant Propagation

500 Han Bouman & Annemiek Tiekstra
agar stayed also more gelled after autoclaving. It is known that physical and
chemical properties of different agar brands can vary considerably (Scholten
and Pierik, 1998b). The problem of precipitation could be overcome by
autoclaving P separately and mixing it with the rest of the medium after
autoclaving (Dalton et al., 1983; Schenk et al., 1991). In practice, such
procedure is undesirable as it involves much additional labour. Analysis of
fresh adapted media showed that the precipitation had no significant effect
on the available concentrations of Ca and P. Table 5 shows that propagation
was much improved by GAM.
Comparison of mineral concentrations in adapted media with
concentrations used in hydroponics showed that the former concentrations
are mostly 2 to 10 times greater than the latter. So, in a few experiments, a
medium was included based on mineral concentrations 5 times greater than
used in hydroponic cultures. This ‘5x’-medium also gave good results,
comparable with the adapted medium.
Analyses of Gerbera media after culture of plant material did not show
exhaustion for any specific macro-element (results not shown). For
ammonium, the lowest residue was found (15 % remained), but there was
still more than 50 % of the nitrate present. This means that the differences in
growth on the media investigated were unlikely due to exhaustion of one of
the elements but likely due to their relative concentrations in the tissue.
Analysis of plant tissues (results not shown) indicated that the main
differences in elemental content were in S, P (MS only), Mg, Ca and Fe.
This was not only caused by the higher concentrations of these elements in
the adapted medium; for example, although K was rather low in GAM, the
plants from GAM had the same K- content as plants from MS and DKW
media with higher K-concentration. The higher uptake and therefore values
found in plants from adapted media especially for Ca, Mg and Fe could be
the main reason for better growth on these media. Because the Fe
concentration in the three media is the same, greater Fe uptake should then
be a result of the differences in relative ion concentrations, whereas a greater
Ca concentration in the adapted medium is directly responsible for its greater
Ca content.
In our experiments, initially we changed only the relative concentrations of
the macronutrients. From the composition of hydroponic solutions, and also
from analysis of the elemental content of plant tissues, it was evident that
with respect to micronutrients, Mn is present at a high concentration in MS
and DKW, whereas Cu is present at a low concentration, particularly in MS,
if compared with hydroponic solutions (see ratios in Table 4). Table 5 shows
that growth on GAM was much improved by decreasing the Mn and by
increasing the Cu concentration. Gerbera plantlets grown on low Mn,
however, were chlorotic. This was reflected by the elemental analysis, which