During the last three decades, there have been increased efforts to explore suitable substitutes
for agar namely, carrageenan (Lines, 1977), alginates (Scheurich et al., 1980), ficol (Kao,
1981), gelrite (Pasqualetto et al., 1988), starch (Henderson and Kinnersley, 1988; Nene et al.,
1996), isubgol (Babbar and Jain, 1998), and katira gum (Jain and Babbar, 2002). Consequently, a
number of substances have been used with reasonable success as a substitute for agar. These agents
are not expected to reach universal acceptance due to various reasons. Starch, the cheapest of the
gelling agents used, is not expected to find universal acceptance because of its inferior gelling
ability and poor clarity than agar; and it metabolizes too readily (Kuria et al., 2008). Carrageenan
and alginates gel only in the presence of specific ions, and agarose and ficoll are cost prohibitive
(Jain and Babbar, 2002). Gelrite, another gelling agent, though not a perfect replacement for agar,
has found wide acceptance for plant tissue culture media (Pasqualetto et al., 1988). Isubgol, a
highly cost-effective gelling agent, has all the desirable properties, however, its higher melting
point (~70 °C) necessitates adjustments of pH and quick
dispensing (Babbar and Jain, 1998; Jain
and Babbar, 2002; Jain and Babbar, 2005). Guar gum is not expected to be used for routine purposes
for the same reasons (Jain and Babbar, 2005).
Tragacanth gum, a Persian gum, is the sap of several species of Middle Eastern legumes of
the genus Astragalus, including A. adscendens, A. gummifer, and A. tragacanthus. More than 20
taxa of Astragalus have been reported to yield gum (Gentry et al., 1990) and probably all belong
to the Tragacantha group. After incision of stem, the gum seeps from the plant in twisted ribbons
or flakes which can be powdered. When added to water, tragacanth absorbs water and becomes a
gel. The gel is viscous, odorless and tasteless which consists of water-soluble mixture of polysaccharides,
mainly poly-D-galacturonicacid and bassorin (Mohamadnia et al., 2008). One part of
the gum is miscible and the other part forms a gel of exceptional quality. It is the most viscous
water soluble natural gums and it is an excellent emulsifying agent with good stability to heat,
acidity, and age (Gentry et al., 1990).
The objective of this study was to estimate the physical and biological effects of using tragacanth
as a gelling agent in plant tissue culture media. We tested the gum with MS medium for
shoot proliferation of miniature rose, as a woody model plant, and carnation, as a herbaceous model
plant.
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