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aerated vessels often require little or no hardening (AHLOOWALIA & PRAKASH,
2002).
There are numerous differences between leaves formed in vitro and ex vitro:
differences in wax composition, pigmentation content, stomatal response and
photosynthetic performance (HUYLENBROECK et al., 1998). In a study conducted
by HUYLENBROECK et al. (2000) on Calathea plants (Marantaceae) it was shown
that chlorophyll and carotenoid content in leaves formed ex vitro were almost three
times higher than in vitro.
Stomatal aperture can be measured by applying nail varnish to the abaxial surface of
the mature leaf (ROBERTS et al., 1990). The image of the hardened film can then be
analysed. This allows us to assess the degree to which the plant has hardened to in
vivo conditions (ROBERTS et al., 1990).
2.9.10 Applications of in vitro culture
In vitro culture and recombinant DNA technology enable plant improvement through
sexual and para-sexual methods (AHLOOWALIA, 1997). Such methods include
mutation induction, embryo rescue, anther and ovary culture, protoplast fusion and
transgenic methods. Using these methods other flower colours, flower shapes and
growth habits of species in the genus Romulea could possibly be obtained
(AHLOOWALIA, 1997).
2.10 CORM PHYSIOLOGY
One main difference between corms and bulbs is that a corm is a stem base swollen
with food reserves (HUSSEY, 1977a; KRIKORIAN & KANN, 1986). These stem
bases have several nodes, each of which has its own superficial axillary bud
(HUSSEY, 1977a). The leaves around a corm are distinctly different from those of
bulbs. These leaves, which sheath the new corm, are thin and rarely useful as
explants for culture initiation (HUSSEY, 1977a; KRIKORIAN & KANN, 1986).
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