Narcissus and Daffodil

388 E.J.M. Van Damme and W.J. Peumans
activity. Since the lectin is present only at certain stages of development and occurs
in almost all plant tissues, it might also play an active role in plant defence. For
example, the recent discovery that snowdrop and narcissus lectins exhibit toxicity
towards some insects certainly points in this direction. At present the Amaryllidaceae
bulb lectins are considered as storage proteins that can also be mobilised as
defence proteins whenever the plant is attacked by phytophagous invertebrates
(Peumans and Van Damme, 1995; Van Damme et al., 1998a). The occurrence of
multiple isoforms may equip the protein with a broad spectrum of biological activity.
APPLICATIONS OF NARCISSUS LECTINS
Because of their unique and exclusive carbohydrate-binding specificity, lectins
have become very useful tools in glycoconjugate research. In this respect, plant
lectins are often used for the isolation and fractionation of glycoproteins and for
the study of oligosaccharides and glycopeptides (Osawa and Tsuji, 1987; Cummings,
1997; Peumans and Van Damme, 1998). Furthermore, lectins are important
probes in histochemistry and histopathology for the detection of specific carbohydrates
on cells or in tissue sections (Schumacher et al., 1991). An important prerequisite
for the successful application and exploitation of a lectin is its commercial
availability. At present the purified narcissus lectin and preparations derived
therefrom (immobilised lectin, labelled lectin) are available from at least four companies
(EY Laboratories Inc., Sigma Chemical Company, Vector Laboratories Ltd.
and Leuven Bioproducts).
Hitherto, the narcissus lectin has been successfully applied in the purification of
glycoproteins and characterisation of glycopeptides on the surface of cells and/or
proteins. For instance, it was shown that the immobilised narcissus lectin can be
used for the purification of human α 2 -macroglobulin (Van Leuven et al., 1993).
As already mentioned above, the narcissus lectins have a strong inhibitory effect
on the infection of target cells by retroviruses including HIV and cytomegalovirus
in vitro, which makes them very interesting probes in the study of surface components
of some viruses. Based on the highly specific interaction between glycoprotein-
120 (gp120) and the narcissus lectin, an ELISA was developed to determine the
concentration of gp120 in HIV-infected CEM cells in vitro (Weiler et al., 1991).
COMPARISON WITH OTHER LECTINS
The narcissus lectin is a typical representative of the group of monocot mannosebinding
lectins which was first studied in snowdrop (Galanthus nivalis) (Van Damme
et al., 1987). Later it was shown that lectins with similar characteristics and biological
properties also occur in other species of Amaryllidaceae, e.g., Narcissus, Hippeastrum
and Clivia (Van Damme et al., 1988, 1994). It is now clear that this group of
lectins is not confined to Amaryllidaceae species, since examples of lectins isolated
from species belonging to the plant families Alliaceae, Orchidaceae, Araceae, Bromeliaceae
and Liliaceae clearly show DNA and peptide sequence similarity to the
Amaryllidaceae lectins. Hence all these lectins are now considered as members of
the family of monocot mannose-binding lectins (Van Damme et al., 1995, 1998a,b).