Narcissus and Daffodil

Narcissus lectins 387
untreated and trypsin-treated rabbit red blood cells were 1.25 and 0.25 µg/ml,
respectively (Van Damme et al., 1988, 1991a).
Analysis of the mitogenic activity of the narcissus lectin towards human lymphocytes
revealed that the lectin is virtually non-mitogenic towards human mononuclear
cells within the concentration range of 1–200 µg/ml (Kilpatrick et al., 1990).
In vitro tests demonstrated that the mannose-specific narcissus lectin shows activity
against human immunodeficiency virus (HIV). The narcissus lectin inhibits
infection of MT-4 cells by HIV-1, HIV-2 and simian immunodeficiency virus (50%
effective concentration being 0.5–0.6 µg/ml; Balzarini et al., 1991; Weiler et al.,
1990) at concentrations comparable to those for dextran sulphate inhibition of
these viruses. Unlike dextran sulphate, the narcissus lectin did not inhibit the replication
of other enveloped viruses except that of human cytomegalovirus. Furthermore,
the lectin suppresses syncytium formation between persistently HIV-1
or HIV-2 infected HUT-78 cells and uninfected MOLT-4 cells (Balzarini et al.,
1991). The narcissus lectin was also shown to prevent rabies virus attachment to
susceptible cells, and affect rubella virus multiplication after the attachment step
(Marchetti et al., 1995).
The lectin was also tested for its toxicity to insects when incorporated into an
artificial diet, as part of a search for the possible function of the lectin in the plant.
The narcissus lectin shows antimetabolic effects towards nymphal stages of the rice
brown planthopper Nilaparvata lugens (Powell et al., 1995) and the peach-potato
aphid Myzus persicae (Sauvion et al., 1996). Insect feeding trials with the narcissus
lectin showed that it exhibits a significant antimetabolic effect towards third instar
nymphs of the rice brown planthopper, although it is less active than the Galanthus
nivalis lectin, the LC50 for the narcissus lectin being 11 µM compared with 4 µM for
the snowdrop lectin (Powell et al., 1995). Similarly, addition of the narcissus
lectin to artificial diets in a concentration range of 10–1500 µg/ml to test the
toxicity and growth-inhibitory effects on nymphal development of the peachpotato
aphid revealed that, although narcissus lectin does not induce significant
mortality, its addition to the diet at 1500 µg/ml resulted in growth inhibition
(Sauvion et al., 1996).
PHYSIOLOGICAL ROLE OF NARCISSUS LECTIN IN PLANTA
The concentration of lectin in various tissues throughout the life cycle of narcissus
was studied by Van Damme and Peumans (1990b). This study revealed that the
lectin is present in almost all plant tissues, representing as much as 10% of the total
protein content during certain stages of development. This is in contrast to most
of the other plant lectins studied thus far, since their distribution is in most cases
confined to one or a few tissues and their concentrations are much lower. Since in
narcissus, as in other Amaryllidaceae species, the changes in lectin content of the
old and new bulb units coincides with the loss and accumulation of storage compounds,
it has been suggested that these lectins may function as storage proteins
which are rapidly degraded as the shoot starts to grow. Furthermore, these lectins
are present in large quantities in a typical storage organ, the bulb, supporting this
hypothesis. Most probably these lectins must be considered as storage proteins
which, as well as their storage role, have an additional carbohydrate-binding