Narcissus and Daffodil

Narcissus lectins 383
very complex elution pattern, indicating that the lectin preparations are mixtures
of isoforms (Van Damme et al., 1988; Van Damme and Peumans, 1990a). The
occurrence of multiple isolectins was confirmed by isoelectric focusing, where the
purified lectins yielded an extremely complex pattern of polypeptide bands of
different intensity, indicating that many isolectins were present, some in higher
concentrations than others. Molecular cloning and sequence analysis of different
cDNA clones encoding the lectin from Narcissus ‘Fortune’, combined with Southern
blot analysis, further revealed that the different isoforms were encoded by
different genes which differed slightly from each other in their sequences (see
below; Van Damme et al., 1992).
A detailed study of the isolectin composition in different species and cultivars of
Narcissus revealed pronounced inter- and intraspecies differences in the isolectin
patterns. Furthermore, analyses of lectin preparations isolated from different
tissues at different developmental stages indicated that the isolectin composition is
both tissue-specific and developmentally regulated. Finally, it was shown that related
cultivars show similar isolectin patterns (Van Damme and Peumans, 1990a).
Developmental regulation of lectin concentration
A detailed study of the developmental changes and tissue distribution of the lectin
in Narcissus ‘Carlton’ using a very sensitive enzyme-linked immunosorbent assay
(ELISA) has shown that the lectin occurs in almost all plant tissues, where it is
present in a very high concentration at the beginning of the growing season (Van
Damme and Peumans, 1990b).
In the bulb, the lectin accounts for 10 to 15% of the total tissue protein during
the dormant phase. However, as the shoot starts to grow the lectin concentration
in the bulb rapidly decreases. At flowering time almost all lectin has disappeared
from the bulb. By the end of the growing season the outer bulb scales have been
degraded. By this time new bulb units have been formed inside the bulb, and by
the end of the growing season they accumulate high concentrations of lectin as
they expand.
High lectin concentrations are also found in the aerial plant parts of narcissus.
However, the lectin concentrations in the aerial parts are about one order of magnitude
lower than in the bulb. As the shoot emerges from the bulb, lectin concentrations
in leaves, stems and flower parts gradually decrease. By flowering time
almost all lectin has disappeared from these tissues.
Molecular cloning of Narcissus lectin
In order to clone the narcissus lectin a cDNA library was constructed from
poly(A)-rich RNA isolated from young developing ovaries, which are known to
contain high concentrations of lectin. Screening of the cDNA library constructed
with mRNA isolated from Narcissus ‘Fortune’, using a previously isolated cDNA
encoding snowdrop (Galanthus nivalis) lectin (Van Damme et al., 1991b), resulted
in the isolation of multiple lectin cDNA clones (Van Damme et al., 1992). Although
the lectin clones showed a high degree of overall sequence homology within their
coding region, they clearly differed from each other in their nucleotide sequences
and deduced amino acid sequences. All cDNA sequences contained an open