LANGENBERGER, M.W. and A.R. DAVIS.* Department of Biology, University of Saskatchewan, 112 Science Place, Saskatoon, Saskatchewan, Canada S7N 5E2. - Patterns of floral nectar production in relation to nectary ultrastructure of caraway (Carum carvi L., Apiaceae).
Despite their tiny size, the perfect florets of many members of the
Apiaceae present a significant opportunity to investigate separated
phases of nectar production by the same nectaries. Florets of caraway
were protandrous and dichogamous, each lasting 7-15 days but
producting nectar for 4-12 days in an interrupted fashion. Nectar
secretion began during a floret's male phase (stamen elongation and
anther dehiscence) but then ceased in an intermediate, neutral phase
of stamen loss and style elongation before a second bout of secretion
resumed during the female phase (stigma receptivity). Female-phase
florets produced a total of about 2.2 times more nectar sugar than
male-phase florets, and 1.5 times more on a daily basis. Total
reabsorption of uncollected male-phase nectar did not result in
greater nectar-sugar production by the same florets once in the female
phase. Also, nectar-sugar composition differed between the two
separated sexual phases, being hexose-rich initially but
hexose-dominant during the female phase. Therefore, despite
involvement of the same nectaries, it appears that nectar secretion in
each sexual phase of caraway florets is at least a
partially-independent process. Currently we are utilizing stereology
of transmission-electron micrographs to quantitatively investigate
ultrastructural features of the nectaries throughout floret phenology,
hoping to elucidate the basis for some of these observed differences
between sexual phases.
Key words: Apiaceae, caraway, Carum carvi, dichogamy, floral nectar, nectary ultrastructure