Floral nectary structure, nectar production, and carbohydrate composition in theLiliumAsiatic hybrid ‘Trésor’

Abstract

Floral nectary structure, nectar production, and carbohydrate composition were compared from petals (“inner tepals”) and sepals (“outer tepals”) of Lilium Asiatic hybrid ‘Trésor’ (Liliaceae). The six nectaries each occupied a narrow furrow bordered by two convergent ridges extending adaxially from the petal and sepal base. Each sepal nectary furrow was shorter and more concealed. In both nectary types, many vascular bundles comprising xylem and phloem supplied 5.5–8 layers of nectariferous parenchyma cells below the epidermis, which lacked stomata. Transmission electron microscopy of sepal nectaries demonstrated that parts of the outer epidermal wall adhered to an intact but uplifted cuticle in nectar-secreting flowers. Both apoplastic and symplastic routes were continuous from the vascular bundles to the nectary epidermis. Starch breakdown from amyloplasts throughout the nectary likely augmented nectar production. Nectar solute concentration from another Asiatic hybrid, ‘Orange Pixie’, was also significantly higher in petals. In ‘Trésor’, significantly more nectar was available from sepals, possibly reflecting reduced evaporation from multiple nectar droplets within the covered nectary furrow. However, for both hybrids, the same quantity of nectar sugar was produced by petals and sepals. Nectar composition from petals and sepals also was alike, in ‘Orange Pixie’ averaging 67/19/14 (= sucrose/fructose/glucose) and 59/25/17, respectively, and in ‘Trésor’ averaging 68/23/10 and 62/27/12, respectively.