Micromorphology of flowers, anatomy and ultrastructure of Chamomilla recutita (L.) Rausch. (Asteraceae) nectary

Abstract

Investigations of the micromorphology of flowers and the structure of nectaries in Chamomilla recutita L. (Rausch.) were carried out with the use of stereoscopic, light, scanning and transmission electron microscopy. Biseriate glandular trichomes consisting of 5-6 cell layers were found on the surface of the corollas of ray and disc florets. Accumulation of secretion within the subcuticular space was accompanied by degradation of trichome cells. Secretion release followed rupture of the cuticle in the apical part of the trichome. The ovary of the ray florets exhibited characteristic ribs covered with epidermis composed of radially elongated palisade cells. Nectariferous glands were present only in the disc florets. The ring-like nectary (93 × 163 µm; height × diameter) was located above the inferior ovary. The gland structure was formed by single-layer epidermis and 5-8 layers of specialised nectariferous parenchyma. Nectar was released via modified 15-20 µm wide stomata. The guard cells were slightly elevated above the surface of the other epidermal cells or were located slightly below them. The stomatal cells were characterised by small external and internal cuticular ledges. No vascular bundles were observed in the nectary. The gland was supplied by branches of vascular bundles reaching the style and ending at the nectary base. The nectariferous tissue was formed by isodiametric cells with a diameter of 11-20 µm. The cell interior was filled with electron dense cytoplasm containing a large nucleus, numerous pleomorphic plastids, mitochondria with a distinct system of cristae, Golgi bodies, ER profiles, and ribosomes. The plastid stroma was characterised by presence of pastoglobuli, intraplastid tubules, and lighter zones. Several small vacuoles were found in each cell. Plasmodesmata were visible in the walls of some cells. Lighter periplasmic space in which apoplastic transport of nectar might take place was observed between the plasmalemma and the cell wall. The presence of an osmiophilic substance in the intercellular spaces additionally corroborates this assumption.