title: Annular floral nectary with oil-producing trichomes in Salvia farinacea (Lamiaceae): Anatomy, histochemistry, ultrastructure, and significance.
abstract: OBJECTIVE
  Many angiosperms produce nectar that entices pollinator visits. Each floral nectary tends to embody a singular form, such as the receptacular ring arising beneath the ovary in mint flowers (Lamiaceae). Exceptionally, the annular floral nectary in Salvia farinacea possesses modified stomata plus secretory trichomes. This first study of nectary ultrastructure within the largest genus of Lamiaceae examined this unusual condition.
  
  
  METHODS
  Nectary anatomy, histochemistry, and ultrastructure were investigated from fresh and fixed material using light microscopy and scanning electron and transmission electron microscopy.
  
  
  RESULTS
  The annular nectary encircled the ovary plus extended ventrally as a projection. Modified stomata occurred only in the projection's abaxial epidermis. Conversely, peltate trichomes with a basal cell, a stalk cell, and 4-7 head cells were interspersed among the ovary lobes and covered the projection's adaxial surface. Phloem and xylem supplied the nectary interior, where parenchyma cells had numerous mitochondria and plastids with little starch, but few dictyosomes and little endoplasmic reticulum. Nectar accumulated as a drop opposite the projection's abaxial surface, escaping through stomatal pores and probably the cuticle. However, the annular nectary's glistening trichomes secreted a Sudan-positive product largely retained below the distended cuticle, but not nectar.
  
  
  CONCLUSIONS
  This first ultrastructural study of co-occurring secretory trichomes and modified stomata on a mint nectary suggests multiple interactive functions for this atypical structure. These trichomes-possibly generating a substance informative to pollinators or as an ovarian defense against phytophagy-produced oil in an aqueous milieu, rather than contributing fluid to nectar.
authors.affiliation: College of Life Sciences, Shaanxi Normal University, Xi'an 710062, China.
authors.forename: Xiaohui
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada.
authors.forename: Vipen K
authors.initials: VK
authors.lastname: Sawhney
authors.affiliation: Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, S7N 5E2, Canada.
authors.forename: Arthur R
authors.initials: AR
authors.lastname: Davis
mesh_terms: D035264:Flowers / Q000033:anatomy & histology / Q000378:metabolism / Q000648:ultrastructure*; D046529:Microscopy, Electron, Transmission; D052585:Phloem / Q000033:anatomy & histology / Q000378:metabolism / Q000648:ultrastructure; D057048:Plant Nectar / Q000378:metabolism; D054046:Plant Stomata / Q000033:anatomy & histology / Q000378:metabolism / Q000648:ultrastructure; D018087:Plastids / Q000378:metabolism / Q000648:ultrastructure; D054817:Pollination; D027544:Salvia / Q000033:anatomy & histology / Q000378:metabolism / Q000648:ultrastructure*; D064201:Trichomes / Q000033:anatomy & histology / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D057048:Plant Nectar
keywords: Lamiaceae; Salvia farinacea; annular floral nectary; modified stomata; nectar; oil; secretory trichomes; ultrastructure; vascular tissue