Micromorphology of trichomes in the flowers of the horse chestnut Aesculus hippocastanum L.

Abstract

A b s t r a c tAesculus hippocastanum L. is an ornamental tree appreciated for its beautiful flowers and leaves. The flowers of this species contain secondary metabolites exhibiting pharmacological activity. They also produce essential oils and coloured "nectar guides", which enable insects to reach nectar and pollen. The aim of the study was to investigate the types and characteristics of chestnut flower trichomes, which may contain biologically active substances. The analyses were performed using light, fluorescence, and scanning electron microscopy. Three types of trichomes were found on the sepals and the surface of the ovary, whereas the corolla petals exhibited two types of hairs and papillae. The hairs differ in terms of their length and number of cells. The perianth and pistil had no capitate hairs, whereas the ovary exhibited the presence of colleters.Histochemical assays revealed that all the types of trichomes and papillae contained lipids or essential oils; hence, they can be classified as glandular structures. The "nectar guides" were characterised by higher density of secretory hairs than that on the rest of the petal surface, which implies that these petal fragments may emit stronger fragrance.

The uncommon cavitated secretory trichomes inBauhinia s.s.(Fabaceae): the same roles in different organs

“…Rolfe, Cymbidium tracyanum L.Castle, Cyclopogon elatus (Sw.) Schltr., Vanilla dubia Hoehne (Orchidaceae; Vogel, ; Stpiczyńska, ; Wiemer et al ., ; Pansarin & Pansarin, ), Bulbine inflata Oberm. (Asphodelaceae; Naidoo et al ., ), Anadenanthera peregrina (Fabaceae; Marinho et al ., ), Aesculus hippocastanum L. (Sapindaceae; Chwil et al ., ), Citrus sinensis (L.) Osbeck (Rutaceae; Marques et al ., ), Jacaranda oxyphylla Cham. [= J. caroba (Vell.)…”

“…Therefore, the presence of structures that are responsible for the synthesis and release of scent in their floral organs is expected. The vast majority of studies refer to such scent glands as epithelial osmophores (Vogel, ; Endress, ; Marinho et al ., ), with rare reports of trichomes acting in the long‐distance attraction of pollinators (see Vogel, ; Stpiczyńska, ; Guimarães, Di Stasi & Maimoni‐Rodella, ; Wiemer et al ., ; Naidoo et al ., ; Chwil et al ., ; Nadia, Menezes & Machado, ; Marinho et al ., ; Marques et al ., ; Pansarin & Pansarin, ; Boff et al ., ).…”

Characteristics of the secretory structures in the flowers of Rosa rugosa Thunb.

“…In Aesculus hippocastanum, C h w i l et al [17] found colleters to occur also on the ovary of the pistil. Colleters are also present on bud scales and young leaves in Alnus [18].…”

Biological Flora of the British Isles:Aesculus hippocastanum

“…Horse‐chestnut is primarily pollinated by insects and is often regarded as an important bee plant as the flowers provide abundant nectar and pollen for insects (Maurizio & Grafl, ) and glandular trichomes on the sepals and ovary produce olfactory attractants (Chwil, Weryszko‐Chmielewska, Sulborska, & Michońska, ). Synge () lists horse‐chestnut as an important source of pollen early in the year, before Tilia spp.…”

“…Horse-chestnut is primarily pollinated by insects and is often regarded as an important bee plant as the flowers provide abundant nectar and pollen for insects (Maurizio & Grafl, 1969) and glandular trichomes on the sepals and ovary produce olfactory attractants (Chwil, Weryszko-Chmielewska, Sulborska, & Michońska, 2013). Apis mellifera and bumblebees (Free, 1963;Maurizio & Grafl, 1969;Percival, 1955;Weberling, 1989), but flowers are also visited by hoverflies (Kugler, 1970), solitary bees such as Osmia spp.…”