Nectar and oleiferous trichomes as floral attractants in Bulbophyllum saltatorium Lindl. (Orchidaceae)

Abstract

Although many Orchidaceae have deceit flowers that produce no reward, the most common reward, when present, is nectar. Bulbophyllum, however, is unusual in that the labellar secretions of most species investigated to date lack sugars, and, therefore, cannot be considered true nectar. The African species Bulbophyllum saltatorium is an exception in that it produces not only nectar but also possesses specialized, capitate oleiferous trichomes. The nectary of B. saltatorium is borne on the labellum and is represented by a deep, narrow, median longitudinal groove, having a small aperture, and flanked by trichomes. Isodiametric epidermal cells lining this groove secrete nectar which collects both in the groove and on the surface of the labellum. As well as a nectary, the labellum of B. saltatorium also bears three types of unicellular trichomes: the longest trichomes are borne distally and abaxially; the marginal ones form a rim around the entire labellum, and finally, massive, capitate trichomes occur proximally and adaxially. These are oleiferous, containing large quantities of oil which might function as precursors of volatile components of fragrance or provide a food-reward. To the best of our knowledge, this is the first time for such oleiferous trichomes to be described for Bulbophyllum. Therefore, apart from their color and markings, flowers of this species are able to attract pollinators in at least two, possibly three ways: food-reward in the form of nectar; fragrance; and possibly food-rewards in the form of food-hairs.

Nectar-Secreting and Nectarless Epidendrum: Structure of the Inner Floral Spur

“…Numerous pit-fields with plasmodesmata traversing anticlinal cell walls between epidermal cells, as well as periclinal walls between epidermal and parenchyma cells, may also be indicative of symplastic transport. Abundant plasmodesmata connections have also been reported for the nectary tissues of other plant species having thick collenchymatous cell walls, such as M. coccinea ( Stpiczyńska et al, 2004 ), as well as those with thin-walled nectary cells (e.g., Nepi, 2007 ; Stpiczyńska et al, 2011 , 2018 ). Our results generally agree with the model proposed by Vassilyev (2010) for the functioning of the nectary.…”

“…The thick cell walls of E. nocturnum were particularly remarkable in their possession of wall protuberances thought to improve efficient transport across the plasmalemma. Although cell wall protuberances have frequently been reported for the nectaries of other angiosperms ( Fahn, 1979 ; Kronestedt-Robards and Robards, 1991 ), they have rarely been recorded for Orchidaceae ( Pais and Figueiredo, 1994 ; Stpiczyńska et al, 2018 ). The involvement in intense secretory activity of the epidermal cells enclosing the cuniculus of investigated species of Epidendrum is confirmed by the presence of numerous secretory vesicles that gather next to the plasmalemma, the extensive arrays of endoplasmic reticulum, the abundant mitochondria, and the dictyosomes, as well as invaginations of the plasmalemma that increase the surface area for secretion and possible reabsorption of nectar.…”

“…In Orchidaceae, nectar is the most common floral food-reward, and here, perigonal nectaries located on the labellum predominate ( Bernardello, 2007 ; Davies and Stpiczyńska, 2008 ). They may occur in shallow depressions, as in Epipactis ( Pais, 1987 ; Kowalkowska et al, 2015 ), on the labellar callus, as in Maxillaria anceps ( Davies et al, 2005 ), in the median furrow of the labellum, as in Listera ( van der Cingel, 2001 ) and Bulbophyllum ( Stpiczyńska et al, 2015 , 2018 ), in the labellum base, as in Cleistes ( Pansarin et al, 2012 ), Elleanthus ( Nunes et al, 2013 ) and Psilochilus ( Pansarin and Amaral, 2008a ), but also on the column, as in Maxillaria coccinea and Ornithidium sophronitis ( Stpiczyńska et al, 2004 , 2009 ), or in the mentum, as in Dendrobium finisterrae ( Kamińska and Stpiczyńska, 2011 ). However, the most frequently encountered type of nectary, occurring both in this enormous family and also in other angiosperms, is the nectary spur, which is present in at least 0.60% of angiosperm genera ( Mack, 2013 ; Mack and Davis, 2015 ).…”

Microsporogénesis y micromorfología del polen de la planta Alcea rosea (Malvaceae)

“…Los tricomas nectaríferos florales han sido registrados en algunos grupos de plantas (Vogel, 1997;Lopes et al, 2002;Stpiczyńska et al, 2018;Tölke et al, 2018;Tölke et al, 2019). Sin embargo, estos son característicos de la mayoría de las Malvaceae, en esta familia se ha indicado la presencia de tricomas nectaríferos multicelulares glandulares densamente agrupados en la superficie del cáliz, corola y algunas veces en la base del andróforo o androginóforo (Sawidis et al, 1987;Judd & Manchester, 1997;Vogel, 2000;Bayer & Kubitzki, 2003;Espolador-Leitão et al, 2005;Goldberg, 2009;Lattar et al, 2009;Muneratto et al, 2014;Lattar et al, 2018).…”

Labellum and gynostemium micromorphology in Polystachya (Orchidaceae)

“…Reproductive biology and pollination strategy have been studied for some groups of epidendroids, e.g. Maxillaria (Davies et al 2004;Davies et al 2013), Psilochilus (Pansarin and Amaral 2008), Stanhopea (Pansarin and Amaral 2009), Epidendrum (Pansarin and Pansarin 2014), Gomesa , Bulbophyllum (Stpiczyńska et al 2015(Stpiczyńska et al , 2018, Catasetinae (Pansarin and Maciel 2017) and Heterotaxis (Krahl et al 2019). Flowers of Polystachya display a remarkable range of labellar trichomes (Davies et al 2002, Davies in Kull et al 2009, Pansarin and Amaral 2006.…”