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1

Evidence for the dual role of floral secretory cells in Bulbophyllum

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Stpiczynska M. , Davies K. L.

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nr 2

EN

Floral epidermal cells of most species of Bulbophyllum Thouars studied to date produce both lipid-rich foodrewards and fragrance. Since fragrances largely consist of terpenoids and have an affinity for lipophilic stains, the simultaneous presence of lipid-rich food-rewards frustrates identification of fragrance-secreting cells by conventional histochemistry. Furthermore, since both lipid-rich food-rewards and fragrances are probably synthesized by a similar complement of organelles, interpretation of TEM images can prove difficult. All members of section Racemosae Benth. & Hook. f. investigated to date, however, are unusual in their secretion of a predominantly proteinaceous food-reward, and lipids are seemingly absent. This might enable their use as models for the identification and characterization of fragrance-secreting tissues and organelles. Three members of sect. Racemosae were chosen, namely Bulbophyllum dissitiflorum Seidenf., B. lilacinum Ridl. and B. tricorne Seidenf. & Smitinand. All produced food-rewards. Of these, one (B. dissitiflorum) lacked fragrance and was used as a control, whereas the remaining two species produced fragrance. Having established that the food-reward was mainly proteinaceous in each case, and did not test positively for lipid, we undertook further histochemical investigations, as well as light microscopy, SEM and TEM. Specialized palisade-like epidermal cells of all species contained protein bodies and rough endoplasmic reticulum consistent with the production and secretion of a protein-rich food-reward. Cuticular pores were also present. In fragrant species, these cells also contained abundant smooth endoplasmic reticulum, oil droplets and many, well-developed, spherical plastids with numerous plastoglobuli, similar to those found in the osmophores (fragrance-producing structures) of other orchids. Indeterminate, osmiophilic cytoplasmic inclusions were also present. By contrast, the non-fragrant species lacked oil droplets and other osmiophilic inclusions and the plastids were scant, poorly developed, often elongate or irregular in shape and contained few plastoglobuli. Smooth endoplasmic reticulum was also less frequent. Since food-rewards tested negatively for lipid, it is probable that any oil droplets present were involved in fragrance production, especially since they were absent from the non-fragrant species. Thus, the unusual absence of lipids from the food-rewards of sect. Racemosae provided a rare opportunity, permitting, for the first time, the unraveling of these two secretory processes (food-reward and fragrance) in Bulbophyllum and clearly demonstrating the plasticity of these cells and their dual role in secretion.

2

Nectary structure of Ornithidium sophronitis Rchb.f. (Orchidaceae: Maxillariinae)

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Stpiczynska M. , Davies K. L. , Gregg A.

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nr 2

EN

Most orchids do not produce floral food-rewards. Instead, they attract pollinators by mimicry or deceit. When present, the most common floral food-reward is nectar. To date, nectary structure has been described for only two species of Maxillaria sensu lato, namely Maxillariella anceps and Ornithidium coccineum (formerly Maxillaria anceps and M. coccinea, respectively). Here, we describe that of a third species, Ornithidium sophronitis (formerly Maxillaria sophronitis). This species possesses floral characters concomitant with ornithophily. A ‘faucet and sink’ arrangement is present, with nectar secreted by a protuberance on the ventral surface of the column, collecting between column and tepal bases. The nectary of O. sophronitis shares many features with that of O. coccineum. It has a single-layered epidermis and 3- 5 layers of small, subepidermal, collenchymatous, secretory cells. Beneath these occur 2-3 layers of larger, subsecretory, parenchymatous cells supplied by phloem. Nectary cell vacuoles contain osmiophilic material and proteinaceous intravacuolar bodies. Moreover, distension of the nectary cuticle occurs as nectar accumulates between it and the secretory epidermis. Subsecretory cells, however, have thinner walls and contain flocculent, intravacuolar precipitates that may be related to the presence of flavonoids. Since the floral and nectary structure of O. sophronitis is very similar to that of closely related Ornithidium coccineum, it may have evolved in like manner in response to similar pollinator pressures.

PL

U większości Orchidaceae występują kwiaty mimetyczne lub zwodnicze, które nie wytwarzają atraktantów pokarmowych. Jednak spora grupa storczyków wabi zapylacze obecnością nektaru kwiatowego. Dotychczas budowa nektarników została zbadana jedynie u dwóch gatunków Maxillaria sensu lato: Maxillaria anceps i Ornithidium coccineum. W niniejszej pracy zostały opisane nektarniki u Ornithidium sophronitis (poprzednia nazwa: Maxillaria sophronitis). W kwiatach O. sophronitis, podobnie jak u wcześniej badanego O. coccineum występuje szereg cech związanych z ornitofilią, u obydwu gatunków istnieją również liczne analogie w budowie nektarnika. Nektarnik O. sophronitis ma postać zgrubienia na brzusznej stronie kolumny. Wydzielony nektar zbiera się w zbiorniczku utworzonym pomiędzy podstawą kolumny i listków okwiatu. Nektarnik zbudowany jest z epidermy i 3-5 warstw małych, subepidermalnych, kolenchymatycznych komórek sekrecyjnych. Poniżej znajdują się 2-3 warstwy większych komórek miękiszu subsekrecyjnego. W warstwie tej przebiegają pasma floemu. W wakuolach komórek wydzielniczych występuje osmofilny materiał i ciała białkowe, a kutykula pokrywająca komórki epidermy nektarnika uwypukla się pod wpływem nagromadzonego nektaru. Komórki miękiszu położonego pod warstwą sekrecyjną mają cienkie celulozowe ściany i zawierają kłaczkowate osady w wakuoli, przypuszczalnie związane z obecnością flawonoidów. Podobieństwo budowy kwiatu i mikromorfologii nektarnika O. sophronitis do blisko spokrewnionego gatunku Ornithidium coccineum wskazuje na to, że gatunki te ewoluowały w podobny sposób ze względu na podobną presję zapylaczy.

3

Structure of the cuniculus nectary in Brassavola flagellaris Barb. Rodr. (Laeliinae Benth., Orchidaceae)

80%

Stpiczynska M. , Davies K. L. , Kaminska M.

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nr 1

EN

To date, the structure of the cuniculus nectary has not been studied in detail. Furthermore, the secretory mechanism of such nectaries has not been investigated. The present paper describes, for the first time, the structural organization and ultrastructure of the cuniculus nectary in the moth-pollinated orchid Brassavola flagellaris Barb. Rodr. This tubular structure is situated between the perianth tube and ovary and, in its possession of thick, cellulose cell walls, resembles the nectary of ornithophilous taxa. The presence of large secretory vesicles that fuse with the plasmalemma indicate that granulocrine nectar secretion occurs in this species. The lumen of the cuniculus is lined with unicellular hairs. However, the cuticle overlying the whole epidermal surface lining the lumen (both glabrous and pubescent regions) was coated with nectar residues and became distended and cracked, indicating that this entire tissue is probably involved in nectar secretion.