Structure and functioning of oil cavities in the shoot apex of Metrodorea nigra A. St.-Hil. (Rutaceae)

Abstract

This study investigates the histology and subcellular features of secretory cavities during the development of the shoot apex of Metrodorea nigra A. St.-Hil. in order to better understand the functioning of these glands. This Rutaceae species is a very suitable model for studying secretory cavity life span, since the shoot apex exhibits both dormant and growth stages during its annual cycle. Shoot apices were collected during the dormant and growth stages from populations of M. nigra growing under natural conditions. Materials were processed using standard techniques for light and electron microscopy. The secretory cavities originate under the protodermis, and their initiation is restricted to the early developmental stage of shoot organs, which are protected by a hood-shaped structure. Secretory cavities have a multi-seriate epithelium surrounding a lumen that expands schizolysigenously. Oil production begins before lumen formation. When the shoot apex resumes development after the dormant stage, the glands remain active in oil secretion in the developing shoot apex and fully expanded leaves. The mature epithelial cells are flattened and exhibit very thin walls, large oil bodies, leucoplasts surrounded by endoplasmic reticulum, and mitochondria with unusual morphology. The tangential walls of the epithelial cells facing the lumen undergo continuous peeling. The vacuole extrusion appears to be the primary mode of release oil into the lumen, in an exocytotic way. The continuity of oil secretion is ensured by the replacement of the damaged inner epithelial cells by divisions in the parenchyma layer that surround the oil gland, likely a meristematic sheath.

Nectar Replaced by Volatile Secretion: A Potential New Role for Nectarless Flowers in a Bee-Pollinated Plant Species

“…Evidences of cell divisions in the nectary parenchyma, with the newly derivate cells integrating into the secretory tissue, were a common cytological feature to nectariferous and nectarless flowers. This process, quite similarly to that which occurs in meristematic tissues, has been reported in nectaries ( Nepi, 2007 ) and secretory canals and cavities ( Machado et al, 2017a ) revealing the regenerative potential of secretory cells.…”

Estruturas secretoras em folha e caule de Esenbeckia febrifuga (A.St.-Hil.) A. Juss. ex Mart. e Esenbeckia grandiflora Mart. (Rutaceae)

“…Nas espécies analisadas as cavidades possuem epitélio multisseriado, assim como em Zanthoxylum rhoifolium L. (Krause 2013) e Metrodorea nigra A. St.-Hill. (Machado et al 2017). Diferentemente dessas, há cavidades secretoras cujo epitélio é circundado por várias camadas de células e por uma bainha, que no processo de expansão da cavidade se incorpora tardiamente ao epitélio.…”

“…Importantes características das cavidades secretoras de óleo presentes em Esenbeckia febrifuga e E. grandiflora também foram observadas em Metrodorea nigra (Machado et al 2017), como: a origem da cavidade proveniente de células abaixo da protoderme; a formação esquizolisígena das cavidades; presença de epitélio multisseriado com células achatadas de paredes muito delgadas, que se desintegram e são repostas continuamente. Esse fato sugere que essas três espécies podem ter proximidade filogenética.…”

“…As células epiteliais achatadas de paredes delgadas encontradas em E. febrifuga, E. grandiflora e, também em Metrodorea nigra (Machado et al 2017), segundo Liu & Hu (1998), são evidências do desenvolvimento esquizógeno das cavidades.…”

“…Posteriormente, ao longo das sucessivas secreções, ocorre lisigenia no processo de ampliação do lúmen, sendo assim chamada de esquizolisígena. Esse fato também foi observado em outros gêneros de Rutaceae, como Pilocarpus (Spegazzini et al 2002, Muntoreanu et al 2011, Metrodorea (Machado et al 2017) e Citrus (Bennici & Tani 2004). Este fenômeno não é exclusivo da família, ocorrendo também em Fabaceae (Rodrigues et al 2011a, b).…”