Structure and development of the secretory cavities of Myrtus communis leaves

Abstract

The structure and development of Myrtus communis L. secretory cavities has been studied in young and expanded leaves, using light and scanning electron microscope. Secretory cavities are continuously formed during leaf development, but in mature leaves the rhythm of their appearance shows steep decrease. Each secretory cavity is developed from a single epidermal cell, which undergoes a periclinal division followed by anticlinal and several oblique cell divisions. The lumen of the secretory cavity is initiated by cell wall separation, i.e., schizogenously. The secretory cells line the cavity, where the secreted material is collected. Secretory cavities are covered by modified epidermal cells, which do not seem to form any special aperture. Essential oils seem to be discharged after mechanical treatment of the leaf.Additional key words: anticlinal and periclinal divisions, essential oils, myrtle, scanning electron microscope.

The flower of Myrtus communis (Myrtaceae): Secretory structures, unicellular papillae, and their ecological role

“…Contradictory views have been suggested concerning the origin of the intercellular space of the secretory cavity. It has been supported that in the vegetative parts of M. communis the lumen is schizogenously formed (Brocheriou and Belin-Depoux, 1974;Kalachanis and Psaras, 2005). Moreover, recent ontogenetic investigations on the vegetative organs of other genera of Myrtaceae (Eucalyptus, Callistemon, Eugenia, Leptospermum, Melaleuca, Psidium) showed schizogenous development of the lumina in this family (Brocheriou, 1976;Brocheriou and Belin-Depoux, 1974;Carr and Carr, 1970;Fahn, 1979).…”

“…List et al (1995) reported that glands of M. alternifolia leaves are covered by modified epidermal cells and that under a differential pressure the secreted oil was able to pass the epidermal lining. Kalachanis and Psaras (2005) showed that secretory pockets of M. communis leaves are capped by one to four modified epidermal cells without any opening and that under vacuum of the SEM column the secreted material passed through the cap cells covering the secretory cavity. In accordance with List et al (1995), and Kalachanis and Psaras (2005), our light microscope examinations revealed that the cap cells of the floral secretory cavities of myrtle are thicker-walled epidermal cells, that stain intensely with TBO and PAS.…”

“…According to Brocheriou and BelinDepoux (1974), Ciccarelli et al (2003), and Kalachanis and Psaras (2005), Myrtus secretory cavities develop from a single epidermal cells. Data reported here show that the ontogeny of these pockets follows a schizolysigenous development, a term introduced by Tschirch (1906) to describe the oil glands ontogeny of Myrtaceae.…”

“…In plants, these structures can develop through cellular disintegration (lysigenous spaces), cell separation (schizogenous spaces), or a combination of both (schizolysigenous) (Fahn, 1979(Fahn, , 1988. Within the same species M. communis, Ciccarelli et al (2003) and Kalachanis and Psaras (2005) showed, respectively, a schizolysigenous and schizogenous development for leaf glands.…”

“…Detailed studies on the formation of secretory structures in different myrtaceous genera and species have been conducted by Carr (1969, 1970), who studied Eucalyptus oil glands; Brocheriou and Belin-Depoux (1974) described Eucalyptus and Myrtus; List et al (1995) analysed the leaf glands of Melaleuca alternifolia; Ladd et al (1999) Ciccarelli et al (2003) and Kalachanis and Psaras (2005). Unfortunately, there is not yet a common interpretation of the ontogeny of the glands.…”