Stipular extranuptial nectaries new to Polygala: morphology and ontogeny

Abstract

Although taxonomic studies indicate that approximately one-third of the genera of Polygalaceae have nodal glands, few anatomical data are available on the structure and ontogeny of these secretory organs. We studied the as yet unknown origin, structure and function of such glands in Polygala laureola. During field observations, we detected glucose in the secretion using Glicofita Plus® and visitors were recorded. Vegetative shoot apices and nodal glands were examined using light microscopy and scanning electron microscopy. The presence of glucose in the secretion allowed us to identify these nodal glands as extranuptial nectaries. Secretory cells occupy a medullary position and are surrounded by phloem. Vascular bundles are concentric, and xylem is only observed at the basal region of the nectary. Nectar is released during the daytime through a pore at the top of the nectary. A stipular origin was confirmed by the fact that the procambial strand is connected to the leaf trace, opposite the leaf gap. The occurrence of stipular extranuptial nectaries in a nodal position is new to Polygala.

Morphology, ontogeny and structure of the stipular nectaries in Caamembeca spectabilis (Polygalaceae)

“…However, this study showed that the position and the vascularization of nodal glands originated in the leaf trace, in fact, are treated as modified stipules in Caamembeca spectabilis, as well as in Caamembeca laureola (cited as Polygala laureola) (Aguiar-Dias et al 2011).…”

“…The secretory tissue is delimited only by phloem, with the xylem staying below the nectariferous cells, features found by Aguiar-Dias et al (2011). Francino et al (2006) observed in Chamaecrista trichopoda (Caesalpinioideae) nectaries structurally similar as C. spectabilis, but also connected to xylem.…”

“…To describe nectaries we used the morphological terms available elsewhere (Marques and Peixoto 2007;Aguiar-Dias et al 2011).…”

“…Probably in the secretory tissue, the sap drawn up from the phloem turns into pre-nectar and later in nectar, so it can be released out to the environment. Aguiar-Dias et al (2011) did not mention suberin as a structure pertaining to EFNs of Polygala laureola (= Caamembeca laureola). In the present study, the large wall evidenced in the epidermal cells encrusted with suberin, in EFNs of Caamembeca spectabilis, is a new finding for this genus.…”

“…Recent anatomical studies found that nodal nectaries of Caamembeca laureola (cited as Polygala laureola) are connected to the leaf trace, classifying them as stipular nectaries (Aguiar-Dias et al 2011). However studies with the nodal ENFs of Caamembeca are clearly relevant to unravel whether this structure is shared among all species.…”