Structure and Development of the Axillary Complex and Extrafloral Nectaries in Capparis retusa Griseb.

Abstract

The structure, organization and development of the axillary complex and extrafloral nectary in Capparis retusa Griseb. was analysed for the first time. The axillary complex presents three uniserial descending buds. Subordinated shoots originate from the distal and middle bud, while the proximal bud is usually quiescent. Close to the top of the axillary complex there is a subglobulous and umbilicated extrafloral nectary, normally visited by nectivore ants; a chronological coincidence between secretion, production and ant patrolling activities has been observed. The nectary structure differentiates at the second caulinar node, from an axillar meristem separated from the surrounding cells by a shell zone. On the fourth node a remarkably developed nectary primordium can be observed, inside which procambial strands develop acropetally. In the central region of the nectary primordium homogenous parenchyma differentiates progressively, later acquiring characteristics of nectariferous tissue. The mature nectary is vascularized by xylem and phloem, and the procambial differentiation is completed in a basipetal way. The first serial bud differentiates at the third node, from meristem cells near the base of its supporting leaf. The complex nodal structure with three buds completes its development at the eighth caulinar node. Ramular traces are observed as vascular semicylinders penetrating into the base of the buds to constitute a vascular system similar to that of the shoot. The scheme is repeated in the extrafloral nectary, giving rise to prolific branching in the periphery of the nectariferous tissue.

Functional genomics of nectar production in the Brassicaceae

“…The vascular tissue can be composed of both phloem and xylem, e.g., in Capparis retusa/Capparidaceae (Di Sapio et al, 2001), or have only phloem, as seen in Arabidopsis (Baum et al, 2001) and B. napus (Davis et al, 1986). In other families, nectary vascularization is missing completely (e.g., Swietenia/Meliaceae, petaline nectaries: Paiva, 2011; Boswellia/Burseraceae, nectariferous ring: Giuliani et al, 2012).…”

Nectar production and presentation

“…Phloem and xylem are present in Capparis retusa (Brassicaceae; Di Sapio et al, 2001), Ecballium elaterium (Cucurbitaceae; Fahn & Shimony, 2001), Solanum stramonifolium (Solanaceae; Falcão et al, 2003), and Hexisea imbricata (Orchidaceae; Stpiczyńska et al, 2005a) (see also the examples reported by Fahn (2000) and Nepi (2007)). …”

A novel indirect defence in Brassicaceae: Structure and function of extrafloral nectaries in Brassica juncea

“…The closest relative of Brassicaceae that possess extrafloral nectaries is Capparis retusa (order Brassicales, family Capparaceae), where the nectaries look like umbilicated glands containing a specialized parenchyma vascularized with xylem and phloem (Di Sapio, Gattuso & Prado 2001). Moreover, floral nectaries in many species of Brassicaceae have been described as protuberant gland structures surrounded by modified stomata, which maintain a firm contact between cells and subjacent parenchyma cells (Davis, Peterson & Shuel 1986; Davis et al .…”