Nectary structure and nectar presentation in the Mediterranean geophyte,Urginea maritima(Hyacinthaceae)

Abstract

The morphology, anatomy, and ultrastructure of the floral nectary of Urginea maritima (L.) Baker were investigated at three stages of nectary development. The plant possesses a typical gynopleural (septal) nectary with secondary presentation. The nectary consists of one layer of epithelium secretory cells and one to four layers of subsidiary cells subtended by two to six layers of parenchyma (subnectary) cells. The nectary releases the nectar at a point two-thirds towards the summit of the ovary by means of carpellary sutures. Nectar secretion appears to depend largely on the hydrolysis of starch grains stored in amyloplasts at the intermediate stage. The hydrolysis process most likely commences in the epithelium layer followed by the subsidiary tissue and then the parenchyma cells of the ovary wall. A symplastic transfer of the secreted nectar occurs by plasmodesmata connecting the subsidiary cells to the parenchyma and the epithelial secretory cells. However, microchannels in the cell wall of the epithelial cells may facilitate the apoplastic transfer of the nectar into the nectary cavity. The old stage of nectary development is characterized by a crystallized form of nectar, collapse of the parenchyma cells, complete starch hydrolysis, and disappearance of the amyloplasts and endoplasmic reticulum.Résumé : Les auteurs ont étudié la morphologie, l'anatomie et l'ultrastructure des nectaires floraux de l'Urginea maritima (L.) Baker, à trois stades du développement des nectaires. La plante possède un nectaire (septé) gynopleural typique avec présentation secondaire. Le nectaire comporte une couche épithéliale de cellules sécrétrices et 1-4 couches de cellules subsidiaires sous-tendues par 2-6 couches de cellules de parenchyme (sous-nectaire). Les nectaires relâchent le nectar à un point situé aux deux tiers vers le sommet de l'ovaire, au moyen de structures carpellaires. La sécrétion du nectar semble dépendre de l'hydrolyse de grains d'amidon en réserve dans des amyloplastes au stade intermédiaire. Le processus d'hydrolyse commence vraisemblablement dans la couche épithéliale, suivi du tissu subsidiaire et par après des cellules de parenchyme de la paroi ovarienne. On observe un transfert symplastique du nectar sécrété par des plasmodesmes reliant les cellules subsidiaires au parenchyme et aux cellules épithéliales. Cependant, des microcanaux dans la paroi cellulaire des cellules épithéliales pourraient faciliter le transfert apoplastique du nectar dans la cavité à nectar. Le dernier stade du déve-loppement des nectaires se caractérise par une forme cristalline de nectar, un affaissement des cellules de parenchyme, une hydrolyse complète de l'amidon et une disparition des amyloplastes et du réticulum endoplasmique.

Biomonitoring airborne pollution: a case study of “Urginea maritima” species in Bentael natural reserve – Lebanon

“…After launching pollution alarms, we chose to study an exceptional plant in the reserve: "Urginea maritima". This plant's characteristics are numerous: it was declared rare by the United Nations Environment Programme [3], has a succulent root system, has rodenticide effects and its bulb highly accumulates heavy metals [4].…”

Morphological and anatomical adaptations of the perennial geophyte Urginea maritima (L.) baker (liliaceae) to the mediterranean climate

“…Moreover, the flowering occurrence in autumn, after a very dry season (summer), can be interpreted as a preference of the plant to produce nectar with high viscosity. High viscosity of nectar is due to the shortage in the available water within the bulb after a very dry summer and some water loss from nectar by evaporation (Al-Tardeh et al, 2008c). This phenomenon was, also, reported in other species of Asteraceae (Wist and Davis, 2006).…”

“…Small specimens (~9 mm 2 ) of the adventitious roots (Al-Tardeh et al, 2006), bulbs (Al-Tardeh et al, 2008a), leaves (Al-Tardeh et al, 2008b) and floral parts (Al-Tardeh et al, 2008c) were fixed (Table 1) in the fixative solution at room temperature for 3-4 hours.…”

“…For the morphometric evaluation of the relative volume of the histological components of the adventitious roots (Al-Tardeh et al, 2006), leaves (Al-Tardeh et al, 2008b), bulbscales (Al-Tardeh et al, 2008a), and flowers (Al-Tardeh et al, 2008c), a transparent sheet bearing a square lattice of points arrays, 10 mm apart, was laid over light micrographs. The point-counting technique analysis was then applied (Steer, 1981).…”

“…Competition for pollinators is regarded as a possible selective pressure leading to the shift of flowering season from spring (the main flowering season under Mediterranean climatic conditions) to autumn, as it occurs in some geophytes with hysteranthous leaves, as is the case of U. maritima (Dafni et al, 1981;Al-Tardeh et al, 2008c). The latter exposes to the pollinators both its pollen and its nectar with sugar concentration varying from 10-75% (Dafni and Dukas, 1986) in order to attract different pollinators (Corbet, 1978).…”