The patterns of water content and reserve allocation in the bulb parts of red squill (Urginea maritima (L.) Baker) and the plant's adaptive strategy to Mediterranean climate (Crete, Greece) were investigated. The different bulb parts serve varying ecological functions in terms of their resources and their importance for these functions. The basal plate is the active centre, developing one or two apical meristems and roots in autumn, as well as the flowering bud in late summer. The middle of the bulb (approximately the third bulb scale) stores the resources and the tunics (the outer covering structures) that provide mechanical defense. The water content and reserve allocation patterns synchronize the plant's phenological development with the seasonality of the Mediterranean climate. The adaptive strategies are based on the development of a deciduous semisubterranean life form primarily for the avoidance of drought, herbivores, and other environmental hazards, as well as nutrient shortage. The presence of cells containing lipids, polysaccharides, raphides, water, mucilage, bufadienolides, the presence of sclerenchyma, the tightly packed epidermis, and the presence of the tunics facilitate this.Résumé : Les auteurs ont examiné les patrons de teneur en eau et l'allocation des réserves dans les parties du bulbe du Urginea maritima (L.) Baker, ainsi que les stratégies d'adaptation de la plante au climat méditerranéen (Crête, Grèce). Les différentes parties du bulbe servent différentes fonctions écologiques, en termes de ressource et de leur importance pour ces fonctions. La plaque basale constitue le centre d'activité, développant à l'automne un ou deux méristèmes et des racines, ainsi que le bourgeon floral à la fin de l'été. Le milieu du bulbe (environ la troisième écaille du bulbe) emmagasine les ressources, et les tuniques (structures enveloppantes externes) servent à la défense. La teneur en eau et les patrons d'allocation des réserves synchronisent le développement phénologique de la plante selon le caractère saisonnier du climat méditerranéen. Les stratégies d'adaptation reposent sur le développement d'une forme vitale décidue semi-souterraine, surtout pour éviter la sécheresse, les herbivores et les autres aléas environnementaux, ainsi que l'emmagasinage des nutriments. Ceci est facilité par la présence de cellules contenant des lipides, polysaccharides, raphides, eau, mucilage, bufadienolides, la présence de sclérenchymes, l'épiderme bien serré et la présence de tuniques.
BackgroundTransverse cortical microtubule orientation, critical for anisotropic cell expansion, is established in the meristematic root zone. Intending to elucidate the possible prerequisites for this establishment and factors that are involved, microtubule organization was studied in roots of Arabidopsis thaliana, wild-type and the p60-katanin mutants fra2, ktn1-2 and lue1. Transverse cortical microtubule orientation in the meristematic root zone has proven to persist under several regimes inhibiting root elongation. This persistence was attributed to the constant moderate elongation of meristematic cells, prior to mitotic division. Therefore, A. thaliana wild-type seedlings were treated with aphidicolin, in order to prevent mitosis and inhibit premitotic cell elongation.ResultsIn roots treated with aphidicolin for 12 h, cell divisions still occurred and microtubules were transverse. After 24 and 48 h of treatment, meristematic cell divisions and the prerequisite elongation ceased, while microtubule orientation became random. In meristematic cells of the p60-katanin mutants, apart from a general transverse microtubule pattern, cortical microtubules with random orientation were observed, also converging at several cortical sites, in contrast to the uniform transverse pattern of wild-type cells.ConclusionTaken together, these observations reveal that transverse cortical microtubule orientation in the meristematic zone of A. thaliana root is cell division-dependent and requires severing by katanin.
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.
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