Water Content and Reserve Allocation Patterns Within the Bulb of the Perennial Geophyte Red Squill (Liliaceae) in Relation to the Mediterranean Climate

291 NOTE / NOTE Water content and reserve allocation patterns within the bulb of the perennial geophyte red squill (Liliaceae) in relation to the Mediterranean climate Sharaf Al-Tardeh, Thomas Sawidis, Barbara-Evelin Diannelidis, and Stylianos Delivopoulos Abstract: 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. Key words: bulb, geophytes, Mediterranean climate, Urginea maritima, water content. Re´sume´ : Les auteurs ont examine´ les patrons de teneur en eau et l’allocation des re´serves dans les parties du bulbe du Urginea maritima (L.) Baker, ainsi que les strate´gies d’adaptation de la plante au climat me´diterraneén (Creˆte, Gre`ce). Les diffe´rentes parties du bulbe servent diffe´rentes fonctions ećologiques, en termes de ressource et de leur importance pour ces fonctions. La plaque basale constitue le centre d’activite´,de´veloppant a` l’automne un ou deux me´riste`mes et des raci- nes, ainsi que le bourgeon floral a` la fin de l’e´te´. Le milieu du bulbe (environ la troisie`me ećaille du bulbe) emmagasine les ressources, et les tuniques (structures enveloppantes externes) servent a` la de´fense. La teneur en eau et les patrons d’allocation des re´serves synchronisent le de´veloppement pheńologique de la plante selon le caracte`re saisonnier du climat me´- diterraneén. Les strate´gies d’adaptation reposent sur le de´veloppement d’une forme vitale dećidue semi-souterraine, surtout pour e´viter la sećheresse, les herbivores et les autres aleás environnementaux, ainsi que l’emmagasinage des nutriments. Ceci est facilite´ par la pre´sence de cellules contenant des lipides, polysaccharides, raphides, eau, mucilage, bufadienolides, la pre´sence de scle´renchymes, l’e´piderme bien serre´ et la pre´sence de tuniques. Mots-cle´s:bulbe, geóphytes, climat me´diterraneén, Urginea maritima, teneur en eau. [Traduit par la Re´daction] Introduction of and (or) resistance to desiccation and drought, and development of subterranean organs that contain specialized stor- Evolution of geophytes in climatic areas with marked sea- age compounds (De Hertogh and Le Nard 1993; sonal changes has led to their adaptation to periods of high Kamenetsky et al. 2003, 2005). A variety of carbohydrates, and low temperatures and (or) drought. To survive extreme including starch, soluble sugars, glucomannans, and fructan environments, geophytes have undergone adaptations that are variously present in the underground storage organs of may include increased capacity for water binding, tolerance geophytes (De Hertogh and Le Nard 1993; Miller et al. Received 7 June 2007. Published on the NRC Research Press Web site at botany.nrc.ca on 5 March 2008. S. Al-Tardeh, T. Sawidis, B. Diannelidis, and S. Delivopoulos.1 Department of Botany, School of Biology, Aristotle University, Thessaloniki 541 24, Greece. 1Corresponding author (e-mail: [email protected]). Botany 86: 291–299 (2008) doi:10.1139/B07-130 # 2008 NRC Canada 292 Botany Vol. 86, 2008 1997). In addition, there is a possibility that some storage lis L., Scilla hanburyi Baker, U. maritima, Urginea undulata proteins act as a temporary store for nitrogen in several per- (Desf.) Steinh., Pancratium maritimum L., and ennial species (Bewley 2002; S. Al-Tardeh, unpublished Pamianthe parviflora Meerow, are of tropical origin and are data) and are reutilized to support plant growth (Cyr and characterized by possessing perennial storage organs, a dis- Bewley 1989, 1990) tinct flowering stem, seed dispersal immediately after flow- Urginea maritima (L.) Baker has value as an ornamental, ering, and germination without dormancy. Indeed, this flowering after almost 6 years from germination (McCor- prevents the risks of long seed exposure to environmental ohan 1990), when the bulb reaches a critical mass (Pascual- hazards and allows for the exploitation of pollinators during Villalobos and Fernandez 1999). It is also a deciduous plant autumn (Dafni et al. 1981; De Hertogh and Le Nard 1993; possessing leaves with mesophytic characters that optimize Al-Tardeh et al. 2007). its adaptation to the seasonal fluctuation of the environmental Previously, we conducted detailed studies on the anatomi- conditions of the Mediterranean climate. This optimization cal features of the roots (Al-Tardeh et al. 2006) and the occurs by protecting the plant from environmental hazards leaves (Al-Tardeh et al. 2007) of U. maritima as adaptive and herbivores and by abundant production of nutrients strategies for this species to the Mediterranean climate. In over a short period (rainy season; Al-Tardeh et al. 2007). this study, we examine the water content and allocation pat- The roots of U. maritima play an important role in storing terns of reserves in the bulb parts of U. maritima to gain a and utilizing water and nutrients (Al-Tardeh et al. 2006). better understanding of aspects of this species’ life history The bulb, which is usually only half buried in the soil, is such as maintenance, growth, and reproduction. The ultimate tunicated and mostly globular. It can reach 5–15 cm in di- goals are to identify the structure and the function of the ameter and consists of fleshy, smooth scales (modified leaf bulb and to suggest reasons for the abundance of the plant bases) that overlap one another. It has little odour, but its in the Mediterranean region. More specifically, the objective inner scales have a mucilaginous, bitter, acrid taste, owing of this study is to explore the plant’s efficiency in water and to the presence of bitter glycosides. Extracts of the bulb reserve storage during the long summer drought and its de- scales of U. maritima contain a variety of reserves such as fense mechanisms against herbivores and other environmen- cardiac glycosides of the bufadienolide type (Kopp et al. tal hazards. 1996), which are the major glycoside constituents, antho- cyanins (Vega et al. 1972), flavonoids (Fernandez et al. 1972), fatty acids, polysaccharides (Spies et al. 1992), and Materials and methods calcium oxalate (Cogne et al. 2001). Study site and plant material The order in which the different organs of plants are differentiated is important. When the leaves are differentiated The study site was located at Souda (35833’N and before the floral parts, growth is usually synanthous˛ i.e., the 24807’E), a town about 10 km south of Chania, on the island foliage is produced before flowering such as in Hyacinthus, of Crete (the fifth largest Mediterranean island), southern Lilium, Narcissus, and Tulipa. However, in some genera or Greece. Souda’s climate is of the Mediterranean type and species the flower bud is initiated before the vegetative bud most of its annual rainfall occurs in autumn–winter, while that produces the leaves. This generally leads to the produc- the summer is very hot and dry. The mean annual air tem- tion of hysteranthous plants, i.e., flowering takes place in the perature is 18.1 8C. January (mean temperature, 10.8 8C) absence of foliage and before leaves emerge. The synan- and February (mean temperature, 10.8 8C) are the coldest thous pattern of flowering occurs in late spring, whereas the months, whereas July (mean temperature, 26.3 8C) and Au- hysteranthous pattern occurs at the end of summer (De Her- gust (mean temperature, 26 8C) are the warmest. It is also togh and Le Nard 1993). characterized by high humidity and low barometric pressure In hysteranthous plants, the photosynthesis rate is very owing to the close location to the sea and the mountains. low from flower emergence until anthesis. The bulb reserves Individuals of U. maritima with a bulb diameter of 10 cm, are sufficient to allow flower stem elongation and flowering. growing wild in Souda, were collected at the end of the The contrast to hysteranthous growth is proteranthous spring of 2005, soon after the seasonal dieback of the growth, i.e., the foliage dies down before the flower is pro- leaves. This particular period was chosen for three reasons: duced (e.g., Boophane haemanthoides Leighton (Du Plessis (i) to quantify the total nutrient content in the bulb’s compo- and Duncan 1989). Thus, all photosynthesis takes place be- nent parts available for reproduction and growth; (ii) by this fore flowering. time the plant has recycled the resources from the herba- Depending on the basis of their storage organs and life ceous aboveground plant parts for reusage; and (iii) it is be- cycles, two patterns can be distinguished among hysteran- fore inflorescence initiation begins in early September. The thous geophytes: the ‘‘Urginea type’’ and the ‘‘Crocus bulbs were sectioned through their longitudinal median axes type’’. In the hysteranthous geophytes of Crocus type, such to determine their chronological age for the selection plants as Crocus, Merendera, Colchicum, and Sternberhia, the cap- of the same age.

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