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Titre : Nuovi approcci in Tamarix spp. per l’identificazione tassonomica e la caratterizzazione funzionale in condizioni di stress salino

New approaches in Tamarix spp. for taxonomic identification and functional characterization under salt stress

Auteur : Abbruzzese, Grazia

Université de soutenance : Università degli studi della Tuscia - Viterbo

Grade : Dottorato di ricerca in Ecologia forestale 2011

Résumé partiel
In a recent period, many researchers have tried to elucidate the complex physiological and biochemical mechanisms, combined with morphological adaptations, involved in plant salt tolerance (Greenway e Munns, 1980 ; Hasegawa et al., 2000 ; Ashraf e Harris 2004 ; Munns et al., 2006 ; Flowers e Colmer, 2008). Ecologically, halophytes are the native flora of saline soils and have developed several physiological and biochemical strategies of adaptations including the filtration of salts by roots and the compartmentation and extrusion of salts from leaf tissues. Frequently observed morpho-anatomical adaptations of plants from saline and dry habitats are an increase in leaf succulence and thickness of leaf cuticle, some variations of stomata morphology, an early lignification of cell walls and an increase in cutin deposition on the walls of epidermal cells (Waisel 1972 ; Robinson et al. 1997 ; Wahid, 2003 ; Kim e Park, 2010). These xeromorphic adaptations are common or shared between desert plants and other species commonly found in physiologically dry habitats. These features play a crucial role in conserving the water balance in plants inhabiting salty soils characterized by extremely negative water potentials. Because of the complexity and variability of salt tolerance trait, it is difficult to develop early morpho-functional indicators for the selection of plant tolerant material. The main focus of this study is the research of new approaches for the identification of morpho-functional indicators to salt tolerance in Tamarix. This genus is represented by 54 species and consists of mostly halophytic shrubs and dwarf trees native to arid and semiarid regions of Eurasia and Africa (Baum, 1978). Tamarisks show a wide ecological plasticity and can tolerate different stress factors, such as drought, elevated temperatures, high solar radiation (Cleverly et al., 1997 ; Zhuang e Chen, 2006), and high salinity (Glenn et al., 1998 ; Vandersande et al., 2001). Tamarisks are characterized by the presence of salt glands, which are specialized structures for the extrusion of excess salts from leaf tissues ; as a result, these species belong to recretohalophytes group. Such adaptive features play an important role in regulating ionic balance (Ramadan, 1998), maintaining or stabilizing osmotic and turgor pressure under high salinity (Ding et al., 2009). Therefore a better understanding of salt secretion and physiological role of salts accumulated in Tamarix shoots is needed. For this purpose, a salt experiment was carried out with three species of Tamarix coming from Israel (T. aphyl la, T. jordani s and T. tetragyna). These are considered model species for salt tolerance studies because they commonly inhabit extreme environments like the desert areas of North Africa and Middle East and along the shores of the Dead Sea (Waisel, 1961 ; Thomson et al., 1969 ; Bar-Nun e Poljakoff-Mayber, 1977 ; Hagemeyer e Waisel, 1988 ; Solomon et al., 1994 ; Jones et al., 2006). The plants were cultivated in 8 L-pots and distributed in four randomized blocks (control and three salt treatments : 150, 300 and 450 mM NaCl solution). After 41 days, all the species studied were able to tolerate and photosintetize actively also under the highest salt stress level. These data confirm the higher salt tolerance of these species that can be categorized, according to increasing productivity, in the following order : T. aphyl la, T. tetragyna and T. jordanis. Concerning the physiology of ions, the main useful traits to characterize the degree of salt tolerance in these species are : the ability to limit sodium content in leaf tissues and the level of salt extrusion.

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