Factors Influencing Seed Germination of the Pastoral Plant Retama Raetam Subsp

BIOLOGIJA. 2017. Vol. 63. No. 2. P. 134–151 © Lietuvos mokslų akademija, 2017 Factors influencing seed germination of the pastoral plant Retama raetam subsp. bovei (Fabaceae): interactive effects of fruit morphology, salinity, and osmotic stress Kaouther Mechergui1, The aim of this work was to study the morphology of retama seeds and the combined effects of salt and water stress on Hela Mahmoudi2, the seeds germination of four Tunisian populations of Retama raetam. Seeds were harvested from Bouhedma National Park, Mohamed Larbi Khouja1, Meknassi, Oueslatia, and Rtiba. In this study we were interested in evaluating different parameters of germination in presence of Wahbi Jaouadi1, 3* the salinity and osmotic stress. The results revealed that this species can withstand salinity up to 15 g/l of salt (the germination 1 Laboratory of Forest Ecology, percentage of the Rtiba population reached 42%) and it can also National Research Institute tolerate severe drought resulted in significant doses of PEG of Rural Engineering, 6000 Water, and Forestry (INRGREF), (germination percentage reached 29% to the water potential of University of Tunis Carthage. –1.6 MPa of Oueslatia population). The morphological traits of Rue Hedi Karay B.P.N°10 Ariana 2080, Tunisia the seeds were measured to find a relationship between the size of the seeds and their germination capacity under salinity and os- 2 Unit of Physiology and Biochemistry motic stress. Results have shown that for the correlation between of Plant Responses to Abiotic Constraints, morphological traits of seeds and the germination percentage, Faculty of Sciences of Tunis, the seed weight is a major factor in promoting germination under University of Tunis El Manar, 2092 Tunis, Tunisia stress and confirmed that saline water and sprouting inhibition have impact on the small caliber of seeds. 3 The Sylvo-Pastoral Institute of Tabarka, BP. n° 345, Tabarka 8110, Keywords: Retama raetam, population, morphological traits, salt Jendouba University, Tunisia stress, water stress, germination INTRODUCTION tam, locally named as “R’tm”, is a desert shrub na- tive to several countries of North Africa (Algeria, The genus Retama belongs to the family Fabaceae Egypt, Libya, Morocco, and Tunisia), temperate (500 genera and 1,000 species). It includes three Asia (Israel, Jordan, Lebanon, Palestine, and Syria), species (Retama monosperma, Retama raetam and and South-eastern Europe (Sicily in Italy) (GRIN Retama sphaerocarpa) with a large distribution in Database, 2011). In Morocco, it is largely located in the East Mediterranean region, North Africa, and desert regions and in the Middle Atlas. Retama rae- in the Canary Islands (Mahane 2009). Retama raetam with steno-Mediterranean and saharo-sindic distribution mainly grows in dune and desert habitats where it can withstand extreme aridity. For this * Corresponding author. E-mail: [email protected] reason it is often used in dune stabilization and in Factors influencing seed germination of pastoral plant Retama raetam subsp. bovei (Fabaceae)... 135 restoration of desert areas (Boulila et al., 2009). derlying mechanism of this pharmacological ef- Retama reatam has a very productive vertical fect has been hypothesised as inhibition of renal and horizontal root system that can reach 20 m. glucose reabsorption (Maghrani et al., 2005). Re- The Retama species contributes to the bio-fertil- tama raetam species has developed a particular- isation of poor soils because of its aptitude to as- ly important root system and is adapted to arid sociate with fixing nitrogen bacteria Rhizobia areas. Cellulose remains the major component (Boulila et al., 2009; Selami et al., 2014). There- of the cell wall (27% for young roots and 80% for fore, the genus of the Retama is included in a re- adult roots), hemicelluloses (14.3% for young vegetation programme for degraded areas in roots and 3.6% for adult roots) and pectins semi-arid Mediterranean environments (Car- (17.3% for young roots and 4.1% for adult roots) avaca et al., 2003). Retama raetam is also a me- (Bokhari et al., 2015). Previous pharmacological dicinal and aromatic plant present in humid to studies on this plant have revealed its antibacte- arid bioclimatic regions and it is a famous herbal rial, antifungal, antihypertensive, anti-oxidant, drug in Tunisia (Saad et al., 2014). Actually, in antiviral, diuretic, and hypoglycemic properties, traditional medicine, Retama raetam is used for and hepatoprotective, nephroprotective and cy- the treatment of several diseases such as diabetes totoxic effects (Maghrani et al., 2005; Ed- and hypertension, and its shoots are also used as douks et al., 2007; Hayet et al., 2007, 2008; Ko- an antidote against snake bites (Maghrani, 2005). riem et al., 2009; Algandaby et al., 2010; Research undertaken on genus Retama showed Edrizi et al., 2010). Retama raetam appears to be that the aqueous extract had diuretic and hypo- a valuable candidate as a forage resource in Sinai glycaemic effects (Maghrani, 2005). Even more, (Egypt). This fodder species should be consid- oral administration of 20 mg/kg of this aqueous ered valuable nonconventional forage in extract reduced significantly the glucose levels in the Mediterranean arid ecosystem (Naser et al., the blood of diabetic rats (Maghrani, 2005). 2013). Although present in low quantities in Moreover, administration of Retama raetam branches/leaves and seeds of Retama monosper- aqueous extracts induces a decrease in the tri- ma, lipids are an important fraction in terms of glyceride concentrations in the plasma of nor- quality given their high unsaturated fatty acids, mal and diabetic rats and leads to a significant particularly oleic, linoleic and linolenic acids decrease in weight (Maghrani, 2005). All whose therapeutic virtues are highly recom- the fractions from the Tunisian halophyte Reta- mended (El Hamdani, Fdil, 2015). The fact that ma raetam showed a potent antioxidant activity the linoleic acid is considered to be beneficial in and some of them exhibited interesting antibac- cancer and diabetic prevention provides some terial qualities (Saad et al., 2014). The phenolic scientific basis for the traditional use of the plant concentration in this species is very high, espe- as an antidiabetic, and for its pharmaceutical in- cially for the ethyl acetate fraction, and is proba- dication as antileukemic (El Hamdani & Fdil, bly responsible for its important biological ac- 2015). Based on this, further pharmacological tivities (Saad et al., 2014). The RP-HPLC data investigations to screen other potential bioactivi- revealed a large number of phenolic acids and ties of fatty acids of Retama monosperma may be flavonoids inRetama raetam shoots, with cou- recommended (El Hamdani, Fdil, 2015). marin and syringic acid as major phenolics. The highest mineral content is that of Al, Fe, Mg, Also, Retama raetam is a source of natural anti- Zn, Ca, K, Na, and P. However, the composition oxidants useful in medical and food industries of the plant is mainly dependent on the compo- (Saad et al., 2014). In the south-eastern region of sition of the soil which is influenced primarily by Morocco (Tafilalet), this plant is largely recom- the nature of the rocks from which the soil is de- mended by traditional herbal healers for diabe- rived. In Algeria, the plant grows in Sahara and tes control and phytotherapy. This ethnobotani- Atlas regions and is used in folk medicine to re- cal information has been recently verified duce blood glucose and skin inflammations experimentally (Maghrani et al., 2003). The un- (Baba, 1999) The Saharan plant Retama raetam 136 Kaouther Mechergui, Hela Mahmoudi, Mohamed Larbi Khouja, Wahbi Jaouadi (Fabaceae family) is used as a locally available able nutritional quality for browsing animals. adsorbent for removal of copper ions from aque- Moreover, this species may represent an alterna- ous solution. The aerial parts of Retama raetam tive feedstuff to the conventional forage and can be used as an inexpensive biosorbent and as a promising substitute fodder in the Mediterra- suitable alternatives for the removal of copper nean ecosystem. (Naser et al., 2013). Concerning ions from wastewater (Cheriti et al., 2009). seed germination, literature data (Gutterman, Among xerophytic shrubs, Retama raetam has 1993; Izhaki, Ne’eman, 1997; Seglie et al., 2012) a potential economic importance. It plays a sig- show that the percentage of germination in Re- nificant role in soil protection and stabilization tama is very low due to physical dormancy against wind or water erosion and provides an caused by the impermeability of seed coat to wa- important dietary source for livestock species ter (Kigel, 1995). Hence, studies have also been such as camels, goats, and sheep (Laudadio, carried out on seed morphology and seed germi- 2009). Additionally, this species represents a vi- nation under abiotic factors (salt stress and os- able fuel source for humans (Cheriti et al., 2009). motic stress) to get new data on the endemic It also has medicinal and potential industrial val- taxon of Tunisia Retama raetam subsp. bovei in ues since its roots are used to treat diarrhoea, view of conservation and habitat restoration. the leaves are used to help aching joints, back pain, and eye troubles (Said et al., 2002). Shrubs MATERIALS AND METHODS are key components in these ecosystems as they influence both biotic and abiotic conditions. Plant material Woody species may create “islands of fertility” Seeds of Retama raetam were collected in 2014 by improving the availability of water and nutri- from four natural habitats, namely, Meknassi, ents (Moro et al., 1997) or by protecting against Bouhedma, Rtiba, and Oueslatia (Fig. 1). After direct irradiance and overheating (Moro et al., the collection, the seeds were stored in a cold 1997; Lopez-Pintor et al., 2000). In addition, room. The climatic conditions prevailing in the legume species can increase soil fertility due each region were considered. Before the germi- to nitrogen-enriched litter deposition or direct nation tests, damaged and insect-infected seeds release of nitrogen from roots (Dart, 1998).

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