Ecologia Mediterranea

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Effects of abiotic stress on the germination of Pennisetum dichotomum Effets de stress abiotiques sur la germination de Pennisetum dichotomum Abstract Seeds germination of Pennisetum dichotomum was tested for three alternating temperatures (10, 25, 35 o C) at different hydric potentials (0, –1, –3, –7, –10 and –16 bar) applied with different concentrations of sodium chloride (0-3-6-12 or 15g/l of NaCl). The highest germination parameters (germination rate, germination percentage) were obtained with no osmotic potential (0 bar) under 25 o C. Germination rate decreased progressively with increasing NaCl dose, and the lower value of this parameter was reached with 15g/l of NaCl. Compared to control (0g/l of NaCl) P. dichotomum seeds, the radical length (RL) and the hypocotyl length (HL) of the NaCl-treated ones were severely decreased at 12 and 15g/l concentrations. In another way, seedling growth of P. dichotomum was shown more sensitive than germination seeds to salinity stress. Introduction Plant growth and productivity are adversely affected by various abiotic and biotic stress factors (Hasegawa et al. 2000). Plants are frequently exposed to many stress conditions such as low temperature, salt, drought, flooding, heat, oxidative stress and heavy metal Keywords: germination rate, hydric potential, salt stress. ecologia mediterranea – Vol. 38 (2) – 2012 Chiraz CHAFFEI HAOUARI 1,* , Afef HAJJAJI NASRAOUI 1 , Houda GOUIA 1 , Ali HAOUARI 2 1. Faculté des sciences Tunis, Dép. Biol., Unité de recherche 2. Institut des régions arides Mednine (INRA) *Corresponding author: Université Tunis El Manar, Campus universitaire, Faculté des sciences de Tunis, Dép. biol., Unité de recherche : nutrition et métabolisme azotés et protéines de stress, El Manar I, 1060 Tunis-Tunisia Mail: chiraz_ch2001@yahoo.fr; Fax: 216 71 885 480 toxicity. Excessive salinity and drought are the most important environmental factors that greatly affect plant growth and productivity worldwide. Osmotic and water stresses cause pleiotopic effects, and stress tolerance is a complex and polygenic trait that involves morphological, physiological, as well as biochemical changes. P. dichotomum is a fountain grass and an attractive perennial grass with a densely clumped growth form and erect stems that grow 2 to 3 feet high. The small flowers of P. dichotomum are grouped in pink or purple, bristly, upright inflorescences 6-15 inches long. Fruits are small, dry achenes adorned with long showy bristles. P. dichotomum plants are constantly confronted with various biotic and abiotic stress factors such as low or high temperature, salt, drought, flooding, heat, oxidative stress and heavy metal toxicity (Tuteja et al. 2010) Pennisetum dichotomum is a highly aggressive, fire-adapted colonizer that readily outcompetes native plants and rapidly reestablishes after burning. P. dichotomum is a Native range of Northern Africa. Among important factors, water availability and temperature determine whether or not dispersed seeds germinate (Sloan 2009). Under favorable conditions (water, temperature), the seed begins to 17
CHIRAZ CHAFFEI HAOUARI, AFEF HAJJAJI NASRAOUI, HOUDA GOUIA AND ALI HAOUARI 18 germinate and the embryonic tissues development towards a seedling. One of the most important abiotic factors limiting plant germination and early seedling stages is water stress brought about by drought and salinity (Mantovani & Iglesias 2010). However, the presence of salt in the medium culture cause inhibitory effects on the seed’s water uptake and retard and/or suppress germination (Alatar 2011). Salinity and drought affect the plants in a similar way reducing water potential (Legocka & Kluk 2005). Water stress acts by decreasing the percentage and rate of germination and seedling growth. The detrimental effects of NaCl on seeds germination are a consequence of both a water deficit resulting in osmotic stress and the effects of excess sodium ions on key biochemical processes. Seed germination and early seedling growth are critical stages for the establishment of plant populations under saline conditions (Srivastava et al. 2000). Plants differs in their upper limit of salinity tolerance as the increase in salinity concentration usually delays and reduces seed germination (Srivastava et al. 2000). The degree to which salinity affects germination by an osmotic effect or specific ion toxicity and whether salt tolerance varies in different species is still a subject of studies (Pilar et al. 2011). The temperature variations have a major impact on a number of processes which regulate seed germination, including membrane permeability and the activity of membranebound as well as cytosolic enzymes (Ajmal Khan & Gulzar 2003) and its interaction with the variable soil water content in the surface layers of the soil. By consequence salinitytemperature interaction, determines seed germination pattern in many salt affected environments. Despite the importance of Pennisetum dichotomum, there is no available information on its autecology, and most drought resistant grasses of the Tunisia desert. The aim of this study is to investigate the effects of osmotic stress generated by NaCl and depth with temperature on germination characteristics (germination period and germination percentage) and seedling growth of Pennisetum dichotomum. Materials and methods Pennisetum dichotomum is a graminous (Mian 2003) grasses which inflorescence is a dense, spicate, terminal panicle. This is a useful grazing plant, much browsed by camels (Mandaville 1990). Seeds of P. dichotomum were collected during April, 2009, from naturally growing stands in the sandy soil of Mednine- South of Tunisia. Seeds were separated from inflorescences and stored dry at 4oC. During September 2009, stored seeds were sterilized with 0.5% sodium hypochlorite solution for 1 min and washed twice with distilled water. Effect of temperature on germination Seeds were germinated on double-layered with Whatman No. 1 filter papers placed in 10cm diameter plastic dishes. Seeds were placed (30 seeds per Petri dishes) in a growth chamber (26 o C/70% relative humidity during the day, 20 o C/90% relative humidity during the night). The photoperiod was 16 h daily with a light irradiance of 150 µmol m -2 . s -1 at the canopy level. All of the Petri dishes were kept in dark incubators maintained at room temperature at four alternating night and day temperature regime (10, 25 and 35 o C) representing the seasonal common temperatures prevailing in some selected meteorological stations in south Tunisia (Mednine: 33 o 20’ 56.27” N, 10 o 29’ 41.26” E). Effect of depth In the nature, every sort is characterized by an optimal depth of sowing. This optimal depth depends on intrinsic characteristics of the semen. The basic rule is to sow a seed in a depth equal to 2-5 times the diameter (Seabloom 2007). In the present experiment six values of depth were tested: 1, 2, 3, 4, 5 and 6 cm. Effect of water potential and NaCl doses Seeds were submitted to germination using osmotic potentials (0, – 0.2, – 0.4, – 0.6 and - 0.8 MPa) of sodium chloride solutions according to Murillo-Amador et al. (2002). Twenty-five seeds were germinated on double-layered with Whatman No. 1 filter papers ecologia mediterranea – Vol. 38 (2) – 2012
Page 1 and 2: ecologia mediterranea Vol. 38 (2) -
Page 3 and 4: ecologia mediterranea Revue interna
Page 5 and 6: Pr Thierry DUTOIT Éditeur en chef
Page 7 and 8: SÉLIMA BERCHI, AMEL AOUATI, KAMEL
Page 17: SÉLIMA BERCHI, AMEL AOUATI, KAMEL
Page 21 and 22: CHIRAZ CHAFFEI HAOUARI, AFEF HAJJAJ
Page 23 and 24: CHIRAZ CHAFFEI HAOUARI, AFEF HAJJAJ
Page 25 and 26: CATERINA MAGRINI, MICHELE CENTO, EM
Page 27 and 28: CATERINA MAGRINI, MICHELE CENTO, EM
Page 29 and 30: Les communautés bryophytiques du l
Page 31 and 32: Du point de vue de la structure du
Page 33 and 34: ecologia mediterranea - Vol. 38 (2)
Page 35 and 36: Leptodictyo riparii-Fissidentetum c
Page 37 and 38: ait être assimilé en l’état à
Page 39 and 40: lent sur ces placages limoneux. Ain
Page 41 and 42: Meyran O., 1914. Catalogue des mous
Page 43 and 44: T. S. KSIKSI, N. O. ALSHAYGI 44 200
Page 45 and 46: T. S. KSIKSI, N. O. ALSHAYGI 46 Pig
Page 47 and 48: T. S. KSIKSI, N. O. ALSHAYGI 48 tre
Page 49 and 50: T. S. KSIKSI, N. O. ALSHAYGI 50 Roo
Page 51 and 52: Existing areas and past changes of
Page 53 and 54: Material and methods Area studied T
Page 55 and 56: zier 2004) wetland inventories. The
Page 57 and 58: Results Surface and number of exist
Page 59 and 60: Discussion Mediterranean wetlands:
Page 61 and 62: treated differently in each country
Page 63 and 64: DGF (Direction générale des forê
Page 65 and 66: Plant communities in the Tamanrasse
Page 67 and 68: elong to two major geomorphological
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The Rhus tripartita and Olea europa
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Table 2 - The Cassia aschrek-Panicu
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from sandy-silty, sandy to sandy-gr
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complex ecological situation and th
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Tamarix aphylla (Rudich & Danin 197
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Towards the establishment of a natu
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Introduction The structural complex
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Methods Species richness The field
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kurnet-es-sauda Eig.; Allium chlora
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tidissima, and J. excelsa) and the
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projects should abide strictly by t
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Myers N., Mittermeier R.A., Mitterm
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Micromeria graeca (L.) Benth. Micro
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enlargement of this bioclimatic env
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à grande échelle au sein du proje
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at wood, bark and pith anatomy of t
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ecologia mediterranea Editor-in-Chi
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