Influence of NaCl Seed Priming on Growth and Some Biochemical Attributes of Safflower Grown under Saline Conditions
Subject Areas : Research On Crop EcophysiologyElouaerMohamed Aymen 1 , Ben Fredj Meriem 2 , Zhani Kaouther 3 , Hannachi Cherif 4
1 - Sousse University, High Institute
of Agronomy, Chott Mariem, 4042, Tunisia
2 - Sousse University, High Institute
of Agronomy, Chott Mariem, 4042, Tunisia
3 - Sousse University, High Institute
of Agronomy, Chott Mariem, 4042, Tunisia
4 - Sousse University, High Institute
of Agronomy, Chott Mariem, 4042, Tunisia
Keywords:
Abstract :
Reserarch on Crop Ecophysiology Vol. 9/1, Issue 1 (2014), Pages:13 - 20 Original Research Influence of NaCl Seed Priming on Growth and Some Biochemical Attributes of Safflower Grown under Saline Conditions Elouaer Mohamed Aymen 1 *, Ben Fredj Meriem 1, Zhani Kaouther 1,Hannachi Cherif 1 Sousse University, High Institute of Agronomy, Chott Mariem, 4042, Tunisia * Corresponding author E-mail: aymenouaer@gmail.com Received: 17 July 2013 Accepted: 12 November 2013 Abstract This experiment was conducted to evaluate the effects of NaCl priming on growth traits and some biochemical attributes of safflower (Carthamus tinctorius L. cv Safola) in salinity conditions. Seeds of safflower were primed with NaCl (5 g L-1) for 12 h in 23 °C. Primed (P) and non primed (NP) seeds were directly sown in the field. Experiments were conducted using various water concentrations induced by NaCl (0, 3, 6, 9 and 12 g L-1) in salinity experiment. Results showed that growth (plant height, fresh and dry weight) and biochemical (chlorophyll, proline and proteins content) of plants derived from primed seeds were greater of about 15 to 30% than that of plants derived from non primed seeds. It seems that salinity tolerance in priming resulted plants was due to higher potential of these plants to accumulate more biochemical attributes (more chlorophylles, proline and proteins in primed plants than controls ones). Keywords: Biochemical attributes, Growth parameters, Safflower, Salinity, Seed priming Introduction Salt stress is certainly one of the most serious environmental factors limiting the productivity of crop plants (Ashraf, 1999). This is due to the fact that salinity affects most aspects of plant physiology, growth and development (Borsani et al., 2003). One metabolic response to salt stress is the synthesis of compatible osmolytes (Hasegawa et al., 2000). These organic compounds are thought to mediate osmotic adjustment, protecting cellular structures and oxidative damage by their free radical scavenging capacity (Smirnoff, 1993). Metabolic acclimation via the accumulation of compatible solutes is often regarded as a basic strategy for the protection and survival of plants under abiotic stress (Sakamoto and Murata, 2000 Shabala and Cuin, 2006). Many plant species accumulate significant amounts of glycine betaine, proline, and polyols in response to high salinity (Di Martino et al., 2003). In addition to the conventional role of these compatible solutes in cell osmotic adjustment (Bray, 1993), they are also suggested to act as low molecular-weight chaperones, stabilizing the photosystem II complex, protecting the structure of enzymes and proteins, maintaining membrane integrity and scavenging ROS (Mansour, 1998 Noiraud et al., 2001). The production of Reactive Oxygen Species (ROS) in cells increases during abiotic and biotic stresses like salt stress, as does the level of ROS-induced damage. Elevated production of ROS can seriously disrupt cellular homeostasis and normal metabolisms through oxidative damage to lipids, protein, and nucleic acid (Bandeoglu et al., 2004). Seed priming is a pre-sowing treatment that involves exposure of seeds to low external water potential that limits hydration. This hydration is sufficient to permit pre-germinative metabolic events but insufficient to allow radicle protrusion through the seed coat. This technique has become a common seed treatment that can increase emergence, growth, yield and salt tolerance mainly under unfavorable environmental conditions (Ashraf and Rauf 2001). Higher salt tolerance of plants from primed seed seems to be the results of a higher capacity of osmotic adjustment (proline or carbohydrate synthesis) in leaves. Sivritepe et al. (2003) confirmed that NaCl seed priming increased proline concentration and salt tolerance of melon seedlings. Farhoudi et al. (2007) suggested that canola seed priming with NaCl improved salinity tolerance in canola seedlings because it decreased cell membrane injury and increased seedling proline concentration. Seed priming is one of the physiological methods which improve plant growth and yield. Therefore, the present study was conducted to examine the effect of NaCl priming on some aspects of growth and physiology, including protein, chlorophyll and proline content of safflower under salt stress. Materials and methods The experiment was carried in the experimental field research of Chott Mariem High Institute of Agronomy, (Tunisia) in November 2011. Safflower seeds were primed with 5 g L-1 NaCl solution for 12 hours, at 22 °C. After priming, primed and non primed seeds (control seeds) were sown directly in the soil at the month of November. Throughout their vegetative cycles, plants from primed and control seeds were irrigated with saline water at five levels of NaCl concentrations (0, 3, 6, 9 and 12 g L-1). The experiment was arranged as factorial in a completely randomized design with three replications and 20 plants per replication and two factors which were priming treatment (NaCl primed seeds and control seeds) and salinity levels (0, 3, 6, 9 and 12 g L-1 NaCl). Photosynthetic pigments such as chlorophyll a and b content were calculated (663 and 640 nm) according to the method of Lichtenthaler (1987). Protein content was estimated at 595 nm according to the method of Bradford (1976) using bovine serum albumin as standard. Free proline was estimated at 520 nm according to the method of Bates et al. (1973) and pure proline was used as standard. Plants were harvested at the flowering stage and were recorded on shoot fresh and dry weight (g plant-1), shoot chlorophyll a content (mg g-1fresh weight), shoot chlorophyll b content (mg g-1 fresh weight), shoot chlorophyll (a + b) content (mg g-1 fresh weight), shoot proline content (μg.g-1 fresh weight), shoot protein content (mg.g-1 fresh weight). Growth and biochemical parameters of safflower were evaluated with analysis of variance (ANOVA) and Duncan multiple range test (p NP P NP P NP P NP P NP 162a 143c 153b 135cd 141c 122e 132d 118f 124e 109g 423a 214c 312b 165d 156de 146e 143e 129f 131f 98g 158a 119c 142b 106d 109d 93e 98e 86f 77g 58h Means followed by the same letter are not significantly different at 5% level according to Duncan test. P: Primed seed, NP: Non Primed seed Table 2. Effect of NaCl priming and salinity on chlorophyll, proline and proteins contents of safflower under NaCl stress Treatments Chlr (a) (mg g-1 F.Wt.) Chlr (b) (mg g-1 F.Wt.) Chlr (a + b) (mg g-1 F.Wt.) Proline (μg g-1 F. Wt.) Proteins (mg g-1 F. Wt.) Seed Priming NaCl (g L-1) 0 3 6 9 12 P NP P NP P NP P NP P NP 1.628a 1.236e 1.532b 1.195f 1.402c 0.952fg 1.306d 0.806g 1.224e 0.671h 0.824a 0.627c 0.706b 0.514d 0.596d 0.394f 0.467e 0.271g 0.334f 0.194h 2.574a 1.914c 2.298b 1.704e 2.094b 1.692e 1.802d 1.042g 1.604f 0.834h 61.18e 52.52f 102.24d 62.02e 119.84c 104.68cd 154.67b 114.52c 196.42a 158.08b 0.385e 0.197h 0.421d 0.243g 0.474c 0.286f 0.502b 0.306ef 0.543a 0.342ef Means followed by the same letter are not significantly different at 5% level according to Duncan test. P: Primed seed, NP: Non Primed seed Maximum shoot proline content of 196.42 μg g-1 fresh weight was recorded in plant derived from primed (P) seeds from the treatment applied with 12 g L-1 NaCl. Minimum proline content of 52.52 μg g-1 fresh weight was recorded from plant derived from control seeds with the application of 0 g L-1 NaCl. Highest shoot protein content was recorded in plant derived from primed seeds with the application of 12 g L-1 NaCl (0.543 mg g -1 Fresh Weight). The Lowest shoot proteins were observed in plant derived from control seeds with the application of 0 g L-1 NaCl (0.197 mg g-1 Fresh Weight). The treatment of seed priming has increased shoot protein content by 35% in primed seed (P) than non primed seed (NP). Mean values of the data revealed significant increase in shoot protein content with the application of additional increment of salinity. Shoot protein content was enhanced with the application of 3, 6, 9 and 12 g L-1 salinity levels, respectively. Discussion The present study confirmed that plant height recorded in plants derived from primed seeds were significantly different from non-primed treatments when exposed to different salinity levels. Similar results are also reported by Sivritepe et al. (2003) in melon. It was observed that boosting levels of salinity has gradually decreased plant height which might be due to decreased physiological activities resulting from water and nutrients stress occurring under salinity stress. The adverse effect of salinity on plants may lead to disturbances in plant metabolism, which consequently led to reduction of plant growth and productivity (Shafi et al., 2009). Seed priming and salinity levels have extensively affected shoot fresh and dry weight (g plant-1) of safflower. Shoot weight decreased progressively with the rise of stress level compared with control. Fortmeir and Swchuber (1995) also reported similar results in barley. The increase in salinity levels resulted in the development of water and nutrient stresses. The toxic effect of sodium at high salt levels and physical damage to roots decreased their ability to absorb water and nutrient which caused marked reduction in photosynthesis, enzymatic process and protein synthesis (Tester and Davenport, 2003), which resulted in stunted growth and poor leaf area development. The decrease in the rate of photosynthesis due to leaf area might be responsible to decrease shoot fresh and in turn dry weight. It is evident from results that primed seeds in comparison with control seeds resulted in more crop growth rate (Basra et al., 2003). Therefore, it is concluded that seed priming could be more effective in improving safflower growth parameters. These results agree with the finding of Harris et al. (2001) and Basra et al. (2003). They reported greater plant weight following seed priming. Salinity drastically affects photosynthesis due to decreasing chlorophyll content and commonly showed adverse effects on membrane stability (Parida et al., 2002). Salinity reduced the chlorophyll a and b content with increasing NaCl concentrations. Increasing salinity decreased chlorophyll content in plants (Scalet et al., 1995). Salinity caused decreases in phototsynthetic pigment contents and photosystem II electron transport activity in plants (Potluri and Devi Prasad, 1996). The reduction of photosynthetic pigment in the present study might have been degradation of chlorophyll by chlorophyllase and reactive oxygen species generated during photorespiration under salinity. Salt induced osmotic stress as well as sodium toxicity trigger to the formation of reactive oxygen species (ROS) such superoxide (O2.), hydrogen peroxide (HO), hydroxyl radical (OH) and singlet oxygen (O2-), which can damage mitochondria and chloroplast by disrupting cellular structure (Singh et al., 1987). It is attributed to a salt-induced weakening of protein-pigment-lipid complex and due to the suppression of the specific enzyme which is responsible for synthesis of green pigments (Souza et al., 2004) or increases chlorophyllase enzyme activity (Sreenivasulu et al., 1999). Leslie and Romani (1988) have showed that salicylic acid seed priming treatment stimulates photosynthetic machinery and increase the content of chlorophyll. El-Tayeb (2005) has found that Barley seeds presoaked with 1mM salicylic acid under salinity (0, 50, 100, 150, 200 mM NaCl) increased the photosynthetic pigment like chlorophyll ‘a’, ‘b’ and caratenoids in shoots and roots of 15 day old seedlings compared to seedlings treated with NaCl alone. In the present investigation, seed priming with NaCl had maintained significantly higher total chlorophyll contents and its fractions ‘a’ and ‘b’ compared to control which recorded highest reduction. Similar increase in chlorophyll content has been reported by several authors, Saha and Gupta (1998) in mungbean, Afria et al. (1998) in Gaur and Cengiz et al. (2002) in tomato. The increase in chlorophyll content in these treatments was attributed to decrease in chlorophyllase activity and de novo synthesis of structural component of proteins which are responsible for chlorophyll degradation (Subater and Rodriguez, 1978). Proline plays an important role in reducing the injurious effects of salinity and an acceleration of the repairing processes following stresses. Proline has already been reported to act as an osmoprotectant and associated with mechanism of salt tolerance under salinity stresses (Yu Lei and Shaozheng, 2000). It protects folded protein structures against denaturation, stabilizes cell membranes by interacting with phospholipids, functions as a hydroxyl radical scavenger, or serves as an energy and nitrogen source (Aspinal and Paleg, 1981). Accumulation of solutes like proline can help the plant systems to adopt in saline environment (Garcia et al., 1997). Sivritepe et al. (2003) confirmed that, NaCl seed priming increased proline concentration and salt tolerance in melon seedling, under saline condition compared to non-priming seed. Farhoudi et al. (2007) suggested that canola seed priming with NaCl improved salinity tolerance in canola seedling because seed priming decreased seedling cell membrane damage and increased seedling proline concentration. Recent studies suggest that proline may play as an enzyme stabilizing role (Bhattacharjee and Mukherjee 2002 Maggio et al., 2002) and reduce lipid peroxidation (Jain et al., 2001 Farhoudi et al., 2007) under salt stress. Our results showed that safflower shoot from Primed group had the highest proline concentration under the highest salinity level. Proteins that accumulate in plants under saline conditions may provide a storage form of nitrogen that is re-utilized later (Turan et al., 2007) and may play a role in osmotic adjustment. Proteins may be synthesized de novo in response to salt stress or may be present constitutively at low concentration and increase when plants are exposed to salt stress (Pareek et al., 1997). In the present study, both salt stress and NaCl seed priming caused an increase in shoot protein. However, this effect was more in plant derived from primed seed than plant derived from control seed. While working with wheat, Al-Hakimi and Hamada (2001) found that seed priming with ascorbic acid counteracted adverse effects of salt stress by increasing leaf soluble proteins, which protect the membrane and membrane bound enzymes (Jeng and Sung, 1994). Thus, increased in leaf protein due to seed priming was one of the reasons that contributed in improved growth of safflower under saline conditions. 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