Effects Of Salinity And Salicylic Acid Pretreatment Biology Essay

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In order to study the effect of salinity and salicylic acid treatments on seed germination characteristics of artichoke, a laboratory study was conducted in Agriculture and Natural Resources Research Center, Hamadan. The test was implemented in factorial experiments based on a completely randomized design with three replications. The first factor was salicylic acid in 4 levels (0, 0.5, 1 and 1.5 mM) and the second factor was sodium chloride (NaCl) solution in 4 levels (0, 50, 100 and 150 mM). Before sowing, seeds were soaked in salicylic acid solution for 24 h. Then, seeds were sown in sterile Petri-dishes, containing 5 ml sodium chloride solution (with treatment concentrations). Artichoke seed germination parameters such as germination percentage, root length, shoot length, root and shoot dry weight were evaluated. The results showed that with increasing in NaCl concentration in different treatments, seed germination, root and shoot lengths and fresh and dry weight of seedlings reduced. Therefore, the concentration of 150 mM of NaCl reduced germination percent (84.58%) in compared to the control treatment. In addition, salicylic acid had positive effect on germination percent and biomass, so that it adjusted salinity tension in seedlings. Pretreatment of salicylic acid reduced root and shoot lengths but root and shoot dry weights increased in compared to control.

Key words: salicylic acid, germination, salinity, artichoke, seedling growth

1. INTRODUCTION

Globe artichoke (Cynara scolymus L.) is an herbaceous perennial plant native to the Mediterranean Basin. Nowadays, artichoke heads production is widely distributed all over the world (121,000 ha), even though it is mainly concentrated in Mediterranean regions, which produce 800 thousand tons per year (about 65% of the global production). Soil or water salinity is one of the environmental stress inducing factors, which complicates the nourishment, and metabolic processes of medicinal herbs in addition to interrupting and reducing water absorption capacity by plants (Levitte, 1980).

Almost 20% of cultivated area of the world and half of the world's irrigated lands are stressed by the salinity (Chinnusamy et al., 2005). Also in Iran, 3.5 million hectares are suffering from severe salinity. The high concentration of soluble salts at surface layers of the soil affects germination and thus, the establishment of the plants. Improving germination rate of seeds can help to improve the establishment of seedlings, particularly under salinity stress (Jithesh et al., 2006).

Increased resistance of crops to salinity can mitigate the effects of soil salinity on the germination of seeds (He et al., 2002). Therefore, besides selecting methods for recovering saline soils, the introduction of salinity-tolerant species and cultivars and breeding the crops for salinity tolerance can be an economical and useful method for overcoming salinity (Poustini, 1995; Levitte, 1980). Factors such as "gene control, seed size, seed coat, biological adaptation, deep tillage, soil moisture, oxygen concentration and temperature" can affect the germination and seedling emergence (Lopez et al., 1999). In addition, low temperature, low moisture, and seed coat are factors that reduce seed germination, emergence, and vigor (Metwally et al., 2003).

Heydecker (1973) proposed the theory of seed priming. It is a technique for controlling seed slow absorption and post-dehydration (Heydecker and Coolbear, 1977). After treatment with initiators, plant seeds exhibit not only enhanced emergence rate and even emerge of seedlings (Harris et al.,1999) but also improved resistance or tolerance to cold (Lu and Fu, 1990), drought (Wang et al., 2004) and salt (Ruan et al., 2003).

Salicylic acid has drawn the great attention of researchers due to its ability to induce systemic acquired resistance (SAR) in plants leading to defense mechanism against various biotic and abiotic stresses (Radhakrishnan and Balasubramanian, 2009; Zao et al., 2009; Syeed et al., 2011 and Idrees et al., 2011). Seed imbibitions with Salicylic acid leads to an activation of germination and seedling growth (Shakirova et al., 2003 and Singh et al., 2010).

It has been shown that SA plays a role in plant adaptive responses to osmotic stress (Singh & Usha, 2003), chilling and drought (Senaratna et al., 2000), high temperatures (Clarke et al., 2004), and high salinity (Khodary, 2004). Salicylic acid is a signaling molecule, naturally occurs in plants and belongs to a group of Phenolic compounds and plays a major role in various physiological processes such as growth and development (Khodary, 2004; Huang et al., 2008). Derivatives of salicylic acid, acetyl salicylic acid after absorption, are converted rapidly to salicylic acid (Popova, et al., 1997; Rajasekaran et al., 2002; Metwally et al., 2003).Gul and Weber (1999) declared that germination of Allenrolfea occidentalis under salinity conditions (0, 200, 400, 600, 800, and 1000 mM sodium chloride) reduced with increasing in salinity. Curtis and Lauchli (1985) studied effect of salinity on kenaf germination and announced that seed germination was reduced a little at concentrations above 200 mM. They also described that germination of kenaf with 37 mM NaCl tolerance reduced only after 150 mM sodium chloride. Salicylic acid plays an important role in resistance to environmental stresses (Eltayeb, 2005).

Cutt and Klessig (1992) showed that salicylic acid played a role in seed germination and introduced as removing oxidative damages during seed germination of wild type and mutant of Arabidopsis. Rajasekaran et al. (2002) and Shakirova et al. (2003) determined that external application of salicylic acid may stimulate seed germination. Since the number of plants per unit area (density) is important for farmers, thus at first the farmers should know accurate information of germination percent to calculate the number of seeds per unit area (Harper and Balke, 1981).

Therefore, given the medicinal value of Artichoke, the objective of the current research was to study the responses of Artichoke seedlings to salinity stress and to investigate the possibility of mitigating the effects of salinity stress on this medicinal plant by pre-treating its seeds with salicylic acid.

2. MATERIALS AND METHODS

In order to study the effect of salinity and salicylic acid treatments on seed germination characteristics of Artichoke, a laboratory test was conducted in Agriculture and Natural Resources Research Centre, Hamedan. The test was implemented in factorial experiments based on a completely randomized design with three replications. The first factor was salicylic acid in 4 levels (0, 0.5, 1 and 1.5 mM) and the second factor was sodium chloride (NaCl) solution in 4 levels (0, 50, 100 and 150 mM). Seeds were disinfected by 0.2 % Mancozeb fungicide and 2% hypo chloride sodium for 2 min. Then seeds soaked in salicylic acid solution for 24 h. After that, seeds were washed with distilled water. before starting the experiment, gamma sterile Petri-dish set and bed seed (Wattman paper) and 25 seeds were transferred on filter paper in Petri-dishes, containing 5 ml sodium chloride solution (with treatment concentrations). All Petri-dishes were placed in the germinator at 24±1° C. All Petri-dishes were monitored daily and germinated seeds (according to exit the root shell to the size of 2 mm from seed test) were recorded in each Petri-dish. After 8 days of the experiment, seed germination percentage was calculated, and then root length and shoot length of seeds were measured with a ruler. In order to determine the dry weight of root and shoot, samples were first washed with distilled water and after removing the root and shoot, they were put in oven with temperature 70 ° C for 18 hours and finally, root and shoot dry weights were measured by a digital scale (0.0001g). Collected data entered in Excel software and were analyzed by SAS statistical software in the form of factorial experiment based on completely randomized design. Comparing all means by Duncan's multiple test range was conducted in level 5%. All graphs were plotted with Excel software.

3. RESULTS AND DISCUSSION

3.1. Germination percentage

Results showed that NaCl treatment, salicylic acid pretreatment and its interaction had significant effect on germination percent (p<0.01). Germination percent reduced in untreated seed (with salicylic acid) when salinity increased (table 1) that maximum germination related to control and minimum germination related to NaCl 150 mM. Therefore, salicylic acid adjusted salinity effects and increased germination in salinity conditions. In lack of salinity conditions, Salicylic acid pretreatment increased germination in compared to control that maximum germination related to 1.5 mM and minimum germination related to control (distilled water). Salicylic acid pretreatment showed positive effect on reduction of salinity destructive effects (fig. 1a).

3.2. Root and shoot lengths

NaCl treatment had significant effect on root length and shoot length but salicylic acid had no significant effect on both them. In addition, there was insignificant effect in salicylic acid Ã- NaCl interaction. NaCl treatment reduced root length and shoot length that the longest and shortest of root length were 49.95 mm (control) and 47.40 mm (150 mM), respectively. The longest and shortest of shoot length were 7.87 mm (control) and 5.96 mm (150 mM NaCl), respectively. Salicylic acid reduced root length and shoot length that the longest related to control (fig. 1b and fig. 1c).

3.3. Root and shoot dry weights

NaCl, salicylic acid, and its interaction had significant effect on root dry weight, but salicylic acid NaCl Ã- salicylic acid interaction had no significant effect shoot dry weight. Salinity reduced root and shoot dry weights that the greatest root dry weight and shoot dry weight were 0.063 and 0.070 mg/plant (control) and the lowest were 0.030 and 0.040 mg/plant (150 mM NaCl), respectively. In reverse, salicylic acid increased root and shoot dry weights that the greatest root dry weight and shoot dry weight were 0.06 and 0.065 mg/plant (1.5 mM salicylic acid) and the lowest were 0.04 and 0.041 mg/plant (control), respectively (fig. 1d and fig. 1e).

.

3.4. Root and shoot fresh weights

Results showed that NaCl had significant effect on root and shoot fresh weights but salicylic acid had no significant effect on both them. With increasing in salinity, root and shoot fresh weights reduced, so that the highest root fresh weight and shoot fresh weight were 0.05633 and 0.65 mg/plant (control) and the lowest were 0.2750 and 0.24 mg/plant (150 mM NaCl), respectively. Salicylic acid increased root and shoot fresh weights. In this treatment, the greatest root fresh weight and shoot fresh weight were 0.48 and 0.45 mg/plant (1.5 mM salicylic acid) and the lowest were 0.34 and 0.36 mg/plant (control), respectively (fig. 1f and fig. 1g).

Table 1: Effects of salicylic acid, NaCl and interaction between themes on germination characteristics and seedling growth of artichoke

Treatments

Germination (percent)

Root length

(mm)

Root fresh Weight (mg/plant)

Root dry Weight (mg/plant)

Shoot length

(mm)

Shoot fresh Weight (mg/plant)

Shoot dry Weight (mg/plant)

Salicylic Acid

Distilled water (control)

72.92 b

49.95 a

0.34 b

0.04 b

7.87 a

0.36 a

0.041 b

0.5 mM

100.00 a

43.18 a

0.40 ab

0.05 a

6.71 ab

0.41 a

0.064 a

1mM

99.58 a

41.47 a

0.36 ab

0.05 a

6.70 ab

0.38 a

0.061 a

1.5 mM

100.00 a

47.40 a

0.48 a

0.06 a

5.96 b

0.45 a

0.065 a

P value

*

ns

**

*

**

ns

*

NaCl

Distilled water (control)

100.00 a

51.90 a

0.5633 a

0.063 a

8.98 a

0.65 a

0.07 a

50 mM

98.33 a

46.83 ab

0.4158 b

0.050 b

7.08 b

0.41 b

0.06 b

100 mM

89.58 b

43.93 ab

0.3183 bc

0.040 bc

5.55 b

0.26 c

0.05 bc

150 mM

84.58 b

39.33b

0.2750 c

0.030 c

5.63 b

0.24 c

0.04 c

P value

*

**

**

**

*

*

**

Interaction Salicylic AcidÃ-NaCl

P value

ns

ns

ns

ns

ns

ns

ns

ns, * and **: Not significant, significant at 5% and 1% probability levels, respectively.

Amounts of P value are means of square in ANOVA.

Similar letters in each column (between two horizontal lines) indicate no significant difference at 5% probability levels (Duncan test).

Fig 1: Effects of Interaction Salicylic AcidÃ-NaCl on characteristics and seedling growth of artichoke (a) germination , (b) root length, (c) root length, (d) root dry weight, (e) shoot dry weight, (f) root fresh weight and (g) shoot fresh weight.

4. CONCLUSION

Reducing of germination in salinity conditions related to increase in osmotic pressure and subsequent reduction in osmotic potential of soil solution that reduced water absorption by seed. This resulted seed water stress. In addition, reducing and delaying of germination may be affected by ions that had toxic effect on seedlings. Salinity stress collects different free radicals into cells and damages to membranes, proteins and nucleic acids. Salicylic acid has an important role in this condition and develops resistance to environmental stresses, especially salinity. In other hand, Salicylic acid reduced negative effects of environmental stresses. Results showed that salicylic acid pretreatment in 0.5 mM emitted negative effects of different salinity treatments, so that germination percent was 100% in all S. A. pretreatments.

Cutt and Klessig (1992) reported the effect of salicylic acid on seed germination, Harper and Balke (1981) reported that salicylic acid had role in ions absorption and transition and Barkosky and Einhellig (1993) declared that membrane infiltration was affected by salicylic acid. These researches are consistent with these results. In addition, these results confirm researches of Rajasekaran, et al., (2002) and Shakirova et al., (2003) that reported salicylic acid had positive effect on seed germination.

It seems that Salicylic Acid decreases toxic and destructive effect of salinity stress through influencing on antioxidant system and therefore increases germination. Salicylic acid regulates ion absorption by roots and stomata conductivity. It is recorded harmonic role for salicylic acid, Abscisic Acid, Jasmonic acid and ethylene in plant morphology regards to respond to environments stresses. Results showed that shoot and root lengths of Artichoke reduced due to salicylic acid, but dry and fresh weights of shoot and root increased that these results are consistent with Khodary (2004) about corn. Results showed that salicylic acid increased dry and fresh weights of shoot and root of Maize in salinity conditions.

Shakirova et al., (2003) reported that the mechanism of Salicylic Acid for increasing shoot in plants and causing cell division and elongation related to produce of other substances such as auxin. Fariduddin et al., (2003) found that salinity reduced cell division and salicylic acid (antioxidant) could prevent auxin oxidation that resulted increasing in dry weight of shoot and root.

It has concluded that, salicylic acid pre-treatment have positive effect on Artichoke germination and affect antioxidant protective system of Artichoke. Therefore, it increases seedling resistance to salinity conditions. This treatment can improve germination even in 0.5 mM NaCl and can emit salinity effect on germination. Also increasing in root and shoot fresh weights showed that water absorption in salinity conditions increased by salicylic acid pre-treatment. It is realized that before sowing, salicylic acid pre-treatment with upper than 0.5 mM for 24 h could affect positively seedling germination and root and shoot dry weights. It can moderate salinity effects in sensitive stage of growth, especially in saline lands. It is concluded that it can be developed optimum situation for reduction of salinity and increasing in germination of Artichoke as medicinal plant about economical, natural resources covering and preventing of erosion in saline regions.

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