Physiology of Development and Germination - Research Paper Example

The Effect of Different Sodium Chloride (NaCl) Concentration on the Rate of Soybean (Glycine max L.) Germination Introduction Seed germination is a complex phenomenon involving many physiological and biochemical changes and leading to the activation of embryo (Bewley & Black, 1985). Seeds vary in their rate of germination. In normal conditions, soybean seeds should germinate in one to two days. However, any unfavorable change may jeopardize the process of germination to a large extent. Salinity, considered to be a biological hazard, induces numerous disorders in seeds and propagules during germination (Mayer & Poljakoff-Mayber, 1989). It either completely inhibits germination at higher levels or induces a state of dormancy at lower levels. It first reduces imbibition of water because of the lowered osmotic potential of the medium (Bliss et al., 1985). Second, it causes toxicity; that is, it changes enzymatic activity, hampers protein metabolism, upsets plant growth regulators balance, and reduces the utilization of seed reserves. It may elicit changes at ultrastructural, cellular and tissue, or even at organ levels (Dell’Aquila & Spada, 1993). Salinity interacts with certain plant and environmental factors during germination. Among these plant factors are seed coat, dormancy, seed age, seed polymorphism, and seedling vigor. Environmental factors include temperature, light, availability of water, and oxygen (Pessarakli, 1999). In this experiment, it will be determined if salt will interfere with the rate of germination of soybean seeds. To assure that all other factors are held constant, a standard germination test will be undertaken under optimum conditions for seed germination. Materials and Methods 1. Four different concentrations of NaCl solutions should be prepared. These are 0.5M, 1M, 2M and 3M NaCl solutions. Distilled water is used to dissolve the salt. For 0.5M NaCl solution, 0.5M NaCl = 0.500 moles NaCl 1.00 L of distilled water 0.500 moles NaCl x 58.5 g NaCl = 29.2 g NaCl will be dissolved in 1 L of distilled 1 mole NaCl water to produce 0.5M NaCl solution For 1M NaCl solution, 1M NaCl = 1.00 moles NaCl 1.00 L of distilled water 1.00 moles NaCl x 58.5 g NaCl = 58.5 g NaCl will be dissolved in 1L of distilled 1 mole NaCl water to produce 1M NaCl solution To make 2M NaCl solution, 117 g NaCl will be dissolved in 1L distilled water. To make 3M NaCl solution, 175.5 g NaCl will be dissolved in 1L distilled water. 2. Five rectangular plates (12”x5”) will be lined with paper towels pre-moistened by different solutions. Plate A is the control and it will be moistened with distilled water. Plate B will be moistened by the 0.5M NaCl solution, Plate C will be moistened with 1M NaCl solution, Plate D will be moistened with 2M NaCl solution and Plate E is moistened with 3M NaCl solution. 3. Thirty soybean seeds will be distributed evenly in the rectangular plates and the plates will be placed in the greenhouse. 4. In the next three days, the paper towels in the plates will be moistened twice a day (10 AM and 4 PM) with the appropriate salt solution to prevent water loss due to evaporation. Also, the germinated seeds in each plate will be counted and recorded. . For this experiment, we will define germination as the breaking of the seed coat and the emergence of the radicle. 5. In the fourth day, the number of germinated will be totaled and compared. Results and Discussion Table 1. Number of Germinated Soybean Seeds in Different Plates per Day Plates Day 1 Day 2 Day 3 Day 4 Total Plate A (Control) 5 6 4 2 17 Plate B (0.5M NaCl Solution) 6 5 4 3 18 Plate C (1M NaCl Solution) 0 3 2 1 5 Plate D (2M NaCl Solution) 0 1 2 1 4 Plate D (3M NaCl Solution) 0 0 0 1 1 With the obtained results, the Chi-Square Test will be used because it will be compared how well an observed breakdown of germinated seeds over various categories fits some expected breakdown, such as an equal breakdown of seeds in different salt concentrations. A chi-square test is more formally described as comparing an observed frequency distribution to an expected frequency distribution. Overall, what the hypothesis testing involves is (a) figuring a number for the amount of mismatch between the observed frequency and the expected frequency and then (b) seeing whether that number is for a greater mismatch than you would expect by chance. The chi-square test is effective in the measurements that relate to the number of germinated seeds in particular NaCl concentrations. The observed number or germinated seeds can then be compared with an expected number which is calculated. The chi-square (χ2) test is based on calculating the value of χ2 from the equation: χ2 = Σ(O - E)2, where O represents the observed results, E represents the results we expect. E In this case, the first thing is to do is produce a null hypothesis. With the χ2 test, the null hypothesis is Ho: There is no difference between the observed germinated seeds and the expected germinated seeds. Table 2. Observed and Expected Frequencies for the Rate of Germination in Different NaCl Concentrations. NaCl concentration Observed Frequency (O) Expected Frequency (E) Differences (O - E) Differences Squared (O - E)2 Difference Squared Weighted by Expected Frequency (O - E)2 E Plate A (Control) 17 30 - 13 169 5.63 Plate B (0.5M NaCl Solution) 18 30 - 12 144 4.80 Plate C (1M NaCl Solution) 5 30 - 25 625 20.80 Plate D (2M NaCl Solution) 4 30 - 26 676 22.53 Plate D (3M NaCl Solution) 1 30 - 29 841 28.03 With this, it can be calculated: χ2 = Σ(O - E)2 E = 5.63 + 4.80 + 20.80 + 22.53 + 28.03 χ2 = 81.79 Using the table of chi-square critical values at the Engineering and Statistics Handbook website, it was determined that at degrees of freedom = 4 and significance level of 0.05, we have obtained a value (81.79) greater than the posted critical value at 9.488. Thus, we will reject the null hypothesis and assume that there is indeed a significant difference between the observed and expected number of soybean seeds that germinated in different NaCl concentrations. It seemed more reasonable to conclude that the number of germinated seeds in each NaCl concentration were truly different. Comparing the results we have obtained to other literature, Hosseini, Powell and Bingham (2002) conducted a germination and seedling growth of soybean (Glycine max L.) cv. Williams that were examined on paper towels pre-moistened with a range of saline solutions (germination: 0–500 mMolal NaCl; seedling growth: 0–330 mMolal NaCl). The Na+, K+ and Ca2+ concentrations in the embryonic axis immediately before germination and in the seedling 3.5 days after germination were measured. Germination decreased at NaCl concentrations of 330 mMolal (81% germination) and above. At 420 mMolal NaCl, only 40% of seeds germinated, and at 500 mMolal NaCl there was no germination. Seedling growth rate decreased drastically with increasing salinity. At 220 mMolal NaCl, seedling growth rate had declined to 5% of the control, whereas at 330 mMolal NaCl seedling growth was almost zero 3–4 days after germination. Thus, soybean seeds were more tolerant of salinity in the germination than in the seedling phase. This study validates the results we have obtained when at 1M, 2M and 3M NaCl concentrations; there is a steep decline in the number of soybean seeds that germinated. Conclusion and Recommendations In this experiment, we have proven that increasing the NaCL concentration will have a significant effect in the rate of germination of soybean. Although we observed that there is a slight difference in Plate A (control) and Plate B (0.5M NaCl), we can account this at the fact that an ample amount of NaCl is needed for a seed to germinate. However, increasing the NaCl concentration to 1M, 2M and 3M, the soybean seed rate of germination was obviously affected and it drastically decreased. Germination and salinity interaction has been previously studied on the premise that it has dual action; that is, osmotic and toxic actions. Wahid et al. (1998) reported that incubation of seeds in salt solution followed by reduced germination in water gave credence to the major role of ion toxicity. It is also noticeable that the overall germination of seeds barely exceeded 50 percent. However, in this experiment, other factors might have affected the rate of germination such as the seed coat, seed dormancy, seed age, seed polymorphism, and seedling vigor. Environmental factors that could affect seed germination like temperature, light, availability of water, and oxygen might have interfered with the results obtained. Thus, it is recommended that a more viable experiment could be conducted where environmental factors will be controlled and monitored. The soybean seeds could also be removed of the seed coat to prevent this factor to interfere with the results. References Bewley, J. and Black, M. (1985). Seeds: Physiology of Development and Germination. New York: Plenum Press. Bliss, R.D., Platt-Aloia, K.A. and Thomson, W.W. (1986). The Inhibitory Effect of NaCl on Barley Seed Germination. Plant Cell Environment, 9: 727– 733. Dell’Aquila, A and Spada, D. (1993). The Effect of Salinity Stress upon Protein Synthesis of Germinating Wheat Embryos. Annals of Botany. 72: 97– 101. Engineering and Statistics Handbook Website. (n.d.). Critical Values of the Chi-Square Distribution. Retrieved 01 March 2007 at http://www.itl.nist.gov/div898/handbook/eda/section3/eda3674.htm Hosseini, M.K., Powell, A.A., and Bingham I.J. (2002). Comparison of the Seed Germination and Early Seedling Growth of Soybean in Saline Conditions, Seed Science Research, 12(3): 165-172. Mayer, A.M. and Poljakoff-Mayber, A. (1989). Germination of Seeds. 4th ed. Oxford, UK: Pergamon Press. Pessarakli, M. (1999). Handbook of Plant and Crop Stress (2nd Edition), New York, NY, USA. Wahid, A. Javed, L.H., Ali, I., Baig, A., and Rasul, E. (1998). Short Term Incubation of Sorghum Caryopses in Sodium Chloride Levels: Changes in Some Pre and Post Germination Physiological Parameters. Plant Science, 139(2): 223-232. Read More