Plant Growth and Developemnt

Name of the Student
Professor’s Name
Plant Biology
1st November 2015
Plant Growth and Development
Experimental Design to Study the Effects of Different Concentrations of Auxin on Shoot Growth
Introduction
Auxin is a plant hormone that helps in the growth of shoot meristem and prevents sprouting. It is liberated from the shoot apices and acts to increase the length of the plant and decreases the development of lateral branches or sprouts (Simon & Petrasek, 2011). The present article reflects the action of auxin applied in different concentrations to the plants. The experiment was also undertaken to understand whether auxin at different concentrations, significantly influences the growth of sprouts.
Methodology
Auxins at different concentrations were applied to decapitated pea seedlings. 2 concentrations of auxin were applied to 2 groups consisting of decapitated pea seedlings while a third group was kept as control and did not receive any dose of auxin. The doses of auxin used were 500ppm and 5000ppm.
Hypothesis testing &Statistical Interpretation
The hypothesis that was tested through this experiment was:
Whether auxin prevents sprouting in decapitated seedlings, with any concentrations of auxin?
Whether different concentrations of auxin significantly alter the length of sprouts?
For hypothesis (I), our analysis was based on the acceptance the null hypothesis and rejection of the alternative hypothesis.

The null hypothesis contends that auxin does not prevent sprouting in decapitated seedlings, under any concentrations, and specific concentrations would be required to visualize a significant reduction in sprouting. However, if any such difference in sprout length does occur, just under any concentrations of auxin, it will indicate such observations have happened due to chance. The Wilcoxon sum rank statistic was used as the statistical test of significance. The null hypothesis will be retained if the computed Wilcoxon sum rank statistic is less than the critical Wilcoxon sum rank statistic (Ikewelugo & Anaene, 2012). This means for prevention of sprouting; auxin must be available in effective concentrations.
For hypothesis (II), our analysis was based on the rejection of the null hypothesis and acceptance of the alternative hypothesis. The null hypothesis contends that different concentrations of auxin do not significantly alters sprout length, and any such difference must have happened due to chance factors of random sampling, and such difference may be ignored (Cox, 2006). The alternative hypothesis contends that different concentrations of auxin do significantly alters sprout length (as evidenced by literature and textbooks), and any such difference must not have happened due to mere chance factors of random sampling. Hence, such difference cannot be ignored and should be retained. The alternate hypothesis will be retained if the computed Wilcoxon sum rank statistic is more than the critical Wilcoxon sum rank statistic (Ikewelugo & Anaene, 2012). This means different concentrations of auxin do significantly alter sprout length.
Results

Fig 1: reflects the mean length of sprouts in the control and 5000ppm treated seedlings.
Calculation of Wilcoxon Statistic
Wilcoxon Values
W’ = n (N+1) – W
= 8(18+1) – 36
= 152-36
= 116
(Where N1=8 and N2=10)
Smaller value =36, compared to larger value of W=116
Critical Wilcoxon statistic =56
Since, the Wilcoxon statistic (smaller value) is lesser than the critical Wilcoxon statistic, it signifies that 5000ppm auxin was just not enough to reduce the sprout length significantly than the controls. This is because the null hypothesis was retained in this case.

Fig 2: reflects the mean length of sprouts in the control and 500ppm treated seedlings
W’= 10(26+1) – 215
= 55.
(Where N1=10 and N2=16)
Smaller value =45, compared to larger value of W=215
Critical w= 103
Since, the Wilcoxon statistic (smaller value) is lesser than the critical Wilcoxon statistic; it signifies that 500ppm auxin was just not enough to reduce the sprout length significantly than the controls. This is because the null hypothesis was retained, in this case, too.

Fig 3: reflects the mean length of sprouts in the 500ppm and 5000 ppm treated seedlings.
W’ = 8(24+1) -94.5
= 105.5
(Where N1=8 and N2=16)
Smaller value =94.5, compared to larger value of W=105.5
Critical Wilcoxon statistic =72
Since, the Wilcoxon statistic (smaller value) is more than the critical Wilcoxon statistic; it signifies that mean length treated with 500ppm auxin and 5000ppm auxin was significantly different. This is because the null hypothesis was rejected and the alternative hypothesis was accepted.
Discussion and Conclusion
The experiments adequately addressed our hypothesis and speculations. Our first assumption was that, auxin does not prevent sprouting in decapitated seedlings, under any concentrations, and specific concentrations would be required to visualize a significant reduction in sprouting. This assumption was hold to be true because, neither 500 ppm auxin (Fig 2) nor 5000 ppm auxin (Fig 1), reduced the sprout length, significantly than the controls. As the Wilcoxon statistic (smaller value) is lesser than the critical Wilcoxon statistic; it signifies that 500 ppm or 5000 ppm auxin was just not enough to reduce the sprout length significantly than the controls. This is because the null hypothesis was retained in this case. Perhaps to note a significant difference in sprout length a higher concentration of auxin may be required. On the other hand, it is also possible since only one type of auxin was used the difference was not significant and evidence suggests plants do require different auxins (Simon & Petrasek, 2011).
The second assumption tested for the role of auxin. This means auxin at different concentrations will impact the growth of sprouts in a different manner too, and higher doses of auxin will inhibit sprout length more compared to lower doses of auxin. We exactly saw from Fig 3, that 5000 ppm inhibited sprout growth greater than 500 ppm auxin concentrations. This was evident from the lower sprout length observed with the 5000 ppm concentration of auxin compared to 500ppm auxin concentration treated seedlings. Such assumption was accepted based on the retention of the alternative hypothesis and rejection of the null hypothesis. As the Wilcoxon statistic (smaller value) is more than the critical Wilcoxon statistic; it signifies that mean length treated with 500ppm auxin and 5000ppm auxin was significantly different. This is because the null hypothesis was rejected and the alternative hypothesis was accepted.
References
Cox, D. R. Principles of Statistical Inference. Cambridge University Press. 2006:197.Print
Ikewelugo, Cyprian; & Anaene, Oyeka.. “Modified Wilcoxon Signed-Rank Test”  
Open Journal of Statistics, 2012:172–176. Print
Simon, S; & Petrášek, P. “Why plants need more than one type of auxin”. Plant
Science,2011, 180:454–460. Print