Lower Gibberellic Acid Concentration, Longer the Stem Elongation
Introduction:
Hormone technology used widely in horticulture and agriculture. Plant hormones are the chemical messengers that could regulate or stimulate the growth and development of plants [Gossett]. The five major classes of plant hormones are auxin, cytokinins, gibberellins, ethylene and abscisic acid.
Auxin can cause the loosing of cell wall and increase the synthesis of cell-wall material and protein. Then initiate the growth and development of root at the stem base. Cytokinins has the function that can affect the cell division and formation of shoot. It also work for then intermodal length and delay the senescence of tissues. Gibberellins are the hormones that can cause elongation of stem. Abstisic acid is the plant growth regulator that produced in leaf and alternate leaves into bud covers. Ethylene can cause the rapidly growing of the dividing cells especially in the darkness. It also inhibit the expansion of leaf and elongation of stem. Ethylene cause thicker stem and allow the ripening of fruit.
This lab, our group designed a experiment to observe the effect of concentration of GA on the length of stems. According to our discussion, higher concentration of GA will cause more elongation of stem.

Hypothesis: Higher concentration of Gibberellic acid grew longer stem.

Methods:
Week 1 - Two-week-old bush bean plants were obtained and labeled by small flags with 0.04%, 0.2%, 1.0% and O%. The original lengths of stems were measured from the surface of soil to the top of the SAM in the unit of centimeter. After the measurement, three different spray bottles containing 0.04%, 0.2% and 1.0% of GA were pumped twice on respective two-week-old bush bean plants. Two sprays of distilled water were treated as a control and pumped on the 0% plant. All of the solutions and distilled water were sprayed at the SAM.
Week 2 – Allowing one week for the plants to grow. The new lengths of stems were measured in the same way above as a comparison of the elongation of stem. The percentage change of length of stem was calculated by using the equation below:
[(New length – Original length)/Original length]x100%

Results:
Table 1. The Data collection and Calculation of Lab 6. Concentration of GA | Length of stem before adding GA /cm(Week 1) | Length of stem after adding GA /cm(Week 2) | %change | 1.0% | 8.0 | 24.6 | 207.5% | 0.2% | 7.9 | 35.2 | 345.6% | 0.04% | 5.9 | 40.7 | 589.8% | 0.0%(Control) | 8.2 | 13.8 | 68.3% |

Figure 1. Comparison between Week1 and Week 2’s length of stem.

Figure 2. Trend of Elongation with GA concentration.

Discussion:
The hypothesis was rejected. Even though all of the four treatments showed growth in length of stem and three of them with GA did have elongation of stem compared to the Control, lower concentration of GA showed more evident growth of stem than the higher concentration. For example, 0.04% plants grow almost 6 times of length rather than the 1.0% only grow twice of the length in one week [Figure 1 and Table 1]. The trend of elongation in Figure 2 above shows a suddenly percentage growth from 0% to 0.04% and then decreased when higher concentration of GA was added [Figure 2].
Using a smaller scales of concentration of GA, such as divided then concentration in every 0.02% of GA. Then find out the concentration shows the best growth of the bean plants. That could be useful while the length of stem is needed, a low concentration and higher efficiency.
Reference:
1. Gosset, D. R. Hormones (Botany). Salem Press Encyclopedia of Science. http://eds.b.ebscohost.com.proxy.lib.miamioh.edu/eds/detail/detail?sid=6eb90718-72af-4a93-8ae5-65629fded5f7%40sessionmgr112&vid=1&hid=117&bdata=JnNpdGU9ZWRzLWxpdmU%3d#db=ers&AN=89551730 January, 2013.

2. Kende, Hanse, Zeecaart, Jan A.D, The Five ‘Classical’ Plant Hormone. http://www.ncbi.nlm.nih.gov.proxy.lib.miamioh.edu/pmc/articles/PMC156991/pdf/091197.pdf The Plant Cell, 7/1/1997, Vol. 9, Issue 7, p. 1197-1210