Determining the Metabolism of Gibberellic Acid in Four Genotypes of Brassica rapa

Laura Sablyak
Biology 240W
September 30th, 2012

Abstract The goal of this experiment was to evaluate how the plant hormone, Gibberellic acid (Ga3), affects how the four different genotypes (wild type, elongate, petite, and the rosette) in the Brassica rapa plant (also known as Wisconsin Fast Plant) use the plant hormone in their plant growth. There were three treatments used on the four genotypes; including water, Ga3 and cycocel, which was sprayed 1-2 times for each genotype. Gibberellic acid is a plant hormone, (Ga3) that acts as a stimulant for growth and development for the plant. Cycocel however is a plant inhibitor and inhibits growth and development (Farabee M.J., 2010). The experiment was held in a flat that consisted of a water mat underneath the Styrofoam holder to collect water from the reservoir to the wicks that helps prevent algae from growing (McKeon et al., 2003).

The wild type and petite genotypes had normal amounts of Ga3 already while the elongate over produced Ga3 and rosette under produced Ga3. In the end of the experiment, the genotypes, wild type and elongate, had the most growth in the control whereas the genotypes, petite and rosette, had the most growth in the Ga3. In all of the genotypes, cycocel had growth but no as much as water and Ga3. Each genotype had a unique way of using Ga3 and by doing so shows how the plant is using Ga3.
Ga3 is already found in plants and this experiment helped show how plants used this natural plant hormone throughout the different genotypes of Brassica rapa.

Introduction A plant hormone is generally described as an organic compound that is combined in one part of the plant and transferred to another part, in low concentrations. Hormones are very important to how the plant develops and what rate of growth the plant will have. The 6 main classes of these hormones are abscisic acid, auxin, cytokinin, gibberellic acid, ethylene, and brassinosteriods. Abscisic acid is a plant inhibitor and also causes dormancy, which makes meristems come to a standstill. However, Auxins increase cell elongation and cell division also providing growth of roots. Cytokinins alongside with Auxins also promote growth and increase cell division and develop the growth of shoot meristems.
Gibberellins promote growth and break seed dormancy, which results in germination. Gibberellins can provide elongation of internodes as well. Ethylene is a naturally found gaseous compound that helps fruit ripen along with the aging of flowers and leaves. Brassinosteriods inhibit root growth and help differentiate xylem, and slow down or even stop leaf abscission (Farabee, M.J., 2010). Gibberellic acid’s effects on plants are stimulating cell growth and cell elongation. These effects are seen in stem growth as well as root growth. Stems and inter nodal lengths can be increased along with root system development. Cell division increases in the production of larger leaves. Gibberellic acid leads to bigger plants with bigger shoots and leaves in many plants (Farabee, M.J., 2010). The plant use in the experiment is Brassica rapa, or the Wisconsin Fast Plant because it has a rapid life cycle around 35-40 days, small (15cm in height) and has a variety of recognizable genetic traits (McKeon et al., 2003). The genotypes used in this experiment are Wild type, Petite (dwarf mutant), Elongate (tall mutant) and Rosette (dwarf mutant). The goal of the experiment was to find how the four different genotypes of the Wisconsin Fast Plant are using gibberellic acid for their plant growth (McKeon et al., 2003).

Materials and Methods The first part of the experiment started with getting into groups of four to six people and then receiving a flat of Brassica rapa seedlings that were divided into 3 sections water, Ga3, and Cycocel for each group. Each flat was divided into 32 Styrofoam sections and each section had all four genotypes such as wild type (Wt), rosette (Rs), petite (Pt), and elongate (El). After receiving the flat of the Brassica rapa seedlings, groups had to pluck the Brassica rapa seedling leaves to one plant per cell. After the thinning of the plant, measurements were then taken of the height of all the Brassica rapa seedlings with a ruler in millimeters. The measurements were recorded by the height of each seedling within the three sections and what day it was measured. After the measurements were taken, the Brassica rapa flat was then placed underneath a light for eight days starting Tuesday and ending the next Tuesday. However, Saturday and Sunday weren’t accounted for the data within the experiment due to students not being able to access the lab building. The light was on a timed cycle that ran from at 7am and 7pm. The members of the group were all assigned certain days of the week to record what kind of plant growth they saw and what day they came down to record it. After all the measurements were recorded, each section labeled water, Ga3, and cycocel was sprayed with the appropriate solution that had the same solution labeled, with 1-2 sprays inside each genotype. The water section only got the water treatment and the Ga3 only got sprayed with the Ga3 treatment. After the full 7 days were completed and recorded, the groups came into lab on the 8thh day to record their flat one more time for final measurements. Then the students found the average of their groups’ data and then entered it into onto angel where all the other groups entered their group’s averages as well. The students then had to take the class average including their group and all the other students’ data to gather the data that would be used in their graphs (McKeon et al., 2003).

Figure 1. Plant set up and treatments
This graph depicts how the Brassica rapa plant was divided into 3 different sections for each treatment, water, Ga3, and cycocel which included all 4 genotypes.

Results and Discussion
Wildtype

Figure 2. The average heights of genotype wild type (wt) undergoing the three treatments: water, Ga3, and cycocel. Petite

Figure 3.Average heights of the genotype, petite (pt), undergoing the three treatments: water, GA3, and cycocel.

Elongate

Figure 4. The average heights of genotype elongate undergoing the three treatments: water, Ga3, and cycocel.
Rosette

Figure 5 Average heights of the genotype, rosette (rs), undergoing three treatments of water, GA3, and cycocel.

In this experiment, the goal was to determine how the four genotypes of the Fast Plant are using gibberellic acid to reach different heights during their development. My hypothesis was that the gibberellic acid would have the highest growth within all genotypes and be higher than the control in all of the three treatments. I thought this because gibberellic acid stimulates growth and by increasing the gibberellic acid content that’s already found in plants, the gibberellic treatment in all of the four genotypes would have surely been the highest and most successful treatment in stimulating plant growth. I was correct in figure 3 and figure 4 but however in figure 1, and figure 2, I stand corrected. In figures 1 and 2, the control has the highest growth instead of the gibberellic acid and this stumped me. I thought that by having gibberellic acid already in all of the four genotypes naturally, that increasing the gibberellic acid content with the gibberellic acid treatment, that all four genotypes would have the highest growth.
The wild type and petite genotypes had normal amounts of Ga3 already while the elongate over produced Ga3 and rosette under produced Ga3. In the end of the experiment, the genotypes, wild type and elongate, had the most growth in the control whereas the genotypes, petite and rosette, had the most growth in the Ga3. In all of the genotypes, cycocel had growth but no as much as water and Ga3. Each genotype had a unique way of using Ga3 and by doing so shows how the plant is using Ga3.

Works Cited
McKeon, Brian Sr., and Warren, James Jr. 2012. Plant Hormones. Biology 240: Form and Function, A laboratory Manual (Penn State Erie, The Behrend College).
Reece, J.B., Urry, L.A., Cain, M.L., Wasserman, S.A., Minorsky, P.V., Jackson, R.B. 2011 Biology 9th ed. Benjamin/Cummings, 2011
Maas, Ken. "Plant Hormones and Plant Growth Regulators." Plant Hormones. N.p., n.d. Web. 02 Oct. 2012. <http://www.dbi.ufla.br/amauri/fitormonios/Kenh.htm>.
Farabee, M.J. "Plant Hormones, Nutrition, and Transport." Plant Hormones/Nutrition. 18 May 2010. Web. 02 Oct. 2012. <http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookplanthorm.html>.