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Effects of Gibberellic Acid on Wild Type and Rosette Plants of the Genus Brassica

INTRODUCTION There are a variety of methods to stimulate plant growth, one such method is the utilization of plant hormones. Although plant hormones are produced in very small quantities, plant hormones have a significant impact on plant growth and development (Reece et al., 2014). There are a variety of plant hormones and each hormone has a different effect on the plant depending on the site of action, the concentration of the hormone, and the developmental stage of the plant (Reece et al., 2014). The major plant hormones are Auxin, Cytokinins, Gibberellins (GA), Abscisic Acid, Ethylene, Brassionosteroids, Jasmonates and Strigolactones. Auxin stimulates cell elongation, enhances apical dominance, and retards leaf abscission (Reece et al., 2014). Cytokinins regulate cell division, promote lateral bud growth, and stimulate seed germination (Reece et al., 2014). Gibberellins stimulate stem elongation and promote seed germination (Reece et al., 2014). Abscisic Acid inhibits growth and promotes seed dormancy (Reece et al., 2014). Ethylene promotes ripening and flowering (Reece et al., 2014). Brassionosteroids promote cell expansion and division in plant shoots and promotes seed germination (Reece et al., 2014). Jasmonates regulate fruit ripening, floral development, and seed germination (Reece et al., 2014). Strigolactones promote seed germination and controls apical dominance (Reece et al., 2014). Hormones can work together to promote or demote a response within a plant. For example, Auxin works closely with Gibberellin, Cytokinins, and Ethylene in various stages of plant development (Reece et al., 2014). In terms of plant growth, Auxin and Gibberellin work in concert to promote stem elongation by the auxin elongating the cells and gibberellin elongating stems (Reece et al., 2014).

Gibberellin, commonly referred to as Gibberellic Acid (GA) can be found in some plants naturally (Reece et al., 2014). However, scientists can obtain GA by growing cultures of the fungus, Gibberella fujikuroi, then isolating the compound (Gupta et al., 2017). The effects of GA is most notable in certain mutant plant varieties as opposed to wild-type plants because wild-type plants naturally produce the optimal amount of the GA hormone (Reece et al., 2014). Since plant hormones are produced in very low concentrations, the impact on the plant is dependent upon both the concentration of the hormone and the number of hormones involved (Reece et al., 2014). However, there is typically no response if GA is applied to wild-type plants (Reece et al., 2014). An experiment was conducted to investigate the effects of Gibberellic acid on wild type and rosette plants of the genus Brassica. Brassica are rapid cycling plants which complete their life cycle in 35-45 days (Williams et al., 2007). The wild type plant is the Brassica plant without gene mutation. The single gene mutant plant, rosette Brassica, possesses less than one-tenth of GA than a normal plant within the genus B. rapa (Rood et al., 1989). To determine the impact of GA on the rosette phenotype of the Brassica rapa plant and the wild-type Brassica four hypotheses were tested. The first hypothesis is that there will be no difference in height of the rosette Brassica rapa when treated with GA or the one treated with water. The second is an alternate hypothesis which states that the rosette Brassica rapa treated with GA will be taller than the rosette Brassica rapa treated with water. The third hypothesis is that there will be no difference in height between the wild-type Brassica plant treated with GA and the wild-type Brassica plant treated with water. The fourth and alternate hypothesis is there the wild-

type Brassica Plant treated with water will be taller than the wild-type Brassica plant treated with GA. MATERIALS & METHODS The materials for this experiment included four styrofoam cups, soil, 12 fertilizer pellets, 6 rosette B. rapa seeds, 6 wild-type Brassica seeds, deionized water with a dropper, gibberellic acid with a dropper, tap water, a ruler and a pencil. The experiment began by taking the four styrofoam cups and punching a hole in the center of the bottom of each cup with a pencil. This hole allowed water to drain and enter as necessary. Then approximately 1 inch of moistened soil was added to each cup. From here, 3 fertilizer pellets were added to each cup and then covered by an additional inch of soil. To ensure each cup was managed properly, the 2 cups were labeled with “rosette” and 2 cups were labeled “wild-type.” Then within the two groups of cups, one of each group was marked with “water” and one with “gibberellic acid.” This action resulted in the following labels: rosette-water, rosette-gibberellic acid, wild type – water, and wild type-gibberellic acid. Utilizing the tip of a wet pencil, 3 rosette B. rapa seeds were placed in each cup labeled rosette-water and the cup labeled rosettegibberellic acid and placed just barely below the surface of the soil. Then utilizing the tip of the wet pencil, 3 wild-type Brassica seeds were placed in each cup labeled wild type-water and the cup labeled wild type-gibberellic acid and placed just barely below the surface of the soil. Then the plants were placed on long plans containing water located inside an environmental chamber. Once the plants were planted, they were left to grow for 7 days, adding water to the pan daily. After the seven days, the tallest plant (as measured with a ruler) was preserved in each cup and the other plants were

uprooted and disposed of in the garbage. On the 8 th day, one drop of water was added to the base of the plant in each cup labeled rosette-water and wild type-water and one drop of gibberellic acid was added to the base of the plant in each cup labeled rosetteGA and wild type-GA. This step was repeated on day 9, 10, 13, 14, and 15. After each drop was placed, a measurement was recorded for each plant. To obtain the height measurement, the ruler was used in centimeters to measure the distance between the base of the plant to the highest node of the plant. This step was also repeated on day 9, 10, 13, 14, and 15. On day 15, the final measurement was taken and the plants were properly disposed. RESULTS The data in Figure 1, reflects the recorded height (in centimeters) of each rosette plant treated with water or gibberellic acid. The data reflected was recorded over the course of 8 days, with 6 days of recorded data. The rosette plant treated with GA had an average rate of growth of .3cm and grew .6cm higher than the rosette plant treated with water. 3.5 Rosette-GA

Height (Centmeters)

3 Rosette- water

2.5 2 1.5 1 0.5 0 Day 8

Day 9

Day 10

Rosette - H2O group

Day 13

Day 14

Day 15

Rosette - GA group

Figure 1. Influence of gibberellic acid (GA) on the height of rosette plants treated with water (▲) and gibberellic acid (■).

The data in Figure 2, reflects the recorded height (in centimeters) of each wild type plant treated with water or gibberellic acid. The data reflected was recorded over the course of 8 days, with 6 days of recorded data. The wild type plant treated with water had an average rate of growth of .5cm and grew 2.3cm higher than the wild type plant treated with GA. 8 7

Wild-type-Water

Height (centmeters)

6 Wild-type - GA

5 4 3 2 1 0 Day 8

Day 9

Day 10

Wildtype - H2O group

Day 13

Day 14

Day 15

Wildtype- GA group

Figure 2. Influence of gibberellic acid (GA) on the height of wild type plants treated with water (♦) and gibberellic acid (●)

DISCUSSION The growth of the rosette Brassica plant was accelerated when treated with GA (Figure 1), however the growth of the wild-type plant treated with GA was inhibited (Figure 2). Further highlighting that GA has the greatest impact on mutant plants as compared to wild-type plants which already have the optimal amount of GA (Reece et al, 2014). As previously mentioned, Auxin and Gibberellin work in concert to promote stem elongation (Reece et al, 2014). The loosening of the cell wall by Auxin to stimulate

cell elongation allowed the GA treatments in the rosette plant to foster stem elongation. (Reece et al, 2014). This process facilitated the rosette-GA type plant to grow to a height of 3.1cm compared to the rosette-water plant which only reached 2.5cm (Figure 1). A rosette plant has only one-tenth the amount of GA as wild-type plant, therefore of the rosette plant treated with water had a 20% shortfall in growth (Reece et al, 2014). These results support the hypothesis that the rosette plant treated with GA would grow taller than the rosette plant treated with just water. Further, the wild-type plant treated with GA reached a recorded height of 4.5cm which was 34% smaller than that of the wild-type plant that was just treated with water. The results in Figure 2, support the hypothesis that the wild-type plant treated with water will grow taller than the wild-type plant treated with GA. Although, there is typically no response when GA is applied to wild-type plants it appears from our results that our plant’s growth was inhibited (Reece et al., 2014). Since the plant’s response was dependent on the concentration of the GA, site of GA interaction, and the stage of development of the plant, these factors could have inhibited growth of our wild-type plant treated with GA (Reece et al., 2014). The experiment did not focus or measure the concentrations of GA, the stage of development or the site of interaction to further explain the difference in the growth and development of the wild. There were a few errors in the data. The recorded height was a bit higher than expected. It is possible that participants in the group measured the plant from the base of the soil to the top of the plant instead of to the highest node. Although it seems that all data was measured that way, which minimized the variance in the data.

CONCLUSION Based on the results of this experiment, Gibberellic acid can induce stem elongation in rosette Brassica rapa plants. The alternate hypothesis that rosette Brassica rapa plants would grow taller when treated with GA than with water is accepted. Thus, the main hypothesis that there would be no difference in height of the rosette Brassica rapa when treated with GA or the one treated with water is rejected. Further, the addition of GA to the wild-type Brassica plant inhibited its growth. The alternate hypothesis that wild-type Brassica plants would grow taller when treated with water than with GA is accepted. Therefore, the hypothesis that there would be no difference in height between the wild-type Brassica plant treated with GA and the wildtype Brassica plant treated with water is rejected. To improve this experiment, it is recommended that plant measurements be consistent and reflective of the length from the base to the highest node. It would also be advised to measure with specificity the amount of hormones added to each plant, to measure the stage of development of each plant, and to note where each hormone is applied in order to determine how GA can inhibit plant growth in wild-type plants. Finally, GA could be of great use to the agriculture and horticulture communities for plants that are lacking gibberellic acid. It is important for these communities to be knowledgeable of which plants are deficient in GA as not to impact the growth of plants that naturally have the optimal amount.

REFERENCES Gupta, Ramwant, and S K Chakrabarty. “Gibberellic Acid in Plant: Still a Mystery Unresolved.” Plant Signaling & Behavior 8.9 (2013): e25504. PMC. Web. 21 Oct. 2017. Reece, Jane B., Lisa A. Urry, Michael L. Cain, Steven Alexander Wasserman, Peter V. Minorsky, Rob Jackson, and Neil A. Campbell. Campbell Biology. Tenth ed. Boston: Pearson, 2014. Print. pp.840-845 Rood, Stewart B., David Pearce, Paul H. Williams and Richard P. Pharis. “A GibberellinDeficient Brassica Mutant—rosette.” Plant Physiology. 89.2 (1989): 482-487. Web. 13 July 2016. Wendell, D. L., & Pickard, D. (2007). Teaching Human Genetics with Mustard: Rapid Cycling Brassica rapa (Fast Plants Type) as a Model for Human Genetics in the Classroom Laboratory. CBE— Life Sciences Education, 6(2), 179–185. http://doi.org/10.1187/cbe.07-02-0010...