Hormones Lab.

Laayla Muhammad
Lab Section: 807
March 10, 2009


Indoleacetic acid (IAA), type of Auxin hormones that promote cell elongation in growing tissues and effect patterns cell differentiation, are used in this experiment on cucumber seedlings to test root growth. The cucumber seedling with IAA concentration of 10.0 mg/L will experience the most root growth because normal amount of concentration of this particular hormone causes stimulation of cell growth; meaning the lower the concentrations, the lower amount of root growth will take place. With the control group having the average root growth of 38.6 mm, the second highest cucumber seedling with the IAA concentration of 10.0 mg/L was 35.5 mm. The seedlings with concentration of 1.0 mg/L and 0.1 mg/L had lower root growths of 17 mm and 9.3 mm and the class average were as followed: the control group averaging out to 38.4 mm, 10.0 mg/L to 36.6 mm, 1.0 mg/L to 23.1 mm, and 0.1 mg/L to 20.3 mm. My hypothesis was right, that besides the control group with the most root growth, as the concentration of IAA increased so did the root growth of the cucumber seedlings; meaning that 0.1 mg/L of concentration was ended up inhibiting the root growth, while concentration of 10.0 mg/L greatly stimulated with 35.5 mm. All of this recorded data agrees with the class average length of the growth roots that also showed as concentration of Auxin increase, so does the length of the cucumber roots, besides the control group which shows cell elongation as well.




Figure 1.1- Average group data used to reveal effects of IAA (type of auxin hormone) given in different concentrations to roots, displaying root elongation (length) in mm.


Gibberellic Acid is one of many types of Gibberellins hormones that promote stem elongation in plants, but has more of a dramatic effect on mutant plants with dwarfed growth. In this experiment, comparing normal and dwarfed plants receiving two different treatments of water and gibberellic acid, I hypothesize that the dwarfed plant with gibberellic acid will experience highest amount of stem elongation meaning it will have the greatest change in height and the dwarfed plant with water will barely grow. The control for the normal plant given just water had the most height change of 20.5 cm and the dwarfed one given just water had the least height change of only 6.90 cm. Normal plant with GA had less change in height (13.5 cm) compared to the dwarfed plan given GA (17.6). The class data shows that normal plants with water grew 14.8 cm and with GA grew 16.8 cm while dwarfed plant with water grew 6.8 cm, but with GA grew 13.4 inches.


Figure 2.1 – Group average used to reveal effects of gibberellic acid (type of gibberellins hormone) on normal and dwarfed plants given two different treatments with their heights being measured in centimeters.



A growth response to gravity, gravitropism, is involved with differential inhibition of cell elongation by the hormone auxin. Gravitropism can be positive where roots grow in the direction of gravity and negative meaning away from the direction of gravity. I hypothesize that the corn seedling planted with the root oriented directly downward will grow the most when compared to: 1) upward, 2) horizontal, and 3) cut off (1 mm) at the root tip and placed horizontally. This is because they will be able to find soil, water and essential minerals easier. Results show that seeds planted downward had a net growth of 2.4 cm with the class average of 3.0 cm, but root planted horizontally grew even more with 3.5 cm. Root placed upward only grew 0.8 and the horizontal root with excited tips did not grow. The class data shows horizontally planted root grew the most with 4.1 cm, but upward one also grew 4.0 cm while the root that was horizontal with its tip excised still grew the least with only 1.2 cm. Roots horizontally orientated experiences the most net growth and planting them upward will result in barely any or no changes. My hypothesis was partially correct since roots planted downward receive essential minerals to grow more than upward positioned roots and roots with excised tips placed horizontally.


Figure 3.1 – Net growth of spouted corn roots measured in centimeters after positioning the roots in four different orientations in order to record root gravitropic response.