Hormones regulate various aspects of development, growth, and physiology of higher plants. One of the ways that hormones can influence plants is senescence (aging). Our experiment concentrated on the effects of the hormones auxin, cytokinin, and abscisic acid upon. Senescence was calculated by studying the fluctuation of chlorophyll in Triticum aestivum (wheat) leaves. We compared the chlorophyll concentration of the wheat leaves that were treated with the hormones to the concentration of untreated leaves (control). Ten samples each containing ten wheat leaves were treated with the hormone, abscisic acid in different percentages with acetone. The abscisic acid was diluted with acetone to form percentages ranging form 0% to 100%. The first group had 0% abscisic acid, the second 25%, third group 50%, fourth group 75%, and the last grouped was 100% abscisic acid. We tried different proportions of abscisic acid and acetone to see what the hormone does. Using acetone as our blank, we compared the amount of chlorophyll left in the leaves with a spectrophotometer. The spectrophotometer measured the absorbency of the acetone/ chlorophyll extract at 652 nanometers. The hormone, abscisic acid, delayed the aging of the leaves, bred less chlorophyll.

The effect of plant hormones on chlorophyll decomposition in leaf tissue is the subject of study. Senescence, or aging, is a process in plants that is influenced by hormones. The changing color of leaves is a sign that shows the process of decomposition of chlorophyll. Hormones are responsible for the aging of leaves and ultimately the breakdown of chlorophyll. Abscisic acid is a hormone known to inhibit growth of the plant. The hormone should slow the aging of the plant and the decay of chlorophyll(Lewis 576-578). We hypothesized that abscisic acid would promote the aging of plants. We predicted that there would be a declining effect in the chlorophyll concentration in the second week. We concluded that abscisic acid would inhibit plant growth.
Methods As found on pages in this lab manual 16-2 through16-4,(Dickinson college Faculty, 1997).
-Tables and Figures on subsequent pages.
When we soaked the leaves in abscisic acid at different percentages, we observed the following results: 0% abscisic acid had an average of .575 mg chlorophyll/g tissue, 25% abscisic acid had an average of .215 mg chlorophyll/g tissue, 50% abscisic acid had an average of 0.172 mg chlorophyll/g tissue, 75% abscisic acid had an average of 0.187 mg chlorophyll/g tissue, and 100 % abscisic acid had an average of 0.220 mg chlorophyll/g tissue. In Figure 1, we graphed the amount of chlorophyll during the second week at varying concentrations of abscisic acid.

By comparing the amounts of chlorophyll extraction from non-senescent leaf tissue the first week, to the extraction of chlorophyll from hormone-treated (abscisic acid) leaves. In the second week, we calculated the different amounts of milligrams of chlorophyll to grams of tissue from each week. We also calculated the different percentages of abscisic acid and the amount of chlorophyll from each week. We found that the non-treated leaves had an absorbency of 1.27 mg chlorophyll/g tissue. These data supported our hypothesis that abscisic acid would inhibit growth and not allow the chlorophyll to age as it normally would. This is shown by the decline of chlorophyll concentration as seen in Table 1. We noted the amount of chlorophyll concentration in leaves after being mixed in an acetone solution the first week. Week two we compared the controlled results to the leaves that were soaked in different percentages of abscisic acid for a one week time period. We found that the percentage of chlorophyll concentration declined during the absorption period. There was a drastic drop from 0% concentration of abscisic acid to 25% concentration of abscisic acid. The amount of chlorophyll concentration dropped approximately by 2/3 , followed by a slight continual decrease and then it fairly leveled off. This drop enables one to see that the hormone had an effect on the leaves. The decline indicated that there was an obvious effect on chlorophyll with the use of abscisic acid. Abscisic acid caused the amount of chlorophyll to lower by two thirds the amount. An obvious effect was that abscisic acid caused the metabolism in the leaves to lower to a state of dormancy. This state is a level of living that allows that plant to be