Date of Graduation

1989

Document Type

Dissertation/Thesis

Abstract

Cytokinins are an integral part of plant growth and development, involved in many physiological processes and found in several forms. This investigation sought to follow the uptake of the cytokinin, {dollar}\\sp{lcub}14{rcub}{dollar}C-8N{dollar}\\sp6{dollar}-benzyladenine (BAP), by lettuce seeds through time, trace the movement of the metabolites through several areas of the seedling, and identify the BAP metabolites. Lettuce seeds (Lactuca sativa L. cv. Grand Rapids) were exposed to a two hour pulse of the radioactive BAP. These seeds were harvested at 4 hour intervals from 2-48 hours. Seedlings incubated from 36-48 hours were cut (depending on age) into; root, stem, shoot tip and seed coats. Each of these groups was extracted in 70% methanol and their radioactive metabolites isolated by high performance liquid chromatography (HPLC). Radioactive fractions were pooled and reduced for further analysis by thin layer chromatography (TLC). A 2 hour exposure was found to be sufficient to break dormancy. The content of the radioactive BAP was highest after 2 hours and decreased through 12 hours, followed by a small increase from 16-20 hours (germination), and again a decrease to level off at 24-32 hours. After the 36 hours the majority of the radioactivity was present in the shoot/seed coat complex. When the seed coat was removed from the shoot (40 and 44 hours), it was found to have twice the radioactivity of the shoot. After 48 hours the seed coat still contains most of the radioactivity, and the shoot tip contained 4 times more than the stem. The major compound identified throughout the time periods was BAP, exclusively found from 2-20 hours. BAP riboside was found in addition to BAP from 24-32 hours. The 40 and 44 hour extracts contained BAP and its riboside in the shoot and BAP in the seed coat. The 48 hour extract contained BAP and its riboside in both the shoot tip and the seed coat. This study produced information on the following points. A cytokinin exposure of 2 hours or less is needed to break dormancy in these seeds. These results indicate the directional control of cytokinin movement, perhaps for detoxification. Transport in the seedling is prior to 36 hours, with the seed coat a major area of accumulation. The riboside seems to be the active form.

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