Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Richard J. Gladon


A new pathway for ethylene (C[subscript]2H[subscript]4) biosynthesis, which utilizes [delta]-aminolevulinic acid (ALA) as a precursor of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of C[subscript]2H[subscript]4, is presented. ALA enhanced ACC accumulation to 410% and C[subscript]2H[subscript]4 production to 232% of the control. The C[subscript]2H[subscript]4 production rate varied with the ALA concentration and the stage of tomato fruit development. As the ALA concentration increased from zero to 40 mM, the C[subscript]2H[subscript]4 production rate increased. Both treated and untreated pericarp discs from fruits at the pink stage of development yielded the largest C[subscript]2H[subscript]4 production rate;Fruit discs treated with ALA accumulated significantly more ACC than did those treated with either methionine or water. Moreover, fruit discs treated with either ALA or ACC showed a significant increase in C[subscript]2H[subscript]4 production over discs treated with either methionine or water. Neither glutamate nor [alpha]-ketoglutarate had any significant effect on either ACC accumulation or C[subscript]2H[subscript]4 production by tomato fruits;Radioactivity from (2,3-[superscript]3H)ALA was detected in both ACC and C[subscript]2H[subscript]4, and radioactivity from (4-[superscript]14C)ALA was detected in ACC and CO[subscript]2 but not in C[subscript]2H[subscript]4. However, radioactivity from (5-[superscript]14C)ALA was detected in CO[subscript]2, and its amount was greater than that obtained from (4-[superscript]14C)ALA. Neither ACC nor C[subscript]2H[subscript]4 showed any radioactivity when (5-[superscript]14C)ALA was supplied to the fruit discs. In addition, when (2,3-[superscript]3H)ALA or (4-[superscript]14C)ALA was supplied to the fruit discs, radioactivity was detected in other metabolites such as fumarate, succinate, malate, glutamate, glutamine, [alpha]-ketoglutarate, and methionine, but the amount of radioactivity was insignificant as compared with the amount of radioactivity found in C[subscript]2H[subscript]4 and ACC;A new pathway for C[subscript]2H[subscript]4 biosynthesis is presented, and this pathway may have an important relationship to chlorophyll biosynthesis and the associated degreening processes in ripening tomato fruit.



Digital Repository @ Iowa State University,

Copyright Owner

Diaa El-Deen Ahmed El-Rayes



Proquest ID


File Format


File Size

54 pages