Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Joseph S. Burris


The present study was initiated to: (1) characterize the anatomical development of soybean (Glycine max (L.) Merr.) hypocotyls from cultivars (Amsoy 71 and Beeson 80) sensitive to inhibition of hypocotyl elongation and excessive radial expansion when grown at 25 C, (2) describe the timing of changes in hypocotyl anatomy and the relationship of these changes to the inhibition of elongation, and (3) compare the anatomical development of hypocotyls from 25 C sensitive cultivars to hypocotyls of non-25 C-sensitive cultivars (Corsoy 79 and Oakland). Seedlings grown in rolled towels at 20, 25, or 30 C were sampled at days one through seven after planting to determine hypocotyl length, percent dry matter, and hypocotyl diameter. Cross-sectional diameter, cortex width, vascular cylinder diameter, pith diameter, and cell number and size of the pith and cortex regions were measured along a transect across the middle of cross-sections taken from a 2 cm region of the hypocotyl immediately below the hypocotyl hook. Hypocotyls collected on days two through seven from each temperature-cultivar combination were fixed and stored in FAA until examination. There was a temporal relationship between hypocotyl elongation, hypocotyl diameter, and cortex width. As hypocotyl length increased in response to increased temperature, there was an associated decrease in diameter and width of the cortex. Size of cortex cells, and to some degree cortex cell number, were responsible for the change in cortex width leading to a change cortex width and hypocotyl diameter. Alterations in hypocotyl diameter and length were most noticeable at days three and four after planting. At this time, the inhibition of elongation and increase in diameter of Amsoy 71 at 25 C was most evident, as were the linear responses to temperature among the other cultivars. Pith diameter contributed to the overall increase in diameter over time in all cultivars, but was not important in the differences in hypocotyl diameter among temperatures within each cultivar. It was concluded that calculation of hypocotyl diameter from length and weight data may underestimate diameter compared to direct measurement in cross-sections of hypocotyls less than three days old.



Digital Repository @ Iowa State University,

Copyright Owner

Stephen Robert Malone



Proquest ID


File Format


File Size

189 pages