Fatty Acid Composition and Nitrate Uptake of Soybean Roots during Acclimation to Low Temperature.

Fatty acid composition of old and new roots was determined for soybeans (Glycine max [L.] Merr. cv Ransom) at root-zone temperatures of 14, 18, and 22 degrees C during a 26-day period. New roots had a greater concentration of polyunsaturated fatty acids than old roots. The ratio of polyunsaturated to saturated fatty acid concentration in new roots exposed to 14 and 18 degrees C peaked at 16 days and declined, while the corresponding ratio in old roots increased throughout the treatment period. Apparently the response of fatty acid composition in old and new roots to low temperature was mediated by tissue aging or differentiation. These findings were contrary to the concept that modifications in fatty acid composition remain constant at lower temperatures.The function of root tissues exposed to lower temperature was evaluated with respect to the ability of the root systems to absorb NO(3) (-). Over the relatively long periods of exposure, the ability of whole root systems to absorb NO(3) (-) was similar at cool and warm temperatures. The effect of cool temperature on functioning of roots appeared to involve reductions in the rates of initiation and differentiation of young root tissues rather than changes in membrane permeability related to alteration of fatty acid composition.