Studies of onion root respiration V. Effect of culturing temperature and seed sample on root respiration and diameter

Abstract

Onion roots from two differents “lots” of sets were grown in nutrient solution at three different temperatures; 20, 25, and 30°C. Gas exchange measurements (in air and O 2) were made at 30°C on 0–5, 0–10, and 0–15 mm segments of the root using the Warburg manometic technique; values for the 5–10 and 10–15 mm segments were for the most part obtained by difference, however, some few measurements were made directly. Roots cultured at the higher temperatures show a decrease in rate of oxygen consumption and carbon dioxide production as compared to those cultured at 20°C. This decrease is not proportional in the case of the two gases exchanged as exemplified by the fact that the respiratory quotient exhibits a decreased value for the roots cultured at the higher temperatures. This indicates that carbon dioxide production is depressed to a greater degree than is oxygen consumption. The most marked changes of his nature are shown by meristematic tissue. The diameter of the roots produced at the three temperatures is not significantly different for any one “lot” of onion sets. However, the diameter of roots produced from different “lots” of sets is markedly different. Because of this, the desirability of reporting measurements of gas exchange per unit weigtht of tissue rather than per root is shown; a practice which should result in more comparable data. Also, in any one series of investigations, it appears to be desirable to use onion sets from the same “lot”. The results are discussed in relation to earlier investigations. It is suggested that onion roots, as well as other plant tissue, be cultured at constant temperature, which should yield more reproducible results in future experimental work.