Cellular Respiration in Onion Root Tips

Abstract

1. The apical portion of onion roots was sectioned into segments 1 mm. long. Cell counts were made on these segments, and cell size was estimated. Oxygen consumption, fresh weight, dry weight, B vitamin concentration (thiamin, riboflavin, niacin), and total nitrogen content were also determined. 2. The 1-2-mm. segment of the root tip contained the greatest number of cells, had the highest dry weight and total nitrogen content, and showed the greatest oxygen consumption. Fresh weight showed an increase from the apex moving basally. The 2-3-mm. segment possessed the highest concentration of the three B vitamins. 3. Wet and dry weight per cell, as well as vitamin content, increased basally. Cells in the 5-6-mm. region showed the greatest nitrogen content, and those in the 3-4-mm. segment the highest rate of oxygen consumption. The cells showed an increase in length and volume as they became more basally located. 4. There are significant variations in the oxygen consumed by 1-mm. root segments over the first 5 mm. of the onion root tip when respiration is based on individual segments, wet weight, dry weight, and milligrams of nitrogen per segment. 5. These results are discussed, and the possibility of fundamental differences in the oxidative metabolism of different regions of the root are suggested.