Respiratory Metabolism of the Germinating Castor Bean

Many studies of the respiratory metabolism and energy changes in fatty seeds have been made, but none of them completely accounts for the relationships between oxygen absorption and carbon dioxide production observed at different stages of the germination. The present is the first of 3 studies now in progress in this laboratory to secure additional light on the significance of the low respiratory quotients reported by Godlewski 1 , Gerber 2 , and Ermakov and Ivanov 3 .

The castor bean has been chosen for special study because of the nearly total absence of carbohydrate at the beginning of germination. Measurements of the respiratory exchange have been made in many stages from the first appearance of the radicle to a total length of the hypocotyl of approximately 10 cm. Stages up to 30-40 mm. length can be measured conveniently in the ordinary Brodie-Warburg respirometer. Stages beyond this have been studied over periods of 2 to 8 days on moist paper in tightly stoppered bottles covered with opaque paper and kept in the dark. Low quotients are obtained as soon as the growth of the radicle gets well started (length of 1 to 4 mm.).

Attention is directed to only 2 significant results. 1. The wide difference between the R. Q. of the endosperm and that of the young plant inclusive of the cotyledons, which in the castor bean are easily stripped out of the endosperm, and 2. that this difference seems to be due more to the lower CO₂ output of the endosperm than to the larger 0₂ absorption. These contrasts are illustrated by the accompanying table, where the 0₂ and CO₂ are expressed in cu. mm. per hour per 100 mg. of the whole germinating seed, endosperm alone, and young plant alone, respectively.