The Conversion of Fat to Carbohydrate in the Germinating Castor Bean

Abstract

In considering the conversion of fat to carbohydrate in the germinating castor bean, two phases of the problem have been discussed in the preceding papers. The results of chemical analyses made on the beans at various stages of their germination will be presented here. The changes in the fat stores of seeds during germination have been studied by numerous investigators who used many different seeds. Hellriegel (1), Leclerc du Sablon (2), Green (3), Green and Jackson (4), Maquenne (5), Deleano (6), Miller (7-8), Maz6 (9) and many others have investigated the transformation of oil into starch or sugar during germination. For a more detailed bibliography covering this phase of plant chemistry, the reader is referred to the book by Miller (10) and the articles by Deleano (6) and yon Ffirth (11). All of the above investigators observed that sugar was formed in increasing amounts as the oil disappeared in germinating fatty seeds, and several noted that the sugar increased up to a certain point and then decreased along with the oil.The increase in the carbohydrate content in the seedlings of oily seeds necessarily raises the question as to its orgin. Miller (7) working with sunflower seeds found that changes in the protein reserve could not account for the carbohydrate formed. We have observed that there is a slight increase in amino nitrogen in castor beans during their germination, but this increase is exceedingly small, less than 1 per cent. As there is an exceptionally small amount of preformed sugar in ungerminated castor beans it seems likely that the oil must serve as the source of carbohydrate. Miller (10) notes that no one has found free glycerol in germinating seeds or seedlings. However, even if all of the glycerol from the fat which disappeared were utilized for building of carbohydrate, it would not be 311The Journal of General Physiology A simple calculation will be presented below in proof of this. Thus it seems evident that the fatty acid fraction must be utilized in carbohydrate production. This statement is substantiated by the investigations of Leclerc du Sablon (12), Maquenne (5), and Ivanow (13) but yon Fiirth (11) does not agree with their conclusions, or those of Green (3) whose work will be mentioned later. Von Fiirth worked with seedlings with a root length (hypocotyl?) of about 40 mm. We will show later that marked changes in the oil and sugar content did not take place until the hypocotyls were over 35-40 mm. in length. Furthermore yon Flirth (11) felt that Miintz (14) had no right to conclude that the fatty acids of germinating seeds were converted into oxy-acids since the acetyl value of the oil extracted by yon Ffirth did not rise during germination. Miller (8) also found no change in the acetyl value of the oil obtained on extraction of germinated seeds. Green (3) isolated a crystalline acid of unknown structure from germinating castor seeds and believed that this might be an intermediary product in the conversion of the oil to sugar. Von Fiirth (11) was unable to confirm Green's work, a...

Fat Utilization and Composition in Germinating Cotton Seeds.

“…Among these are aspartic and glutamic acids, and alanine (14,15,13,10). The discovery of phosphoenolpyruvic carboxylase (1) and, more recently, its demonstration in leaves of Kalanchoe and other Crassulacean plants (9,16) have provided new information about the actual mechanism of dark CO2 fixation, and it now seems reasonably certain (9,17,18) that the synthesis of oxalacetate by this enzyme must be an important step in the dark CO2 fixation and the resulting acidification in such leaves. 'Malate would then be produced by the rapid reduction of oxalacetate (OAA) by the active malic dehvdrogenase present (17).…”

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Diminuition of the fat reserve and concomitant increase of carbohydrate during germination of oil seeds have been well established (3,7,10,11,12,13,16). Few studies, however, have compared illuminated and unilluminated seedlings, or have controlled the environmental conditions to the degree necessary for calculation of a rate constant and for prediction of fat content at various stages of growth.

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