Contribution of pentose phosphate pathway in developing castor bean endosperm

Abstract

Glucose-1-14C, glucose-6-14C, and glucose-U-14C were used to calculate the contribution of the PPP in developing castor bean endosperm tissues. Depending on the age of the seed 5–12% of the glucose-14C used was metabolized via the PPP and 88–95% via the EMP pathway. When lipid synthesis was rapid (20- to 28-day period) the PPP contribution was also at a maximum. During the 30- to 51-day period when lipid synthesis decreased so did the PPP contribution.With the data obtained from the PPP contribution the amount of NADPH produced during the experimental period was calculated. Also, the amount of fatty acids synthesized during that period was determined from glucose-U-14C data and thus the amount of NADPH required was calculated. Assuming that all the NADPH produced in the PPP was utilizable in fatty acid synthesis it was found that it was only sufficient to supply 50–75% of the reducing hydrogen required for fat synthesis. Therefore, the rest of the reducing hydrogen must come from some other sources, possibly NADH.