Soybeans (Glycine max IL.l Menf. cv. NC 69-2774) were used to study the nonstructural carbohydrate and nitrogen content of plant tissues, and nitrogenase activity tbrougbout the development of male-sterile and malefertile plants. Male (10,15,17), and the influence of source-sink manipulation on the carbohydrate content of soybean leaves, stems, pods, and seed is shown in several studies (4,5,13,15,19,20). Only a few reports mention the effect of altered source-sink relations on soybean nitrogenase activity (7,12) Sampling was initiated at 80 DAE and continued at 10-day intervals until 140 DAE. The final sampling (140 DAE) was taken when the fertile siblings were physiologically mature. At each sampling date five sterile and five fertile plants were harvested from one plot in each of the eight replications. The plants were cut off at ground level, and separated into stems plus petioles, trifoliolate leaves, and pods plus seed. The numbers of pods and leaves from each plant were counted and all samples were maintained separately. The samples were dried, weighed, and prepared for Kjeldahl nitrogen analysis.Plants selected for tissue extraction and acetylene reduction assay were taken from one of the harvested plots in two randomly selected replications. In each of the two replications, the excised root systems of the five sterile and five fertile harvested plants were removed from the ground, and plant identity was recorded. Four root samples of each plant type in each replication were used in the acetylene reduction assay. Carbohydrate and lipid were extracted from the entire root of the fifth plant of each type in each replication, and from 10-g fresh wt portions of leaf, stem plus petioles, and pods plus seed from these same plants. All

Developing soybean (cv. Dare) cotyledons harvested at 30 days after flowering were pulse-labeled with II-'4Cloleoyl-CoA. The metabolic interrelation of radiolabeled unsaturated fatty acids between the major glycerolipid classes was determined at various time intervals. At chase time zero, 1I4CIoleic acid accounted for 99.2% of the total glycerolipid radioactivity, and phospholipids contained 92% of the total incorporated radioactivity. With time, phospholipids were metabolized in triacylglycerol biosynthesis and radioactivity was detected in polyunsaturated fatty acids. The hypothesis that phospholipids were metabolc intermediates in polyunsaturated fatty acid biosynthesis was tested by comparing the theoretical and the actual amount of radiolabeled oleic acid that was associated with triacylglycerol as a function of time. The radioactive oleic acid found in triacylglycerol at various intervals was derived from phospholipids via a diacylglycerol intermediate. Assuming no phospholipid desaturation, the potential or theoretical amounts of 1j4Cjoleic acid that could be transferred to triacylglycerol from phospholipids was defined by a system of differential equations. The results demonstrated that the decline in 114CIoleic acid from phospholipid after long chase intervals was equal to the total amount of radioactive unsaturated fatty acids found in neutral lipids. The difference between the theoretical and actual amounts of It4CIoleic acid present in triacylglycerol after long time intervals was equal to the amount of radioactivity present in polyunsaturated fatty acids. Based upon those findings in soybeans, the desaturation of oleic acid associated with phospholipids was highly probable.For the past decade, the mechanism of polyunsaturated fatty acid biosynthesis in plant tissues has been a subject for debate. An important issue of that debate has been the nature of the substrate for the 18:12 desaturase system. In one opinion, the thio-ester theory, the reaction, was described as a consecutive desaturation of 18:l-CoA to form 18:2-CoA and 18:3-CoA, which occurred before any of the unsaturated fatty acids were incorporated into