Relationships between Respiration Rate and Adenylate and Carbohydrate Pools of the Soybean Fruit

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Abstract
Relationships between respiration rate, adenylate and carbohydrate pools of the soybean fruit during rapid seed growth were evaluated. Plants at mid pod-fill were subjected to different concentrations of CO2 to alter the amount of photosynthate produced and, thus, available to the fruit. Respiration rate of the intact fruits was measured, along with glucose, sucrose and starch concentrations, adenylate energy charge (AEC) and total adenylate pool (.SIGMA.AdN) in the pod wall, seed coat, and cotyledons. The concentration of sucrose remained relatively constant in the pod wall (1.0 mg/100 mg dry weight), seed coat (6.5 mg/100 mg dry weight), and cotyledons (4.5 mg/100 mg dry weight) at moderate and high respiration rates. Furthermore, AEC remained relatively constant in the pod wall (0.55), seed coat (0.24) and cotyledons (0.44) during changes in respiration rate. The amount of assimilate transported to the fruit, and its flux through the sucrose pools of the fruit parts, were probably important in the regulation of the respiration rate of the fruit. The average .SIGMA.AdN in the seed coat (1300 pmol/mg dry weight) was significantly greater than in the cotyledons (750 pmol/mg dry weight) and pod wall (300 pmol/mg dry weight). In addition, the .SIGMA.AdN in the seed coat and cotyledons increased with increasing respiration rate of the fruit. The high .SIGMA.AdN in the seed coat and its increase with increases in respiration rate of the fruit suggest that an energy-requiring process is involved in the movement of sucrose through the seed coat.