Mobilization and Incorporation of Photoassimilated C by Growing Vegetative and Reproductive Tissues of Adult Pinus resinosa Ait. Trees

Variations in translocation and incorporation of ¹⁴C-labeled photosynthate in actively growing vegetative and reproductive tissues of 20-year-old Pinus resinosa trees with time were investigated. Five hours after exposure of 1-year-old needles on second order branches to ¹⁴CO₂, 90% of the recoverable activity was still in the needles. The 1-year-old bark showed a small amount of activity, but terminal sinks had accumulated little ¹⁴C. After 24 hours, activity in the 1-year-old needles decreased to 59% while actively growing terminal and lateral shoots and 2nd year cones had accumulated considerable tracer. Whereas activity in the 1-year-old bark increased, recovery from the 1-year-old wood was only 1.8%. After 1 week, relative activity in the 1-year-old needles had declined to 27%. Recovery of ¹⁴C from various sinks was high and in the following order: 2nd year cones > terminal needles > lateral needles > terminal internode > lateral internodes > 1-year-old wood. Ninety per cent of the ¹⁴C recovered after 5 hours was in the ethanol-soluble form, but by the end of 1 week only half was in the soluble fraction. Incorporation of tracer into insoluble compounds was high in expanding internodes and in 1-year-old xylem, and low in 2nd year cones. Total activity in the terminal internode generally declined toward the distal end while specific radioactivity increased. Only 5% of the ¹⁴C recovered from cones was localized in developing seeds, but specific radioactivity of seeds was higher than in the cone scales and axis.