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Distribution of ¹⁴C Photosynthates in Timothy (Phleum pratense L.) During the Vegetative Stage of Growth¹

¹¹CO₂ was applied at two stages of growth to leaf blades at different positions on the main shoot or tillers of timothy (Phleum pratense L.). Before treatment some plants had been defoliated to maintain two intact top leaves or two intact basal leaves, while on the rest all or none of the extended leaf blades had been removed. Tillers were not defoliated. Plants were either autoradiographed or dissected and extracted with 85% ethanol to measure partitioning of the radioactivity.

The tracer moved from the main shoots to all sinks at both stages of growth, even under severe defoliation. Tillers exported label consistently to roots and very inconsistently to main shoot or sister tillers. Top blades of the main shoot sent more assimilate to elongating leaves above them, while the basal blades sent more to tillers and roots. The presence of actively growing tillers favored more transport out of blades on mainshoots. Defoliation treatments had only a minor effect on distribution of the label.

Key Words: Defoliation • Translocation • Photosynthates • Tiller Dependence • Main shoot-to-tiller relationship

² Research Scientist, Canada Department of Agriculture, SteFoy, Qué Professor, Department of Agronomy, Cornell University, Ithaca, N.Y. 14850.

Received for publication June 8, 1971.