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A Comparison of ¹⁴C-Labeled Photosynthate Export from Two Leaf Positions in a Corn (Zea mays L.) Canopy¹

The time course and direction of ¹⁴C-labeled photosynthate export from upper and lower leaf positions in a corn (Zea mays L.) canopy were compared at five different stages from silking to kernel maturity. Export of ¹⁴C-assimilates was slower from the lower than from the upper position. Some of the difference was due to more accumulation of ¹⁴C in leaf starch at the lower position. The direction of export from a given leaf position changed as development progressed, indicating that sink demand strongly influenced the direction photosynthate moved. Transport of ¹⁴C from upper leaves was predominantly downward, whereas direction of export from lower leaves changed from downward to upward as the ear became the dominant sink.

Key Words: Translocation • Sugars • Starch

² Former graduate research assistant (now Reader in Botany, Berhampur University, Berhampur 4, India); former Assistant Professor of Agronomy (now Research Agronomist, DEKALB AgResearch, Inc., DeKalb, III. 60115); and Assistant Professor of Agronomy, respectively. The advice of Dr. Dale Smith is gratefully acknowledged.

Received for publication January 20, 1972.