Translocation of C14 in Sugarcane

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Abstract
This paper describes translocation of labelled photosynthate in the variety H (Hawaii) 37-1933 grown and fed C14O2 under normal conditions of climate and nutrition. Sucrose is the principal compound translocated down the leaf to the stalk, down the stalk to the stubble and roots, up the fed stalk to the spindle, and up other stalks in the same plant. New sucrose quickly enters the veins and moves primarily downward, following the veins to midrib and sheath, at velocities up to 2.5 cm/minute. Upon arriving at the stalk, sucrose goes first to the center and then turns downward. After moving down 1-9 joints, some sucrose finds its way into an upward-moving system. New sucrose moves into lalas (lacteral shoots) and suckers in a few hours and gets to the tops of all stalks in a large plant within 24 hours. Sucrose reaching young stems, leaves, and roots is converted to other compounds used in growth. Each day''s sucrose proceeds to the stem where most is stored in ripening joints and some is added to mature joints. Velocities of translocation from the fed blade down the stalk range from 42 to 150 cm/hour; 12 determinations average 84 cm/hour. Percentage of counts leaving the fed part ranges from 17% to 54%/hour. Causes of this variation are discussed. Rate of translocation from a leaf area of approximately 82 cm2 into the stalk is estimated at 10.7 mg C14 sucrose/hour. Slope of the translocation profile in the stalk decreases with time. Shape of the profile may be caused by a separation of transport from storage, by the upward translocation of sucrose, or both. Rank of leaf affects total amount and velocity of translocation. Old blades, e.g. blade 12, translocate less in amount and more slowly than mature blades of middle rank, e.g. blades 5-8, because old blades must compete with streams coming down from the younger blades.