Effect of Moisture Supply upon Translocation and Storage of 14C in Sugarcane

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Abstract
The role of moisture in the mechanism of translocation of photosynthate was studied. Equal portions of 14CO2 were supplied to 20-cm lengths of attached blades for 5 or 10 min. in bright sun, and translocation terminated after 90 min., 5 hr., 24., or 6 wk. Low moisture supply, controlled by adding NaCl to a complete nutrient solution, allowing a cut stalk to wilt, or witholding irrigation in the field, decreased velocity, and percentage rate of translocation. The surplus sucrose not used in growth moved more slowly down the phloem and was stored in the stalk. Translocation was inhibited 93 to 94% by low moisture while photosynthesis in the same leaves was inhibited only 18%, indicating that the effect of moisture supply upon translocation was primary. Low moisture supply retarded profile development in the stem and a loss in moisture gradient was associated with a steepened slope of the profile, indicating a flow mechanism of translocation rather than diffusion. A slow pressure-flow mechanism operates superimposed upon this general mass transport is the more rapid process of photo-translocation.