Export of 14C‐Assimilates in Cotton Leaves1

Abstract

AbstractA study was made of the export of 14C‐assimilate in mature leaves of ‘Stoneville 213’ cotton (Gossypium hirsutum L.). Fruiting branches and subtending leaves of field grown plants were pulse‐labeled with 14CO2 for 5 min at about mid‐day. The amount of 14C‐assimilate transported to the cotton boll from the subtending leaves, bracts or boll wall, as well as the amount of 14C‐assimilate remaining in the leaves and bracts, were determined over a 22‐hour period. During this translocation period, leaves and bracts export 14C‐assimilate to the boll wall, ovules and lint; whereas the boll wall does not export 14C. assimilate. The leaves are the dominant source of assimilate for cotton bolls throughout the season.There is a differential rate of export and retention of H2O soluble and insoluble (starch) assimilate from the leaves and bracts. There is an initial rapid phase of transport of H2O soluble compounds from both leaf and bract sources. About 80% of these compounds disappear 6 hours after exposin the sources to 14CO2. After 22 hours, over 90% of this pool is depleted. In contrast, there is a retention of 14C in the starch fraction up to 6 hours after pulse‐labeling the sources with 14CO2. After 6 hours, there is a slow export of 14C‐assimilate from the starch fraction stored in the sources. Cotton leaves export assimilate stored as starch slowly. At the end of 22 hours, 90 to 95% of the 14C‐assimilate disappears from mature leaves and bracts.