During ontogeny of Gossypium hirsutum L. floral buds (squares), increases in area and dry mass (DM) of floral bracts and the subtending sympodial leaf followed a sigmoid growth curve with increasing square age. The maximum growth rates of the bract area and bract DM occurred between 15 and 20 d after square first appearance (3 mm in diameter). Net photosynthetic rate (PN) of the sympodial leaf at first fruiting branch position of main-stem node 10 reached a maximum when the subtended square developed into a white flower. Floral bracts had much lower PN and higher dark respiration than the subtending leaf. The amount of 14CO2 fixation by the bracts of a 20-d-old square was only 22 % of the subtending leaf, but 56 % of 14C-assimilate in the floral bud was accumulated from the bracts, 27 % from the subtending leaf, and only 17 % from the main-stem leaf at 6 h after 14C feeding these source s. Hence floral bracts play an important role in the carbon supply of developing cotton squares. and Duli Zhao, D. M. Oosterhuis.
DPC played an important role in regulating the production, translocation and partítioning of i‘*C-assimilates in cotton {Gossypium hirsutum L.) plants. Seed soaking with DPC increased the partítioning of cotton assimilates into roots aitd main stem, and decreased the partítioning into seedling tip which was beneficial for the seedling. After the appearance of a square, spraying with DPC decreased the partítioning of assimilates into the main stem, branches and their growing points, and increased the partítioning into reproductíve organs and roots. This helped to avoid or reduce spindling, ensured a steady growth, coordination of the relatíon between vegetatíve and reproductíve organs, and improved the development of floral buds. From bloom to boll-setting,. sprayings with DPC greatly increased the partítioning of assimilates into reproductíve organs and decreased the partítioning into vegetatíve organs, which was usefiil for the growth and development of squares and bolls.