In cotton (Gossypium hirsutum L.) grown in controlled-environment growth chamber the effects of K deficiency during floral bud development on leaf photosynthesis, contents of chlorophyll (Chl) and nonstructural saccharides, leaf anatomy, chloroplast ultrastructure, and plant dry matter accumulation were studied. After cotton plants received 35-d K-free nutrient solution at the early square stage, net photosynthetic rate (PN) of the uppermost fully expanded main-stem leaves was only 23 % of the control plants receiving a full K supply. Decreased leaf PN of K-deficient cotton was mainly associated with dramatically low Chl content, poor chloroplast ultrastructure, and restricted saccharide translocation, rather than limited stomata conductance in K-deficient leaves. Accumulation of sucrose in leaves of K-deficient plants might be associated with reduced entry of sucrose into the transport pool or decreased phloem loading. K deficiency during squaring also dramatically reduced leaf area and dry matter accumulation, and affected assimilate partitioning among plant tissues. and Duli Zhao, D. M. Oosterhuis, C. W. Bednarz.
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.