Influence of potassium deficiency on photosynthesis, chlorophyll content, and chloroplast ultrastructure of cotton plants

In cotton (Gossypium hirsutum L.) grown in controlled-environment growth ch amber the effects of K deficiency during floral bud development on leaf pho tosynthesis, contents of chlorophyll (Chl) and nonstructural saccharides, l eaf 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 (P-N) of the uppermost ful ly 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 associa ted with dramatically low Chl content, poor chloroplast ultrastructure, and restricted saccharide translocation, rather than limited stomata conductan ce 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 dramat ically reduced leaf area and dry matter accumulation, and affected assimila te partitioning among plant tissues.