Localization of ?-glycerophosphatase activity in cotton fiber during differentiation

Abstract

The distribution of β-glycerophosphatase activity in the outer integument of cotton (Gossypium hirsutum L.) ovules was determined histochemically at the electron microscope level. Both a linted cultivar and a lintless mutant line were examined from 1 day preanthesis to 3 days postanthesis. No enzyme activity was observed in the lintless line at any stage. In the linted cultivar there was no enzyme activity before anthesis, but as fibers were initiated on the day of anthesis, activity was observed in the expanding fiber cell wall and nucleus. As the fibers started elongating, enzyme activity was particularly concentrated in the cytoplasm and wall where directional growth towards the micropyle occurs. By 2 days postanthesis, β-glycerophosphatase activity was decreasing in the cell wall and nucleus, but was increasing in the nucleolus. Enzyme activity in the nucleolus was highest at 3 days post-anthesis, but nuclear β-glycerophosphatase activity was not observed then. These results indicate that β-glycerophosphatase activity was associated with differentiating fiber cells, specifically with those sites where distinct anatomical, and perhaps catabolic, changes were occurring. The significance of the results is discussed in relation to possible mechanisms of cotton fiber differentiation.