Adding gelling agents to cotton ovule culture media leads to subtle changes in fiber development

Young cotton (Gossypium hirsutum) ovules will produce fiber in vitro when floated on a defined culture medium. Our laboratory is interested in examining the effects of altered gravity environments on fiber development as a model for the effects of gravity on cell expansion and cellulose biosynthesis. Since liquid culture media are unsuitable for altered gravity experiments, addition of gelling agents to cotton ovule culture media is necessary. In this study we have systematically examined the effects of four gelling agents at several concentrations on fiber production in culture. A rapid screening method using toluidine blue O staining indicated that after 3 wk in culture, fiber growth on 0.15% (wt/vol) Phytagel(TM) medium was similar to fiber growth on liquid medium. More detailed analysis of fiber development revealed that fiber length was not influenced by the addition of Phytagel(TM). Accumulation of cellulose, however, was reduced 50-60% compared with fibers produced in liquid media after 3 wk in culture. The fiber cellulose content rose with additional time in culture for both solid and liquid media treatments. By 4 wk in culture, the difference in cellulose content of fiber cell walls grown on solid versus liquid media was less than 20%. This variance in growth response on gelled media could be due to differences in media matric potential, to the immobility of ions trapped within the gel, or to toxicity of contaminants copurifying with Phytagel(TM). By identifying why ovule growth and fiber cellulose biosynthesis are reduced in cultures grown on gelled media, it will be possible to reveal new information about these processes in a system that is less complicated than physiological systems at the whole plant level.