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 f loated on ii defined culture medium. Our laboratory is interested in examin ing the effects of altered gravity environments on fiber development as a m odel for the effects of gravity on cell expansion and cellulose biosynthesi s. Since liquid culture media are unsuitable for altered gravity experiment s, addition of gelling agents to cotton ovule culture media is necessary. I n this study we have systematically examined the effects of four gelling ag ents at several concentrations on fiber. production in culture. A rapid scr eening method using toluidine blue 0 staining indicated that after 3 wk in culture, A fiber growth on 0.15% (wt/vol) Phytagel(TM) medium was similar t o fiber growth on liquid medium. More detailed anal, sis of filer developme nt revealed that fiber length was not influenced by the addition of Phytage l(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 med ia treatments. By 4 wk in culture, the difference in cellulose content of f iber 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, o r to toxicity of contaminants copurifying with Phytagel(TM) . By identifyin g 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 sy stems at the whole plant level.