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Auxin Effects On Chara Development And Cytoskeleton.     Q. Jin and K.H. Hasenstein, Biology Department, University of Louisiana, Lafayette 70504-2451

  Although auxin is recognized as maybe the most important plant growth regulator, the understanding of its effects on the cytoskeleton and organ development especially in the green algae Chara is incomplete. We used α-naphthylacetic acid (NAA) and indole-3-acetic acid (IAA) to analyze their effects on Chara. NAA (10-5M) induced elongation of thalli within the first 14 days, but inhibited elongation thereafter. α-NAA also depolymerized microtubules (MTs) in developing antheridia within 2 h of incubation.  Repolymerization of MTs occurred by 5 h. In contrast, IAA (10-5M) caused MT depolymerization after 3 h and repolymerization occurred 4 h after IAA application. NAA reduced the endogenous IAA levels in Chara by about 40% after two weeks and 50% after three and four weeks. NAA had no effects on the endogenous ABA levels and changing ABA concentrations did not modify the cytoskeleton.

(Supported by NASA NNA04CK48G)