Early Embryo Development in Fucus distichusIs Auxin Sensitive

Abstract

Auxin and polar auxin transport have been implicated in controlling embryo development in land plants. The goal of these studies was to determine if auxin and auxin transport are also important during the earliest stages of development in embryos of the brown alga Fucus distichus. Indole-3-acetic acid (IAA) was identified in F. distichus embryos and mature tissues by gas chromatography-mass spectroscopy. F. distichus embryos accumulate [3H]IAA and an inhibitor of IAA efflux, naphthylphthalamic acid (NPA), elevates IAA accumulation, suggesting the presence of an auxin efflux protein complex similar to that found in land plants. F. distichus embryos normally develop with a single unbranched rhizoid, but growth on IAA leads to formation of multiple rhizoids and growth on NPA leads to formation of embryos with branched rhizoids, at concentrations that are active in auxin accumulation assays. The effects of IAA and NPA are complete before 6 h after fertilization (AF), which is before rhizoid germination and cell division. The maximal effects of IAA and NPA are between 3.5 and 5 h AF and 4 and 5.5 h AF, respectively. Although, the location of the planes of cell division was significantly altered in NPA- and IAA-treated embryos, these abnormal divisions occurred after abnormal rhizoid initiation and branching was observed. The results of this study suggest that auxin acts in the formation of apical basal patterns inF. distichus embryo development.

Interactions between Auxin Transport and the Actin Cytoskeleton in Developmental Polarity ofFucus distichusEmbryos in Response to Light and Gravity

“…Duncan's multiplerange post hoc test showed that LatB at 30 and 100 nM was significantly different from the control (P # 0.005). The elevated IAA accumulation is consistent with a reduction of IAA efflux, and the magnitude of the LatB effect parallels the NPA effect on IAA accumulation in Figure 5 and as previously reported (Basu et al, 2002).…”

“…Although the presence of IAA in algae so far appears to be universal, the function and transport of IAA have been tested in very few species (Cooke et al, 2002), and sometimes with contradictory findings (Dibb-Fuller and Morris, 1992;Klämbt et al, 1992). In F. distichus, previous evidence has demonstrated that IAA is present and that IAA accumulation is modulated by IAA efflux inhibitors (Basu et al, 2002). Finally, IAA and IAA efflux inhibitor treatment alter F. distichus embryo developmental patterns (Basu et al, 2002).…”

“…Treatment of embryos with indole-3-acetic acid (IAA) efflux inhibitors led to altered developmental patterns in a number of species (Schiavone and Cooke, 1987;Hadfi et al, 1998;Geldner et al, 2000), including F. distichus (Basu et al, 2002). The altered morphology resembles the defects found in plants with a quadruple mutation in four PIN genes , which encode proteins that are likely to be part of the IAA efflux carrier complex (Friml, 2003).…”

“…Although IAA has been found in a range of algae and other plants (Cooke et al, 2002), including F. distichus (Basu et al, 2002), the physiological function and mechanism of movement of this molecule in algae is not yet clear (Cooke et al, 2002). A previous report also indicates that in F. distichus embryos IAA movements are regulated by IAA efflux inhibitors, and that both IAA and IAA efflux inhibitor treatments lead to altered embryo structures, consistent with a role of auxin in F. distichus embryo development (Basu et al, 2002). Very few similar experiments have been performed in other multicellular algae, with the exception of Chara.…”

“…The proteins encoded by the BDL and MP genes so far indicate a role for auxin-regulated gene expression in these development processes (Jurgens, 2003). Finally, treatment of embryos with exogenous auxin alters developmental patterns in both land plants and algal embryos (Schiavone and Cooke, 1987;Hadfi et al, 1998;Basu et al, 2002).…”