A number of recent reports have implicated the plant hormone auxin and its polar transport
in plant embryo and vascular development, using both genetic mutants and auxin transport
inhibitor treatments. Several Arabidopsis mutants have been identified that have
altered embryo development and appear to have a primary defect in auxin response or
homeostasis. We are interested in determining whether auxin transport is also important
during the first embryonic division and are using embryos of the brown alga, Fucus
distichus to test this possibility. Fucus embryos normally develop with a single unbranched
rhizoid, as shown above in panel A, but growth on the auxin, IAA, or the auxin transport
inhibitor NPA (as shown in panel Band C above) leads to formation of embryos with either
branched and multiple rhizoids (Basus et. al., 2002). These embryo alterations are induced by as little as two
hours exposure to these compounds immediately after fertilization and the effects are
complete within the first 6 hours, suggesting that auxin plays a role in initial stages
of development. IAA accumulation in embryos is regulated by auxin transport inhibitors
that act at the site of the auxin efflux carrier, but IAA uptake appears to be carrier
independent. Indole-3-acetic acid (IAA) was identified in Fucus embryos and mature
tissues by gas chromatography-mass spectroscopy. These results suggest that early stages
of Fucus embryo development including orientation of polarity and developmental
pattern are interconnected with auxin transport (Basus et. al., 2002). Current efforts are focused on
understanding how auxin influences the early stages of Fucus embryo development and
the relationship between the role of auxin and the previously established role of the
actin cytoskeleton in Fucus embryo development. The orientation of the position of rhizoid formation in Fucus embryos is sensitive to environmental gradients. We have recently found that in addition to the well characterized response to light, these embryos are also weakly polarized by gravity (Sun et al., 2004). The directional control of the position of rhizoid formation in response to light and gravity are both lost when embryos are treated with auxin and auxin transport inhibitors. Additionally, actin patches, which predict the site of rhizoid formation, are randomized by auxin transport inhibitors. Together, these results are consistent with a mechanism that uses the process of auxin transport to communicate environmental signals to control the position of actin patch formation (Sun et al., 2004).
Sun, H, Basu, S, Brady, SR, Luciano, RL, and Muday, GK (2004) Interactions between auxin transport and the actin cytoskeleton in developmental polarity of Fucus distichus embryos in response to light and gravity. Plant Physiol.: 135: 266-278
Basu, S, Sun, H, Brian, L, Quatrano, RL, and Muday, GK (2002) Early embryo development in Fucus distichus is auxin dependent. Plant Physiology. 130: 292-302
see also [Pubmed List of Papers]
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