Canopy studies on ethylene-insensitive tobacco identify ethylene as a novel element in blue light and plant–plant signalling

Authors

  • Ronald Pierik,

    Corresponding author
    1. Department of Experimental Plant Ecology, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, the Netherlands,
      For correspondence (fax +31 30 2518366; e-mail R.Pierik@bio.uu.nl).
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      Present address: Department of Plant Ecophysiology, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, the Netherlands.
  • Garry C. Whitelam,

    1. Department of Biology, University of Leicester, Leicester LE1 7RH, UK, and
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  • Laurentius A. C. J. Voesenek,

    1. Department of Plant Ecophysiology, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, the Netherlands
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  • Hans De Kroon,

    1. Department of Experimental Plant Ecology, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, the Netherlands,
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  • Eric J. W. Visser

    1. Department of Experimental Plant Ecology, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, the Netherlands,
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For correspondence (fax +31 30 2518366; e-mail R.Pierik@bio.uu.nl).

Present address: Department of Plant Ecophysiology, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, the Netherlands.

Summary

Plants growing at high densities express shade avoidance traits as a response to the presence of neighbours. Enhanced shoot elongation is one of the best researched shade avoidance components and increases light capture in dense stands. We show here that also leaf movements, leading to a more vertical leaf orientation (hyponasty), may be crucial in the early phase of competition. The initiation of shade avoidance responses is classically attributed to the action of phytochrome photoreceptors that sense red:far-red (R:FR) ratios in light reflected by neighbours, but also other signals may be involved. It was recently shown that ethylene-insensitive, transgenic (Tetr) tobacco plants, which are insensitive to the gaseous plant hormone ethylene, have reduced shade avoidance responses to neighbours. Here, we report that this is not related to a reduced response to low R:FR ratio, but that Tetr tobacco plants are unresponsive to a reduced photon fluence rate of blue light, which normally suppresses growth inhibition in wild-type (WT) plants. In addition to these light signals, ethylene levels in the canopy atmosphere increased to concentrations that could induce shade avoidance responses in WT plants. Together, these data show that neighbour detection signals other than the R:FR ratio are more important than previously anticipated and argue for a particularly important role for ethylene in determining plant responses to neighbours.

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