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Overexpression of oat phytochrome A gene differentially affects stem growth responses to red/far-red ratio signals characteristic of sparse or dense canopies

Authors

  • J. J. CASAL,

    Corresponding author
    1. Departamento De Ecologia, Faculdad De Agronomia, Universidad De Buenos Aires, Av. San Martin 4453, 1417-Buenos Aires, Argentina
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  • R. A. SÁNCHEZ

    1. Departamento De Ecologia, Faculdad De Agronomia, Universidad De Buenos Aires, Av. San Martin 4453, 1417-Buenos Aires, Argentina
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Dr J. J. Casal Departamento de Ecologia, Faculdad de Agronomia, Universidad de Buenos Aires, Av. San Martin 4453, 1417-Buenos Aires, Argentina.

ABSTRACT

The effects of overexpression of oat phytochrome A on neighbour detection and on stem-growth responses to changes in red light (R), far-red light (FR) and blue light (B) simulating neighbours were investigated in transgenic tobacco seedlings grown under natural radiation. In wild-type (WT) seedlings, stem extension growth was promoted: (1) by lowering the R:FR by means of daytime supplementary FR, end-of-day FR, neighbours reflecting FR, or selective light filters placed around the base of the shoot to reduce R without affecting FR; and (2) by lowering phytochrome-absorbable radiation (R+FR) reaching the stem. Transgenic seedlings only responded to reductions in R:FR involving no significant changes in FR irra-diance, i.e. end-of-day FR and filters placed around the stem to reduce R. Neither daytime supplementary R nor selective filters placed around the stem to reduce B affected stem growth in any genotype. In growing canopies, WT seedlings responded to the reduction of R:FR caused by FR reflected in neighbour plants. Transgenic seedlings responded to plant density about a week later, when mutual plant shading reduced R and (to a lesser extent) FR below sunlight levels. Overexpression of phytochrome A impaired early neighbour detection.

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