Abstract - Elongation growth and flowering time in Arabidopsis thaliana - the role of temperature and phytochrome

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Plants respond to both diurnal temperature alternations (thermoperiodism) and to the annual temperature cycle. The red to far-red fluence ratio (R:FR) of the light is another essential environmental factor, and temperature can interact with this light signal and its photoreceptors, phytochrome, to affect plant growth and development. Wild type (WT) and phytochrome mutants of the model plant Arabidopsis thaliana were chosen in this thesis to investigate interactions between temperature and phytochromes on elongation growth and flowering time.
The effect of diurnal temperature alternations was studied by growing WT plants under 16 day (DT) and night (NT) temperature combinations (DT and NT 12, 17, 22 and 27°C). A. thaliana showed a classical elongation response to these treatments as inflorescence stem length increased with increasing DT and decreased with increasing NT. Flowering time accelerated with increasing NT. The effect of the difference between DT and NT (DIF) depended on the average daily temperature (ADT). In plants grown under two opposite DT/NT combinations, the shorter inflorescence stems at negative DIF (DTNT).
The role of the phytochromes B, D, and E in thermoperiodic responses was assessed by growing WT and phytochrome single and double mutants under two opposite DT/NT regimes (positive and negative DIF). The effect of DIF on elongation growth was attenuated in the genotypes lacking phyB, while a phyD or a phyE mutation had no or a slightly positive influence on the temperature effect, respectively. For all genotypes tested, plants flowered earlier at negative than positive DIF.
The interaction between different phytochromes and ambient growth temperature in the regulation of flowering time was investigated by growing WT and different phytochrome mutants at constant 22 or 16°C. The classical early-flowering phenotype of the phyB mutant was at 22°C but not at 16°C. The phyA phyB phyD phyE quadruple mutant, however, flowered early compared to the phyA phyB phyD mutant irrespective of temperature, demonstrating that phyE controls flowering also at 16°C. Flowering time in the different phytochrome mutants correlated with the transcript level of FT, a promoter of flowering.
In conclusion, the results presented in this thesis state a requirement for phyB for a complete thermoperiodic control of elongation growth in A. thaliana. Furthermore, it demonstrates that the phyB control of flowering is temperature sensitive, and that phytochrome control of flowering is mediated at least partly through FT.

Keywords: Arabidopsis thaliana; day temperature; night temperature; DIF; phytochrome A-E; mutant; thermoperiodism; elongation growth; flowering time; FT

E. Thingnæs. 2003. Elongation growth and flowering time in Arabidopsis thaliana - the role of temperature and phytochrome. Doctor Scientiarum Theses 2003:6. Agricultural University of Norway. ISBN: 82-575-0543-9

Publisert: 17.02.03
Oppdatert: 23.09.09
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