Poster: Hormones

Abs # 593: Combined effects of increased gibberellin and auxin levels in transgenic tobacco

Presenter:	Israelsson, Maria , maria.israelsson@genfys.slu.se
Authors	Israelsson, Maria  (A)   Moritz, Thomas  (A)
Affiliations:	(A): Department of Forest Genetics and Plant Physiology

We have produced transgenic gibberellin (GA) over-producing tobacco (Nicotania tabacum) by expressing the genes coding for two different GA 20-oxidases under the CaMV35S promoter; AtGA20ox1 from Arabidopsis thaliana and PttGA20ox1 from hybrid aspen (Populus tremula x P. tremuloides) respectively. Independent lines carrying either construct were put through an initial characterisation, representative lines were then selected and subsequently crossed with a previously described auxin over-producing line harbouring the Agrobacterium tumefasciens genes iaaM and iaaH (Sitbon et al. 1992). The growth pattern and phenotypes of the GA, IAA and GA/IAA transgenic tobacco lines were compared to wt under green house LD conditions. We detected a difference already between the two GA over-producing lines, where ectopic AtGA20ox1 expression led to a more characteristic slender GA phenotype than did over-expressing PttGA20ox. Differences in substrate affinity of AtGA20ox1 and PttGA20ox1 in the early hydroxylated and non-hydroxylated GA biosynthesis pathway will be discussed. Moreover, in the GA/IAA lines we observed a marked increase of root formation, particularly adventitious roots; curled epinastic leaves; delayed flowering and increased height increment compared to IAA plants but decreased height increment compared to the GA plants. The combined effect of increasing GAs and auxin will be discussed in relation to the general plant responses these plant growth substances elicit.