Altered development of Arabidopsis thaliana carrying the Agrobacterium tumefaciens ipt gene is partially due to ethylene effects

Transgenic Arabidopsis thaliana plants containingthe Agrobacterium tumefaciens cytokinin-biosynthesis geneipt were produced to study the effect of increasedcytokinin (CK) levels on the development of this rosette plant species. Inthreeindependently transformed lines (ipt-156, 158 and 161),Arabidopsis plants had smaller leaves, an underdevelopedroot system and decreased apical dominance in inflorescence stems. The smallertransgenic leaves were highly serrated along the margins, pale green and hadpointed leaf tips. In cross section, transgenic leaves had smaller cells andirregularly shaped epidermal cells. In the ipt-161 line,leaves and hypocotyls frequently exhibited purple color due to anthocyaninproduction. The most severe phenotype was observed in tissue cultureconditions,while growth in soil reduced or eliminated some phenotypic effects. Compared toC24 wild type plants, ipt-161 plants accumulated zeatinandzeatin riboside with an approximate 10-fold increase in the total pool of CKs.Astudy of the progeny resulting from crosses between theipt-161 transgenic line and the ethylene insensitivemutants ein1, ein2 andeti5 suggested that part of the altered developmentexhibited by the ipt transgenic plants was caused byincreased ethylene levels.