<div>Background: Optimization of co-cultivation parameters during Agrobacterium-mediated transformation to Euphorbia tirucalli evaluated were bacterial density, infection period, acetosyringone (AS) concentration and co-cultivation temperature. Optimized parameters resulted in high transformation efficiency 3 fold increase at transient GUS expression .The optimized conditions were Agrobacterium tumefaciens growth phase of A600nm 0.17, infection period of 30 min, addition of acetosyringone (AS) in co-cultivation medium (100 &micro;M) and cocultivation temperature of 25&deg;C. 
 
Methods: Nodal explants were used for&nbsp; transformation. Bacterial culture was added to 50 ml of liquid YEP medium with kanamycin and rifampicin and grown until reaching the growth phase (A600nm). Bacterial density ranged from A600nm 0.17, 0.56, 0.8 and 1.2 OD were used in the present study. The co-cultivation medium made of solid MS medium consisted of NAA 2 mg L-1 and various concentrations of AS at 0, 50, 100, 200, 400, 600 and 800 &micro;M. Histochemical analysis of gus gene expression was carried out. 
 
Result: Higher bacterial density resulted in more transformation efficiency, but also higher necrosis in the explants. Dilution of bacterial suspension reduced necrosis in explants and resulted in higher transformation. The transformation efficiency is 72% when the infection process was carried out with acetosyringone in co-cultivation medium (100 &micro;M). Our studies proved that among the optimized conditions, cocultivation temperature and acetosyringone were the critical parameters during Agrobacterium mediated transformation.</div>

An Attempt to Establish an Agrobacterium-mediated Transient Expression in Euphorbia tirucalli (L.) an Important Medicinal Plant