Auxin pulses and a synergistic interaction between polyamines and ethylene inhibitors improve adventitious regeneration from apricot leaves and Agrobacterium-mediated transformation of leaf tissues

The effect, on adventitious regeneration from apricot leaf explants and transformation of leaf tissues, of auxins pulses with NAA and 2, 4-D was tested. Addition of the polyamines putrescine and spermidine to the regeneration medium, alone or in combination with the ethylene inhibitors silver thiosulphate and aminoethoxyvinylglycine, were also tested to design a procedure that improved transformation efficiency. Spermidine at 2 mM in combination with 0.5 M aminoethoxyvinylglycine and four-day pulses with two different concentrations of 2, 4-D increased significantly shoot regeneration. Spermidine at the same concentration but in combination with 60 M silver thiosulphate and four-day pulses with 9 M 2, 4-D also increased stable transformation events and GFP-expressing calluses probably by inducing a larger amount of dividing cells where Agrobacterium transferred its T-DNA. Since regeneration from apricot leaves occurs mostly from developing calluses, it is important to obtain many GFP-expressing calluses and, given that transformation efficiencies (number of transformed shoots per total number of explants) in woody plants are generally very low, approaches that allow the optimization of T-DNA transfer and total number of transformed cells obtained, will improve probabilities of obtaining transformed shoots.