Ethylene biosynthesis and endogenous polyamines in relation to development of in vitro cultured kiwifruit explants

The relationship between polyamines and ethylene is controversial because the degree of interference of one pathway with the other may differ according to species, stage of development and experimental procedure. In this paper, we modify ethylene biosynthesis by the addition of aminoethoxyvinylglicine (AVG) or 1-aminocyclopropane-1-carboxylic acid (ACC) and study how it affects polyamine content and development of kiwifruit explants (Actinidia deliciosa CS Liang. & AR Fergusson). Cultured under ventilation where ethylene did not accumulate in the culture vessels, kiwi explants had higher ACC synthase activity and lower polyamine content than those grown without ventilation. In explants cultured in the reference medium, putrescine was the more abundant polyamine and spermine was only detected in the free fraction irrespective of ventilation. Under ventilation, addition of ACC to the culture medium inhibited organogenesis, there was less spermidine and spermine was not detected. Addition of AVG to the culture medium increased both the number of shoots and the amount of polyamines, and inhibited ACC synthase, so S-adenosylmethionine (SAM) led to increasing synthesis of spermidine and spermine. The increase in putrescine is more difficult to explain on the basis of inhibition of ethylene biosynthesis. The increase in the number of shoots in kiwi explants due to AVG addition may be attributed to the lack of ethylene in the atmosphere of the vessels or the increase in free polyamines.