Involvement of free and conjugated polyamines and free amino acids in the adventitious rooting of micropropagated cork oak and grapevine shoots

The recent advances in biotechnology have boosted interest in the differentiation processes, including adventitious rooting. Differentiation processes depend on endogenous factors, among which auxins and polyamines are believed to play a major role. A positive correlation between polyamine accumulation and the induction of adventitious rooting by auxin has been observed in numerous woody species, suggesting that polyamines could be used as markers of the rooting process. The aim of the present work is to investigate whether primary and secondary nitrogen metabolism is involved in adventitious root induction by auxin treatments in cork oak (Quercus suber L.) and grapevine (Vitis vinifera L.) shoots cultured in vitro. For this purpose, we followed the profile of free and conjugated polyamines, free amino acid pools and 15N-labelling profiles during root induction and expression. We have also observed the effects of cyclohexylamine (CHA), an inhibitor of spermidine synthase. Taking the results together, it is possible to conclude that: (a) glutamine is the most abundant free amino acid in grapevine, while in cork oak, asparagine and arginine are the major amino acids; (b) in grapevine, auxin did not significantly affect the glutamine levels, but changed the 15N-enrichment and labelling pattern of arginine; (c) auxin affected asparagine levels and 15N-labelling pattern of glutamine in cork oak; (d) in both cork oak and grapevine, free putrescine (Put) can be considered as a marker of in vitro root induction; (e) in both species, the presence of CHA resulted in the accumulation of free Put; (f) no Put catabolism was detected in the form of 15N-NMR products, namely 15N-γ-aminobutyric acid; (g) the CHA-induced accumulation of Put only increased grapevine rooting rate.