Flax crop yield is limited by various environmental stress factors, but the largest crop losses worldwide are caused by
Fusarium infection.
Polyamines are one of the many plant metabolites possibly involved in the plant response to
infection. However, in flax plants the
polyamine composition, genes involved in
polyamine synthesis, and in particular their regulation, were previously unknown. The aim of this study was to investigate the
polyamine synthesis pathway in flax and its involvement in response to pathogen
infection. It is well established that
polyamines are essential for the growth and development of both plants and fungi, but their role in pathogen
infection still remains unknown. In our study we correlated the expression of genes involved in
polyamine metabolism with the
polyamine levels in plant tissues and compared the results for flax seedlings treated with two pathogenic and one non-pathogenic strains of Fusarium. We observed an increase in the expression of genes participating in
polyamine synthesis after
fungal infection, and it was reflected in an increase of
polyamine content in the plant tissues. The highest level of
mRNA was characteristic for
ornithine decarboxylase during
infection with all tested, pathogenic and non-pathogenic, Fusarium strains and the
arginine decarboxylase gene during
infection with the pathogenic strain of Fusarium culmorum. The main
polyamine identified in the flax seedlings was
putrescine, and its level changed the most during
infection. Moreover, the considerable increase in the contents of cell wall-bound
polyamines compared to the levels of free and conjugated
polyamines may indicate that their main role during pathogen
infection lies in strengthening of the cell wall. In vitro experiments showed that the
polyamines inhibit Fusarium growth, which suggests that they play an important role in plant defense mechanisms. Furthermore, changes in metabolism and content of
polyamines indicate different defense mechanisms activated in flax in response to
infection by pathogenic and non-pathogenic Fusarium strains.