Coping with spring frost-effects on polyamine metabolism of Scots pine seedlings

Polyamines (PA) are ubiquitous polycations known to be involved in several phases of plant development as well as in tolerance to abiotic stresses. Phenols are complex secondary metabolites produced via the phenylpropanoid pathway that contain, e.g., cell wall compounds and antioxidants. Phenols are known to enhance chilling tolerance of plants. PA and phenolic pathways are connected via conjugation. In boreal coniferous forests spring frost has been considered to have severe effects on the survival of tree seedlings. Such effects are likely to increase in the future. The present study focuses on the role of PA and phenylpropanoid syntheses in the coping strategies of Scots pine exposed to cold temperatures during the vulnerable early seedling phase in late spring and early summer. We found that spring frost affects the expression of genes regulating PA metabolism and phenylpropanoid synthesis differently in above and below ground parts of the seedlings, whereas PA or phenol contents in tissues were not affected. The results suggest that Scots pine seedlings may not have time to develop metabolite level responses during a short period of freezing stress and, therefore, the originally different PA levels, especially in roots, may influence the tolerance of Scots pine seedlings to spring frost.