Changes of secondary metabolites in Pinus sylvestris L. needles under increasing soil water deficit

Abstract

A multiphasic response to water deficit was found in Scots pine primary and secondary metabolism. First, an increase of terpenoids coincided with the stomatal closure. Second, an accumulation of proline, ABA, and shikimic acid was detected when photosynthesis was negligible. Drought-induced mortality is characterized by a major needle yellowing followed by severe defoliation and whole branch death. Before these external visual symptoms of drought stress take place, different alterations occur in plant metabolism. This study aims to detect changes in primary and secondary metabolism of Pinus sylvestris L. in response to a decrease in soil water availability. We analyzed needle water potential, photosynthetic characteristics, and concentrations of proline, terpenoids, shikimic acid, total polyphenols, and abscisic acid (ABA) in P. sylvestris through a 55-day soil water deficit period. Concentrations of most metabolites varied with the decrease in soil water availability, but changes in different compounds were triggered at different times, highlighting a multiphasic response. Increases in monoterpene and sesquiterpenoid content at moderate water deficit coincided with stomatal closure which preceded the accumulation of proline, ABA, and shikimic acid under severe water deficit when net photosynthesis was negligible. This work confirms that most of the secondary metabolites under investigation in Pinus sylvestris did not increase until a moderate to severe water deficit was experienced, when photosynthesis was limited by stomatal closure.