Cyanogenic glycosides can function as nitrogen reservoir for flax plants cultured under N-deficient conditions

Soil nitrogen (N) deficiency is a common phenomenon that plagues both naturally growing plants as well as agricultural crops, ultimately affecting their growth and productivity. The aim of our study is to determine the effect of short-term N deprivation on secondary metabolites production in developing and mature leaves of flax (Linum usitatissimum L.). Two weeks under low-N conditions decrease plant growth, N concentration, and soluble proteins content in leaves. Reduction in photosynthesis intensity was also observed. A decrease of cyanogenic glycoside content under N-deficient conditions was most visible in mature leaves. However, the content of linamarin and lotaustralin was about 10-fold higher in younger than in mature leaves, in which play probably protective role due to the possibility of toxic HCN release. Despite the N deficit, flax plants accumulated nitrogen in cyanoglycosides. N from cyanoglycosides can be used to synthesise amino acids; this possibility is supported by the high activity of β-cyanoalanine synthase, especially in N-deficient leaves. On the other hand, the content of different types of phenolic compounds increased in N-deficient plants, especially in young leaves, possibly replacing cyanoglucosides in protective functions. Our results indicated that cyanogenic glycosides could be an important nitrogen source for flax plants grown under temporary N-deficient conditions.