Is the C:N ratio a reliable indicator of C allocation to primary and defence-related metabolisms in tomato?

► C:N ratio was a reliable indicator of C allocation to defence-related metabolites. ► The form of N supply impacted the concentration of chlorogenic acid. ► Lignin concentration was not influenced by C:N ratio. ► The glycoalkaloid tomatine and phenolics showed the same response to C:N.