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The effect of exogenous spermine (SPM) on Castilleja tenuiflora shoots developing under nitrogen deficiency (ND) stress was evaluated. Shoots cultivated in a temporary immersion system were subjected to four experimental treatments: (1) control; (2) exogenous SPM; (3) ND; and (4) ND+SPM. Shoots were longer in the ND+SPM treatment (6.3 ± 0.5 cm) than in the ND treatment (4.2 ± 0.5 cm). The total chlorophyll content was similar in the control and SPM treatments (0.41 µg mg−1 FM) and the highest values of total phenolic content were detected at 21 days in the ND+SPM treatment (84.1 ± 0.05 GAE g−1 DM). In the ND+SPM treatment, the phenylalanine ammonia lyase activity increased earlier than in ND treatment, and reached its maximum at day 21 (3.9 ± 0.2 µmol E‐CIN h−1 mg−1 protein). Compared with the control, the ND and ND+SPM treatments resulted in increased secondary metabolites contents in both root and aerial parts. The strongest effect was in the roots, where the SPM and ND+SPM treatments both resulted in increased quercetin content (4.3‐fold that in the control). Our results showed that SPM partially counteract the damage caused by ND and results in increased contents of valuable bioactive compounds.

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