Free polyamines and proline were determined with HPLC according to Németh et al. (2002) (link). During sample preparation, 200 mg of plant sample was homogenized in liquid nitrogen, extracted with 2 mL of 0.2 M ice-cold perchloric acid (HClO 4 ). The prepared samples were placed on ice for 20 min and centrifuged at 10,000 × g for 20 min at 4 °C. According to the method described by Smith and Davies (1985) (link), the polyamine fraction was derivatized with dansyl chloride. To 100 μL of the supernatant, 200 μL of saturated sodium carbonate and 400 μL of freshly dissolved dansyl chloride (5 mg/mL) in acetone were added in a 2-mL Eppendorf tube. The samples were homogenized and incubated in the dark at 60 °C for 60 min. Subsequently, 100 μL of proline solution (100 mg/mL) was added and the mixture was incubated for a further 30 min at room temperature in the dark. The dansyl derivatives were then extracted with 500 μL of toluene for 30 s and the upper, organic phase was transferred to 1.5-mL Eppendorf tubes using a Pasteur pipette. The samples were evaporated under vacuum. Danzylated polyamines and proline were dissolved in 1 mL of 100% methanol and filtered through a 0.2-μm-pore-size Teflon membrane filter. Danzylated polyamines (Put, Spd, Spm) and proline were analyzed using acetonitrile carrier medium in a WATERS W 2690 (Milford, USA) HPLC instrument.