Sugar beet is strongly resistant to salt-alkalinity. Understanding the physiological alkali stress resistance mechanism of sugar beet is important for fully utilizing saline–alkaline soil. Sugar beet seedlings from cultivars KWS0143 (alkali-tolerant) and Beta464 (alkali-sensitive) were treated with five concentrations of mixed alkaline solutions (NaHCO₃: Na₂CO₃, 2:1), namely, 0 (control), 25, 50, 75, and 100 mM (mole concentration was calculated in Na⁺). A sharper decrease in dry weight per plant (87.1%) and total root length (91.7%) of Beta464 were observed compared to the 61.5% and 85.0% decrease in those of KWS0143 under 100 mM alkali treatment. With increasing alkaline stress, Na⁺ accumulation hindered K⁺ and Ca²⁺ absorption by roots. Free polyamines contents and phosphoenolpyruvate carboxylase (PEPC) activity in roots of both cultivars were all significantly enhanced by 50 and 75 mM alkali treatments. KWS0143 exhibited higher dissociated putrescine (Put), spermine (Spm), as well as spermidine (Spd) levels within the roots compared to Beta464 under alkali conditions. Root free Spd contents of KWS0143 and Beta464 increased by 154.2 and 64.5% treated with 50 mM alkali in comparison with the control. After treated with the dose of 25 mM, root succinic acid (SA) contents of KWS0143 and Beta464 increased by 90.4 and 14.3%, respectively, compared to the plants subjected to the control. Our results imply that polyamines and PEPC contribute to the tolerance of sugar beet to alkali stress. Those results could be useful for enriching the theory of plant stress response.

甜菜对盐碱具有很强的抵抗力。了解甜菜的生理抗碱胁迫机制对于充分利用盐碱土壤非常重要。用五种浓度的混合碱性溶液（NaHCO ₃：Na ₂ CO _3，2：1）处理来自品种KWS0143（耐碱）和Beta464（对碱敏感）的甜菜幼苗，即0（对照），25， 50、75和100 mM（摩尔浓度以Na ⁺计算）。在100 mM碱处理下，相比于KWS0143分别降低了61.5％和85.0％，Beta464的单株干重（87.1％）和总根长（91.7％）明显降低。随着碱胁迫的增加，Na ^+的积累阻碍了钾的吸收⁺和Ca ²⁺被根吸收。50和75 mM碱处理均显着提高了两个品种根中的游离多胺含量和磷酸烯醇丙酮酸羧化酶（PEPC）活性。与碱性条件下的Beta464相比，KWS0143的根部具有更高的离解腐胺（Put），亚精胺（Spm）和亚精胺（Spd）水平。与对照相比，用50 mM碱处理的KWS0143和Beta464的无根Spd含量增加了154.2和64.5％。与接受对照的植物相比，以25 mM的剂量处理后，KWS0143和Beta464的根琥珀酸（SA）含量分别增加了90.4和14.3％。我们的结果表明，多胺和PEPC有助于甜菜对碱胁迫的耐受性。