Soil salinization seriously restricts the growth and yield of soybeans. However, little information is available on the early growth stages of soybeans which are subjected to the gibberellin biosynthesis inhibitor, prohexadione-calcium (Pro-Ca). This study aimed to investigate the effects of exogenous Pro-Ca on saline-alkali stress-induced damages to photosynthesis and antioxidant defenses in soybean (Glycine max L.) seedlings. At the V3 growth stage, salt-tolerant genotype Hefeng 50 (HF50) and salt-sensitive genotype Kenfeng 16 (KF16) were subjected to 110 mmol L⁻¹ mixed saline-alkali stress respectively, and then 100 mg L⁻¹ Pro-Ca was sprayed on the leaves. Our results showed that saline-alkali stress accelerated the degradation of thylakoids, inhibited chlorophyll synthesis, reduced shoot dry weight, electron transfer rate (ETR), and peroxidase (POD) activity, the concentration of ascorbic acid (AsA) and soluble sugar, but enhanced the concentration of proline, hydrogen peroxide (H₂O₂) and the rate of superoxide radical (O₂^∙−) generation. Additionally, saline-alkali stress induced a lower decrease of the net photosynthetic rate (P_n), potential activity of PSII (F_v/F₀), and maximum quantum yield of PSII (F_v/F_m) in salt-tolerant HF50 than in salt-sensitive KF16. Nevertheless, foliar spraying of exogenous Pro-Ca increased the chlorophyll content, P_n, F_v/F₀, and F_v/F_m. These results were more prominent when Pro-Ca was applied to KF16 under saline-alkali conditions. Furthermore, exogenous application of Pro-Ca retarded the degradation of thylakoids, increased the ETR and the accumulation of AsA, soluble sugar, and proline, activated the activities of superoxide dismutase (SOD), catalase (CAT), and POD, and decreased the concentration of malondialdehyde (MDA), electrolyte leakage (EL), O₂^∙−, and H₂O₂. These results indicated that Pro-Ca could effectively protect soybean seedlings against damage from saline-alkali stress by regulating seedling phenotype, photosynthetic apparatus, antioxidant defense, and osmoregulation.

土壤盐渍化严重制约了大豆的生长和产量。然而，关于受赤霉素生物合成抑制剂原己二酮钙 (Pro-Ca) 作用的大豆早期生长阶段的信息很少。本研究旨在研究外源钙离子对盐碱胁迫引起的大豆 ( Glycine max L.) 幼苗光合作用和抗氧化防御损伤的影响。在V3生长阶段，耐盐基因型合丰50（HF50）和盐敏感基因型垦丰16（KF16）分别经受110 mmol L ^-1混合盐碱胁迫，然后100 mg L ^-1Pro-Ca 喷在叶子上。我们的研究结果表明，盐碱胁迫加速了类囊体的降解，抑制了叶绿素的合成，降低了茎干重、电子转移率 (ETR) 和过氧化物酶 (POD) 活性、抗坏血酸 (AsA) 和可溶性糖的浓度，但提高脯氨酸、过氧化氢 (H ₂ O ₂ )的浓度和超氧自由基 (O ₂ ^∙− ) 的生成率。此外，盐碱胁迫导致净光合速率 ( P _n )、PSII 的潜在活性 (F _v /F ₀ ) 和 PSII 的最大量子产率 (F _v /F _m) 在耐盐 HF50 中比在盐敏感 KF16 中。然而，叶面喷洒外源性 Pro-Ca 增加了叶绿素含量、P _n、F _v /F ₀和 F _v /F _m。在盐碱条件下将 Pro-Ca 应用于 KF16 时，这些结果更为突出。此外，外源性应用 Pro-Ca 延缓了类囊体的降解，增加了 ETR 和 AsA、可溶性糖和脯氨酸的积累，激活了超氧化物歧化酶 (SOD)、过氧化氢酶 (CAT) 和 POD 的活性，并降低了丙二醛 (MDA)、电解质泄漏 (EL)、O ₂ ^∙−和 H ₂ O _{2 的}浓度. 这些结果表明 Pro-Ca 可以通过调节幼苗表型、光合器官、抗氧化防御和渗透调节来有效保护大豆幼苗免受盐碱胁迫的损害。