Department of Botany, Islamia College Peshawar, Peshawar, Khyber Pakhtunkhwa, Pakistan.
Xinjiang Key Laboratory of Desert Plant Roots Ecology and Vegetation Restoration, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, 830011, People's Republic of China.
BMC Plant Biol. 2024 Jun 18;24(1):572. doi: 10.1186/s12870-024-05294-z.
Nitrogen (N) availability is crucial in regulating plants' abiotic stress resistance, particularly at the seedling stage. Nevertheless, plant responses to N under salinity conditions may vary depending on the soil's NH to NO ratio.
In this study, we investigated the effects of different NH:NO ratios (100/0, 0/100, 25/75, 50/50, and 75/25) on the growth and physio-biochemical responses of soybean seedlings grown under controlled and saline stress conditions (0-, 50-, and 100-mM L NaCl and NaSO, at a 1:1 molar ratio).
We observed that shoot length, root length, and leaf-stem-root dry weight decreased significantly with increased saline stress levels compared to control. Moreover, there was a significant accumulation of Na, Cl, hydrogen peroxide (HO), and malondialdehyde (MDA) but impaired ascorbate-glutathione pools (AsA-GSH). They also displayed lower photosynthetic pigments (chlorophyll-a and chlorophyll-b), K ion, K/Na ratio, and weakened O-HO-scavenging enzymes such as superoxide dismutase, catalase, peroxidase, monodehydroascorbate reductase, glutathione reductase under both saline stress levels, while reduced ascorbate peroxidase, and dehydroascorbate reductase under 100-mM stress, demonstrating their sensitivity to a saline environment. Moreover, the concentrations of proline, glycine betaine, total phenolic, flavonoids, and abscisic acid increased under both stresses compared to the control. They also exhibited lower indole acetic acid, gibberellic acid, cytokinins, and zeatine riboside, which may account for their reduced biomass. However, NH:NO ratios caused a differential response to alleviate saline stress toxicity. Soybean seedlings supplemented with optimal ratios of NH:NO (T3 = 25:75 and T = 4 50:50) displayed lower Na and Cl and ABA but improved K and K/Na, pigments, growth hormones, and biomass compared to higher NH:NO ratios. They also exhibited higher O-HO-scavenging enzymes and optimized HO, MDA, and AsA-GSH pools status in favor of the higher biomass of seedlings.
In summary, the NH and NO ratios followed the order of 50:50 > 25:75 > 0:100 > 75:25 > 100:0 for regulating the morpho-physio-biochemical responses in seedlings under SS conditions. Accordingly, we suggest that applying optimal ratios of NH and NO (25/75 and 50:50) can improve the resistance of soybean seedlings grown in saline conditions.
氮（N）供应在调节植物的非生物胁迫抗性方面至关重要，尤其是在幼苗阶段。然而，植物在盐胁迫条件下对 N 的反应可能因土壤中 NH 与 NO 的比例而异。
本研究通过控制和盐胁迫条件（0-、50-和 100-mM L NaCl 和 NaSO，摩尔比为 1:1）下生长的大豆幼苗，研究了不同 NH:NO 比例（100/0、0/100、25/75、50/50 和 75/25）对幼苗生长和生理生化反应的影响。
与对照相比，随着盐胁迫水平的增加， Shoot length、Root length 和 leaf-stem-root dry weight 显著下降。此外，Na、Cl、过氧化氢（HO）和丙二醛（MDA）的积累显著增加，抗坏血酸-谷胱甘肽池（AsA-GSH）受损。它们还显示出较低的光合色素（叶绿素-a 和叶绿素-b）、K 离子、K/Na 比以及在两种盐胁迫水平下削弱的 O-HO 清除酶，如超氧化物歧化酶、过氧化氢酶、过氧化物酶、单脱氢抗坏血酸还原酶、谷胱甘肽还原酶，而在 100-mM 胁迫下，抗坏血酸过氧化物酶和脱氢抗坏血酸还原酶减少，表明它们对盐环境敏感。此外，脯氨酸、甘氨酸甜菜碱、总酚、类黄酮和脱落酸的浓度在两种胁迫下均高于对照。它们还表现出较低的吲哚乙酸、赤霉素、细胞分裂素和玉米素核苷，这可能是它们生物量减少的原因。然而，NH:NO 比例导致了缓解盐胁迫毒性的差异反应。补充 NH:NO 最佳比例（T3=25:75 和 T4=4 50:50）的大豆幼苗显示出较低的 Na 和 Cl 以及 ABA，但改善了 K 和 K/Na、色素、生长激素和生物量，与较高的 NH:NO 比例相比。它们还表现出较高的 O-HO 清除酶，并优化了 HO、MDA 和 AsA-GSH 池状态，有利于幼苗更高的生物量。
综上所述，在 SS 条件下，NH 和 NO 比例对幼苗的形态-生理-生化反应的调节顺序为 50:50>25:75>0:100>75:25>100:0。因此，我们建议施用 NH 和 NO 的最佳比例（25/75 和 50:50）可以提高盐胁迫下大豆幼苗的抗性。
