Heavy metal pollution seriously impairs crop production and poses serious concerns for human health. Exogenous application of biomolecules has been efficiently tested for enhancing plant resistance to metal toxicity. Current study evaluates the possible effect of 5-aminolevulinic acid (ALA) in Brassica juncea L. seedlings subjected to lead (Pb) stress. Our results showed that shoot length, root length and chlorophyll contents were significantly recovered in Pb stressed seedlings after ALA application, accompanied by reduction in the Pb accumulation. Significant reduction in the contents of reactive oxygen species (ROS) like superoxide anion, hydrogen peroxide and malondialdehyde were also observed in ALA treated seedlings under Pb stress. Furthermore, we also noticed enhancement in the activities of antioxidative enzymes like superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), glutathione reductase (GR), glutathione-S-transferase (GST) and dehydroascorbate reductase (DHAR). We further noticed that ALA upregulated the expression of SOD (7.30 folds), POD (6.11 folds), CAT (3.52 folds), DHAR (6.42 folds), GR (6.04 folds), and GST (5.58 folds) under the Pb stress. However, RBOH1 (gene involved in ROS generation) and CHLASE (chlorophyllase) expressions were reduced in ALA treated seedlings grown under Pb stress (RBOH1 expression decreased to 3.44 from 6.50 fold and CHLASE expression decreased to 2.97 from 5.58 fold). Phenolic contents were increased in the presence of ALA and expression of genes like CHS (chalcone synthase; 7.50 fold) and PAL (phenylalanine ammonia lyase; 4.77 fold) was also stimulated by ALA under Pb stress. Furthermore, contents of the Krebs cycle metabolites (fumarate, succinate, malate and citrate) were also enhanced accompanied by upregulated expression of genes like CS (citrate Synthase; 8.13 fold), SUCLG1 (succinyl CoA ligase 1; 7.40 fold), SDH (succinate dehydrogenase; 5.10 fold) and FH (fumarate hydratase; 5.65 fold). In conclusion, current investigation revealed that ALA attenuated Pb toxicity by modulating the transcription patterns of key enzymes involved in plant defense system.

重金属污染严重影响农作物生产，严重威胁人类健康。生物分子的外源应用已被有效地测试用于增强植物对金属毒性的抗性。目前的研究评估了 5-氨基乙酰丙酸 (ALA) 在芥菜中的可能作用L. 幼苗受到铅 (Pb) 胁迫。我们的结果表明，在 ALA 施用后，铅胁迫幼苗的枝条长度、根长度和叶绿素含量显着恢复，同时铅积累量减少。在铅胁迫下，ALA 处理的幼苗中也观察到活性氧 (ROS) 含量显着降低，如超氧阴离子、过氧化氢和丙二醛。此外，我们还注意到超氧化物歧化酶 (SOD)、过氧化氢酶 (CAT)、愈创木酚过氧化物酶 (POD)、谷胱甘肽还原酶 (GR)、谷胱甘肽-S-转移酶 (GST) 和脱氢抗坏血酸还原酶 (DHAR) 等抗氧化酶的活性增强. 我们进一步注意到 ALA 上调了SOD（7.30 倍）、POD（6.11 倍）、Pb 应力下的CAT（3.52 倍）、DHAR（6.42 倍）、GR（6.04 倍）和GST（5.58 倍）。然而，在 Pb 胁迫下生长的 ALA 处理的幼苗中，RBOH1（参与 ROS 生成的基因）和CHLASE（叶绿素酶）表达降低（RBOH1表达从 6.50 倍降至 3.44，CHLASE表达从 5.58 倍降至 2.97）。在 ALA 存在和CHS（查耳酮合酶；7.50 倍）和PAL等基因表达的情况下，酚类含量增加（苯丙氨酸解氨酶；4.77 倍）也在铅胁迫下受到 ALA 的刺激。此外，三羧酸循环代谢物（延胡索酸、琥珀酸、苹果酸和柠檬酸）的含量也随着CS（柠檬酸合成酶；8.13 倍）、SUCLG1（琥珀酰辅酶 A 连接酶 1；7.40 倍）、SDH（琥珀酸）等基因的表达上调而增加脱氢酶；5.10 倍）和FH（延胡索酸水合酶；5.65 倍）。总之，目前的研究表明，ALA 通过调节参与植物防御系统的关键酶的转录模式来减弱 Pb 的毒性。