Silicon (Si) is a beneficial nutrient for crop plants, and is gaining increased attention because of its involvement in regulation of abiotic stress tolerance. The present study was carried out to explore the underlying physiological and biochemical mechanisms of foliar Si-induced enhancement in wheat tolerance against cadmium (Cd) stress. Surface sterilized seeds of two wheat cultivars, viz., Inqalab-91 (sensitive) and Sahar-2006 (tolerant), were sown in plastic pots. Foliar application of Si (3 mM) was done at 20 days after sowing under control (−Cd) and Cd stress (25 mg kg−1 soil) conditions. Plants were harvested after 3 weeks of foliar spray, and data regarding morphological growth, oxidative metabolism, photosynthetic pigments, gas exchange attributes, metabolite accumulation, and ion homeostasis were recorded. The experimental treatments were arranged in completely randomized design with four replicates per treatment. Cadmium stress was found to significantly decrease the morphological growth, photosynthesis, and photosynthetic pigments in both wheat cultivars, while significantly increased malondialdehyde (MDA) content, hydrogen peroxide (H2O2) content, and electrolyte leakage (EL) that triggered oxidative stress. The Cd-induced changes in superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione S-transferase (GST), and glutathione reductase (GR) activities varied with cultivar and Si application. Plants treated with Si revealed better growth, higher accumulation of total soluble proteins, anthocyanins, total soluble sugar, flavonoids, and phenolics contents, and efficient antioxidant defense system as indicated by increased ascorbic acid and glutathione pools, and higher activities of SOD, POD, CAT, and APX particularly under Cd stress. Application of Si reduced Cd-mediated oxidative stress and increased photosynthetic pigments and net photosynthetic rate in both wheat cultivars. Further, Si application enhanced mineral ions in normal (−Cd) and Cd-stressed plants, and significantly decreased the Cd uptake. The Si-induced effects were more prominent in Sahar-2006 than that in Inqalab-91 for most of the studied traits, particularly under stress conditions. In short, foliar application of Si alleviates the adverse effects of Cd on wheat growth by strengthening antioxidant defense system, enhancing metabolite accumulation, improving plant nutrient status, and decreasing the Cd uptake.

中文翻译：

---

叶面硅诱导小麦镉毒害的生理生化基础

硅 (Si) 是一种对作物有益的营养物质，并且因其参与调节非生物胁迫耐受性而受到越来越多的关注。本研究旨在探讨叶面硅诱导小麦对镉 (Cd) 胁迫耐受性增强的潜在生理和生化机制。将两种小麦品种的表面灭菌种子播种在塑料盆中，即 Inqalab-91（敏感）和 Sahar-2006（耐受）。在控制 (-Cd) 和 Cd 胁迫 (25 mg kg-1 土壤) 条件下，播种后 20 天进行 Si (3 mM) 的叶面施用。叶面喷洒 3 周后收获植物，记录有关形态生长、氧化代谢、光合色素、气体交换属性、代谢物积累和离子稳态的数据。试验处理按完全随机设计排列，每个处理重复四次。发现镉胁迫显着降低了两种小麦品种的形态生长、光合作用和光合色素，同时显着增加了引发氧化应激的丙二醛 (MDA) 含量、过氧化氢 (H2O2) 含量和电解质泄漏 (EL)。镉诱导的超氧化物歧化酶 (SOD)、过氧化物酶 (POD)、过氧化氢酶 (CAT)、抗坏血酸过氧化物酶 (APX)、谷胱甘肽 S-转移酶 (GST) 和谷胱甘肽还原酶 (GR) 活性的变化因品种和硅的应用而异。用硅处理的植物表现出更好的生长，总可溶性蛋白质、花青素、总可溶性糖、类黄酮和酚类物质的含量更高，抗坏血酸和谷胱甘肽池的增加以及 SOD、POD、CAT 和 APX 的活性更高，特别是在镉胁迫下。Si 的应用减少了 Cd 介导的氧化应激，增加了两种小麦品种的光合色素和净光合速​​率。此外，Si 的施用增强了正常（-Cd）和 Cd 胁迫植物中的矿物离子，并显着降低了 Cd 的吸收。对于大多数研究的性状，尤其是在压力条件下，Si 诱导的影响在 Sahar-2006 中比在 Inqalab-91 中更为突出。总之，叶面喷施硅通过加强抗氧化防御系统、增强代谢物积累、改善植物养分状况和减少镉吸收来减轻镉对小麦生长的不利影响。