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<p>Copper (Cu) toxicity is inimical to plant growth and development. The present study aimed to alleviate the detrimental effects of Cu toxicity in sunflower plants through citrulline (CIT) seed priming. The pot experiment was executed in a completely randomized factorial design with four replications of each treatment. Ten-day-old seedlings from seeds primed for 24&#xa0;h in 2, 3, and 4 mM CIT were transplanted into Cu-spiked soil (400&#xa0;mg kg<sup>‒1</sup> CuSO<sub>4</sub>), and data were recorded after 45 days. Copper toxicity increased leaf Cu, which significantly diminished growth, chlorophyll, photosynthetic efficiency, leaf relative water content, and nutrient levels. The oxidative stress due to Cu toxicity is reflected as enhanced levels of superoxide radical (O<sub>2</sub><sup>•‒</sup>), hydroxyl radical (•OH), hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>), oxidized glutathione (GSSG) and methylglyoxal (MG) that damaged membrane integrity, measured as malondialdehyde (MDA) levels, electrolyte leakage (EL), and lipoxygenase activity (LOX). Citrulline seed priming improved nutrient acquisition and diminished leaf Cu accumulation. Citrulline increased the endogenous hydrogen sulfide and nitric oxide levels alongside intensified antioxidant defense to mitigate oxidative stress. Citrulline enhanced photosynthesis via improved nutrient acquisition and diminished oxidative damage under Cu toxicity. Higher glutathione reductase activity due to CIT seed priming increased glutathione levels to support MG detoxification and phytochelatins accumulation. Histochemical analyses visualized lower O<sub>2</sub><sup>•‒</sup>, H<sub>2</sub>O<sub>2</sub>, lipid peroxidation, and membrane damage in leaves of CIT-treated plants under Cu toxicity. Citrulline improved membrane integrity, chlorophyll, photosynthetic efficiency, and nutrient uptake, which enhanced plant biomass under Cu toxicity. Citrulline-mediated osmoregulation, redox balance and diminished leaf Cu assisted in mitigating metal phytotoxic effects, particularly in plants primed with 3 mM concentration.</p>

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Citrulline Reduces Copper Toxicity in Sunflower (Helianthus annuus L.) by Modulating Photosynthesis, Osmoregulation, Redox Homeostasis, and Nutrient Relations

  • 期刊论文

  • 发表日期：

    2025年7月24日

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  • Arslan Hafeez,
  • Rizwan Rasheed,
  • Muhammad Arslan Ashraf,
  • Iqbal Hussain

摘要

Copper (Cu) toxicity is inimical to plant growth and development. The present study aimed to alleviate the detrimental effects of Cu toxicity in sunflower plants through citrulline (CIT) seed priming. The pot experiment was executed in a completely randomized factorial design with four replications of each treatment. Ten-day-old seedlings from seeds primed for 24 h in 2, 3, and 4 mM CIT were transplanted into Cu-spiked soil (400 mg kg‒1 CuSO4), and data were recorded after 45 days. Copper toxicity increased leaf Cu, which significantly diminished growth, chlorophyll, photosynthetic efficiency, leaf relative water content, and nutrient levels. The oxidative stress due to Cu toxicity is reflected as enhanced levels of superoxide radical (O2•‒), hydroxyl radical (•OH), hydrogen peroxide (H2O2), oxidized glutathione (GSSG) and methylglyoxal (MG) that damaged membrane integrity, measured as malondialdehyde (MDA) levels, electrolyte leakage (EL), and lipoxygenase activity (LOX). Citrulline seed priming improved nutrient acquisition and diminished leaf Cu accumulation. Citrulline increased the endogenous hydrogen sulfide and nitric oxide levels alongside intensified antioxidant defense to mitigate oxidative stress. Citrulline enhanced photosynthesis via improved nutrient acquisition and diminished oxidative damage under Cu toxicity. Higher glutathione reductase activity due to CIT seed priming increased glutathione levels to support MG detoxification and phytochelatins accumulation. Histochemical analyses visualized lower O2•‒, H2O2, lipid peroxidation, and membrane damage in leaves of CIT-treated plants under Cu toxicity. Citrulline improved membrane integrity, chlorophyll, photosynthetic efficiency, and nutrient uptake, which enhanced plant biomass under Cu toxicity. Citrulline-mediated osmoregulation, redox balance and diminished leaf Cu assisted in mitigating metal phytotoxic effects, particularly in plants primed with 3 mM concentration.