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<p>Calcium is a vital macronutrient and signaling molecule that regulates numerous physiological and biochemical processes in plants, yet its effects on <i>Ocimum basilicum</i> L. remain underexplored. In this study, <i>O. basilicum</i> plants were treated with foliar calcium chloride at 0, 2.5, 5, 10, and 15 mM to evaluate growth, photosynthesis, antioxidant defense, elemental composition, and essential oil biosynthesis. The results showed that 10 mM calcium treatment markedly increased leaf area, as well as photosynthetic rate, stomatal conductance, transpiration rate, and internal carbon dioxide concentration compared to the control. Chlorophyll fluorescence parameters such as the maximum quantum efficiency of PSII, effective quantum yield of PSII, electron transport rate, and photochemical quenching improved, while non-photochemical quenching decreased, indicating enhanced photochemical efficiency. At the biochemical level, 10 mM calcium enhanced carbonic anhydrase, nitrate reductase, and Rubisco activities, along with higher accumulation of phenolics, flavonoids, and proline. Antioxidant enzyme activities, catalase, superoxide dismutase, and peroxidase, were elevated, while hydrogen peroxide and superoxide anion levels declined, reflecting alleviated oxidative stress. Scanning electron microscopy analysis revealed denser and increased trichome size, and energy-dispersive X-ray spectroscopy showed improved accumulation of magnesium, iron, zinc, and calcium. Gas chromatography mass spectrometry profiling indicated significant increases in essential oil composition. In contrast, the highest concentration, 15 mM, showed diminished benefits, possibly due to calcium-induced toxicity or nutrient imbalance. These findings demonstrate that calcium functions both as a growth promoter and a potential stressor, highlighting the need for precision nutrient management; moreover, foliar calcium application represents a simple, low-cost agronomic strategy that enhances productivity, stress tolerance, and economic value of <i>O. basilicum</i>, while also revealing a mechanistic link between trichome modifications and essential oil biosynthesis.</p>

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Calcium-Mediated Dose-Dependent Regulation of Growth, Photosynthetic Performance, Antioxidant Defense, and Essential Oil Constituents in Ocimum basilicum L.

  • 期刊论文

  • 发表日期：

    2026年1月5日

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  • Asif Hussain Hajam,
  • Gausiya Bashri

摘要

Calcium is a vital macronutrient and signaling molecule that regulates numerous physiological and biochemical processes in plants, yet its effects on Ocimum basilicum L. remain underexplored. In this study, O. basilicum plants were treated with foliar calcium chloride at 0, 2.5, 5, 10, and 15 mM to evaluate growth, photosynthesis, antioxidant defense, elemental composition, and essential oil biosynthesis. The results showed that 10 mM calcium treatment markedly increased leaf area, as well as photosynthetic rate, stomatal conductance, transpiration rate, and internal carbon dioxide concentration compared to the control. Chlorophyll fluorescence parameters such as the maximum quantum efficiency of PSII, effective quantum yield of PSII, electron transport rate, and photochemical quenching improved, while non-photochemical quenching decreased, indicating enhanced photochemical efficiency. At the biochemical level, 10 mM calcium enhanced carbonic anhydrase, nitrate reductase, and Rubisco activities, along with higher accumulation of phenolics, flavonoids, and proline. Antioxidant enzyme activities, catalase, superoxide dismutase, and peroxidase, were elevated, while hydrogen peroxide and superoxide anion levels declined, reflecting alleviated oxidative stress. Scanning electron microscopy analysis revealed denser and increased trichome size, and energy-dispersive X-ray spectroscopy showed improved accumulation of magnesium, iron, zinc, and calcium. Gas chromatography mass spectrometry profiling indicated significant increases in essential oil composition. In contrast, the highest concentration, 15 mM, showed diminished benefits, possibly due to calcium-induced toxicity or nutrient imbalance. These findings demonstrate that calcium functions both as a growth promoter and a potential stressor, highlighting the need for precision nutrient management; moreover, foliar calcium application represents a simple, low-cost agronomic strategy that enhances productivity, stress tolerance, and economic value of O. basilicum, while also revealing a mechanistic link between trichome modifications and essential oil biosynthesis.