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<p>Water deficit stress is a major limiting factor for the guar (<i>Cyamopsis tetragonoloba</i>) yield in dry and semi-arid regions, as it interferes with physiological processes and diminishes photosynthetic efficiency. This study investigated the effectiveness of foliar applications of methyl jasmonate (MeJA) and chitosan (CHT), both individually and in combination, in enhancing the drought tolerance of two commercial guar varieties, RGC-986 and BR-2017, under three irrigation regimes (Ir1: 100% field capacity (FC), Ir2 70% FC and Ir3 40% FC). The results showed that these plant elicitors significantly mitigated the physiological stress caused by drought. Overall, BR-2017 exhibited superior resistance to water deficit stress and demonstrated better physiological and biochemical responses compared to RGC-986. Pod number and seed yield per plant were negatively affected by water deficit stress but improved with MeJA, CHT or their combination, the highest amount of these traits was observed in BR-2017 and 50 µM MeJA and 25 µM MeJA under well-watered conditions, in BR-2017, confirming their role in sustaining productivity under stress. A combined treatment of 25 µM MeJA and 150 mg/L CHT increased the total chlorophyll content of BR-2017 by 14.51% and maintained the stability of chlorophyll a under moderate water-deficit conditions. Photosynthetic efficiency improved substantially, with BR-2017 showing a 30.24% increase in photosynthetic rate with the 25 µMMeJA + 150 mg/L CHT treatment under moderate water deficit stress. Under well-watered conditions, transpiration rates in BR-2017 decreased by 38.19% with the combined MeJA and CHT treatment, leading to a significant increase of 78.97% in photosynthetic water use efficiency (16.93 µmol CO₂ mmol⁻<sup>1</sup> H₂O) with the 200 mg/L CHT under moderate water deficit stress. Stomatal conductance increased by up to 53.57% with the 200 mg/L CHT under well-watered conditions, while intercellular CO₂ concentration increased with the 25 µM MeJA + 150 mg/L CHT treatment under moderate water deficit stress. RGC-986 showed higher enzymatic antioxidant activity consistently, while BR-2017 exhibited lower hydrogen peroxide levels and superior proline accumulation, suggesting different adaptation mechanisms. These findings highlight the potential of MeJA and CHT in activating antioxidant defense systems, optimizing photosynthetic performance and improving drought resilience in guar cultivation.</p>

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Applying Exogenous Methyl Jasmonate and Chitosan Enhances the Antioxidant Enzyme Activity and Photosynthesis of Guar Varieties Under Water Deficit Stress

  • 期刊论文

  • 发表日期：

    2026年2月16日

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  • Sara Khurizadeh,
  • Ruhollah Naderi,
  • Seyed Abdolreza Kazemeini,
  • Heidar Meftahizadeh,
  • Saeid Hazrati

摘要

Water deficit stress is a major limiting factor for the guar (Cyamopsis tetragonoloba) yield in dry and semi-arid regions, as it interferes with physiological processes and diminishes photosynthetic efficiency. This study investigated the effectiveness of foliar applications of methyl jasmonate (MeJA) and chitosan (CHT), both individually and in combination, in enhancing the drought tolerance of two commercial guar varieties, RGC-986 and BR-2017, under three irrigation regimes (Ir1: 100% field capacity (FC), Ir2 70% FC and Ir3 40% FC). The results showed that these plant elicitors significantly mitigated the physiological stress caused by drought. Overall, BR-2017 exhibited superior resistance to water deficit stress and demonstrated better physiological and biochemical responses compared to RGC-986. Pod number and seed yield per plant were negatively affected by water deficit stress but improved with MeJA, CHT or their combination, the highest amount of these traits was observed in BR-2017 and 50 µM MeJA and 25 µM MeJA under well-watered conditions, in BR-2017, confirming their role in sustaining productivity under stress. A combined treatment of 25 µM MeJA and 150 mg/L CHT increased the total chlorophyll content of BR-2017 by 14.51% and maintained the stability of chlorophyll a under moderate water-deficit conditions. Photosynthetic efficiency improved substantially, with BR-2017 showing a 30.24% increase in photosynthetic rate with the 25 µMMeJA + 150 mg/L CHT treatment under moderate water deficit stress. Under well-watered conditions, transpiration rates in BR-2017 decreased by 38.19% with the combined MeJA and CHT treatment, leading to a significant increase of 78.97% in photosynthetic water use efficiency (16.93 µmol CO₂ mmol⁻1 H₂O) with the 200 mg/L CHT under moderate water deficit stress. Stomatal conductance increased by up to 53.57% with the 200 mg/L CHT under well-watered conditions, while intercellular CO₂ concentration increased with the 25 µM MeJA + 150 mg/L CHT treatment under moderate water deficit stress. RGC-986 showed higher enzymatic antioxidant activity consistently, while BR-2017 exhibited lower hydrogen peroxide levels and superior proline accumulation, suggesting different adaptation mechanisms. These findings highlight the potential of MeJA and CHT in activating antioxidant defense systems, optimizing photosynthetic performance and improving drought resilience in guar cultivation.