Drought tolerance mechanisms across C3 and C3–C4 intermediate photosynthetic types revealed by physiological and gene expression profiling

Abstract

Abstract Abiotic stress, particularly drought, significantly reduces crop yields and threatens global agricultural sustainability. This study investigated drought and recovery responses in four plant species with contrasting photosynthetic types:  Triticum aestivum  (C3),  Helianthus annuus  (C3),  Chenopodium album  (intermediate-C4), and  Alternanthera brasiliana  (C4-like). Drought markedly reduced plant fresh biomass (up to 80% in  H. annuus ) and relative water content, particularly in  C. album . Oxidative damage intensified, with  H. annuus  showing the greatest increase in hydrogen peroxide (258%) and  C. album  exhibiting the highest malondialdehyde accumulation (284%). Antioxidant enzymes were strongly activated; catalase activity increased dramatically in  C. album  (837%) and  H. annuus  (630%). Proline levels increased sharply, particularly in  T. aestivum  and  C. album , indicating enhanced osmotic adjustment. Carotenoid content also rose significantly in  H. annuus  (141%), suggesting photoprotective adaptation. Gene expression analysis revealed upregulation of  TaP5CS  in  T. aestivum , correlating with proline accumulation, and  CaHSP26  in  C. album , potentially stabilizing photosystem II. Principal component analysis identified catalase activity, root-to-shoot ratio, hydrogen peroxide, and proline as major contributors to drought response variance. These findings highlight species-specific strategies for drought tolerance and recovery, with C3 species showing strong enzymatic and osmotic adjustments, and intermediate-C4 and C4-like species exhibiting greater tissue integrity and ROS balance. This comparative framework provides valuable insights for developing drought-resilient crops.