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Study Reveals Flexible Carbon‑Concentrating Mechanisms in Amphibious Plant H. difformis
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A recent study revealed that the heterophyllous plant Hygrophila difformis develops high physiological plasticity in its carbon-concentrating mechanisms (CCMs) to cope with both land and water environments, shedding light on how aquatic plants switch and regulate carbon assimilation between C3 and C4‑like pathways.
Led by Prof. HOU Hongwei from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences (CAS), the study has been published in Horticulture Research.
Carbon dioxide diffuses slowly in water, leaving aquatic plants chronically short of carbon sources and driving the evolution of diverse CCMs. While the well-studied species are fully submerged plants, the CCMs in amphibious plants remain poorly understood.
H. difformis, a typical heterophyllous plant, adapts to terrestrial and aquatic habitats via phenotypic plasticity, yet its underlying physiological regulatory mechanisms remain unclear.
In their initial anatomical and physiological analysis of H. difformis, the researchers found that the terrestrial leaves of H. difformis display typical anatomical and photosynthetic traits of C3 plants, with δ13C values and Rubisco activity that align with the standard C3 photosynthetic pathway. By contrast, submerged leaves show markedly elevated δ13C values and exhibit a metabolic shift toward C4‑like photosynthesis, combined with a stronger capacity for bicarbonate utilization.
Further, enzymatic activity and multi‑omics data confirmed that submerged H. difformis activates an NAD‑ME type, single‑cell C4‑like photosynthetic pathway. Key C4 enzymes were significantly upregulated under submergence, while core enzymes, genes, and metabolites of the Calvin cycle were suppressed—pointing to metabolic reprogramming that features inhibited C3 photosynthesis alongside activated C4 CCMs underwater.
Further analyses revealed that submerged leaves develop dimorphic chloroplasts in mesophyll cells—an adaptation to the low CO2 and weak light conditions underwater. The team also performed a genome‑wide identification of the carbonic anhydrase (CA) gene family in H. difformis, identifying a total of 21 CA genes.
According to researchers, this study demonstrates that H. difformis relies on a combination of morphological, structural, and physiological plasticity in its environmental adaptation.
It clarifies the transition and regulation of carbon assimilation between C3 and C4‑like pathways in aquatic plants, while also establishing H. difformis as a valuable model plant for investigating heterophylly in aquatic species, the researchers said.
Phenotypic, anatomical, and physiological adaptation of H. difformis in terrestrial and submerged conditions. (Image by IHB)
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