Duckweeds, a group of fast-growing aquatic plants, are good candidates for bioenergy production, CO₂ capture, and “carbon neutrality” because of their simple structure, fast growth rate, and high starch content. At present, duckweed cultivation mainly focuses on a photoautotrophic mode, which makes it challenging for duckweed to obtain a high growth rate and biomass accumulation, and thus is not the optimal trophic mode for duckweed industrial applications.  

Previous study has shown that duckweed (Spirodela polyrhiza) is not an obligate photoautotrophic plant and can thrive on a variety of exogenous organic carbons in the presence or absence of light (photoheterotrophic, mixotrophic, and heterotrophic). Among these growth modes, mixotrophic duckweed benefits from both the photosynthesis and respiration metabolic pathways and grows much faster than its photoautotrophic and heterotrophic counterparts alone or in combination. This indicates that there may be a synergistic effect and “crosstalk” between chloroplasts (photosynthesis) and mitochondria (respiration). However, the molecular mechanism underlying such a metabolic pathway remains largely unknown in mixotrophic duckweed. 

Recently, a research team led by Prof. HOU Hongwei from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences revealed the molecular mechanism of mixotrophic growth. This study was published in New Phytologist. 

In this study, the researchers used tools of biochemistry, physiology, and multi-omics to dissect the metabolic mechanisms of mixotrophic duckweed. The researchers discovered that, compared to photoautotrophic duckweed, the CO₂ concentrating mechanism and photosynthetic pathways of mixotrophic duckweed are significantly inhibited.  

However, using proteomic and metabolomic techniques, they found that the respiration pathway of mixotrophic duckweed was found to be significantly enhanced (glycolysis, tricarboxylic acid cycle, pentose phosphate pathway, and fermentation), which caused the increase in intracellular CO₂ concentration and the decrease in O₂ concentration.  

These results led to the inhibition of photorespiration and oxidative damage in mixotrophic duckweed, reducing the massive consumption of material and energy and achieving maximum biomass accumulation. 

Duckweed is a potential candidate for bioenergy and food production. This study lays the groundwork for exploiting the metabolic switch in duckweed to enhance bioenergy and food output.

Morphological changes of duckweed among diverse trophic modes. (Image by IHB) 

(Editor: MA Yun)