Herbicide isoproturon-specific binding in the freshwater macrophyte Elodea densa--a single-cell fluorescence study

Area of Science:

• Plant Physiology
• Environmental Toxicology
• Photosynthesis Research

Background:

• Phenylurea herbicides, like Isoproturon (IPU), are widely used in agriculture.
• Understanding their impact on non-target aquatic plants is crucial for ecological risk assessment.
• Elodea densa is a common freshwater macrophyte sensitive to environmental changes.

Purpose of the Study:

• To investigate the effects of Isoproturon (IPU) on the photosynthetic activity of Elodea densa leaf cells.
• To quantitatively evaluate the interaction between IPU and the D1 protein within the photosystem II (PSII) complex.
• To determine the binding affinity and bioaccumulation patterns of IPU in this aquatic plant.

Main Methods:

• Utilized fast induction kinetics of PSII chlorophyll a in vivo fluorescence.
• Measured fluorescence parameters (FI/FP ratios) to assess photosynthetic efficiency.
• Quantified IPU bioaccumulation and dissociation constants (Kd) at the thylakoid and cellular levels.

Main Results:

• A significant effect of IPU on photosynthesis was observed at concentrations as low as 5 µg/L.
• FI/FP ratios proved to be a reliable indicator for quantifying the IPU/D1 protein complex dissociation constant (Kd = 1.2 x 10⁻⁷ M).
• The D1 protein was identified as the primary binding site for IPU in Elodea densa, influencing bioaccumulation.

Conclusions:

• Isoproturon directly impacts the photosynthetic apparatus of Elodea densa, primarily by interacting with the D1 protein.
• The study provides a quantitative method to assess herbicide binding and its effects on aquatic plant photosynthesis.
• Findings highlight the sensitivity of Elodea densa to IPU and underscore the importance of the D1 protein in herbicide action.