Sensitive detection of heavy metal stress in aquatic plants by dissolved oxygen-quenched fluorescence/materials movement-induced beam deflection method

Abstract

Sensitive detection of heavy metal (HM) stress in aquatic plants by dissolved oxygen (DO)-quenched fluorescence/materials movement-induced beam deflection method is demonstrated. Egeria densa Planchon and Cu²⁺ were used as a model aquatic plant and HM ion, respectively. Reproducibility and experimental errors of the method were first investigated in a control culture solution only containing 10⁻⁶ M Ru (II) complex (Tris (2,2’-bipyridyl) ruthenium (II) chloride) without addition of any fertilizer and Cu²⁺. Changes of DO concentration (∆DO) and deflection (∆DE) during the monitoring periods were used as parameters to quantitatively evaluate the experimental errors and detection limits. Averages or means ($\overline{\Delta DO }$, $\overline{\Delta DE }$) and standard deviations (σ_∆DO, σ_∆DE) of ∆DO and ∆DE in seven control experiments with different aquatic plants sheets during both the respiration and photosynthesis processes were obtained. Next, DO and deflection at the middle vicinities of the aquatic plant were monitored during 2 h of both respiration and photosynthesis in presence of 10^–10 ~ 10^–6 M Cu²⁺. Experimental results showed that the aquatic plant began to suffer from the HM stress in some extent in presence of 10^–9 M Cu²⁺. When the concentration of Cu²⁺ was higher than 10^–8 M, changing trends of both DO and deflection with time were not reversed during the respiration and photosynthesis, implying that the materials movements in the physiological activities had been altered greatly. It is demonstrated that the method could sensitively detect the HM stress in the aquatic plants given by nM HM ions in culture solution without addition of a fertilizer. Furthermore, detection limits of the method were quantitatively discussed by considering $\overline{\Delta DO }-3$ σ_∆DO and $\overline{\Delta DE }+3$ σ_∆DE as the minimum detectable changes of DO and deflection caused by the HM stress, respectively.

Graphical Abstract