Differential Response of Floating and Submerged Leaves of Longleaf Pondweed to Silver Ions

Abstract

In this study, we have investigated variations in the potential of floating and submerged leaves of longleaf pondweed (Potamogeton nodosus) to withstand silver ion (Ag+)-toxicity. Both floating and submerged leaves changed clear colorless AgNO3 solutions to colloidal brown in the presence of light. Transmission electron microscopy revealed the presence of distinct crystalline Ag-nanoparticles (Ag-NPs) in these brown solutions. Powder X-ray diffraction pattern showed that Ag-NPs were composed of Ag0 and Ag2O. Photosystem (PS) II efficiency of leaves declined upon exposure to Ag+ with a significantly higher decline in the submerged leaves than in the floating leaves. Similarly, Ag+ treatment caused a significant reduction in the carboxylase activity of the ribulose bisphosphate carboxylase/oxygenase in leaves. The reduction in this carboxylase activity was significantly higher in the submerged than in the floating leaves. Ag+ treatment also resulted in a significant decline in the levels of non-enzymatic and enzymatic antioxidants; the decline was significantly lower in the floating than in submerged leaves. X-ray photoelectron spectroscopy revealed the presence of Ag2O in these leaves. Inductively coupled plasma mass spectrometry analysis revealed a three-fold higher Ag content in the submerged than in floating leaves. Our study demonstrates that floating leaves of longleaf pondweed have a superior potential to counter Ag+-toxicity compared with submerged leaves, which could be due to superior potential of floating leaves to reduce Ag+ to less/non-toxic Ag0/Ag2O-nanoparticles/nanocomplexes. We suggest that modulating the genotype of longleaf pondweed to bear higher proportion of floating leaves would help in cleaning fresh water bodies contaminated with ionic forms of heavy metals.

Light promoted brown staining of protoplasm by Ag+ is ideal to test wheat pollen viability rapidly

“…Previously, we reported the potential of (i) live leaf cells; and (ii) chloroplasts to reduce Ag + to generate AgNPs in presence of high-intensity light (~600 μmol PFD m -2 s -1 ) under ambient conditions [ 10 , 11 ]. As evident from Fig 3A , over 60 percent of wheat pollen stored for 4 h under ambient conditions failed to turn brown on incubation with Ag + -viability medium in presence of light, revealing loss in viability on storage.…”

“…for generating desired energy, redox power and range of carbon skeletons. Several such biomolecules promote photoreduction and biotransformation of Ag + to AgNPs [ 10 , 17 , 18 ]. Guo and co-workers [ 18 ] recorded sunlight promoted biotransformation of Ag + into AgNPs by biomolecules from root exudates.…”

“…As evident from Fig 1B, the protoplasm of pollen turned evenly brown on incubation in medium containing Ag + , in presence of high-intensity visible light. It is well established that solution containing Ag + turns brown due to the generation of AgNPs [9][10][11][13][14][15]. Following incubation of pollen in 300 mM KNO 3 containing 0 and 0.5 mM Ag + in presence and absence of light, the media were diluted with an equal proportion of distilled water to create hypotonic conditions (i.e.…”

“…In light of limitations in prevailing pollen viability protocols, we attempted to develop novel and more reliable protocol(s) for testing wheat pollen viability. Previously we reported that living cells and chloroplasts have the potential to generate silver nanoparticles as they possess strong reducing strength [9][10][11]. These findings from our team prompted us to evaluate if wheat pollen viability can be tested based on their potential to generate AgNPs from Ag + .…”

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“…for generating desired energy, redox power and range of carbon skeletons. Several such biomolecules promote photoreduction and biotransformation of Ag + to AgNPs [10,17,18]. Guo and co-workers [18]…”