Abstract
A rapid and continuous growth of silver nanoparticles (AgNPs) via their precursor “silver nitrate” (AgNO3) has increased their environmental risk because of their unsafe discharge into the surrounding environment. Both have damaging effects on plants and induce oxidative stress. In the present study, differential responses in the morpho-physiological and biochemical profiles of P. glaucum (L.) seedlings exposed to various doses of AgNPs and AgNO3 were studied. Both have forms of Ag accelerated the reactive oxygen species (ROS) production, which adversely affected the membrane stability as a result of their enhanced accumulation, and resulted in a significant reduction in growth, that is, root length, shoot length, fresh and dry biomass, and relative water content. AgNO3 possessed a higher degree of toxicity owing to its higher accumulation than AgNPs, and induced changes in the antioxidants’ enzyme activity: superoxide dismutase (SOD), peroxidase (POD), catalases (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX), and glutathione reductase (GR) activity, as well as proline content, total phenolic, and total flavonoids contents (TFCs) under all tested treatments (mM). A decline in photosynthetic pigments such as total chlorophyll content and carotenoid content and alterations in quantum yield (Fv/Fm), photochemical (qP), and non-photochemical quenching (NPQ) indicated the blockage of the electron transport chain (ETC), which led to a significant inhibition of photosynthesis. Interestingly, seedlings exposed to AgNPs showed less damaging effects on P. glaucum (L.) seedlings, resulting in relatively lower oxidative stress in contrast to AgNO3. Our results revealed that AgNO3 and AgNPs possessed differential phytotoxic effects on P. glaucum (L.) seedlings, including their mechanism of uptake, translocation, and action. The present findings may be useful in phytotoxic research to design strategies that minimize the adverse effects of AgNPs and AgNO3 on crops, especially in the agriculture sector.
Highlights
Pearl millet (P.glaucum L.) is one of the premium and important food crops that occupy the sixth rank in the world, with a huge cultivated area (60%) in Africa and (35%) in Asia
Root and shoot length were reduced to 41% and 21% at 2 mM AgNO3, whereas AgNPs under the same treatment were noted to cause a reduction of 28% and 15% for root and shoot length, respectively (Table 1), which indicated a smaller decrease in growth parameters at a lower concentration
The results showed a significant reduction in total chlorophyll (Figure 4a) dependent on the decrease in Fv/Fm and qP values in P.glaucum seedlings exposed to AgNO3, whereas a lower reduction in photosynthetic parameters was noticed in the case of AgNPs-treated seedlings when both were compared with the control (Figure 2a,b)
Summary
Pearl millet (P.glaucum L.) is one of the premium and important food crops that occupy the sixth rank in the world, with a huge cultivated area (60%) in Africa and (35%) in Asia NPs are extensively being used in physics, chemistry, agricultural science, environmental science, medicine [8], but with plant still needed attention.
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