Silver nanoparticles affect germination and photosynthesis in tobacco seedlings

Abstract

Extensive commercialization of silver nanoparticles (AgNPs) raises the risk of their accumulation in the soil-plant system. Once released into the environment, AgNPs are prone to chemical transformations, which makes it hard to determine whether their phytotoxic effects are purely NP-related or a consequence of released Ag+ ions. In this study the effects of 25, 50, 75, 100 and 150 μM AgNPs and AgNO3 on seed germination and early growth of tobacco (Nicotiana tabacum L.) seedlings were compared. Additionally, the effect on photosynthetic performance and pigment content were investigated. Germination rate and index values indicated delayed and slower germination in some AgNP treatments. Lower AgNP concentrations stimulated root growth, but induced prominent reduction in fresh weight. Contrary, all AgNO3 concentrations inhibited root growth but only the higher ones decreased fresh weight. Obtained results imply that the observed AgNP toxicity could be ascribed to NP form and can be correlated with high AgNP stability in the solid medium. On the other hand, majority of AgNP and AgNO3 treatments induced an increase in chlorophyll content which was accompanied with significantly lower values of relative electron transport rate and coefficient of photochemical quenching, implying an inhibition of the electron transport chain. Similar impact of AgNPs and AgNO3 on photosynthesis can be correlated with lower stability of AgNPs in the liquid medium, resulting in AgNP aggregation and dissolution of Ag+ ions.

Phytotoxicity of Silver Nanoparticles on Tobacco Plants: Evaluation of Coating Effects on Photosynthetic Performance and Chloroplast Ultrastructure

“…Interestingly, AgNP-CTAB also agglomerated rapidly, but after 48 h re-stabilization of small agglomerates was observed. Rapid agglomeration of commercial AgNP-citrate in liquid ½ strength MS medium was also reported by [ 25 ]. In contrast, in a proteomic study of tobacco plants exposed to AgNP-citrate in ultrapure water, AgNPs proved to be very stable and thus more available for uptake, causing a severe impact on photosynthesis by down-regulating photosynthesis-related proteins [ 63 ].…”

“…Carotenoids were also found to play a significant role in antioxidant defence against AgNP-induced ROS in rice [ 30 , 61 ], so it is possible that carotenoids also protected leaves of tobacco plants against ROS, since only a mild oxidative stress was noticed after exposure to 100 µM AgNP-citrate [ 11 ]. Furthermore, reduced values of ΦPSII and qP accompanied by increased carotenoids and xanthophylls were found in tobacco seedlings upon exposure to AgNP-citrate [ 25 ], which may imply that AgNP-citrate causes the same response in tobacco plants regardless of the developmental stage.…”

“…On the other hand, impact of AgNO 3 on pigment content and F v /F m in Brassica seedlings was stronger than that of AgNPs [ 34 ]. Similarly, in tobacco seedlings, AgNO 3 had a more negative effect on relative electron transport rate and qP than the corresponding treatments with AgNP-citrate, while the content of photosynthetic pigments increased after treatment with these nanoparticles [ 25 ]. This discrepancy in results with respect to the current study can be correlated with the plant developmental stage; it could be that seedlings, given the increased need for nutrients, are more susceptible to AgNO 3 -imposed stress compared to fully developed adult plants.…”

“…Furthermore, the characteristics of AgNPs such as size, concentration, and charge [ 18 , 19 ] as well as the experimental conditions including duration and method of exposure [ 20 , 21 , 22 ] also play significant roles, influencing the stability of AgNPs and their susceptibility to transformation [ 19 , 23 ]. In recent studies, it was revealed that AgNP stability is also dependent on the composition and type of the exposure medium [ 24 , 25 ]. The use of various surface coatings in their synthesis influences the physiochemical properties of AgNPs, not only by reducing particle agglomeration and enhancing their stability but also by modulating toxic effects [ 4 , 18 , 26 , 27 ].…”

“…Moreover, it was found that AgNPs significantly disrupt photosynthesis in terrestrial plants, where significant decreases in electron transfer and the rate of photosynthesis were observed [ 34 , 35 , 45 ]. Significantly lower values of relative electron transport rate and coefficient of photochemical quenching were also obtained in tobacco seedlings exposed to AgNPs [ 25 ]. However, there are also reports that treatments with AgNPs did not induce any significant change in PSII efficiency [ 46 , 47 ].…”