Salinity occurring in intensively used agricultural, industrialized, and urbanized areas is one of the main factors in soil degradation. The effect of silver nanoparticles (AgNPs) on plant growth under environmental stresses is still not fully understood. Two experiments were conducted on the response of Asiatic lilies to treatment with colloidal AgNPs. In Experiment I, the study aimed to evaluate the effect of treating 'Osasco' lily bulbs with colloidal AgNPs (0, 25, 50, 100, and 150 ppm) on growth, flowering, and bulb yield, as well as the production of bulblets. Compared with the control, the applied colloidal AgNPs at all concentrations caused an acceleration of flowering and an increase in bulb diameter and the fresh weight of the aboveground part of the plants and bulbs. In addition, treatment with colloidal AgNPs at concentrations of 100 and 150 ppm increased bulblets’ number and fresh weight. In Experiment II, the effects of colloidal AgNPs (100 ppm) and NaCl stress (600 mM) on the growth parameters, assimilation pigment content, and chemical composition of 'Bright Pixi' lily leaves were evaluated. As a result of the application of colloidal AgNPs, plants flowered faster and had increased height, petal width, fresh bulb weight, bulb diameter, and several scales in the bulb. Under NaCl stress, plants had reduced fresh weight of the aboveground part and bulb, bulb diameter, number of scales in a bulb, and contents of assimilation pigments, N, K, Ca, Cu, Mn and Zn. Colloidal AgNPs offset the adverse effects of salinity on bulb yield by increasing fresh bulb, bulb diameter, and the number of scales in lily bulbs. In conclusion, using colloidal AgNPs can contribute to developing new methods of bulbous plants production and an effective strategy to protect plants from ever-increasing land salinization.
Hydrogen peroxide (H2O2) is produced predominantly in plant cells during photosynthesis and photorespiration, and to a lesser extent, in respiration processes. It is the most stable of the so– called reactive oxygen species (ROS), and therefore plays a crucial role as a signalling molecule in various physiological processes. Intra- and intercellular levels of H2O2 increase during environmental stresses. Hydrogen peroxide interacts with thiol-containing proteins and activates different signalling pathways as well as transcription factors, which in turn regulate gene expression and cell-cycle processes. Genetic systems controlling cellular redox homeostasis and H2O2 signalling are discussed. In addition to photosynthetic and respiratory metabolism, the extracellular matrix (ECM) plays an important role in the generation of H2O2, which regulates plant growth, development, acclimatory and defence responses. During various environmental stresses the highest levels of H2O2 are observed in the leaf veins. Most of our knowledge about H2O2 in plants has been obtained from obligate C3 plants. The potential role of H2O2 in the photosynthetic mode of carbon assimilation, such as C4 metabolism and CAM (Crassulacean acid metabolism) is discussed. We speculate that early in the evolution of oxygenic photosynthesis on Earth, H2O2 could have been involved in the evolution of modern photosystem II.
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