Silver Nanoparticles Alter Microtubule Arrangement, Dynamics and Stress Phytohormone Levels

Abstract

The superior properties of silver nanoparticles (AgNPs) has resulted in their broad utilization worldwide, but also the risk of irreversible environment infestation. The plant cuticle and cell wall can trap a large part of the nanoparticles and thus protect the internal cell structures, where the cytoskeleton, for example, reacts very quickly to the threat, and defense signaling is subsequently triggered. We therefore used not only wild-type Arabidopsis seedlings, but also the glabra 1 mutant, which has a different composition of the cuticle. Both lines had GFP-labeled microtubules (MTs), allowing us to observe their arrangement. To quantify MT dynamics, we developed a new microscopic method based on the FRAP technique. The number and growth rate of MTs decreased significantly after AgNPs, similarly in both lines. However, the layer above the plasma membrane thickened significantly in wild-type plants. The levels of three major stress phytohormone derivatives—jasmonic, abscisic, and salicylic acids—after AgNP (with concomitant Ag+) treatment increased significantly (particularly in mutant plants) and to some extent resembled the plant response after mechanical stress. The profile of phytohormones helped us to estimate the mechanism of response to AgNPs and also to understand the broader physiological context of the observed changes in MT structure and dynamics.

Strategies for Enhancing Plant Immunity and Resilience Using Nanomaterials for Sustainable Agriculture

“…40 Recent research has shown that these defense hormones can be directly involved in the reaction of plants to nanoparticle stress. 5,41 Abiotic stresses like drought, salinity and extreme temperature, does not directly cause an immune response. Nonetheless, abiotic stress can also induce resistance in plants.…”

“…Different pathogen species can cause different responses of these hormones, for example, due to distinct herbivore feeding strategies: piercing and sucking pests, such as aphids, primarily trigger SA and JA pathways, whereas the JA pathway predominantly mediates the responses to chewing herbivores . Recent research has shown that these defense hormones can be directly involved in the reaction of plants to nanoparticle stress. , …”

“…Generally, due to crosstalk, defense-related signal transduction pathways are interconnected in highly complex signaling networks (Figure b). , The interplay of PTI, ETI, and abiotic stress signaling is not well understood. , Based on the physicochemical properties of nanoparticles, depending on the dose, size, shape, and composition, nanoparticles can be expected to interfere upstream with both biotic and abiotic stress defense signaling pathways in plants if they a) damage the cell wall (CDPK and MAPK pathway ↑), b) get stuck in the apoplast (cell walls, root hairs, or stomata) and interfere with evapotranspiration and photosynthesis , (CDPK, MAPK pathways ↑), c) generate or scavenge ROS, e.g., by (photo)­catalytic processes (MAPK pathway ↑ or ↓), d) in case of smaller nanoparticles ≪50 nm, if they penetrate the cell membrane, interact with organelles in the cytoplasm, and mechanically stress the cytoskeleton (MAPK ↑) or electron transport, and e) release toxic molecules or ions . For example, ROS, which promote the MAPK pathway, can emerge from damaged chloroplast membranes due to impaired electron transport chains in the photosystems.…”

Multilevel approach to plant–nanomaterial relationships: from cells to living ecosystems

“…swollen chloroplast structure, fewer thylakoids, abnormal size of plastoglobules and starch granules, destructive changes in peroxisomes, swollen mitochondrial cristae, and condensed nucleus) have been described (recently reviewed by Rajput et al , 2019 ). Furthermore, the intracellular presence of NM can also affect the copy number of chloroplast and mitochondrial DNA ( Pagano et al , 2022 ), as well as the number and growth rate of the microtubule component of the cytoskeleton ( Angelini et al , 2022 )…”

Abscisic Acid Inhibits Cortical Microtubules Reorganization and Enhances Ultraviolet-B Tolerance in Arabidopsis thaliana

“…Plant growth and morphogenesis change due to disturbed microtubule organization in A. thaliana which suffered from UV-B radiation [ 6 , 26 ]. Microtubule reorganization and corresponding morphology caused by stress are connected with cellular signals, such as nitric oxide [ 6 , 24 , 27 ], brassinosteroid [ 28 ], and ABA [ 29 , 30 ]. It is essential to comprehensively investigate the effects of UV-B radiation on plant growth and the relations of hormone signals and microtubule cytoskeleton.…”