CeO₂ Nanoparticles Seed Priming Increases Salicylic Acid Level and ROS Scavenging Ability to Improve Rapeseed Salt Tolerance

Abstract

Soil salinity is a major issue limiting efficient crop production. Seed priming with nanomaterials (nanopriming) is a cost‐effective technology to improve seed germination under salinity; however, the underlying mechanisms still need to be explored. Here, polyacrylic acid coated nanoceria (cerium oxide nanoparticles) (PNC, 9.2 nm, −38.7 mV) are synthesized and characterized. The results show that under salinity, PNC priming significantly increases rapeseed shoot length (41.5%), root length (93%), and seedling dry weight (78%) compared to the no‐nanoparticle (NNP) priming group. Confocal imaging results show that compared with NNP group, PNC priming significantly reduces reactive oxygen species (ROS) level in leaf (94.3% of H 2 O 2 , 56.4% of • O 2 − ) and root (38.4% of H 2 O 2 , 41.3% of • O 2 − ) of salt stressed rapeseed seedlings. Further, the results show that compared with the NNP group, PNC priming not only increases salicylic acid (SA) content in shoot (51.3%) and root (78.4%), but also upregulates the expression of SA biosynthesis related genes in salt stressed rapeseed. Overall, PNC nanopriming improved rapeseed salt tolerance is associated with both the increase of ROS scavenging ability and the increase of salicylic acid. The results add more information to understand the complexity of mechanisms behind nanoceria priming improved plant salt tolerance.

Improvement of leaf K+ retention is a shared mechanism behind CeO2 and Mn3O4 nanoparticles improved rapeseed salt tolerance

“…2a). This is in accordance with previous studies showed that nanoceria improved salt tolerance in rice (Zhou et al, 2021), cotton (An et al, 2020;Liu et al, 2021), rapeseed (Khan et al, 2022(Khan et al, , 2021Rossi et al, 2016Rossi et al, , 2017, cucumber (Chen et al, 2022), Arabidopsis (Wu et al, 2018a) and (d-f ) K + (d) and Na + (e) content and Na + /K + ratio (f) in the roots of rapeseed treated with control buffer, PNC or PMO under salt stress. Mean ± SE (n = 8) (g and h) The relative expression level of K + and Na + transport related genes in the leaves (g) and roots (h) of rapeseed treated with control buffer, PNC or PMO under salt stress.…”

“…2a). This is in consistent with previous studies, which showed that rapeseed primed with PNC treated plants showed much better root performance than control group under salt stress (An et al, 2020;Khan et al, 2021Khan et al, , 2022. Moreover, it should be noted that although CeCl 3 and MnCl 2 treatment also improved rapeseed root performance than control plants under salt stress, no significant difference of whole plant fresh weight was found among these treatment groups (Figure S2a).…”

“…This is also showed in nano-improved plant salt tolerance. In nano-improved plant salt tolerance, the improved phenotypic performance and increased of ROS scavenging ability (or decreased ROS level) are always observed simultaneously in many plant species, such as rapeseed (Khan et al, 2022(Khan et al, , 2021Li et al, 2022a, b;Rossi et al, 2016Rossi et al, , 2017, rice (Zhou et al, 2021), wheat (Saad-Allah and Ragab, 2020), maize (Liu et al, 2022), cotton (An et al, 2020;Liu et al, 2021), cucumber (Chen et al, 2022;Lu et al, 2020), grapevine (Gohari et al, 2021) and Arabidopsis (Wu et al, 2018a). For example, CeO 2 nanoparticles significantly decreased the ROS content of rapeseed leaf under 200 mM NaCl stress (Li et al, 2022a, b).…”

“…However, the possible commonly shared mechanisms in nano-improved plant salt tolerance are rarely discussed, especially among different nanomaterials. It is suggested that increase of ROS scavenging ability might be one of the commonly employed mechanisms underlying CeO 2 nanoparticles improved plant salt tolerance (Khan et al, 2022). While besides ROS homeostasis, plant's ability to maintain K + /Na + ratio is a hallmark for its salt tolerance.…”

“…Thus, Mn 3 O 4 nanoparticles could be a good candidate for environmental-friendly nanomaterials, and could be used to substitute CeO 2 nanoparticles to improve plant salt tolerance. CeO 2 nanoparticles improved rapeseed salt tolerance via ROS scavenging (Khan et al, 2022(Khan et al, , 2021Li et al, 2022a, b), shortening root apoplastic barrier (Rossi et al, 2017), modulation on plant hormones (Khan et al, 2022), and increase of α-amylase activities (Khan et al, 2021). To test whether Mn 3 O 4 nanoparticles can be used to substitute CeO 2 nanoparticles to improve plant salt tolerance, comparison of its effect on salt stressed plants between Mn 3 O 4 and CeO 2 nanoparticles should be conducted.…”