Cerium oxide nanoparticles improve cotton salt tolerance by enabling better ability to maintain cytosolic K+/Na+ ratio

Abstract

Background Salinity is a worldwide factor limiting the agricultural production. Cotton is an important cash crop; however, its yield and product quality are negatively affected by soil salinity. Use of nanomaterials such as cerium oxide nanoparticles (nanoceria) to improve plant tolerance to stress conditions, e.g. salinity, is an emerged approach in agricultural production. Nevertheless, to date, our knowledge about the role of nanoceria in cotton salt response and the behind mechanisms is still rare. Results We found that PNC (poly acrylic acid coated nanoceria) helped to improve cotton tolerance to salinity, showing better phenotypic performance, higher chlorophyll content (up to 68% increase) and biomass (up to 38% increase), and better photosynthetic performance such as carbon assimilation rate (up to 144% increase) in PNC treated cotton plants than the NNP (non-nanoparticle control) group. Under salinity stress, in consistent to the results of the enhanced activities of antioxidant enzymes, PNC treated cotton plants showed significant lower MDA (malondialdehyde, up to 44% decrease) content and reactive oxygen species (ROS) level such as hydrogen peroxide (H2O2, up to 79% decrease) than the NNP control group, both in the first and second true leaves. Further experiments showed that under salinity stress, PNC treated cotton plants had significant higher cytosolic K+ (up to 84% increase) and lower cytosolic Na+ (up to 77% decrease) fluorescent intensity in both the first and second true leaves than the NNP control group. This is further confirmed by the leaf ion content analysis, showed that PNC treated cotton plants maintained significant higher leaf K+ (up to 84% increase) and lower leaf Na+ content (up to 63% decrease), and thus the higher K+/Na+ ratio than the NNP control plants under salinity stress. Whereas no significant increase of mesophyll cell vacuolar Na+ intensity was observed in PNC treated plants than the NNP control under salinity stress, suggesting that the enhanced leaf K+ retention and leaf Na+ exclusion, but not leaf vacuolar Na+ sequestration are the main mechanisms behind PNC improved cotton salt tolerance. qPCR results showed that under salinity stress, the modulation of HKT1 but not SOS1 refers more to the PNC improved cotton leaf Na+ exclusion than the NNP control. Conclusions PNC enhanced leaf K+ retention and Na+ exclusion, but not vacuolar Na+ sequestration to enable better maintained cytosolic K+/Na+ homeostasis and thus to improve cotton salt tolerance. Our results add more knowledge for better understanding the complexity of plant-nanoceria interaction in terms of nano-enabled plant stress tolerance. Graphic abstract

CeO2 nanoparticles modulate Cu–Zn superoxide dismutase and lipoxygenase-IV isozyme activities to alleviate membrane oxidative damage to improve rapeseed salt tolerance

“…As a potent ROS scavenger, nanoceria (cerium oxide nanoparticles) is known to improve plant salt tolerance, such as in rice, 58 cotton, 23,33 grapevine, 29 Moldavian Balm, 59 and Arabidopsis. 22 For example, in cotton, seeds soaked with nanoceria showed decreased ROS content, upregulated antioxidant enzyme genes, and thus improved biomass under salt stress.…”

“…Chlorophyll content measurement was conducted following a previous publication. 23 Leaf samples (the second true leaf) were mixed with a solution containing acetone and ethanol (1 : 1, v : v) for 24 h under dark conditions on a shaker (50 rpm) to measure the chlorophyll content. Following centrifugation at 2000 rpm for 10 min, the supernatant was collected.…”

“…Photosynthetic performance was measured according to previous publications. 23 Briefly, the carbon assimilation rate, stomatal conductivity, and quantum yield of PS II of the second true leaves were measured by using a portable photosynthetic apparatus Li-6400 XT at day 0 (200 mM NaCl) and day12 (200 mM NaCl). The measurement settings are: 1000 μmol m −2 s −1 photosynthetic photon flux density, 400 μmol mol −1 CO 2 concentration, and 25 °C leaf temperature.…”

“…Wu et al 24 reported that nanoceria having a low Ce 3+ /Ce 4+ ratio reduces ROS content and improves photosynthetic performance in Arabidopsis under light and temperature stresses. To date, the application of nanoceria could help to scavenge ROS to improve salt tolerance in cotton, 23,33 Arabidopsis, 22 and rapeseed. 2,34 However, our knowledge regarding the mechanisms underlying nanoceria improved plant salt tolerance is still limited.…”

Exploring the Adaptive Responses of Plants to Abiotic Stresses Using Transcriptome Data

“…Leaf mesophyll K + retention is related to overall plant salinity tolerance [88,89]. This action is carried out through the activity of K + channels/transporter genes [87,90]. Plants also adjust their osmotic pressure to tolerate salinity by the up-regulation of P5CS and the downregulation of ProDH and MYB60.…”