Thymol improves salinity tolerance of tobacco by increasing the Na+ efflux and enhancing the content of NO and GSH

Plants have evolved a lot of strategies to improve salt tolerance to cope with salt stress. Recent studies have suggested that thymol (a nature medicine) enhances the plant tolerance against abiotic stresses, but the mechanisms are rarely known. Here, we found that thymol played an important role in maintaining root growth under salt stress. Thymol rescued root growth from salt stress via ameliorating ROS (reactive oxygen species) accumulation, lipid peroxidation, and cell death. In addition, thymol enhanced the level of NO (nitric oxide) and GSH (glutathione) to repress ROS accumulation, further protecting the stability of cell membrane. Thymol-induced Na+ efflux in roots and leaves under salt stress may depend on the upregulation of SOS1, HKT1 and NHX1. Consequently, all of these evidences suggested that thymol improved tobacco salt tolerance via enhancing NO and GSH content as well as inducing Na+ efflux.

Thymol improves salinity tolerance of tobacco by increasing the Na + efflux and enhancing the content of NO and GSH

Plants have evolved a lot of strategies to improve salt tolerance to cope with salt stress. Recent studies have suggested that thymol (a nature medicine) enhances the plant tolerance against abiotic stresses, but the mechanisms are rarely known. Here, we found that thymol played an important role in maintaining root growth under salt stress. Thymol rescued root growth from salt stress via ameliorating ROS (reactive oxygen species) accumulation, lipid peroxidation, and cell death. In addition, thymol enhanced the level of NO (nitric oxide) and GSH (glutathione) to repress ROS accumulation, further protecting the stability of cell membrane. Thymol-induced Na+ efflux in roots and leaves under salt stress may depend on the upregulation of SOS1, HKT1 and NHX1. Consequently, all of these evidences suggested that thymol improved tobacco salt tolerance via enhancing NO and GSH content as well as inducing Na+ efflux.

The protein kinase complex CBL10–CIPK8–SOS1 functions in Arabidopsis to regulate salt tolerance

Salt tolerance in plants is mediated by Na+ extrusion from the cytosol by the plasma membrane Na+/H+ antiporter SOS1. This is activated in Arabidopsis root by the protein kinase complex SOS2–SOS3 and in Arabidopsis shoot by the protein kinase complex CBL10–SOS2, with SOS2 as a key node in the two pathways. The sos1 mutant is more sensitive than the sos2 mutant, suggesting that other partners may positively regulate SOS1 activity. Arabidopsis has 26 CIPK family proteins of which CIPK8 is the closest homolog to SOS2. It is hypothesized that CIPK8 can activate Na+ extrusion by SOS1 similarly to SOS2. The plasma membrane Na+/H+ exchange activity of transgenic yeast co-expressing CBL10, CIPK8, and SOS1 was higher than that of untransformed and SOS1 transgenic yeast, resulting in a lower Na+ accumulation and a better growth phenotype under salinity. However, CIPK8 could not interact with SOS3, and the co-expression of SOS3, CIPK8, and SOS1 in yeast did not confer a significant salt tolerance phenotype relative to SOS1 transgenic yeast. Interestingly, cipk8 displayed a slower Na+ efflux, a higher Na+ level, and a more sensitive phenotype than wild-type Arabidopsis, but grew better than sos2 under salinity stress. As expected, sos2cipk8 exhibited a more severe salt damage phenotype relative to cipk8 or sos2. Overexpression of CIPK8 in both cipk8 and sos2cipk8 attenuated the salt sensitivity phenotype. These results suggest that CIPK8-mediated activation of SOS1 is CBL10-dependent and SOS3-independent, indicating that CIPK8 and SOS2 activity in shoots is sufficient for regulating Arabidopsis salt tolerance.

Abiotic Stress Resistance Analysis of Lilium pumilum Overexpressing the LpMT2 Gene

Plant metallothioneins (MT) are cysteine-rich proteins present in plants that can improve a plant’s salt tolerance. Therefore, a greater understanding of the MT gene in lily (Lilium pumilum), Liliaceae, is an important factor in the development and cultivation of improved salt-tolerant varieties and enriching plant resources for saline soils. A type 2 MT gene (GenBank access number: MH319787, designated as LpMT2) was isolated from L. pumilum leaves. The response mechanism to stress was then investigated, which provided the basis for molecular breeding of L. pumilum for stress tolerance. The LpMT2 gene amino acid sequence is highly homologous to that of type 2 MT protein. Quantitative real-time PCR (qPCR) determined that different plant tissues expressed the LpMT2 gene differently and these expressions were dependent on the specific stress. Transgenic plants with LpMT2 gene exhibited significantly increased resistance to salt and oxidative stress compared with untransgenic plants. The LpMT2 transgenic plants had better growth, greater chlorophyll and proline content, less malondialdehyde (MDA) content and cell membrane permeability, greater superoxide dismutase (SOD) activity, less Na+ content, greater K+ content and Na+ efflux, and less K+ efflux. These results determined that the transformed LpMT2 gene in L. pumilium plays an important role in enhancing the plant’s salt tolerance and antioxidant capacity.

Maintenance of K+/Na+ Balance in the Roots of Nitraria sibirica Pall. in Response to NaCl Stress

Using Non-invasive Micro-test Technology (NMT), the Na+, K+ and H+ flux profiles in the root meristem regions were investigated in Nitraria sibirica Pall. seedlings under different NaCl concentrations. NaCl stress increased the K+ and Na+ contents in the roots of N. sibirica seedlings. NaCl stress significantly increased the steady Na+ efflux from the N. sibirica seedling roots. Steady K+ effluxes were measured in the control roots (without NaCl) and in the roots treated with 200 mM NaCl, and no significant differences were observed between the two treatments. The steady K+ efflux from roots treated with 400 mM NaCl decreased gradually. NaCl treatment significantly increased the H+ influx. Pharmacological experiments showed that amiloride and sodium vanadate significantly inhibited the Na+ efflux and H+ influx, suggesting that the Na+ efflux was mediated by a Na+/H+ antiporter using energy provided by plasma membrane H+-ATPase. The NaCl-induced root K+ efflux was inhibited by the K+ channel inhibitor tetraethylammonium chloride (TEA), and was significantly increased by the H+-ATPase inhibitor sodium vanadate. The NaCl-induced K+ efflux was mediated by depolarization-activated outward-rectifying K+ channels and nonselective cation channels (NSCCs). Under salt stress, N. sibirica seedlings showed increased Na+ efflux due to increased plasma membrane H+-ATPase and Na+/H+ antiporter activity. High H+ pump activity not only restricts the Na+ influx through NSCCs, but also limits K+ leakage through outward-rectifying K+ channels and NSCCs, leading to maintenance of the K+/Na+ balance and higher salt tolerance.

Effects of anesthesia with the essential oil of Ocimum gratissimum L. in parameters of fish stress

RESUMO:The effects of anesthesia with the essential oil of Ocimum gratissimum (EOO) in parameters of stress after handling were investigated in silver catfish (Rhamdia quelen). EOO was obtained from the aerial parts by hydrodistillation. Juveniles were anesthetized with 70 or 300 mg L-1 EOO and submitted to air exposure for 1 minute. The fishes were sampled immediately or transferred to anesthetic-free aquaria until sampling. In the first experiment, juveniles had their blood collected at 0, 1, 4, and 8 h after handling to assay plasma cortisol and blood glucose levels. The unanesthetized animals were restrained manually for blood collection. In the second experiment, water samples of the recovery aquaria were collected to evaluate net ion fluxes at 0 - 4 h and 4 - 8 h. Water and ethanol controls were also performed under the same conditions. The results showed that the cortisol levels did not differ among the treatments. Hyperglycemia was verified in fish exposed to 70 and 300 mg L-1 EOO at 1 h and 4 h after handling. After 8 h, cortisol and glucose concentrations were lower or similar than those from immediately after handling for all treatments. EOO anesthesia prevented Na+ efflux observed in the control groups in both flux periods. There were net Cl- and K+ effluxes at 0 - 4 h and influxes at 4 - 8 h after handling in most treatments, and these fluxes did not differ among the treatments. The results suggest that EOO did not impair stress recovery and did not act as an additional handling stressor in silver catfish.