Potassium ion regulates hormone, Ca2+ and H2O2 signal transduction and antioxidant activities to improve salt stress resistance in tobacco

Ameliorative Effects of Exogenous Potassium Nitrate on Antioxidant Defense System and Mineral Nutrient Uptake in Radish (Raphanus sativusL.) under Salinity Stress

“…Higher lipid peroxidation is a common phenomenon under salt stress caused by membrane injury, which leads to the production of a number of free oxygen radicals that ultimately disturbed the plants’ functioning and hence the metabolism . Under salt-induced oxidative stress, the excessive synthesis of ROS is controlled either by – OH and O 2 – or by molecular oxygen excitation (O 2 ) to form singlet oxygen. , The plants then abruptly activate their antioxidant potential system, which is principally regulated by SOD, POD, CAT, and APX antioxidant enzymes, in response to the excessive ROS production in order to scavenge the ROS and maintain the redox equilibrium, hence boosting plant development. − In addition to enzyme antioxidants, nonenzymatic antioxidants including proline, phenolic, and flavonoids work as secondary metabolites to prevent oxidative stress from salt from causing oxidative damage. − Similarly in the current study, the elevated levels of oxidative stress biomarkers were noticed in both Raphanus sativus L. genotypes, which were then reduced by the stimulation of an antioxidant potential system governed by both enzymatic and nonenzymatic antioxidants. Earlier reports also revealed that the higher activities of antioxidants were observed following saline stress in H.…”

Potassium alleviates over‐reduction of the photosynthetic electron transport chain and helps to maintain photosynthetic function under salt‐stress

“…In our previous study with mulberry (Che, Fan, et al, 2022), the results were consistent with an enhanced proton diffusion potential difference that developed across the thylakoid membrane during salt stress. Additionally, in our previous study with tobacco (Che, Yao, et al, 2022), the H 2 O 2 content was increased, accompanied by altered activities of anti-oxidative enzymes, during salt stress. Combining these results or their interpretation, in this study with tobacco we aimed to further test the hypothesis that (1) salt stress leads to overreduction of the electron transport chain, a phenomenon in which, due to the depletion of stromal K + under salt stress, K + ions are unable to enter the thylakoid lumen rapidly enough to chargecompensate for the efflux of H + from the lumen via the ATP synthase, resulting in insufficient ATP to support rapid carbon assimilation; (2) a consequent over-reduced electron transport chain enhances the formation of H 2 O 2 and singlet oxygen, both of which could lead to retrograde signaling (Chan et al, 2016;Foyer & Shigeoka, 2011;Gollan et al, 2015) that affects the expression of many genes involved in photosynthesis; and (3) supplemental potassium can prevent many of the effects of salt stress primarily by alleviating the trans-thylakoid proton diffusion potential difference via rapid charge compensation through a potassium channel as protons exit the thylakoid lumen via the ATP synthase.…”

“…Similarly, electrons from plastoquinol can also reduce oxygen at the plastid terminal oxidase (PTOX) to form superoxide, from which H 2 O 2 is obtained. The upregulation of the genes encoding SOD in tobacco under salt stress was accompanied by an increase in SOD activity (Che, Yao, et al, 2022), facilitating the rapid production of H 2 O 2 . At the same time, the downregulation of genes encoding ascorbate peroxidase (APX), glutathione peroxidase and, to a lesser extent, peroxidase was accompanied by a decrease in APX and peroxidase activities (Che, Yao, et al, 2022), thereby slowing the scavenging of H 2 O 2 .…”

“…The upregulation of the genes encoding SOD in tobacco under salt stress was accompanied by an increase in SOD activity (Che, Yao, et al, 2022), facilitating the rapid production of H 2 O 2 . At the same time, the downregulation of genes encoding ascorbate peroxidase (APX), glutathione peroxidase and, to a lesser extent, peroxidase was accompanied by a decrease in APX and peroxidase activities (Che, Yao, et al, 2022), thereby slowing the scavenging of H 2 O 2 . The combined effect was an increase in the abundance of H 2 O 2 by more than twofold (Che, Yao, et al, 2022), which most probably led to the regulation of the expression of other genes and/or the formation of highly reactive hydroxyl free radicals that induce damage.…”

“…The large amount of ROS produced under salt stress may lead to retrograde signal transduction (Crawford et al, 2018), downregulating the transcription level of most genes related to energy harvesting, conversion, and utilization of the electron transport chain. However, there have been relatively few studies on the involvement of potassium ions in alleviating retrograde signaling (Che, Yao, et al, 2022; Wu et al, 2018) and damage to PSII (Ball et al, 1987; Bezerra et al, 2021; Che, Fan, et al, 2022; Chow et al, 1990) under salt stress. Furthermore, alleviation by K + is often dependent on the concentration present in the growth medium (Bezerra et al, 2021; Chow et al, 1990); a higher K + concentration allows greater retention of cytosolic K + , which allows a plant to accumulate high amounts of Na + in the cytosol without compromising the cytosolic K + /Na + ratio.…”