Living with high potassium: Balance between nutrient acquisition and K-induced salt stress signaling

Growth of soybean plants under saline conditions: the role of potassium and Bradyrhizobium japonicum inoculation

This study aimed to evaluate the effects of potassium (K) and Bradyrhizobium japonicum applications on physiological and microbial parameters in soybean plants under salt stress. The study included treatments of control, potassium (2.2 g K2SO4), bacteria (B), and their combinations (K + B), along with versions exposed to 100 mM NaCl salt stress. Key parameters such as leaf water content (RWC), chlorophyll (SPAD, Chlo a/b), oxidative stress indicators (H2O2 and MDA), proline, protein, antioxidant enzyme activities (APX, POD, and CAT), microbial biomass carbon (MBC), and CO2 release from soil were measured. Salt stress reduced RWC in plants by 15%, while H2O2 and MDA levels increased by 25% and 30%, respectively. However, potassium and bacterial applications improved plant resilience against stress by increasing proline levels by 20%, reducing protein loss by 18%, and enhancing antioxidant enzyme activities to mitigate oxidative damage. In soil microbial activities, MBC increased by up to 161%, and CO₂ release increased by up to 27.7% with K + B application. Under salt stress, MBC and CO₂ release were restored by 122% and 50.8%, respectively, demonstrating the positive effects of potassium and bacterial inoculation on microbial activity. These findings suggest that potassium and Bradyrhizobium japonicum applications could be considered effective strategies for enhancing plant tolerance and soil health under salt stress conditions.

Understanding salinity stress responses in sorghum: exploring genotype variability and salt tolerance mechanisms

Salinity, a significant abiotic stressor, adversely affects global plant growth. To address this, monitoring genetic diversity within a plant species germplasm for salt tolerance traits is vital. This study investigates the responses of ten sorghum genotypes to varying salt stress levels (control, 60 mM NaCl, and 120 mM NaCl), aiming to assess genetic diversity. Using a randomized complete block design with three replications and a split-plot arrangement, salt treatments were assigned to main plots, and genotypes were placed in sub-plots. Physiological attributes, including photosynthetic rate, stomatal conductance, CO2 concentration, leaf area index, chlorophyll concentrations, and antioxidant enzyme activity, were measured during the 50% flowering stage. Fresh forage yield was evaluated at the early dough stage, while dry forage yield and sodium/potassium concentrations were determined post-drying. Salinity induced 10-23% and 21-47% reductions in forage fresh yield at 60 mM and 120 mM NaCl, respectively, across sorghum genotypes. Forage dry yield also declined by 11-33% at 60 mM NaCl and 30-58% at 120 mM NaCl. Increased oxidative stress markers, proline, soluble carbohydrates, and antioxidant enzyme activity accompanied salinity. Genotypes exhibited diverse responses, with Payam showing significant chlorophyll and yield reductions at 60 mM NaCl and notable stress indicators at 120 mM NaCl. Pegah and GS4 demonstrated robust osmoregulation. In stress tolerance indices, Sepideh excelled at 60 mM NaCl, while GS4 outperformed at 120 mM NaCl. Pegah demonstrated high tolerance at 120 mM NaCl. Our findings highlight the importance of combating oxidative stress, managing water-related stress, and maintaining ionic homeostasis for sorghum's salt stress resilience. Key indicators like K/Na ratio, MDA, MSI, SOD, and proline effectively differentiate between tolerant and sensitive genotypes, offering valuable insights for sorghum breeding. Salt-tolerant sorghum genotypes exhibit stable photosynthesis, improved stomatal function, and membrane integrity through efficient osmotic regulation and robust antioxidant enzyme activity. This capability enables them to sustain performance, minimizing final product loss. The results suggest cultivating salt-tolerant sorghum in saline areas for increased sustainable production, with Pegah and GS4 emerging as promising candidates for further testing in salt-affected environments to obtain reliable yield data.

Response of in situ root phenotypes to potassium stress in cotton

Potassium plays a significant role in the basic functions of plant growth and development. Potassium uptake is closely associated with morphological characteristics of the roots. However, the dynamic characteristics of phenotype and lifespan of cotton (Gossypium hirsutum L.) lateral roots and root hairs under low and high potassium stress remain unclear. In this study, potassium stress experiments (low and high potassium, medium potassium as control) were conducted using RhizoPot (an in situ root observation device) to determine the response characteristics of lateral roots and root hairs in cotton under potassium stress. The plant morphology, photosynthetic characteristics, root phenotypic changes, and lifespan of lateral roots and root hairs were measured. Potassium accumulation, aboveground phenotype, photosynthetic capacity, root length density, root dry weight, root diameter, lateral root lifespan, and root hair lifespan under low potassium stress were significantly decreased compared to medium potassium treatment. However, the root hair length of the former was significantly increased than that of the latter. Potassium accumulation and the lateral root lifespan were significantly increased under high potassium treatment, while root length density, root dry weight, root diameter, root hair length, and root hair lifespan were significantly decreased compared to the medium potassium treatment. Notably, there were no significant differences in aboveground morphology and photosynthetic characters. Principal component analysis revealed that lateral root lifespan, root hair lifespan of the first lateral root, and root hair length significantly correlated with potassium accumulation. The root had similar regularity responses to low and high potassium stress except for lifespan and root hair length. The findings of this study enhance the understanding of the phenotype and lifespan of cotton's lateral roots and root hairs under low and high potassium stress.

Effective root responses to salinity stress include maintained cell expansion and carbon allocation

Acclimation of root growth is vital for plants to survive salt stress. Halophytes are great examples of plants that thrive even under severe salinity, but their salt tolerance mechanisms, especially those mediated by root responses, are still largely unknown. We compared root growth responses of the halophyte Schrenkiella parvula with its glycophytic relative species Arabidopsis thaliana under salt stress and performed transcriptomic analysis of S. parvula roots to identify possible gene regulatory networks underlying their physiological responses. Schrenkiella parvula roots do not avoid salt and experience less growth inhibition under salt stress. Salt-induced abscisic acid levels were higher in S. parvula roots compared with Arabidopsis. Root transcriptomic analysis of S. parvula revealed the induction of sugar transporters and genes regulating cell expansion and suberization under salt stress. ¹⁴ C-labeled carbon partitioning analyses showed that S. parvula continued allocating carbon to roots from shoots under salt stress while carbon barely allocated to Arabidopsis roots. Further physiological investigation revealed that S. parvula roots maintained root cell expansion and enhanced suberization under severe salt stress. In summary, roots of S. parvula deploy multiple physiological and developmental adjustments under salt stress to maintain growth, providing new avenues to improve salt tolerance of plants using root-specific strategies.

The anion channel SLAH3 interacts with potassium channels to regulate nitrogen-potassium homeostasis and the membrane potential in Arabidopsis

Nitrogen (N) and potassium (K) are essential macronutrients for plants. Sufficient N and K uptake from the environment is required for successful growth and development. However, how N and K influence each other at the molecular level in plants is largely unknown. In this study, we found loss-of-function mutation in SLAH3 (SLAC1 HOMOLOGUE 3), encoding a NO3- efflux channel in Arabidopsis thaliana, enhanced tolerance to high KNO3 concentrations. Surprisingly, slah3 mutants were less sensitive to high K+ but not NO3-. Addition of NO3- led to reduced phenotypic difference between wild-type and slah3 plants, suggesting SLAH3 orchestrates NO3--K+ balance. Non-invasive Micro-test Technology analysis revealed reduced NO3- efflux and enhanced K+ efflux in slah3 mutants, demonstrating that SLAH3-mediated NO3- transport and SLAH3-affected K+ flux are critical in response to high K +. Further investigation showed that two K+ efflux channels, GORK (GATED OUTWARDLY-RECTIFYING K+ CHANNEL) and SKOR (STELAR K+ OUTWARD RECTIFIER), interacted with SLAH3 and played key roles in high K+ response. The gork and skor mutants were slightly more sensitive to high K+ conditions. Less depolarization occurred in slah3 mutants and enhanced depolarization was observed in gork and skor mutants upon K+ treatment, suggesting NO3-/K+ efflux-mediated membrane potential regulation is involved in high K+ response. Electrophysiological results showed that SLAH3 partially inhibited the activities of GORK and SKOR in Xenopus laevis oocytes. This study revealed that the anion channel SLAH3 interacts with the potassium channels GORK and SKOR to modulate membrane potential by coordinating N-K balance.