The strategic utilization of plant growth-promoting (PGP) rhizospheric bacteria is a sustainable approach to mitigating the negative effects of anthropogenic activities and excessive nickel (Ni) accumulation in plants. Given that the specific effects of symbiotic interactions depend on the direct relationship between the plant species, bacterial strain, and heavy metals (HMs), this study aimed to investigate the effects of Paraburkholderia phytofirmans PsJN seed priming on Ni tolerance in adult Micro-Tom tomato plants (Solanum lycopersicum L.).Sterilized Micro-Tom seeds were bioprimed with P. phytofirmans PsJN for 24 hours and then sown into the soil. Non-primed, imbibed seeds were used as a control. After 10 days, the seedlings were transferred to a Hoagland nutrient solution. Chronic (10 μM Ni) and acute (50 μM Ni) stress conditions were induced by supplementing the Hoagland solution with Ni salt. The experiment lasted approximately 75 days, covering the complete life cycle of the plants. Various physiological and biochemical parameters were analyzed.Significant differences (p < 0.05) were observed between non-primed and bioprimed tomato plants in terms of fruit yield. Bioprimed tomatoes exhibited higher resilience to Ni stress, particularly under acute stress conditions. Non-primed tomatoes treated with 50 μM Ni showed statistically lower concentrations of chlorophyll a and total chlorophylls compared to bioprimed tomatoes. Moreover, proline content was generally lower and more stable in bioprimed plants, indicating reduced oxidative stress.The activity of antioxidant enzymes exhibited distinct patterns between nonprimed and bioprimed tomatoes.The findings suggest that biopriming with P. phytofirmans PsJN enhances Micro-Tom tomato resilience and growth under Ni stress. This technique appears to mitigate Ni-induced stress effects, particularly at higher Ni concentrations, making it a promising strategy for improving tomato performance in Ni-contaminated environments. Future studies should explore the underlying molecular mechanisms and field applications of this biopriming approach.

Abstract Serpentine soils are characterized as a unique environment with low nutrient availability and high heavy metal concentrations, often hostile to many plant species. Even though these unfavorable conditions hinder the growth of various plants, particular vegetation with different adaptive mechanisms thrives undisturbed. One of the main contributors to serpentine adaptation represents serpentine bacteria with plant growth-promoting properties that assemble delicate interactions with serpentine plants. Robinia pseudoacacia L. is an invasive but adaptive species with phytoremediation potential and demonstrates extraordinary success in this environment. To explore more in-depth the role of plant growth-promoting serpentine bacteria, we isolated them and tested their various plant growth-promoting traits both from the rhizosphere and roots of R. pseudoacacia. Based on the demonstrated plant growth-promoting traits such as siderophore production, phosphate solubilization, nitrogen fixation, indole-3-acetic acid production, and ACC deaminase production, we sequenced overall 25 isolates, 14 from the rhizosphere and 11 from the roots. Although more efficient in exhibiting plant growthpromoting traits, rhizospheric bacteria showed a low rate of diversity in comparison to endophytic bacteria. The majority of the isolates from the rhizosphere belong to Pseudomonas, while isolates from the roots exhibited higher diversity with genera Pseudomonas, Bacillus, Staphylococcus, Lysinibacillus and Brevibacterium/Peribacillus/Bacillus. The capacity of the described bacteria to produce siderophores, solubilize phosphate, and fix nitrogen highlights their central role in enhancing nutrient availability and facilitating R. pseudoacacia adaptation to serpentine soils. The findings highlight the potential significance of serpentine bacteria, particularly Pseudomonas, in contributing to the resilience and growth of R. pseudoacacia in serpentine environments.

Many heavy metals (HMs) are essential micronutrients for the growth and development of plants. However, human activities such as mining, smelting, waste disposal, and industrial processes have led to toxic levels of HMs in soil. Fortunately, many plant species have developed incredible adaptive mechanisms to survive and thrive in such harsh environments. As a widespread and ruderal species, Geranium robertianum L. inhabits versatile soil types, both polluted and unpolluted. Considering the ubiquity of G . robertianum , the study aimed to determine whether geographically distant populations can tolerate HMs. We collected soil and plant samples from serpentine, an anthropogenic heavy metal contaminated, and a non-metalliferous site to study the physiological state of G. robertianum . HMs in soil and plants were determined using flame atomic absorption spectrometry. Spectrophotometric methods were used to measure the total content of chlorophylls a and b, total phenolics, phenolic acids, flavonoids, and proline. Principal component analysis (PCA) was used to investigate the potential correlation between HMs concentrations gathered from various soil types and plant samples and biochemical data acquired for plant material. A statistically significant difference was observed for all localities regarding secondary metabolite parameters. A positive correlation between Ni and Zn in soil and Ni and Zn in plant matter was observed ( p <0.0005) indicating higher absorption. Regardless of high concentrations of heavy metals in investigated soils, G. robertianum displayed resilience and was capable of thriving. These results may be ascribed to several protective mechanisms that allow G. robertianum to express normal growth and development and act as a pioneer species.