Electrical impedance spectroscopy (EIS) is a useful tool for the investigation of the structural characteristics of solid materials and also biological tissues. The structural changes in plant or animal tissues reflect the physiological state of the organism. Electrical impedance measurement seems to be applicable both for analytical and research laboratories, since once a stress or a quality trait is correlated with an impedance parameter the method is quick and safe for further analysis of great number of samples. This work attempted to explore the current state of literature in terms of the application of EIS that has already been done on animal and plant tissues, and more specifically searching for the possibility of wider future applicability in plant stress detection.

Plants regulate the extent of nodulation and root colonization by arbuscular mycorrhizal fungi (AMF), a phenomenon named autoregulation of symbiosis. We tested AMF colonization in split roots of various soybean genotypes [Glycine max (L.) Merr. cv. Bragg, Enrei, Harosoy and Williams], where precolonization of one side of the split‐root system by the AMF Glomus mosseae resulted in reduced mycorrhization of the other. AMF precolonization failed to control secondary mycorrhization in the supernodulating Bragg nonsense mutant nts1007 (Q106*), indicating that the GmNARK gene (predicted to encode a leucine‐rich repeats (LRR) receptor kinase related to CLAVATA1 in Arabidopsis) is involved in autoregulation of the AMF symbiosis. Here, we tested whether the allelic En6500 nonsense supernodulating mutant (GmNARK K606*, derived from cv. Enrei) and supernodulating mutants of cv. Williams (Nod1‐3 and Nod2‐4) with yet‐undefined genetic lesions exhibit a similar symbiotic phenotype in mycorrhizal split‐root systems. Surprisingly, these supernodulating mutants retained their ability to autoregulate AMF. To examine possible differences between two allelic mutants, we determined levels of IAA, abscisic acid, coumestrol, daidzein and genistein in mycorrhizal and uninoculated control roots. Compared with wild‐type plants, both mutants showed reduced IAA accumulation in mycorrhizal roots. Roots of cv. Enrei and En6500 exhibited high levels of isoflavonoids not seen in Bragg or nts1007. Taken together, these findings showed that supernodulation mutants, despite a common nodulation phenotype, differ in their ability to autoregulate AMF root colonization. This suggests either that the GmNARK gene product of some mutants is still partially functional (Q106* vs. K606*) or that varietal differences reflected in altered physiological responses suppress the loss of function.

Alfalfa (Medicago sativa L.) plant growth decreases when cultivated under salinity or irrigated with salty water. Inoculation with plant growth-promoting bacteria (PGPB) is a method for mitigating the harmful effects of salinity on plants growth. To investigate salt-tolerant PGPB with salt-tolerant and salt-sensitive alfalfa cultivar interactions under salinity, some physiological and agronomical aspects were investigated. The inoculated plants of alfalfa cultivars with Hartmannibacter. diazotrophicus and Pseudomonas sp. bacteria were compared with non-inoculated plants. Plants were grown in growth room and irrigated with tap water until 6-7 weeks, and then, salinity stress imposed by irrigating with tap water (control), 10 dS m −1 and 20 dS m −1 NaCl. Salinity reduced relative water content (RWC), membrane stability index (MSI), K + , photosynthesis rate (Pn) and stomatal conductance (gs), leaf number, height, and dry weight, and increased sodium in all cultivars. Inoculation of cultivars with both PGPB mitigated the negative effects of salinity on plants growth by increasing the root length and weight, nodule number, chlorophyll pigments, RWC, MSI, Pn, and gs. Chlorophyll pigments, plant height and leaf number, Na + , K + /Na + , and nodule number improved more pronounced through inoculating with Pseudomonas sp., whereas K + , carotenoids, and RWC improved more pronounced through H. diazotrophicus under salinity. The results showed inoculation with two bacteria improved growth performance in salt-tolerant and salt-sensitive cultivars under 10 dS m −1 , but at high salinity (20 dS m −1), inoculation was successful only in salt-tolerant alfalfa cultivars.

Biophoton emission is a well-known phenomenon in living organisms, including plant species; however, the underlying mechanisms are not yet well elucidated. Nevertheless, non-invasive stress detection is of high importance when in plant production and plant research. Therefore, the aim of our work was to investigate, whether biophoton emission is suitable for the detection of cadmium stress in the early phase of stress evolution and to identify certain stress-related events that occur rapidly upon cadmium exposure of barley seedlings parallel to biophoton emission measurements. Changes of biophoton emission, chlorophyll content estimation index, ascorbate level, the activity of ascorbate- and guaiacol peroxidase enzymes and lipid oxidation were measured during seven days of cadmium treatment in barley ( Hordeum vulgare L .) seedlings. The results indicate that the antioxidant enzyme system responded the most rapidly to the stress caused by cadmium and the lipid oxidation-related emission of photons was detected in cadmium-treated samples as early as one day after cadmium exposure. Furthermore, a concentration-dependent increase in biophoton emission signals indicating an increased rate of antioxidative enzymes and lipid oxidation was also possible to determine. Our work shows evidence that biophoton emission is suitable to identify the initial phase of cadmium stress effectively and non-invasively.