Functional Quality, Antioxidant Capacity and Essential Oil Percentage in Different Mint Species Affected by Salinity Stress.

Saline stress is responsible for significant reductions in the growth of plants, and it globally leads to limitations in the performance of crops, especially in drought-affected areas. However, a better understanding of the mechanisms involved in the resistance of plants to environmental stress can lead to a better plant breeding and selection of cultivars. Mint is one of the most important medicinal plants, and it has important properties for industry, and for the medicinal and pharmacy fields. The effects of salinity on the biochemical and enzymatic properties of 18 ecotypes of mint from six different species, that is, Mentha piperita, Mentha mozafariani, Mentha rotundifolia, Mentha spicata, Mentha pulegium and Mentha longifolia, have been examined in this study. The experimental results showed that salinity increased with increasing in stress integrity influenced the enzymatic properties, proline content, electrolyte leakage, and the hydrogen peroxide, malondialdehyde, and essential oil contents. Cluster analysis and principal component analysis were conducted, and they grouped the studied species on the basis of their biochemical characteristics. According to the obtained biplot results, M. piperita and M. rotundifolia showed better stress tolerance than the other varieties, and M. longifolia was identified as being salt sensitive. Generally, the results showed that H2 O2 and malondialdehyde had a positive connection with each other and showed a reverse relationship with all the enzymatic and non-enzymatic antioxidants. Finally, it was found that the M. spicata, M. rotundifolia and M. piperita ecotypes could be used for future breeding projects to improve the salinity tolerance of other ecotypes.

Does co-inoculation of mycorrhiza and Piriformospora indica fungi enhance the efficiency of chlorophyll fluorescence and essential oil composition in peppermint under irrigation with saline water from the Caspian Sea?

Symbiotic associations with endophytic fungi are ecologically important for medicinal and aromatic plants. Endophytic fungi highly affect the quantity and quality of herbal products. In this study, a pot experiment was carried out in the greenhouse to investigate the interactive effects of Piriformospora indica and arbuscular mycorrhizal (AMF) inoculation on the chlorophyll fluorescence, essential oil composition, and antioxidant enzymes of peppermint under saline condition. The results showed that Fo, YNPQ, YNO, and NPQ values were obviously increased under salinity conditions, while essential oil content, chlorophyll a and b, gs, Fm, Fv, ETR, ФPSII and Fv/Fm ratio decreased by increasing salinity. In addition, salt induced the excess Na+ uptake, whereas the opposite trend was observed for P and K+. The synergistic association of P. indica and AMF caused a considerable increase in the antioxidant ability, essential oil content, Fv/Fm ratio, ФPSII, and amount of P and K+ uptake in salt-stressed plants. The main peppermint oil constituents, menthol, menthone, and 1,8-cineole increased considerably in inoculated plants. Besides, the applied endophytic fungi positively enhanced the ability of peppermint to alleviate the negative effect of the salinity stress.

Phosphate solubilization potential and modeling of stress tolerance of rhizobacteria from rice paddy soil in northern Iran.

The purposes of this study were to evaluate the phosphate solubilization activity of bacteria isolated from the rhizosphere of rice paddy soil in northern Iran, and to study the effect of temperature, NaCl and pH on the growth of these isolates by modeling. Three of the most effective strains from a total of 300 isolates were identified and a phylogenetic analysis was carried out by 16S rDNA sequencing. The isolates were identified as Pantoea ananatis (M36), Rahnella aquatilis (M100) and Enterobacter sp. (M183). These isolates showed multiple plant growth-promoting attributes such as phosphate solubilization activity and indole-3-acetic acid (IAA) production. The M36, M100 and M183 isolates were able to solubilize 172, 263 and 254 µg ml(-1) of Ca3(PO4)2 after 5 days of growth at 28 °C and pH 7.5, and to produce 8.0, 2.0 and 3.0 µg ml(-1) of IAA when supplemented with L-tryptophan (1 mg ml(-1)) for 72 h, at 28 °C and pH 7.0, respectively. The solubilization of insoluble phosphate was associated with a drop in the pH of the culture medium and there was an inverse relationship between pH and solubilized P (r = -0.98, P < 0.0952). There were no significant differences among isolates in terms of acidity tolerance based on their confidence limits as assessed by segmented model analysis and all isolates were able to grow at pH 4.3-11 (with optimum at 7.0-7.5). Based on a sigmoidal trend of a three-parameter logistic model, the salt concentration required for 50 % inhibition was 8.15, 6.30 and 8.23 % NaCl for M36, M100 and M183 isolates, respectively. Moreover, the minimum and maximum growth temperatures estimated by the segmented model were 5.0 and 42.75 °C for M36, 12.76 and 40.32 °C for M100, and 10.63 and 43.66 °C for M183. The three selected isolates could be deployed as inoculants to promote plant growth in an agricultural environment.