The Effects of Halomonas sp. and Azotobacter sp. on Ameliorating the Adverse Effect of Salinity in Purple Basil (Ocimum basilicum L.)

The role of plant growth-promoting rhizobacteria (PGPR) on enhancing tolerance of plants to abiotic stresses is well reported, but the effects of RGPRs on plants under salinity stress are not widely studied in the literature. Our study aimed to investigate the effect of Halomonas sp. and Azotobacter sp. on antioxidant activity, secondary metabolites, and biochemicals changes of purple basil under salinity stress conditions. The applied salt concentrations in this study were 50, 100, and 150 mM sodium chloride (NaCl). Salinity stress had a negative effect on plant growth parameters. Moreover, a reduction in some of the osmolytes and oxidative stress markers was observed. Inoculated plants ameliorated the oxidative damage by reducing the hydrogen peroxide (H2O2) contents and by increasing osmolytes (proline, total proteins, and soluble sugars), antioxidant enzymes activities (catalase, ascorbate peroxidase) and secondary metabolites (flavonoids). Overall, among treatments, plants inoculated with Azotobacter showed a better impact on physiological attributes to alleviate the adverse effects of 150 mM NaCl salinity stress on basil growth.

Growth and Element Uptake by Salt-Sensitive Crops under Combined NaCl and Cd Stresses

To test an assumption that organic soil can ameliorate nutritional disorders associated with metal and salinity stresses, we exposed salt-sensitive strawberry and lettuce to four salinity (0–60 mM NaCl) and three contamination (0.3–5 mg Cd/kg) rates in peat (pHH2O = 5.5). The results showed that, even at 20 mM NaCl, salinity stress exerted a dominant effect on rhizosphere biogeochemistry and physiological processes, inducing leaf-edge burns, chlorosis/necrosis, reducing vegetative growth in crops; at ≥40 mM, NaCl mortality was induced in strawberry. Signifiacntly decreased K/Na, Ca/Na and Mg/Na concentration ratios with raising salinity were confirmed in all tissues. The combined CdxNaCl stresses (vs. control) increased leaf Cd accumulation (up to 42-fold in lettuce and 23-fold in strawberry), whereas NaCl salinity increased the accumulation of Zn (>1.5-fold) and Cu (up to 1.2-fold) in leaves. Lettuce accumulated the toxic Cd concentration (up to 12.6 mg/kg) in leaves, suggesting the strong root-to-shoot transport of Cd. In strawberry Cd, concentration was similar (and sub-toxic) in fruits and leaves, 2.28 and 1.86 mg/kg, respectively, suggesting lower Cd root-to-shoot translocation, and similar Cd mobility in the xylem and phloem. Additionally, the accumulation of Cd in strawberry fruits was exacerbated at high NaCl exposure (60 mM) compared with lower NaCl concentrations. Thus, in salinized, slightly acidic and organically rich rhizosphere, pronounced organo- and/or chloro-complexation likely shifted metal biogeochemistry toward increased mobility and phytoavailability (with metal adsorption restricted due to Na+ oversaturation of the caton exchange complex in the substrate), confirming the importance of quality water and soils in avoiding abiotic stresses and producing non-contaminated food.

Mitigating the adverse effects of NaCl salinity on pod yield and ionic attributes of okra plants by silicon and gibberellic acid application

The current study was undertaken to evaluate the responses of okra to salinity and to study the beneficial effects of silicon and gibberellic acid on yield and ionic attributes of okra under salinity stress. For this purpose, a pot experiment was conducted at the Horticultural Farm of the Department of Horticulture, The University of Haripur, Pakistan. Seeds of the okra cultivar ‘Sabz Pari’ were sown in pots. The experiment was established in a complete randomized design with factorial layout and included a total of 14 treatments deriving from the combination of two factors: two salinity levels and seven treatments with silicon or gibberellic acid. Okra seeds were pretreated with either 0, 50, 75 or 100 mg/L of gibberellic acid and then planted into pots. After germination plants were subjected to 0 mmol (control) or 50 mmol salinity; silicon (in the form of potassium silicate) was applied to plants exogenously at the rate of 2 mmol, 3 mmol, or 4 mmol. The following parameters were measured: number of days to flowering, pod length, pod weight, number of pods per plant and pod yield per plant, and the contents of Na+, Cl-, K+, and proline in the leaves. The results revealed that under 50 mmol NaCl salinity okra plants treated with 100 mg/L of GA3 had the shortest time to flowering (48.3 days) and the lowest Na+ ion content (14.9 mg/L) and Cl- ion content (9.8 mg/L), while in these plants we measured an increased pod weight (18.9 g), pod length (14.6 cm), number of pod per plant (22.6), pod yield per plant (1225 g), K+ ion and proline contents (18.9 mg/g and 28.8 μmol/g, respectively). Hence, this study allowed to conclude that the highest salinity level reduced the yield and altered the ionic status of okra plants, whereas GA3 and Si lowered the toxic effects of salinity and 100 mg/L GA3 along with 4 mmol silicon can be used in order to reduce salinity toxic effects