Plant Growth-Promoting Rhizobacterium (PGPR) represents a wide variety of soil bacteria that, when grown in association with a host plant, result in stimulation of growth of their host. The aim of this study was to investigate the influence of inoculation with a PGPR, Pseudomonas fluorescence, alone or in combination with an arbuscular mycorrhizal fungus, Glomus mosseae (Nicol. & Gerd.), on antioxidant enzyme activities (catalase (CAT) and peroxidase (POX)), phosphatase activity, solutes accumulation, growth and minerals nutrient uptake in shoots of bean (Phaseolus vulgaris L.) affected by three levels of salt stress. Salinity decreased bean growth, regardless of the biological treatment and the salt stress level. The plants inoculated with P. fluorescence had significantly greater shoot biomass than the control plants at all salinity levels, whereas the mycorrhizal inoculation treatments were only effective in increasing shoot biomass at a low salinity level. The plants inoculated with P. fluorescence presented higher concentrations of shoots’ K+ and lower concentrations of shoots’ Na+ under high salt conditions. Salt stress increased shoots’ proline concentration, particularly in plants inoculated with the PGPR. Increasing salinity stress raised significantly the antioxidant enzyme activities, including those of total POX and CAT, of bean shoots compared with their corresponding nonstressed plants. The PGPR strain induced a higher increase in these antioxidant enzymes in response to severe salinity. Inoculation with selected PGPR could serve as a useful tool for alleviating salinity stress in salt-sensitive plants.

The experiment was conducted in order to study effects of seeds priming with gibberellic acid (GA3) at 0, 3, 5 and 8 mM on germination, growth and antioxidant enzymes activity in alfalfa seedlings under salinity stress (200 mM NaCl). All control seeds germinated. The rate of germinated seeds was reduced to 48% in the presence of NaCl, and increased to 76% after seeds priming with 5 mM GA3. Priming with 5 mM GA3 was also correlated with an increase of dry weight of seedlings derived from both stressed and non-stressed seeds as well as with the reduction of electrolyte leakage (EL) and malondialdehyde (MDA) level in salt stressed seedlings. The activity of superoxide dismutase, catalase, guaiacol peroxidase and ascorbate peroxidase in primed and non-primed seeds increased in the presence of NaCl and after priming of seeds with 5 mM GA3, whereas only small effect on glutathione reductase activity in both primed and non-primed seeds was observed. The total ascorbate level was higher in both stressed and non-stressed seedlings from primed seeds. These results suggest that GA3 priming might increase the salt tolerance of alfalfa seedlings through enhancing the activities of antioxidant enzymes and reducing the membrane damage as estimated using biomarkers, EL index and MDA content.

ABSTRACT. Priming is one of the seed enhancement methods that might be resulted in increasing seed performance (germination and emergence) under stress conditions, such as salinity. Salinity is a major environmental stress which adversely affects germination and seedling establishment in a wide variety of crops. The experiment was arranged as a factorial in completely randomized design (CRD) at Seed Research Laboratory of College of Agriculture, University of Tehran, Iran. The objective of this research was to evaluate the effect of different priming methods on seed germination of two medicinal plants including lemon balm (Melissa officinalis L.) and cumin (Cuminum cyminum L.) under salinity stress. Treatments were combinations of two levels of salinity stress (0 and 10 dsm -1 ) and five levels of priming (control = non-priming), GA 3 , manitol, NaCl and distilled water) with three replications. Seeds of lemon balm and cumin were primed for 24 h at 25°C. Results revealed that different growth traits (including germination percentage, germination rate, seedling dry weight, plumule and radical length) significantly (p=0.05) decreased with applying salinity. However, priming of seeds with different materials particularly GA 3 was useful for alleviating salt stress effects and improving germination and seedling establishment under salt stress. Under salinity condition, primed seeds possessed more germination and emergence than control. The result of this experiment is consistent with the hypothesis that under salinity stress, priming can prepare a suitable metabolic reaction in seeds and can improve seed germination performance and seedling establishment.

The influence of the colonization with arbuscular mycorrhizal (AM) fungus, Glomus mosseae (Nicolson and Gerdemann), on characteristics of growth, osmotic adjustment compounds and activity of antioxidant enzymes in nodules of salt-stressed soybean (Glycine max (L.) Merr.) was studied in this experiment. The pot experiment was arranged as a factorial in randomized complete block design with four replications at greenhouse of College of Agriculture, Tehran University, Iran. Results indicated that the contents of glycine betaine and proline in nodules were higher in inoculated than in noninoculated plants. AM fungal colonization increased the activities of superoxide dismutase, catalase, and peroxidase in the nodules. The results indicate that the AM fungus is capable of alleviating the damage caused by salt stress on symbiotic nitrogen fixation of soybean plants by increasing the accumulation of compatible osmolytes and by increased antioxidant enzyme activity. Consequently, arbuscular mycorrhiza formation highly enhanced the salinity tolerance of soybean plant, which increased symbiotic nitrogen fixation and promoted plant growth. Posledično tvorba arbuskularne mikorize pri soji močno poveča toleranco na slanostni stres s povečano simbiontsko vezavo dušika, kar pospeši rast.

Bami cultivar of alfalfa (Medicago sativa) was inoculated with salt-tolerant Sinorhizobium meliloti in solution culture with different salt concentrations (0, 50, 75 and 100 mmoles 1-1NaCl) added immediately at the time of inoculation. The results indicated that S. meliloti formed an infective and effective symbiosis with alfalfa under saline and nonsaline conditions. Salinity significantly decreased shoot and root dry weight, nodule weight and mean nodule weight. Roots were more sensitive than shoots, and N2 fixation was more sensitive to salinity than was plant growth. Analyses of ammonium assimilating enzymes in the nodule showed that glutamine synthetase appeared to be more tolerant to salinity than glutamate synthase, and that it limits ammonium assimilation under saline stress.