Drought is one of the major constraints on agricultural productivity worldwide and is likely to further increase. Several adaptations and mitigation strategies are required to cope with drought stress. Plant growth promoting rhizobacteria (PGPR) could play a significant role in alleviation of drought stress in plants. These beneficial microorganisms colonize the rhizosphere/endo-rhizosphere of plants and impart drought tolerance by producing exopolysaccharides (EPS), phytohormones, 1-aminocyclopropane- 1-carboxylate (ACC) deaminase, volatile compounds, inducing accumulation of osmolytes, antioxidants, upregulation or down regulation of stress responsive genes and alteration in root morphology in acquisition of drought tolerance. The term Induced Systemic Tolerance (IST) was coined for physical and chemical changes induced by microorganisms in plants which results in enhanced tolerance to drought stresses. In the present review we elaborate on the role of PGPR in helping plants to cope with drought stress.

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Aim: To investigate the effect of different types of nanoparticles on the compressive strength (CS) and diametral tensile strength (DTS) of type IV dental stones. Materials and methods: A total of 100 specimens were made from the mould for all five groups. Four commercially available nanoparticles (aluminium oxide (Al 2 O 3 ), silicon dioxide (SiO 2 ), zinc oxide (ZnO), and zirconium oxide (ZrO 2 )) were used in this study in a concentration of 10%. CS and DTS tests were performed in a universal test machine. The data were statistically analysed using ANOVA and Student's t-test. Results: The interaction between nanoparticles and the type of dental stone was found to be statistically significant (p < 0.05). CS and DTS values decreased by adding all four nanoparticles. The lowest CS and DTS were observed in 10% ZnO nanoparticles when added to type IV dental stone. Conclusion: It was concluded that the addition of nanoparticles (Al 2 O 3 , SiO 2 , ZnO, and ZrO 2 ) to die stone significantly decreased the CS and DTS for all groups. Among all groups, the incorporation of 10% ZrO 2 nanoparticles (group E) to die stone showed significantly less decrease in CS and DTS compared to Al 2 O 3 , SiO 2 , and ZnO. Incorporation of ZnO nanoparticles, on the other hand, showed a significantly more amount of decrease in the CS and DTS compared to Al 2 O 3 , SiO 2 , and ZrO 2 .