Evaluation of water deficite stress and plant growth-promoting rhizobacteria effect on some of morphological traits and expression level of TDC and STR at the root of Catharanthus roseus

Catharanthus roseus is one of the most extensively investigated medicinal plants. Increase the concentrations of TIAs in plant organs, by biotic and abiotic treatments, is an important breeding objective on C. roseus. The effect of plant growth promoting rhizobacteria, Pseudomonas fluorescens and Azospirillum brasilense separately and in combination along with moisture treatment at two levels were tested in Catharanthus roseus as a factorial experiment based on randomized complete block design in three replications. Effect of treatments was evaluated 30 days after applying moisture treatments on some of morphological traits and Tdc and Str genes expression at the root of plant using qRT-PCR reaction. Water deficit significantly increased root length but it had no significant effect on the expression of these genes. Treatment with A. brasilense in normal condition enhanced length, volume and surface of roots, also significantly increased Str key gene expression. P. fluorescens had a positive and significant effect on the expression of the studied genes under normal and stress conditions compared to the control plants, despite the decrease in the amount of morphological traits. P. fluorescens and A. brasilense, separately, performed better in terms of their effects on the expression of the studied genes and increased the gene expression in normal and stress conditions compared to control plants. It is expected that by increasing the expression of Tdc and Str genes, the product of these genes as well as the final products of TIAs biosynthetic pathway, including ajmalicin content enhance at the root of periwinkle plant.