The in planta effect of selected strains was also assessed through various biochemical parameters including chlorophyll a and b content as well as nitrate reductase activity and proline concentration (Table 3). Inoculation of tomato seeds with the isolated bacterial strains resulted in plants with significantly elevated chlorophyll a, except for the strains Pr17, Pr31 and Pr50. This effect was clearly evidenced with the strain Pr8 where chlorophyll a and b were enhanced by 75% and 32%, respectively. Nitrate reductase was also significantly enhanced after inoculation with almost all strains, except with Pr17 and Pr31. The highest activity was reported for the strains Pr6 and Pr8 and was about 112% and 62%, respectively higher than the control. However, with Pr26 and Pr50 this activity was drastically inhibited. All the strains increased Proline content in tomato plants, with the exception of the strains Pr17 and Pr31. The maximum concentration of proline is recorded in the plants inoculated with strain Pr8 and was four times greater than that of the control plants.