Azospirillum brasilense inoculation, auxin induction and culture medium composition modify the profile of antioxidant enzymes during in vitro rhizogenesis of pink lapacho

Optimal in vitro plant growth can be stimulated by selecting specific nutritional and environmental conditions. However, the culture conditions, dissection, and disinfection of plant material are stressful and may induce disruption of the plant physiological homeostasis. This can be modified by inoculation with rhizobacteria as Azospirillum brasilense, by the culture medium type, and by auxin induction. Here, we performed rooting experiments in two auxin-free culture media with ‘pink lapacho’ (Handroanthus impetiginosus) shoots previously induced with 0, 10, 30, or 50 μM indole butyric acid (IBA) for 3 days and inoculated with A. brasilense Cd and Az39. Peroxidase (PO), phenylalanine ammonia-lyase (PAL), and polyphenol oxidase (PPO) activities were determined on days 0, 3, 6, 9, 12, and 15. Also, weekly absolute rooting percentage was evaluated. All enzymatic activities were higher in A. brasilense-inoculated shoots, linked to early and high rooting percentage. The culture medium type and IBA concentration also affected enzymatic activities. The positive correlation between PO and PAL activities on day 9 and successful final in vitro rooting of H. impetiginosus allows using these activities as early markers of rhizogenesis reducing the selection time of easy-to-root plants. The changes in enzymatic levels performed here are discussed on the basis of their role in rooting and in vitro stress and contribute to the knowledge of the physiology of trees and their interaction with rhizobacteria.