6-Benzylaminopurine and kinetin modulations during in vitro propagation of Quercus robur (L.): an assessment of anatomical, biochemical, and physiological profiling of shoots

For many woody species, such as Quercus robur , cytokinins in the culture medium are required to maintain in vitro plant material. Among synthetic cytokinins, 6-benzylaminopurine (BAP) and kinetin (KIN) are the most frequently used. In addition to inducing shoots, cytokinins can cause morphophysiological disorders. Therefore, we aimed to investigate the anatomical, biochemical, and physiological alterations and profiles of Q. robur shoots exposed to two cytokinins, applied alone and in combination. Shoots previously established in vitro were transferred to WPM culture media supplemented with BAP at concentrations of 0, 1.25, and 3.50 µM combined with KIN at concentrations of 0, 0.62, and 1.25 µM totaling 9 treatments. Anatomical, physiological, and biochemical analyses were performed after 40 days of culture. BAP induced the formation of new buds with anatomically underdeveloped leaves; induced shoot-tip necrosis, which is considered a response to the inefficient transport of water and nutrients; reduced the thickness of the cell walls of phloem fibers; and decreased the content of phenolic compounds and photosynthetic pigments. These responses were less pronounced with co-exposure to KIN. In contrast, KIN alone stimulated a larger area of secondary xylem and more lignified cell walls. BAP can induce shoots with underdeveloped anatomical and biochemical characteristics. Shoots that grew with KIN alone had stem and leaf anatomical characteristics, indicating greater commitment to cellular differentiation than proliferation. When both cytokinins are combined, KIN can partially mitigate the deleterious effects of BAP on in vitro growth.