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 pro les 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 d of culture. BAP induced the formation of new buds with anatomically underdeveloped leaves; induced shoot-tip necrosis, which is considered a response to the ine cient transport of water and nutrients; reduced the thickness of the cell walls of phloem bers; 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 ligni ed 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.

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In order to establish a link between the evolutionary history and the photochemical attributes, measurements of chlorophyll (Chl) a fluorescence were made in Cattleya warneri, C. shofieldiana and C. harrisoniana exposed to high irradiance for 5, 35, and 120 min (hereafter referred to as treatments T5, T35, and T120, respectively). The following questions are addressed: (1) Is the increased energy dissipation enough to counterbalance the excess energy that drives photosynthesis at different times of high irradiance exposure? (2) Is there an influence of the incidence and duration of light radiation on Cattleya species in full sunlight, compared to Cattleya species submitted to low irradiance? Higher relative variable fluorescence at the J-step (Vj) values followed by the lower quantum yield of electron transport (ψEo) indicate the accumulation of reduced Quinone A (QA) proportionally of sunflecks exposure time in C. warneri. The higher performance index (PIABS) and plasticity index values in C. schofieldiana indicate higher efficiency in modulating the photosynthetic apparatus under sunflecks. C. harrisoniana shows the lowest plasticity index, suppression of maximum fluorescence (Fm), and no recovery of PIABS after sunflecks. This study evidences the importance of physiological plasticity in the current geographic distribution of Cattleya in response to light pulses in species derived from fragmented habitats and the maintenance of shade to species of more primitive clades.

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 d 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.

No abstract