In vitro clonal propagation of Billbergia zebrina (Bromeliaceae) and analysis of anatomy and physiology of regenerated plantlets

During in vitro multiplication of horticulture plant species, synthetic cytokinins such as 6-benzyl-aminopurine (BA) can affect the microshoot formation. Murashige and Skoog culture medium (MS) can also act as a morphogenetic response modulator. The aim was to analyze the effects of BA and a gradient of MS salts on the morphophysiological status of Billbergia zebrina microshoots. Plantlets were cultured with a gradient of MS salts (50%, 100%, 150%, or 200%) supplemented with two BA levels (0 or 13 mu M). After 50 days of culture, stomatal parameters, contents of photosynthet-ic pigments, and chlorophyll fluorescence were assessed. Plantlets cultured in all media without BA presented a low budding rate. In contrast, plantlets cultured with BA showed 100% budding. With 13 mu M BA, the leaves presented bigger stomata and wider opening. Plantlets cultured with BA had lower contents of photosynthetic pigments. MS treatments without BA supplementation did not show any change in the pigments' ratios. Plantlets cultured with BA had lower activity of the water-splitting complex and signs of photoinhibition damage. This resulted in the reduced performance of the photosynthetic apparatus. BA exposure can ensure the inducement of adven-titious microshoots. BA at the tested concentration can induce morphophysiological disorders, irrespective of MS salt concentration.