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Effect of cytokinins on tissue structure, plastid development and photosynthetic proteins in tissue culture of PINUS PONDEROSA dougl. cotyledons during organogenesis Mazari Hiriart, Alicia


The cytokinins, benzyladenine and 2-isopentenyl adenine, promoted the in vitro formation of meristematic centers which led to bud and shoot production on excised cotyledons of Pinus ponderosa Dougl. The organogenic response was dependent on the time of exposure to these growth regulators. Differences between meristematic, non-meristematic regions, and cotyledons cultured on growth regulator free medium, were observed by day 5 in culture. Plastids in newly meristematic cells showed poorly developed thylakoid membranes and some grana, whereas cells in non-meristematic tissues and non-cytokinin treated tissues had well developed inner membranes, more thylakoid membranes and grana than plastids of meristematic cells. A decline in total protein content was detected during the first days in culture. The decline was more rapid on growth regulator free than on cytokinin treated cotyledons. This trend contrasted with chloroplast markers (chlorophyll and 5 polypeptides associated with photosynthesis), which were present in lower concentrations in cytokinin treated cotyledons than in those cultured in growth regulator free medium. Both benzyladenine and 2-isopentenyl adenine were effective in inhibiting the accumulation of at least two photosynthetic polypeptides in cotyledons in the first 24 hours in culture. The ability of cotyledons to respond in this way to cytokinins was lost after only three days in culture in growth regulator free medium.

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