Physiological Changes During the Germination of Cattleya aurantiaca (Orchidaceae)

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Abstract
Seeds of C. aurantiaca grown asymbiotically on a medium containing sucrose as the sole source of organic carbon developed into leaf-bearing plants. Those sown on the same medium without sugar reached the protocorm stage but did not differentiate further. Cross transfers of seedlings between the 2 media indicated that following 21-30 days of growth on the sucrose-containing medium, subsequent development may proceed in the absence of sugar. Levels of chlorophyll and ribulose-1,5-diphosphate carboxylase were monitored and related to the ability of young seedlings to photosynthesize. A direct relationship between chlorophyll content and photosynthesis was not found. Increases in the activity of the enzyme were closely paralleled by increases in photosynthesis. A direct relationship was not found between chlorophyll a/b ratios and photosynthetic capacity. Germinating seeds and seedlings grown in the absence of exogenous carbohydrate were unable to convert appreciable amounts of labeled acetate to sugar.