Carbohydrate Changes in the Pseudobulbs of Oncidesa Gower Ramsey ‘Honey Angel’ during Vegetative and Reproductive Growth

Abstract

Pseudobulbs are carbohydrate storage organs in Oncidesa. A current pseudobulb forms on a developing vegetative shoot in each growth cycle and it becomes a back pseudobulb when the next vegetative shoot emerges. Both current and back pseudobulbs store carbohydrates, but their functions might differ because the inflorescence emerges from the new (current) shoot after the shoot has developed to a certain stage. This study investigated carbohydrate storage and use in current and back pseudobulbs. We analyzed carbohydrates in the current pseudobulb at five stages during inflorescence development. Glucose and fructose were the highest in the current pseudobulb in the first two stages, when the inflorescence was 10 to 35 cm tall. Then, both glucose and fructose decreased in the following stages to support inflorescence development, but starch increased at that time. In addition, we used Oncidesa with one or two new vegetative shoots to study the use of carbohydrates in pseudobulbs during growth cycles. In both plants with one or two shoots, glucose and fructose accumulated when current pseudobulbs formed, but plants with two new shoots had smaller current pseudobulbs and lower monosaccharide concentrations. Plants with two shoots also consumed more starch in all back pseudobulbs, whereas in the plants with one new shoot, starch only decreased significantly in the first back pseudobulb, which was closer to the new shoot. In addition, if an inflorescence did not develop in the previous growth cycle, new shoots used the monosaccharides that remained in the youngest back pseudobulb for growth; at the same time, starch accumulated in all back pseudobulbs. The current pseudobulb was the actively growing part. Its main carbohydrates were monosaccharides, which accounted for 25% of dry weight and Oncidesa used these carbohydrates mainly for inflorescence growth. After monosaccharides in the pseudobulb were used, the pseudobulb began to store starch. Back pseudobulbs, in which >50% of dry weight was starch, were the primary storage organs that supported new vegetative shoot growth and partly supported later inflorescence development that emerged from the new (current) shoot.