Carbohydrate Physiology of Orchid Seedlings. III. Hydrolysis of Maltooligosaccharides by Phalaenopsis (Orchidaceae) Seedlings

Germinating seeds and developing seedlings of Phalaenopsis Habsburg and Phalaenopsis Ruth Burton × (Phalaenopsis Abendrot × Phalaenopsis Abendrot) can utilize glucose, maltose, maltotriose, maltotetraose, maltopentaose, maltohexaose, and maltoheptaose as carbon sources. Fresh weight decreased significantly with increased polymerization from glucose through maltoheptaose. Seedling survival declined on higher molecular weight sugars reaching levels which were significantly different from those on glucose. Sugar uptake increased moderately with increasing molecular weight of oligomers. The maltooligosaccharides used in these experiments are hydrolyzed by the orchid seedlings and of the sugars which can support good growth glucose, but not maltose accumulate in culture media. As a result, media which supported seedlings contained substantial levels of glucose, the starting sugars, and decreasing amounts of the next shorter oligomers. This suggests enzymatic endwise hydrolysis of these maltooligosaccharides. Similar results were obtained with Phalaenopsis seedlings produced from seeds which were germinated on sugar-free medium and transferred to a solution containing the same oligomers. Sugars in media which did not support seedlings were not hydrolyzed.