Objective Changes and photoperiod effects on the sugars that regulate the oncidium orchid plant development in growing stages were studied.

Methods Contents of moisture, soluble sugars (i.e., sucrose, glucose, fructose, T6P, etc.), and starch, as well as activities of the enzymes related to sucrose and starch synthesis in the enlarging pseudobulbs and budding leaves and flowers were measured. The effects of sunlight exposure on the changes were determined.

Results The contents of water, sugars (mostly sucrose and fructose), and starch in the pseudobulbs were higher than those in the leaves and varied significantly as the leaf and flower buds were developing. Throughout the stages, the pseudobulbs and leaves remained a high activity of sucrose synthase (SS) but low of sucrose phosphate synthase (SPS). The activity of soluble starch synthase (SSS) was higher than that of granule-bound starch synthase (GBSS), but both were relatively high in the expanding pseudobulbs. Photoperiod significantly affected the water and sugar contents and more so in the pseudobulbs than in the leaves.

Conclusion Affected by photoperiod, the sugars in the oncidium orchid pseudobulbs and leaves experienced dynamic and significant changes throughout the development stages.