Physiological Indices on Top-leaves and Pseudo-bulbs of Oncidium at Different Growth Stages

Changes on the physiological indices including chlorophyll, relative conductivity, soluble sugars, reducing sugars, starch, proline and POD on the top-leaves and pseudo-bulbs of 3-year-old Jinhui orchid, Oncidium, at different growth stages were monitored. It was found that the chlorophyll content in the top-leaves was the lowest, while the relative conductivity highest, at the expanding stage of the plants. They stabilized subsequently. The contents of soluble sugars, reducing sugars and starch in the pseudo-bulbs were higher than those in the top-leaves. Soluble sugars in both tissue parts increased initially, then decreased, and reached a peak at maturation. The reducing sugars in the top-leaves decreased in the beginning followed with an upward trend. Whereas, in the pseudo-bulbs, the content increased at first, then decreased, and followed by an increase, with two separate peaks occurred at the expanding and maturation stages. Starch in the top-leaves and the pseudo-bulbs increased at first, maximized at the lateral bud stage, then declined. In the beginning of the plant growth, both proline content and POD activity decreased, but increased afterward. The POD activity was low at maturation and lateral bud stages, while high at expanding and pseudo-bulb off-shooting stages.