Developmental Changes in Soluble and Cell Wall-bound Invertases in Floral Organs of Lilium longiflorum

Easter lily flower buds at five stages of development (stage 1, 3–4 cm in length; stage 2, 6–7 cm; stage 3, 9–10 cm; stage 4, unopened buds, 13–14 cm; and stage 5, open flower 1 day after anthesis) were harvested, and flower organs were dissected for invertase assay. On a fresh weight (FW) basis, anthers had the highest soluble invertase activity (about 10-fold greater) than all other organs reaching to 15 units/g FW by the stage 2. The activity dropped to about 3 units/g FW at stage 3 and 4, and then increased up to 10 units/g FW in open flowers. Specific activity (units per mg of protein) also showed the same trend. On a specific activity basis, sepal invertase activity steadily increased during bud development, but was relatively constant on a fresh weight basis. stigma, style, and ovary, soluble invertase activity expressed on a FW and specific activity basis steadily increased as bud development. Filament soluble invertase activity on FW basis dropped at the stage 2 and 3, while specific activity steadily increased during bud development. Cell wall-bound invertase activity (released with 1 m NaCl) was present in all flower organs. However, soluble activity accounted for the most of total activity in sepal, ovary and filament (about 90%). About 75% of total activity was soluble in anther and style, whereas nearly equal amounts of soluble and cell wall activities were present in the stigma. The cell wall bound invertase activity increased throughout the bud development in sepal, stigma, style, and ovary parallel to soluble activity. Anther cell wall-bound activity fluctuated in a similar pattern as the soluble activity.