Changes in Sugar-related Enzymes during Wilting of Cut Delphinium Flowers.

Abstract

Abscission of sepals from cut delphinium flowers is prevented by treatment with silver thiosulphate (STS). However, the sepals still wilt and the pistils develop which reduce flower quality. To understand the process of wilting, unrelated to that initiated by ethylene, sugar uptake and metabolism in cut delphinium flowers were examined. STS-treated delphinium sepals wilted 4 to 9 days after harvest accompanied by a decrease in fresh weight while the pistils continued to grow. A decrease in water content with a simultaneous reduction in soluble carbohydrate content suggested that wilting is attributable to a decrease in soluble carbohydrates as the osmoticum. The activities of cell wall and soluble acid invertase, sucrose synthase (SS), and mannitol dehydrogenase (MDH) were measured because these enzymes are related to sink mechanism in sucrose- and mannitol-translocating plants. Cell wall invertase activity and p-chloromercuri-benzenesulfonic acid (PCMBS)-sensitive sucrose uptake by the sepals decreased to a very low level during wilting. When intact florets were supplied with 14C-sucrose, a change in sucrose distribution in sepals corresponded with that in cell wall invertase. Therefore, the reduction in cell wall invertase activity that decreases the soluble carbohydrates as osmoticum could be related to sepal wilting. SS activity that is known to be important in sink metabolism also decreased during sepal wilting, suggesting that SS was related to the wilting. MDH activity in pistils paralleled their rapid growth while cell wall invertase and SS activities remained consistently high except at harvest.