Abstract
Ethylene can hasten an onset of endogenous rise and senescence in plants. Since ethylene exposure to plants induces a formation of abscising layer and leads to abscission of florets, water uptake to petals from flower stalk might be prevented. We indicated that exogeneous ethylene caused complex physiological changes of petals in intact flowering clones of orchid, Dendrobium phalaenopsis cv.during seven days; decrease in both ^1H-NMR relaxation times (T_1 and T_2) and water content, and increase in hue angle indicating tone of color with senescence process. Dynamic states of water are stated as several water compartments such as free water, loosely bound water and bound water which originate from vacuole, cytoplasm and apoplastic region, respectively. Long T_1 of the cellular water in the orchid petals decreased and it well corresponded to water content in the ethylene-treated clones. It suggested that vacuolar water disappeared in the petal tissues. Furthermore, long and short T_2s were not maintained in the petal tissues exposed to ethylene. From these results, change in the vacuolar water component of the petals was better monitored by T_1 while the cytosolic water which relates to their molecular mobility could be shown by short T_2 in the orchid petals. This study clearly indicated a basic information concerning petal senescing process evaluated by NMR relaxation times (T_1, T_2) of water proton in the ethylene-sensitive plant.
