Petal blackening and lack of bud opening in cut lotus flowers (Nelumbo nucifera): Role of adverse water relations

摘要

Lotus flowers (Nelumbo nucifera Gaertn.) are commercially sold as closed buds. When placed in water the buds fail to open and the outer petals show rapid blackening. We investigated whether this is due to adverse water relations. Placing a plastic bag over the flower head delayed petal blackening, indicating that it was induced by early water stress. This treatment did not result in bud opening. A rapid occlusion of the stem xylem was found. Four possible causes of this occlusion were investigated:air. uptake into the xylem, microorganisms in the vase solution, a plant-induced effect, and exuded latex. Preventing the uptake of air into the stem ends did not affect water uptake. Inclusion in the vase water of antibacterial compounds, or antioxidants that inhibit the plant-induced xylem blockage in other species, similarly did not alleviate the xylem occlusion. Cut stems exuded copious latex, close to the opened xylem conduits. Latex exudation was prevented by cutting under water, allow the latex to flow out, and cut again in air, within I cm from the previous cut This treatment did not promote water uptake of the cut stems. A pulse treatment with citric acid also reduced latex flow, but also did not prevent the decrease in water uptake. Treatment with ethephon or GA(3) delayed the xylem occlusion, which suggests that it is induced by the plant itself. Only GA(3) delayed petal blackening. None of these treatments promoted flower opening. It is concluded that adverse water relations are a cause of early petal blackening in cut lotus, but is not a cause of the lack of bud opening. The adverse water relations are apparently due to a plant-induced xylem occlusion which is different from those studied thus far in other species