Variations in the Ethylene Biosynthesis and Sensitivity among Phalaenopsis Cultivars after Emasculation

In Phalaenopsis flowers, senescence can be advanced by emasculation (remove its pollinia and anther cap) and it is accompanied by a sudden upsurge in ethylene production. Previous study in our laboratory had indicated that there were variations in the duration for the appearance of flower wilting after emasculation among 20 Phalaenopsis cultivars tested; and the upsurge in ethylene production paralleled the timing of flower wilting. The object of this study was to correlate ethylene production with ethylene sensitivity as the possible explanation for this variation in response to emasculation among Phalaenopsis cultivars. Two cultivars from the fast-wilting group: Phal. OX Red Shoe and Dtps. Jiuhbao Red Rose, and two cultivars from the slow-wilting group: Dtps. Lih Jianq Firebird and Dtps. Mei Dar Diamond were used in this study; and the single-flower testing system developed in our lab was used to carry out the experiments. The flowers of the fast-wilting group showed symptom of senescence 2 days after emasculation and wilted completely after 5 days and the flowers of the slow-wilting group showed symptom of senescence 13 days after emasculation and wilted completely after 16 days. In the fast-wilting group, increase in ethylene production was observed 12 h after emasculation and reached its peak after 36 h, and in the slow-wilting group, increase in ethylene production was observed 11 days after emasculation and reached its peak at the 14th day. The regulation of ethylene biosynthesis in floral parts of the emasculated flower from these two groups was further studied. In the fast-wilting group, ethylene production from the upper column started to increase 6 h after emasculation, and the lower column started to increase after 12 h; both parts reached their peak after 36 h. The ethylene production rate raise from near 0 to >150 nL C2H4 g-1h-1. ACC oxidase activity in the column also started to increase 6 h after emasculation and reached its peak at 48 h. The magnitude of increase was more than a thousand folds. ACC content in the upper column started to increase 12 h after emasculation and reached its peak after 30 h. In the slow-wilting group, a small rise in ethylene production, ACC oxidase activity and ACC content were observed 8 h after emasculation and then declined to the level of non-emasculated control after 24 h. Until 12 days after emasculation, all of them started to increase again and reaching their peak after 14 days. The magnitude of increase was also over thousand-fold. The above result suggested that in both the fast-wiling and the slow-wilting group, a small amount of wound ethylene was produced between 6 to 12 h after emasculation. In the fast-wilting group, autocatalytic ethylene production was induced by the wound ethylene and resulted in the rapid senescence of flower. In the slow-wilting group, autocatalytic ethylene production was not induced by the wound ethylene and therefore flower senescence was delayed until 12 days later when the natural senescence of the flower took place. The difference in ethylene sensitivity of these two groups of Phalaenopsis was tested by applying low concentration of ethylene from 6 to 24 h to the flower. Treating intact flowers with 0.1 μL L-1 ethylene for 12 h induced the appearance of wilting symptom in 2 days in the fast-wilting group but had no effect in the slow-wilting group. The latter required at least 18 h of ethylene treatment to induce flower wilting. Treating emasculated flowers with 0.1 μL L-1 ethylene did not affect the wilting response in the fast-wilting group, but it induced flower wilting in the slow-wilting group with a 6 h treatment. These results indicated that the fast-wilting Phalaenopsis had higher sensitivity toward ethylene than the slow-wilting Phalaenopsis, and emasculation could increase the ethylene sensitivity in the slow-wilting Phalaenopsis.