Involvement of ethylene in potato microtuber dormancy

Abstract

Potato (Solanum tuberosum L.) single-node explants undergoing in vitro tuberization produced detectable amounts of ethylene throughout tuber development, and the resulting microtubers were completely dormant (endodormant) for at least 12 to 15 weeks. The rate of ethylene production by tuberizing explants was highest during the initial 2 weeks of in vitro culture and declined thereafter. Continuous exposure of developing microtubers to the noncompetitive ethylene antagonist AgNO3 via the culture medium resulted in a dose-dependent increase in precocious sprouting. The effect of AgNO3 on the premature loss of microtuber endodormancy was observed after 3 weeks of culture. Similarly, continuous exposure of developing microtubers to the competitive ethylene antagonist 2, 5-norbornadiene (NBD) at concentrations of 2 mL/L (gas phase) or greater also resulted in a dose-dependent increase in premature sprouting. Exogenous ethylene reversed this response and inhibited the precocious sprouting of NBD-treated microtubers. NBD treatment was effective only when it was begun within 7 d of the start of in vitro explant culture. These results indicate that endogenous ethylene is essential for the full expression of potato microtuber endodormancy, and that its involvement may be restricted to the initial period of endodormancy development.

Figure 1

Changes in the rate of ethylene production by single-node explants during in vitro culture. Groups of three explants were aseptically removed from the culture vessels, incubated overnight at 18°C ± 1°C in sealed tubes, and the accumulated ethylene was determined by GC. Bars indicate ±se (n = 3).

Figure 2

Effects of increasing concentrations of AgNO₃ on microtuber sprouting percentage. Groups of 10 explants were exposed to AgNO₃ via the culture medium. Sprouting percentage was determined after 3 (hatched bars) and 10 (solid bars) weeks of culture. Bars indicate ±se (n = 3).

Figure 3

Effects of increasing concentrations of NBD on microtuber sprouting percentage. On the day after excision and transplanting, three groups of 10 explants were sealed in Plexiglas chambers (4.5 L) containing the indicated concentrations of NBD. The chambers were incubated in the dark at 18°C ± 1°C, and the sprouting percentage was determined after 10 weeks of culture. Bars indicate ±se (n = 3).

Figure 4

Effects of increasing concentrations of ethylene on sprouting percentage in NBD-treated explants. On the day after excision and transplanting, three groups of 10 explants were sealed in Plexiglas chambers (4.5 L) containing 3 mL/L NBD in the absence or presence of the indicated concentrations (microliters per liter) of ethylene. Con, Controls (explants sealed in chambers receiving no treatment). The chambers were incubated in the dark at 18°C ± 1°C, and the sprouting percentage was determined after 10 weeks of culture. Bars indicate ±se (n = 3).

Figure 5

Effects of culture age on NBD-induced precocious sprouting. On the day after excision and transplanting, explants were incubated in sealed Plexiglas chambers (4.5 L) in the dark at 18°C ± 1°C. At the indicated times after the initiation of in vitro culture, three groups of 10 explants were exposed to NBD (3 mL/L). Con, Controls (explants sealed in chambers receiving no treatment). Sprouting percentage was determined after 10 weeks of culture. Bars indicate ±se (n = 3).