Abstract
The ornamental scrub Hydrangea is generally not considered to be
particularly sensitive to the phytohormone ethylene. The present study aimed at
testing ethylene sensitivity in three different Hydrangea lines: 1, 2 and 3 taking into account the effect of temperature. Ethylene response was measured as leaf epinasty and leaf drop. Data indicated that higher temperature accelerates the effect of 2 μl L-1 ethylene over a 12-day period, and if the inhibitor 1-methylcyclopopene 1-MCP is able to attenuate this effect. Breeding line 1 and 3 dropped 3.8±0.6 and 5.0±0.4 leaves on average, respectively, during the 12-day experimental period. Non-treated controls of line 1 and 3 dropped 1.8±0.6 and 1.8±0.4 leaves, respectively. In contrast, line 2 did not show a significant response to ethylene treatment with a leaf drop of 2.1±0.3 leaves, compared to a leaf drop of 0.8±0.3 in non-treated controls.
Furthermore, the type of response between the lines varied. Line 2 was prone to
have higher epinasty/leaf drop ratio, compared to line 1. Interestingly, the data
indicated that ethylene had a flower inducing effect on 180-day sold plants with an acceleration of up to 30 days, compared to controls. 90-day-old plants treated with ethylene did not show decreased time to flower. This suggests that an age and developmental threshold exists for an initiation of flower development utilizing ethylene in Hydrangea. It is likely that the 90-day-old plants were not yet competent for the flower evocation signal, whereas the apical buds of the 180-day-old plants had undergone the required developmental processes making them competent.