Effects of brassinosteroid, auxin, and cytokinin on ethylene production in Arabidopsis thaliana plants

Abstract

Inflorescence stalks produced the highest amount of ethylene in response to IAA as compared with other plant parts tested. Leaf age had an effect on IAA-induced ethylene with the youngest leaves showing the greatest stimulation. The highest amount of IAA-induced ethylene was produced in the root or inflorescence tip with regions below this producing less. Inflorescence stalks treated with IAA, 2,4-D, or NAA over a range of concentrations exhibited an increase in ethylene production starting at 1 microM with increasingly greater responses up to 100 microM, followed by a plateau at 500 microM and a significant decline at 1000 microM. Both 2,4-D and NAA elicited a greater response than IAA at all concentrations tested in inflorescence stalks. Inflorescence leaves treated with IAA, 2,4-D, or NAA exhibited the same trend as inflorescence stalks. However, they produced significantly less ethylene. Inflorescence stalks and leaves treated with 100 microM IAA exhibited a dramatic increase in ethylene production 2 h following treatment initiation. Inflorescence stalks showed a further increase 4 h following treatment initiation and no further increase at 6 h. However, there was a slight decline between 6 h and 24 h. Inflorescence leaves exhibited similar rates of IAA-induced ethylene between 2 h and 24 h. Light and high temperature caused a decrease in IAA-induced ethylene in both inflorescence stalks and leaves. Three auxin-insensitive mutants were evaluated for their inflorescence's responsiveness to IAA. aux2 did not produce ethylene in response to 100 microM IAA, while axr1-3 and axr1-12 showed reduced levels of IAA-induced ethylene as compared with Columbia wild type. Inflorescences treated with brassinolide alone had no effect on ethylene production. However, when brassinolide was used in combination with IAA there was a dramatic increase in ethylene production above the induction promoted by IAA alone.

Fig. 1.

Effects of IAA on ethylene production in Arabidopsis Columbia WT and three auxin-insensitive mutants, axr1-12, axr1-3, and axr2. Inflorescences, 4–6 cm in length with flowers partially open, were taken from 35- to 45-d-old Arabidopsis plants. The inflorescence stalk was cut into five 4 mm sections and put in 12×75 mm test tubes containing 200 μl of 100 μM IAA (white columns) or water control (black columns). The tubes were then sealed, placed in the dark and ethylene analysed after 24 h. Values are expressed as the mean of four replications ±standard error.

Fig. 2.

Effects of different auxins on ethylene production. Inflorescences, 4–6 cm in length with flowers partially open, were taken from 35- to 45-d-old Arabidopsis plants. The inflorescence tip containing the flower was removed and the top 2 cm from the inflorescence stalk (white columns) or the top two leaves (black columns) were used. The inflorescence stalk was cut into five 4 mm sections. The plant parts were put into varying concentrations of (A). IAA, (B) NAA, (C) 2,4-D, or (D) TRP in 12×75 mm test tubes containing 200 μl of treatment solution. The tubes were then sealed, placed in the dark, and ethylene analysed after 24 h. Values are expressed as the mean of four replications ±standard error.