Role of ethylene and jasmonic acid on rhizome induction and growth in rhubarb (Rheum rhabarbarum L.)

Abstract

Experiments were conducted to elucidate the hormonal induction and regulation of rhizome growth in rhubarb (Rheum rhabarbarum L.). It was found that ethylene is the key regulator of rhizome induction and development. The role of jasmonic acid (JA) and its interaction with ethylene in rhizome induction and growth were also examined. Both ethylene and JA have a significant effect on promoting rhizome formation in vitro. Conversely, the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) (1.5 μM) inhibited rhizome induction in multiple-shoot clumps in vitro, and suppressed the stimulatory effects of exogenously applied ethephon (1 mg l⁻¹) and JA (10 ng l⁻¹) in promoting mini-rhizome formation, further confirming the role of endogenous ethylene in the process. In addition, rhizome growth was significantly enhanced in the presence of both ethylene and JA (ethephon 1 mg l⁻¹ and JA 10 ng l⁻¹) compared to JA alone. These results suggest that endogenous ethylene is the key regulator of rhizome growth in rhubarb and JA promotes rhizome formation, possibly through inducing endogenous ethylene synthesis.

Appendix: details of the plant growth regulator application

Plant-cell-tested commercial formulations of growth regulators from Sigma-Aldrich, Canada, were used. Stock solutions of GA₃ (1,000 mg l⁻¹), ABA (100 mg l⁻¹) and JA (1,000 mg l⁻¹) were prepared by dissolving them first in four drops of 95% ethanol and diluted with distilled water to the final stock concentrations. ACC, AVG and ethephon (Sigma-Aldrich, Canada) were dissolved in distilled water to make the stock solutions of concentrations 1,000 mg l⁻¹, 50 mg l⁻¹ and 1,000 mg l⁻¹, respectively. ABA and GA₃ were autoclaved with other media components, whereas all other growth regulators were filter-sterilised and added to the autoclaved culture media after cooling to 45–50°C. An ethanol control (with four drops of 95% ethanol) and a distilled water control were maintained in all three sets of experiments, since most of the plant growth regulators (PGRs) were dissolved in ethanol before making up the stock solution.

The concentrations of each PGR used in each stage of the experiments are given below.

Treatments in stage I

• 10 ng l⁻¹, 1 μg l⁻¹, 10 μg l⁻¹, 1 mg l⁻¹ JA

• 0.1 μg l⁻¹, 1 μg l⁻¹, 10 μg l⁻¹, 100 μg l⁻¹ ABA

• 10 mg l⁻¹, 20 mg l⁻¹, 40 mg l⁻¹, 80 mg l⁻¹ GA₃

• 1 mg l⁻¹, 10 mg l⁻¹, 50 mg l⁻¹ ethephon

• Control DW—control with distilled water (DW)

• Control EtOH—control with ethanol (EtOH)

Treatments in stage II

• 1 mg l⁻¹, 10 mg l⁻¹, 50 mg l⁻¹ ethephon

• 0.5 mM, 1.0 mM, 1.5 mM ACC

• 0.5 μM, 1.0 μM, 1.5 μM AVG

• Control DW—control with distilled water (DW)

• Control EtOH—control with ethanol (EtOH)

Treatments in stage III

• 1 mg l⁻¹, 10 mg l⁻¹ ethephon

• 10 ng l⁻¹, 1 μg l⁻¹ JA

• 1 mg l⁻¹ ethephon and 1.5 μM AVG

• 10 ng l⁻¹ JA and 1.5 μM AVG

• 10 ng l⁻¹ JA and 1 mg l⁻¹ ethephon

• 10 ng l⁻¹ JA, 1 mg l⁻¹ ethephon and 1.5 μM AVG

• Control DW—control with distilled water (DW)

• Control EtOH—control with ethanol (EtOH)