Effectiveness of exogenous GA3 for dormancy breaking in invasive Aegilops tauschii, and effect on germination physiology.
The invasion of Aegilops tauschii has seriously threatened the production of wheat in China. The seeds of A. tauschii display obvious dormancy. This research studied the effectiveness of exogenous gibberellin for breaking seed dormancy and effects on germination behavior and physiological traits of invasive A. tauschii, in order to provide technical support for control efforts. Seeds of A. tauschii were imbibed for 24 h in different concentrations of gibberellic acid (GA3) solution (100, 200, 300, 400, 500 mg . L-1) or imbibed in distilled water as a Control (0 mg . L-1 GA3), under light or dark conditions, and seed germination rate and germination energy measured over a 35 day period. For seeds of Control and 500 mg . L-1 GA3 treatments, superoxide dismutase (SOD) and peroxidase (POD) activities and malondialdehyde (MDA) content were also measured at 7 day intervals over the 35 day experiment, as were endogenous levels of hormones GA3, indoleacetic acid (IAA), zeatin Riboside (ZR) and abscisic acid (ABA). It was found that: (1) The Control treatment germination was 40% and 21% in light and dark conditions, respectively, and exhibited a near linear GA3 dose response, reaching 89% and 71% in light and dark conditions, respectively, for the 500 mg . L-1 GA3 treatment. Both the GA3 and light responses were highly statistically significant, indicating that light exposure enhanced the germination of A. tauschii. (2) Compared with the Control treatment, the activities of SOD and POD in seeds were increased in the 500 mg . L-1 GA3 treatment, the degree of cytoplasmic membrane oxidation was reduced, and the content of MDA was decreased, thus altering seed physiology in a direction favorable for germination. In addition, exogenous treatment with 500 mg . L-1 GA3 promoted the production of endogenous GA3, IAA and ZR in seeds, and decreased the content of endogenous ABA, while the ratios of GA3 ABA, IAA : ABA and ZR : ABA were significantly higher than those of controls imbibed in distilled water, and these GA3 mediated changes would also be expected to promote the germination of A. tauschii.