Research Accomplishment Reports 2009

The Role of Ethylene and Polyamine Interaction in the Time to Radicle Protrusion during Seed Germination

R.L. Geneve
Department of Horticulture

 

Non-Technical Summary

The time between sowing and radicle protrusion is the most vulnerable time for establishment of a usable seedling. Minimizing this time increases the potential for high seedling stand establishment, which equates to increased yield. Ethylene and polyamines share a common biosynthetic precursor and it has been shown that these two pathways can be antagonistic during certain times in plant development. Therefore, the proposed project will investigate the relationship between ethylene and polyamine biosynthesis as determinants for time to radicle protrusion.

2009 Project Description

The major focus of this project was the impact of ethylene on germination, vigor and dormancy in seeds. Ethylene is produced during germination for most seed types, but its physiological role is not completely elucidated.

It was shown using exogenous application of ethylene, ethylene inhibitors and by altering ethylene perception in mutants and transgenic plants that ethylene is involved with determining the time required for radicle emergence. Exogenous application of the ethylene precursor ACC significantly increased germination speed in all seed types evaluated. It was determined that for Arabidopsis, ethylene reduced the seeds sensitivity to ABA and that this interaction may be responsible for the reduced time to radicle emergence in ethylene-treated seeds. However, this relationship between ethylene and ABA was not observed for tomato suggested an alternative mechanism for ethylene's action on tomato seeds.

Ethylene is produced during seed germination and we have demonstrated that its production can be diagnostic for seed vigor. For seeds of corn and tomato that were artificially or naturally aged to reduce their vigor, it was observed that their ability to convert ACC to ethylene was much reduced. It was also observed that treating low vigor seeds with ethylene partially restored vigor to these seed lots.

One of the major impacts on double and triple ethylene response mutants in Arabidopsis was altered response to seed dormancy. The relationship between ethylene and seed dormancy was further evaluated in purple coneflower (Echinacea) because it has been well established that dormant purple coneflower seeds show dormancy released after exogenous ethylene treatment. It was found that non-dormant and ethylene treated seeds have a reduced sensitivity to ABA. However, non-dormant seeds did not require the ability to make ethylene to germinate even in the presence of ABA suggesting that stratification in purple coneflower may have an additional mechanism for dormancy release beside an ethylene-ABA interaction.

2009 Impact

The time between imbibition and radicle protrusion is a vulnerable stage in the plants life cycle and is also diagnostic for seed quality. Developing seed with appropriate genetics or introducing seed treatments that increase germination speed could significantly increase seedling stand establishment, especially under less than ideal growing conditions.

Results from this project suggest that ethylene and its interaction with ABA are important components determining germination speed. Also, this relationship appears equally important as a dormancy release mechanism.

In addition to elucidating the relationship between ethylene and germination speed and dormancy, this research also developed a protocol for "loading" seeds with ACC or ethephon to improve subsequent germination. A key aspect of this protocol was that the plant growth regulators could be loaded into the seeds and the positive effect of the growth regulator retained in dry seeds. This is important because dry seeds can be commercially distributed by the seed producer as a value added product rather than having the grower carry the expense of the facilities required to treat their own seeds.

2009 Publications

Jayasuriya, K.M.G., Baskin, J.M., Geneve, R.L. and Baskin, C.C.(2009). A proposed mechanism of physical dormancy break in sensitive and insensitive seeds of Ipomoea lacunosa (Convolvulaceae). Annals of Botany 103:433-445.

Geneve, R.L. (2009). Physical seed dormancy in selected Caesalpinioid legumes from eastern North America. Propagation of Ornamental Plants 9:129-134.

Fulcher, A., Steele, T., Wilkerson, E., Geneve, R.L., Gates, R. S.(2009). Using transpiration chambers to detect initial transpiration in cuttings and quantify transpiration in seedlings. GreenSys 2009.

Finneseth, C. L.H. and Geneve, R.L. (2009). Laboratory methods to break dormancy in eastern gamagrass (Tripsacum dactyloides L.) seeds. AOSA/SCST annual meeting. FortCollins, CO.

Fulcher, A. and Geneve, R.L.(2009). A photosynthesis-based irrigation model for woody plants. HortScience 44:1037.

Fulcher, A. and Geneve, R.L.(2009). Ecophysiology and comparative foliar micromorphology of big-bracted Cornus selections. HortScience 44:1125.

Finneseth, C.H., Geneve, R.L., and Dunwell, W.(2009). Rudy Haag Burning bush (Euonymus alatus) as a non-invasive alternative to current burning bush cultivars. HortScience 44:1161.

Hildebrand, D., Thoguru, J.R., Jamboonsri, W., Ratliff, G., Sterling, P., Geneve, R. , and Phillips, T.(2009). Nutritional Oils, A Tale of two Crops. Plant Biology 2009.

Stevens, M.E., S.T. Kester and R.L. Geneve.(2009). Adventitious root formation in poplar (Populus) intermodal stem cuttings grown in vitro. Combined Proceedings International Plant Propagators Society 60: in press.

Steele, T., Fulcher, A. ,Gates, R. and R.L. Geneve.(2009). Designing a growth chamber to monitor transpiration. Proceedings of Southern Nursery Association Research Conference 54:111-114.

Fulcher, A. and Geneve, R.L.(2009). Cornus, gas exchange, and drought. Proceedings of Southern Nursery Association Research Conference 54:22-27.