SEED HYDRATION-DEHYDRATION IN AN ALLELOCHEMICAL (COUMARIN) ALTERS GERMINATION AND SEEDLING GROWTH

Authors: Williams, Robert; Peal, Lila; Bartholomew, Paul

Submitted to: Allelopathy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2005
Publication Date: 4/15/2005
Citation: Williams, R.D., Peal, L.K., Bartholomew, P.W. 2005. Seed hydration-dehydration in an allelochemical (coumarin) alters germination and seedling growth. Allelopathy Journal. 15(2):183-196.

Interpretive Summary: Plants can give off chemicals that inhibit the seed germination or growth of neighboring plants. However, these chemical are often found in the soil at low concentrations and at these concentrations their effects on seed germination or growth bioassays are minimal. Seeds in the soil can absorb water and then dry as the soil moisture changes before the conditions are optimum for germination. During this time these chemicals could be absorbed by the seeds, which might affect their germination and growth later. We tested this theory by wetting seeds in an inhibitor (coumarin) and air drying the seeds before allowing the seeds to germinate. When the seeds were hydrated with the inhibitor their subsequent germination was delayed and the final germination was reduced as compared to untreated seeds. Further when the seeds went through several wetting and drying cycles, the effects of the inhibitor increased. This may be one answer to the question of how these chemicals work under field conditions.

Technical Abstract: We examined the effect of imbibition of an allelochemical on subsequent seed germination and seedling growth by exposing radish seeds to coumarin during hydration-dehydration cycles. When seeds were exposed to 10-5 and 10-3 M coumarin during imbibition for 2, 4 or 6 h, and transferred to water, subsequent germination was delayed. The longer the exposure to 10-3 M coumarin, the greater the delay in germination. Seeds exposed to coumarin (10-5 or 10-3 M) for 5 h, and air-dried for 14 h still showed an effect due to the allelochemical pretreatment. Seeds imbibed in 10-5 or 10-3 M coumarin, or water for 5 h, air dried for 14 h and germinated in water, 10-5 M or 10-3 M coumarin, had reduced radicle lengths at 48 h. If the seeds were hydrated in coumarin and dehydrated several times, subsequent radicle elongation was reduced. Seeds hydrated in 10-3 M coumarin for 1 to 3 cycles and germinated in either 10-5 M coumarin or water showed a decrease, while seeds hydrated in water for 1 to 3 cycles and germinated in 10-3 M coumarin showed a slight increase, in radicle length with increased number of cycles.