ACCESSION NO: 0199177 SUBFILE: CRIS
PROJ NO: LAB93685 AGENCY: CSREES LA.B
PROJ TYPE: HATCH PROJ STATUS: NEW MULTISTATE PROJ NO: W-1168
START: 01 OCT 2003 TERM: 30 SEP 2008 FY: 2004
INVESTIGATOR: Cohn, M. A.
PERFORMING INSTITUTION:
PLANT PATHOLOGY & CROP PHYSIOLOGY
LOUISIANA STATE UNIVERSITY
BATON ROUGE, LOUISIANA 70893
Environmental and Genetic Determinants of Seed Quality and Performance
NON-TECHNICAL SUMMARY: Dormancy of weed seeds limits the effectiveness of current weed control practices. Dormancy of crop seeds prevents uniform plant growth and increases seed processing costs. The purpose of this study is to identify seed genes/proteins that prevent germination and maintain the dormant state.
OBJECTIVES: Identify genes associated with seed development, germination, vigor and dormancy
APPROACH: While genetic evidence implicates the participation of abscisic acid (ABA) in the induction of developmental arrest during seed maturation, the role of ABA and its signaling components in the maintenance of dormancy after the seed is shed remain controversial. At least two possibilities exist. In dormant seeds (a) ABA may be required continuously or (b) only its signaling components may be needed. Two components of the ABA-signaling pathway (ABI1, ABI2) encode protein phosphatases (PP). Non-specific inhibitors of PP, phenylarsine oxide (PAO) and H2O2, break dormancy of red rice as pulse treatments. These substances inhibit ABI1 and ABI2 activity in vitro. PPs are also inhibited by mildly acidic pH, the nitric oxides, fructose-2,6-bisphosphate and low temperatures, factors that break dormancy or are early response phenomena of dormancy-breaking. Further research will determine whether ABA-signaling components are involved in the maintenance and release of seed dormancy and identify target genes.
PROGRESS: 2004/01 TO 2004/12
This research contributes to the overall goals of the W-1168 regional project, focusing upon elucidation of the environmental and genetic determinants of seed quality and performance. It is an open question as to whether or not continual translational activity (protein synthesis) is required to maintain seeds in the dormant state. It is not known if proteins that are required to induce dormancy are the same as those that may be required to maintain dormancy after a seed is shed from the mother plant. A chemical genetics approach was initially taken to determine if protein synthesis inhibitors break dormancy of red rice caryopses (naked seeds). (1) Extensive bioassay experiments revealed that cycloheximide (CHX), an inhibitor of eukaryotic protein synthesis, readily broke dormancy when applied as a 24-hour pulse treatment; prolonged exposure to CHX (3-5 days) resulted in seed death or seedling injury. CHX inhibited germination of afterripened, non-dormant seeds. Therefore, while CHX breaks dormancy, it inhibits germination, implying that different sets of proteins may regulate the two processes. (2) In contrast, other eukaryotic (emetine, anisomycin) and the prokaryotic translational inhibitors, chloroamphenicol (CHL) and tetracycline (TET), did not break dormancy. Geneticin and hygromycin B, cross-kingdom translation inhibitors, were also inactive. While these chemicals did not break dormancy, seed viability after treatment was 90%, compared to 94% for the untreated controls. Seedlings grown from treated seeds, after mechanical breaking of dormancy, were normal. (3) The effect of solution pH upon the activity of emetine was determined. Emetine solutions adjusted to pKa 2 or one pH unit above pKa 2 did not break dormancy but did inhibit seedling growth of fully afterripened, non-dormant seeds. Therefore, it is possible that emetine was taken up by dormant seeds but had no physiological effect. (4) TET was inactive over the pH range of 3 to 7 and did not affect seedling growth; these results are consistent with the charged nature of TET across the range of physiological pH (likely preventing seed uptake) and/or its specificity for only prokaryotic translational machinery. Similar results were obtained for CHL. (5) While CHX is commonly used in contemporary biological experimentation as a specific inhibitor of protein synthesis, an extensive literature review suggested that this is not the case. It is highly possible that CHX breaks dormancy by a means other than translational inhibition. Therefore, it is tentatively concluded from the overall data set that new protein synthesis is not required to maintain seed dormancy in red rice, but rather the controlling proteins are synthesized during grain development and are stabilized in the seed after it is shed from the mother plant. The potential implications of these data for interpretation of future genomic and proteomic are highly significant.
IMPACT: 2004/01 TO 2004/12
The results enhance our understanding of the physiological factors that control whether weed or native plant seeds germinate or remain dormant in the soil. Identification of new physiological factors increases the range of seed components that can serve as targets for the design of new, environmentally benign, weed control treatments or modification of cultural practices.
PUBLICATIONS: 2004/01 TO 2004/12
Cohn, M.A. 2004. Physiology of dormancy-breaking mechanisms in red rice (invited symposium talk). Abstract S22MT20BP01, 4th International Weed Science Congress, Durban, South Africa. p. 75.
PROJECT CONTACT:
Name: Cohn, M. A.
Phone: 225-578-1464
Fax: 225-578-1415
E-mail