Graduate Thesis Or Dissertation
 

Seed dormancy in tall fescue (Festuca arundinacea Shreb.) : acquisition, effect on metabolic processes and relief by temperature and growth regulators

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  • Dormancy in seed of Festuca arundinacea Shreb. was studied. The acquisition of dormancy during seed maturation was examined and the effect on dormancy relief by chemical and physical treatments was determined. The implication of endogenous growth inhibitors in dormancy imposition and maintenance was assessed. Germination responses to temperature and growth regulator treatments were evaluated in both dormant and non-dormant seed. Comparisons of respiration, protein synthesis and nett ATP production were made between imbibed dormant and non-dormant seed. Seed developed at 15°C showed more dormancy than those developed at 26.6°C when germinated at 15°C or 26.6°C at any stage of seed growth. However, dormancy was not expressed until the seed was almost mature. Germination response at 26.6°C was established as the dormancy criterion. Dormancy in seed stored at two relative humidity levels (ambient, and with desiccant) at each of three temperatures, -10, 5 and 23°C was most affected by storage at normal room temperature (23°C) and ambient relative humidity. A significant response in dormancy relief was noted after 8 weeks, whereas dormancy status in the other treatments was almost unchanged even after 62 weeks storage. Imbibition of dormant seed at 26.6°C with KNO₃ and thiourea had little effect on dormancy status. Prechilling imbibed seed completely relieved dormancy when germinated at 15 -25°C. High oxygen tensions during germination or imbibition with solutions of sodium azide or 2,4-dinitrophenol failed to relieve dormancy. Removal of the lemma and palea from dormant seed allowed some germination while the presence of these appendages caused reduction in non-dormant seed germination. Leaching of dormant seed with water resulted in little change of dormancy status. Acidic fractions of ether extracts of both dormant and non- dormant seed were inhibitory to germination of non-dormant seed. Separation of extract components by thin-layer chromatography using basic solvent systems revealed the presence of several inhibitory substances. Co-chromatography with abscisic acid indicated the presence of a component at the same Rf value in non-dormant seed extract but not in the extract of dormant seed. Extracts prepared from glumes of dormant and non-dormant seed contained only two prominent components, neither of which could be associated with free abscisic acid. Pretreatment at 1, 5 and 10°C relieved dormancy in imbibed seed after 12 to 24 days treatment. A 15°C temperature was less effective and 20°C had no effect. Constant temperatures were most favourable for germination of non-dormant seed with 13 to 33°C being the germination range and 20 to 25°C the optimum. Alternation of a two-way thermogradient on 20/4, 16/8 and 12/12 hour diurnal cycles resulted in a decrease in total germination as alternation amplitude decreased. Imbibition of dormant seed with solutions of gibberellic acid at concentration up to 500 μM had little effect on dormancy status. Failure to respond may have been partly due to lack of penetration into the seed. Kinetin, at concentrations up to 50 μM had no measurable effect on dormancy, either by itself, or in combination with gibberellic acid. Abscisic acid slowed germination of non-dormant seed at 100 μM and caused complete inhibition at 1000 μM. Gibberellic acid, even at 50 μM concentration relieved this inhibition. Kinetin had no effect. No differences were detected in water uptake into dormant and non-dormant seed over a 60 hour period. Respiration of imbibed dormant seed was shown to be initially higher than that of non-dormant seed. Nett ATP production up to 12 hours and ¹⁴C-leucine incorporation into soluble protein at 24 hours and into insoluble protein at 36 hours were higher for dormant seed. No differences were found between dormant and non-dormant seed in labelling of insoluble proteins at 24 hours or soluble proteins at 36 hours.
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