Doctor of Philosophy (PhD)
Plant Pathology and Crop Physiology
Recalcitrant seeds, which die when desiccated, can be difficult to study because of their generally large size, high metabolism, and poor storage properties. However, recalcitrant seeds from the salt-marsh grass Spartina alterniflora are unique when compared to most other recalcitrant species because the seeds are dormant and small; Spartina pectinata and S. spartinae, which produce orthodox seeds, can be used as controls. Because of these somewhat rare characteristics, S. alterniflora is a good model system to study recalcitrance. In the present study, the following physiological parameters were examined: Cardinal temperatures for germination, a viability test to determine if seeds are dormant or dead, stratification needed to alleviate dormancy, and the effects of dry down rates on viability. For non-dormant seeds, the fastest germination rates occurred between 27-34C. For dormant seeds, viability was established by cutting the coleoptile, which caused live seeds to germinate. Dormancy was alleviated with stratification, with average times to 50% germination of 2.1 and 2.6 months when seeds were stored at 2 and 10C, respectively. Finally, S. alterniflora seeds lost viability when desiccated below 45% moisture content on a dry weight basis (DWB); however, drying rate did not influence death. To investigate the causes of recalcitrant seed death, the putative role of oxidative stress was examined by assays for lipid peroxidation, leakage of cell components, total water-soluble antioxidant capacity (TAR), protein carbonylation and DNA fragmentation as Spartina seeds were dried. While lipid peroxidation was not associated with recalcitrant seed death, artifactual damage was observed when seeds were not freeze-clamped prior to extraction. TAR decreased during initial desiccation of orthodox and recalcitrant Spartina seeds. Protein carbonyl amounts (an indicator of protein oxidation) increased as S. alterniflora and orthodox S. spartinae seeds were desiccated. However, rehydration of dry, orthodox S. pectinata, and subsequent drying, did not alter the TAR or protein carbonyls. DNA fragmentation was not evident during desiccation. These results suggest that lipid peroxidation, membrane damage and DNA fragmentation do not play a role in death due to drying. While protein oxidation and loss of antioxidant capacity changed, these are general responses to drying, rather than to recalcitrance.
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Chappell, James Hammond, "Is oxidative stress the cause of death when recalcitrant Spartina alterniflora seeds are dried?" (2008). LSU Doctoral Dissertations. 3745.