Three questions are considered in the context of the possible effects of seedassociated
mycoflora, typified by Fusarium moniliforme, during hydrated
storage of recalcitrant seeds of the tropical species, Avicennia marina. These
are: 1) whether fungal infection reduces storage lifespan; 2) whether seeds
become more susceptible to fungal attack during storage and whether they
posses defence mechanisms that might suppress fungal proliferation in
hydrated storage (production of antifungal compounds and 13-1,3-glucanase
(EC 3.2.1.39) and chitinase (EC 3.2.1.14)] and 3) whether it is possible to
discriminate ultrastructurally between inherent deteriorative changes and
those that are fungally-induced.
1) The data indicate unequivocally that if fungal activity is curtailed, then the
hydrated storage lifespan of A. marina seeds can be considerably extended.
2) When inoculated immediately with F. moniliforme, newly harvested seeds
were extremely susceptible to the adverse effects of the fungus, while seeds
that had been wet-stored for 4 days showed a considerably heightened
resilience to the effects of the fungus prior to inoculation. The enhanced
resilience, although declining, persisted in seeds stored hydrated for up to 10
days prior to inoculation, being lost after 12 days. This finding was supported
by significant increase in 13-1,3-glucanase and chitinase and in antifungal
compound production during 10 days of wet storage. After 14 days of wetstorage,
seeds become more susceptible to the effects of fungusthanthose in
the newly harvested condition.
3) The resilience of seeds that had been stored in the short-term was
associated with ultrastructural changes indicative of enhanced metabolic
activity associated with the onset of germination (e.g. increase in vacuolation,
well-developed mitochondria and endomembrane system [ER and Golgi
bodies]). However, with sustained stress associated with wet-storage
IV
conditions, the seeds became increasingly badly affected by the fungus,
showing some ultrastructural fungally-induced abnormalities (e.g. nuclear
lobing, presence of lipid bodies and prevalence of Golgi bodies that had many
associated vesicles) and a decrease in 13-1,3-glucanase and chitinase activity.
It is suggested that the decreased susceptibility of A. marina seeds during
short-term storage relies on the ability to create an antifungal environment
prior to infection (through synthesis and accumulation of pre-formed and
induced antifungal compounds and antifungal enzymes), which would also be
an effective strategy during germination in the natural environment. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2004
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/2258 |
| Date | January 2004 |
| Creators | Calistru, Claudia. |
| Contributors | Berjak, Patricia., Pammenter, Norman W., McClean, Michelle. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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