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Title: Chemical genetics of seed germination : modulation of a key step in abscisic acid biosynthesis
Author: Chandler, Jake Owen
ISNI:       0000 0004 5922 2046
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2015
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Cold conditions during imbibition can result in slow or no germination in some maize seed, leading to sub-optimal crop density and uniformity and loss of yield. A novel seed treatment is required that restores germination in seed batches that perform poorly under cold conditions. Germination of seed batches from different varieties was characterised following imbibition under cold conditions which permit no or slow germination. Hydroxamic acid inhibitors of 9-cis-epoxycarotenoid dioxygenase (NCED) stimulate germination through ABA biosynthesis inhibition in other species and had a small significant effect in increasing the proportion of normal seedlings after cold imbibition. This indicated that normal germination of maize may be inhibited by dormancy-related mechanisms during or after imbibition in cold conditions. The maize NCED (ZmNCED) family was characterised. D2 and D4 inhibit other enzymes in the carotenoid cleavage dioxygenase family and exhibit relatively weak inhibition of NCED. ZmNCEDs were cloned for in vitro enzyme inhibition studies to aid identification of NCED-specific inhibitors. An RT-qPCR assay for measuring ZmNCED expression was developed. Seed ZmNCED expression and ABA concentration was elevated under cold conditions, compared to optimal germination conditions. An assay was developed to screen for germination stimulating compounds. 965 of a diverse library of 5074 compounds were identified as potential germination stimulators. Germination stimulating activity was replicated in 171 of these compounds, with some more efficacious than D4. Germination stimulating activity of 88 compounds related to the current lead compound, D4, was assessed at concentrations of 10 ppb to 10 ppm. Compounds were identified that, at less than 10 ppm stimulated germination more than D4 at 312 ppm. The mode-of-action of these compounds will need to be determined and may yield novel targets for germination stimulation. Thus novel seed treatments for improving germination of low vigour maize seed lots under cold conditions could be based on NCED inhibition or the action of the newly identified compounds.
Supervisor: Not available Sponsor: Syngenta
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: SB Plant culture