A comprehensive study on the role of hormones, seed coat and genes during the germination of canola (Brassica napus) seed under adverse environmental conditions
Seed vigor, although not well understood, is a key critical component for yield and is in part due to a well establishment and vigorous stand of canola (Brassica napus) seedling under less than ideal conditions in Western Canada. My objective was to determine what constitutes vigor by studying the response of a black seed line and a yellow seed line imbibed at 8 ºC in either water, saline or osmotic solutions, abscisic acid (ABA), ABA biosynthesis inhibitor, gibberellin (GA4+7), inhibitor of GA biosynthesis and a germination promoter, fusicoccin. Also tested was the effect of seed coat (testa) on seed germination rate and percent germination. Previous studies have established that seed vigor is in part hormonal controlled and genetically controlled. In our study, gene expression was investigated by using transcriptome analysis and hormonal analysis was used to quantitate the changes in hormones and their metabolites during germination. Both the black and the yellow canola seed lines were very sensitive to increasing concentrations of saline and osmotic solutions; however, at the same osmotic potential, osmotic solutions were more inhibitory. The yellow seed line was more sensitive to these conditions than the black seed line. As expected, ABA delayed seed germination, whereas GA4+7 enhanced seed germination and GA4+7 partially overcame the inhibitory effect of ABA. The seed coat was a major factor affecting the germination rate of the yellow seed line; however, GA4+7 overcame the inhibitory effect of the seed coat, whereas ABA exacerbated it. Fusicoccin was more stimulatory to germination than GA4+7; however, unlike GA4+7, it was unable to overcome the inhibitory effect of paclobutrazol, a GA biosynthesis inhibitor. Fluridone, an ABA biosynthesis inhibitor, was unable to overcome the inhibitory effects of a saline solution suggesting that the inhibitory effect was not due to elevated ABA levels. Ethylene, a stimulator of germination, did not appear to be involved in the germination of these two lines. Controlled deterioration at 35 ºC, 85% RH was either partially or completely overcome by exogenous GA4+7. This study demonstrates that the role of hormones, salinity and seed coat on the germination of canola seed under low temperature environmental conditions. During germination, ABA declined while GA4 increased. Higher ABA was found in un-germinated seeds compared to germinated seeds. GA4+7 was lower in seeds imbibed in the saline solution compared to seeds imbibed in water. Un-germinated seeds imbibed in ABA had lower GA4+7 compared to un-germinated seeds imbibed in water; however, the contents of GA4+7 were similar for germinated seeds imbibed in either water or ABA. Phaseic acid (PA) and dihydrophaseic acid (DPA) increased in seeds imbibed in either water, the saline solution or ABA, while they decreased in seeds imbibed in GA4+7. In addition, we found that ABA inhibited GA4 biosynthesis, whereas, GA had no effect on ABA biosynthesis, but altered the ABA catabolic pathway. Gene expression profiles revealed that there are significant differences between un-germinated and germinated seeds. Seeds imbibed in water, GA4+7, a saline solution or ABA had different gene profiles. LEA genes, hormone-related genes, hydrolase-related genes and specific seed germination-related genes were identified and their expression profiles were finely associated with seed germination performance.
DegreeDoctor of Philosophy (Ph.D.)
SupervisorGusta, Larry V.
CommitteeSawhney, Vipen K.; Hucl, Pierre J.; Gray, Gordon R.; Bewley, J. Derek; Bai, Yuguang