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Abstract Detail


Seed Biology

Dahal, Peetambar [1], Argyris, Jason [2], Bradford, Kent J. [2].

Differential expression of gibberellin, abscisic acid and ethylene biosynthesis genes is associated with lettuce seed thermodormancy.

Seeds (cypselas) of cultivated lettuce (Lactuca sativa L.) varieties (e.g., cv. Salinas) exhibit thermo-inhibition or failure to complete germination when imbibed at warm temperatures (above ~30°C). In contrast, an accession of L. serriola (UC96US23), the wild progenitor of lettuce, can germinate at temperatures up to 38°C when imbibed in the light. Gibberellin (GA), abscisic acid (ABA), and ethylene have been implicated in regulating germination and dormancy in lettuce seeds in response to light and temperature. We tested whether variation in expression of genes involved in the synthesis of these phytohormones is associated with the temperature sensitivity of germination of Salinas and UC96US23 seeds. Quantitative RT-PCR was used to assay mRNA abundance of GA 20-oxidase(LsGA20ox1) and GA 3-hydroxylase (Ls3h1) (GA synthesis), nine-cis-epoxycarotenoid dioxgenase (LsNCED4) (ABA synthesis), ACC synthase (LsACS1) and ACC oxidase (LsACO1) (ethylene synthesis) genes in seeds of both genotypes imbibed at either 20 or 35°C in light. Expression of (LsGA20ox1, Ls3h1, LsACS1 and LsACO1) mRNA increased and that of LsNCED4 decreased in both Salinas and UC96US23 seeds imbibed at 20°C, where germination occurs. In contrast, expression of LsGA20ox1, Ls3h1, LsACS1 and LsACO1 genes was low and LsNCED4 expression was enhanced in Salinas seeds imbibed at 35°C, where germination is inhibited. Both germination and expression of LsGA20ox1, Ls3h1, LsACS1 and LsACO1 genes were delayed coordinately in UC96US23 seeds imbibed at 35°C, and LsNCED4 expression was suppressed. These contrasting patterns of germination and gene expression were exhibited over a range of only 3°C when seeds were imbibed at 30 versus 33°C. These results show that the differential expression of genes involved in GA, ABA and ethylene synthesis is controlled by temperature and is associated with differential sensitivity of lettuce genotypes to seed thermodormancy.
Supported by National Science Foundation grant DBI-0421630.


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1 - University of California, Department of Plant Sciences, One Shields Avenue, Davis, CA, 95616-8780, USA
2 - University of California, Davis, Department of Plant Sciences

Keywords:
seed germination
temperature
ABA
GA
ethylene.

Presentation Type: Plant Biology Abstract
Session: P
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM
Number: P29013
Abstract ID:1047


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