| Summary: | Petals and leaves share common evolutionary origins but perform very different functions. However, few studies have
compared leaf and petal senescence within the same species. Wallflower (Erysimum linifolium), an ornamental species closely
related to Arabidopsis (Arabidopsis thaliana), provide a good species in which to study these processes. Physiological
parameters were used to define stages of development and senescence in leaves and petals and to align these stages in the two
organs. Treatment with silver thiosulfate confirmed that petal senescence in wallflower is ethylene dependent, and treatment
with exogenous cytokinin and 6-methyl purine, an inhibitor of cytokinin oxidase, suggests a role for cytokinins in this process.
Subtractive libraries were created, enriched for wallflower genes whose expression is up-regulated during leaf or petal
senescence, and used to create a microarray, together with 91 senescence-related Arabidopsis probes. Several microarray
hybridization classes were observed demonstrating similarities and differences in gene expression profiles of these two organs.
Putative functions were ascribed to 170 sequenced DNA fragments from the libraries. Notable similarities between leaf and
petal senescence include a large proportion of remobilization-related genes, such as the cysteine protease gene SENESCENCEASSOCIATED
GENE12 that was up-regulated in both tissues with age. Interesting differences included the up-regulation of
chitinase and glutathione S-transferase genes in senescing petals while their expression remained constant or fell with age in
leaves. Semiquantitative reverse transcription-polymerase chain reaction of selected genes from the suppression subtractive
hybridization libraries revealed more complex patterns of expression compared with the array data
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