Possible roles for wall-based enzyme activity in aging of daylily petals are presented. We are asking if daylily senescence is controlled in part by reactions associated with. We suggest that membrane changes leading to cell death may be induced in part by lipoxygrenase activity and by ROS that are increasing because of reduced effectiveness of certain protective enzymes. The flowers are insensitive to ethylene, but exogenous ABA prematurely upregulates events that occur during natural senescence, such as loss of differential membrane permeability, increases in lipid peroxidation and the induction of proteinase and RNase activities. The possibility is discussed that ABA is a constituent of the signal transduction chain leading to programmed cell death of daylily petals. Six daylily genes, whose levels increase during senescence, were isolated from a daylily cDNA library. Southern blot analysis showed that all six DSA genes, designated as DSA3, 4, 5, 6, 12 and 15, are members of multigene families. The GenBank database homology search suggested, that DSA3 belongs to the cytochrome P450 superfamily, DSA4 is an aspartic proteinase, DSA5 may be a water stress protein, DSA6 is a putative S-1 type nuclease, DSA12 is very similar to impedance induced protein, and DSA15 is a fatty acid elongase. The accumulation of dsag mRNAs, with the exception of DSA4, is accelerated 3.2 to 43 times in ABA treated prematurely senescing petals. Levels of DSA mRNAs in leaves are very low, less than 4% of the maximum detected in petals, and there is no significant change during senescence. Except for the gene for a putative impedance protein (DSA12), DSAs are also expressed at low levels in daylily roots. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-3177 |
| Date | 01 January 1999 |
| Creators | Panavas, Tadas |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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