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Victoriano Valpuesta, Nathan E. Lange, and Michael S. Reid

Rapid senescence of day lily flowers (Hemerocallis sp. cv. Cradle Song) has been shown to be associated with a rapid disappearance of proteins. Senescence was significantly delayed by pulsing developing flowers with cycloheximide, an inhibitor of protein synthesis. A cDNA library prepared from mRNA extracted from flowers in the very early stages of senescence was probed with mRNA from flowers at different stages of opening and senescence. Characterization of senescence-specific clones, and implications for the control of senescence in this non-climacteric flower will be discussed.

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Royal D. Heins, Nathan Lange, and Thomas F. Wallace Jr.

Ageratum, begonia, marigold, and salvia seedlings in plug cells were stored in coolers to determine the effects of temperature, light, and storage time on growth and forcing time of seedlings after transplanting, and to determine the optimum storage temperatures for each crop. Photosynthetic photon flux densities of 0, 1, and 5 μmol·m-2.s-1 were combined with temperatures of 0.0, 2.5, 5.0, 7.5, 10.0, and 12.5C to create 18 storage environments. Sample plants were removed from each treatment at 1-week intervals for 6 weeks, and were forced into flower. In all four species, temperatures of 0.0 and 2.5C caused chilling injury and then death as plants were stored for progressively longer periods. Storage at 0.0 and 2.5C also delayed flowering when chilling injury was not severe enough to cause death. In general, plants stored better in the light than in darkness. Darkness tended to limit the time seedlings could be stored, but for each crop, the addition of just 1 μmol·m-2.s-1 extended the storage durations to 6 weeks at one or more temperatures. Storage of all four species was possible for 6 weeks, but there were significant variations between the temperatures and storage durations each species could tolerate. Optimal temperatures were 5-7.5C for begonia, 5C for marigold, and 7.5C for salvia and ageratum.

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Nathan E. Lange, Michael S. Reid, Victoriano Valpuesta, Consuelo Guerrero, and Miguel A. Botella

As in many commercially important flowers, especially the monocotyledonous geophytes, senescence of the ephemeral daylily flower (Hemerocallis) does not involve ethylene. By differentially screening a cDNA library constructed from mRNA extracted from daylily petals in the earliest stages of senescence, clones were isolated whose transcription is up-regulated coordinately with the onset of senescence. One of these clones, sen12, was found to be a transcription factor. The deduced amino acid sequence of sen12 contains a MADS-box and an associated K-box similar to transcription factors suggested to control floral morphogenesis in a variety of different species. Northern blot hybridization showed sen12 to be highly upregulated before and during visible flower senescence. The expression of homologous genes during senescence of other flowers will be reported.

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Nathan E. Lange, Victoriano Valpuesta, Carolyn A. Napoli, and Michael S. Reid

The metabolic pathway and function of ethylene during the senescence of many fruits and flowers have been extensively studied, the molecular basis of ethylene-insensitive flower senescence remains unknown. The ephemeral flowers of daylily (Hemerocallis) were used as a model system for the examination of ethylene-insensitive senescence. Senescence-associated cDNA clones were isolated from a cDNA library constructed from mRNA expressed in senescing tepals of daylily flowers. Up-regulated cDNA clones were identified by differentially screening the cDNA library. Sequence analysis of one of the clones, designated as SEN12, indicates that it contains a MADS box domain and an associated leucine-zipper K-box region and may be a transcription factor similar to floral homeotic genes. Northern analysis indicates that SEN12 encodes for a rare message. Therefore, reverse transcriptase polymerase chain reaction (RT-PCR) assays were used to quantitate the abundance of SEN12 transcripts during floral senescence. RT-PCR assays demonstrated that SEN12 transcripts significantly increase in abundance during the earliest stages of flower senescence and continue to increase until the end of senescence. We propose that SEN12 may be involved in controlling senescence in ethylene-insensitive flowers and we are continuing to investigate this hypothesis.

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David W. Burger, J.B. Katcher, Nathan E. Lange, Jose L. Saenz, Scott P. Sherman, and Mark R. Stoutemyer

Graduate students in horticulture at the Univ. of California, Davis, spent an academic quarter learning how to use the Internet and World-Wide Web (WWW) to access and collect information. The collected information was organized and placed on the WWW where it is available to anyone with access to the Internet.