341 Proc. 4 th . Int. Conf. On Postharvest Eds. R. Ben-Arie & S. Philosoph-Hadas Acta Hort. 553, ISHS 2001 SENESCENCE-ASSOCIATED GENE EXPRESSION IN NARCISSUS ‘DUTCH MASTER’ Donald A. Hunter and Michael S. Reid Department of Environmental Horticulture, University of California, Davis, USA E-mail: donhunter@ucdavis.edu Keywords : Daffodil, remobilization, tepals, flower senescence, suppression-subtraction PCR, programmed cell death 1. Introduction Flower senescence is a highly controlled developmental event that culminates in the death of the floral organs. Most research on flower senescence has focused on the perianth, since it typically determines the commercial life of the flower. The mechanism by which the perianth dies differs between species: in some flowers, wilting is the primary symptom of senescence whereas in others, the perianth is shed prior to, or at the time of wilting. Daffodils (Narcissus) are widely grown commercial flowers that are prized for their beauty in spring. The flowers are short-lived and are reported to senesce independently of ethylene action (Woltering and van Doorn, 1988). In addition to the petals and sepals (tepals), daffodil flowers are unique in possessing an additional petaloid structure, the corona. We have used the flowers of the ‘Dutch Master’ cultivar as an experimental model to examine molecular changes associated with the onset of non- climacteric flower senescence, and report here our preliminary results. 2. Materials and methods Plant material Bulbs of ‘Dutch Master’ daffodils were obtained from the Oregon Bulb Company (Oregonbulb.com) and were precooled in pots at 7°C for a total time of 15 weeks. They were then transferred to the greenhouse until just prior to bud break, when they were moved to an interior controlled environment at 20±2°C, relative humidity of ca. 45% and a 12 h photoperiod (15 μmol.m -2 .sec -1 PAR from Cool White fluorescent lamps). Molecular procedures Total RNA was isolated from tepals and coronas by the method of Hunter and Reid (2000). Poly A + RNA was isolated from total RNA with the polyATtract mRNA isolation system (Promega). The subtracted cDNA library was constructed by means of the PCR-select kit (Clontech). Subtracted cDNA sequences were ligated into the pGEM T-Easy vector (Promega) and cloned into E. coli. Isolated plasmids were sequenced at the sequencing facility on the U.C. Davis campus and their sequences were compared with sequences in the GenBank database with the BLASTx tool (Altschul et al., 1990). 3. Results and discussion We selected 94 of the subtracted PCR sequences for further analysis. Among the 94 sequences, we identified a large number as homologous with genes reported in the GenBank database to be associated with senescence or remobilization in plants (Table 1). Of particular interest is the identification of the enzymes of the glyoxylate cycle, presumably associated with remobilization of lipids. The homologies with genes known to be involved in regulation of growth and development are also interesting, as they may provide leads to exploration of the control of senescence in non-climacteric flowers. Some genes, interestingly, showed homology to sequences that in other systems