We have demonstrated that the senescence of Sandersonia aurantiaca (Hook.) flowers is insensitive to ethylene. Treating detached, physiologically mature flowers with propylene (0.5%, 24 h) did not alter the patterns of colour change, fresh weight, or respiration which normally occur as the flowers senesce. Silver thiosulphate (STS, 1 mM) did not extend the vase life of the flowers. Postharvest ethylene production by flowers was negligible, regardless of whether they had been exposed to propylene and or STS. Cycloheximide treatments (1 μM, 100 μM) inhibited the loss of pigment or fading associated with flower senescence. This suggests that de novo protein synthesis is required for pigment degradation in senescing sandersonia flowers. However, 100 μM cycloheximide also caused detached flowers to wilt prematurely, thereby changing the normal sequence of events that occur during senescence in this flower. Exposing flowers to actinomycin D caused a subtle change in their pattern of senescence and in vitro translation of RNA extracted from the flowers produced a pattern of translation products that differed from that of control flowers held in water. The data demonstrate that specific changes in both transcription and translation accompany the ethylene-insensitive senescence of sandersonia flowers. H95038

We have studied nitrogen metabolism during senescence of the ethylene-insensitive flower Sandersonia aurantiaca Hook. We report here on the isolation and characterization of two cDNAs from senescing sandersonia tepals. SAND1 encodes asparagine synthetase (AS; EC 6.3.5.4) and SAND3 encodes glutamine synthetase (GS; EC 6.3.1.2). The accumulation of SAND3 mRNAs was consistently high throughout flower development and senescence and was not associated with senescence per se. SAND1 mRNAs started to accumulate in mature flowers just prior to visual signs of senescence. Sucrose feeding of individual flowers delayed tepal senescence and altered amino acid metabolism. The levels of Asn, Gln and Glu were higher and Asp levels were lower in the sucrose-fed flowers. The senescence-associated peak in Gln was delayed in sucrose-fed flowers compared to controls that were held in water. Sucrose feeding had no effect on the initiation of SAND1 transcription at the onset of flower senescence; however, the later decline in SAND1 mRNA abundance was delayed in sucrose-fed flowers. Elimination of GS activity and the subsequent reduction in Gln levels caused by phosphinothricin treat-ment was associated with a delay of SAND1 mRNA accumulation in senescing flowers.

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