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Laura J. Chapin, Youyoun Moon, and Michelle L. Jones

characterized have a neutral to slightly basic pH optimum ( Bozhkov et al., 2005 ; He et al., 2008 ; Vercammen et al., 2004 ). Flower senescence in petunia was also accompanied by an increase in metacaspase-like activity (GRRase activity) in the corollas ( Fig

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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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Malgorzata Serek

The postharvest quality of miniature pot roses is limited by bud abscission and premature flower senescence. Rosa hybrida `Victory Parade' plants were treated with ethephon to study their sensitivity to ethylene and with silver thiosulfate (STS) to investigate its inhibitory effects on ethylene action. Bud abscission and flower senescence were promoted by spraying plants with ethephon, and the longevity of individual flowers and whole plants was reduced. All STS concentrations (0.4, 0.8, 1.2, 1.6 mM improved postharvest keeping quality. Bud abscission and flower senescence were decreased and the longevity of flowers and whole plants was improved by applying STS. Chemical name used: 2-chloroethylphosphonic acid (ethephon).

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Nichole F. Edelman and Michelle L. Jones

hypocotyl thickening, and an exaggerated apical hook. Collectively, these symptoms are known as the triple response ( Knight et al., 1910 ). Exposure to ethylene at plant maturity can lead to flower, bud, or leaf abscission; flower senescence; leaf chlorosis

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Hye Jin Kwon, Song Kwon, and Ki Sun Kim

This experiment was undertaken to characterize the physiological changes taking place during the petal senescence of Hibiscus syriacus. Five distinctive developmental stages were chronologically suggested. Flower bud dry weight increased almost linearly from Stage I to Stage IV at a rate of ≈15 mg/day. Fresh weight and fresh/dry weight ratio increased much more rapidly between Stage III and Stage IV than during the early stage of development. It showed that petal expansion was partially due to an increased water uptake. The highest osmolality (411 mmol) was found in the fully open flowers. During the subsequent senescence and collapse of the flower, from Stage IV to Stage V, there were a rapid loss of fresh and dry weight and the fall of fresh/dry weight ratio, corresponding to the wilting that characterizes early senescence. A rise in cell sap osmolality coincided with the increase in soluble sugar content and fresh/dry weight ratio, and with the expansion of Hibiscus syriacus petal. Therefore, buds at Stage III, where they are under physiological maturity, might be appropriate to harvest. Hibiscus syriacus flowers showed a small but respiratory peak at Stage IV. The maximum rate of respiration was obtained with fully open flowers (Stage IV), whereas ethylene production remained extremely low until the petals started to open. Ethylene production, ACC synthase, and ACC content increased as the fresh weight of the flowers started to decline. At Stage V, there were a loss of petal fresh weight and a considerable increase in ethylene production (9 nL/g per h). The results of the present study have shown that petal tissue at Stage IV, presenescent stage, was characterized by the increase of soluble sugar and fresh weight, which might be expected to lead to petal expansion and limit turgidity. ABA and the stomata on petal might promote the disorganization.

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Nichole F. Edelman, Bethany A. Kaufman, and Michelle L. Jones

after ethylene exposure), 1, 2, 5, and 7 d. Plants were evaluated for symptoms of flower abscission (drop), flower senescence (wilt), leaf abscission, leaf chlorosis (yellowing), and leaf epinasty (downward curvature). Flower evaluations did not

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Juan O. Quijia Pillajo, Laura J. Chapin, and Michelle L. Jones

environmental stress ( Lim et al., 2007 ; van Doorn and Woltering, 2008 ). Flower senescence can also be accelerated by pollination ( Broderick et al., 2014 ; van Doorn and Woltering, 2008 ). The premature senescence of flowers and foliage caused by abiotic

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Ya-Ching Chuang and Yao-Chien Alex Chang

but is often cut short by early flower senescence or low opening rates of upper flower buds. Flower opening results from the rapid growth and enlargement of petal cells, which are in turn regulated by carbohydrate sources and the cell water potential

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Michael Knee

Chelating agents were applied to petunia flowers to test for the involvement of apoplastic metal ions in ethylene-induced senescence. Compounds varying in polarity and charge were applied directly to the corolla prior to a 24-h treatment with 1 ppm ethylene. Charged and polar chelators were inactive. The only compound that inhibited senescence was 2,2'-dipyridyl, and there was evidence of cellular uptake of this compound. Fe2+ and Zn2+ did not reverse the inhibition of senescence by dipyridyl. Cu2+ as low as 0.1 mM reversed the effect of dipyridyl, but the time of senescence was independent of ethylene treatment. Dipyridyl caused a rapid shift in flower color from red to blue, but untreated flowers became more blue than dipyridyl-treated during 9 days. CO2 and ethylene production were stimulated by ethylene, but inhibited by dipyridyl applied before or after a 24-h ethylene treatment. Continuous ethylene treatments did not reverse the delay of senescence by dipyridyl.

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Amanda S. Brandt and William R. Woodson

We have investigated the patterns of ethylene biosynthesis in carnation (Dianthus caryophyllus L.) genotypes that exhibit extended vase life in comparison to flowers of White Sim'. `White Sim' flowers exhibited typical symptoms of senescence, including petal in-rolling and rapid wilting, beginning 5 days after harvest. In contrast, the other genotypes studied did not show petal in-rolling or rapid wilting associated with petal senescence. The first visible symptom of senescence in these flowers was necrosis of the petal tips, and it occurred from 3 to 7 days after the initial symptoms of senescence were seen in `White Sim' flowers. In all cases, the extended-vase-life genotypes did not exhibit the dramatic increase in ethylene production that typically accompanies petal senescence in carnation. This appeared to be the result of limited accumulation of ACC. In addition, flowers of these genotypes had limited capacity to convert ACC to ethylene. Therefore, we conclude that the low level of ethylene produced by these flowers during postharvest aging is the result of low activities of both ACC synthase and the ethylene-forming enzyme. Treatment of `White Sim' flowers at anthesis with 1.0 μl ethylene/liter resulted in the induction of increased ethylene biosynthesis and premature petal senescence. The extended-vase-life genotypes exhibited varying responses to ethylene treatment. One genotype (87-37G-2) produced elevated ethylene and senesced prematurely, as did flowers of `White Sim'. A second genotype (82-1) was induced to senesce by ethylene treatment but did not produce increased ethylene. A third genotype (799) was unaffected by ethylene treatment. The results of this study suggest these extended-vase-life genotypes are representative of genetic differences in the capacity to synthesize and respond to ethylene. Chemical name used: 1-aminocyclopropane-1-carboxylic acid (ACC).