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Michelle L. Jones and William R. Woodson

Following a compatible pollination in carnation (Dianthus caryophyllus L. `White Sim'), a signal that coordinates postpollination events is translocated from the style to the ovary and petals. In this paper the roles of ethylene and its direct precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), in this signaling were investigated. Following pollination, ethylene and ACC increased sequentially in styles, ovaries, and petals. Ethylene and ACC were highest initially in the stigmatic region of the style but by 24 hours after pollination were highest in the base. Activity of ACC synthase correlated well with ethylene production in styles and petals. In ovaries, ACC synthase activity decreased after pollination despite elevated ethylene production. Lack of ACC synthase activity in pollinated ovaries, coupled with high ACC content, suggests that ACC is translocated within the gynoecium. Further, detection of propylene from petals following application to the ovary provided evidence for movement of ethylene within the flower. Experiments that removed styles and petals at various times after pollination suggest there is a transmissible pollination signal in carnations that has reached the ovary by 12 hours and the petals by 14 to 16 hours.

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Nichole F. Edelman and Michelle L. Jones

The family Solanaceae, which includes both important crop and ornamental species, is generally considered to have high sensitivity to ethylene. Our objectives were to evaluate ethylene sensitivity between accessions with the family Solanaceae and to determine whether similar sensitivity was observed in seedlings and mature plants. For the seedling evaluations, seeds were germinated and grown in the dark on filter paper saturated with 0 or 100 μM 1-aminocyclopropane-1-carboxylic acid (ACC; the immediate precursor to ethylene). The relative hypocotyl length at 100 μM ACC was compared with untreated control (0 μM) seedlings. Mature plants were treated with 0 or 10 μL·L−1 ethylene in the dark for 24 hours. Ethylene responses including flower abscission, flower senescence, and epinasty were observed and quantified. Seedlings and mature plants were classified as having no response, low, medium, or high ethylene sensitivity based on the severity of the ethylene responses observed. Sensitivity differences were observed among seedling, juvenile, and mature plants, and a range of ethylene responses and symptom severity was observed between accessions within a species. The majority of the accessions were classified as medium or high ethylene sensitivity at both the seedling and mature plant stages. Solanum melongena ‘Black Beauty’ (eggplant) had a low response to ethylene at the seedling stage and a high response at the mature plant stage, whereas Petunia ×hybrida ‘Daddy Orchid’ had a high response at the seedling stage and a low response at the mature plant stage. Peppers (Capsicum annum), tomatoes (Solanum lycopersicum), and tomatillos (Physalis ixocarpa) exhibited both floral and vegetative symptoms of ethylene damage, whereas calibrachoas (Calibrachoa ×hybrida), eggplants, nicotianas, and petunias exhibited only floral symptoms. The most common floral response to ethylene treatment was flower abscission, which was observed in almost all of the Solanum, Capsicum, and Nicotiana accessions. We consistently observed ethylene-induced epinasty in the genus Capsicum and in all of the Solanum except eggplant. Our results indicated that developmental stage influenced ethylene sensitivity, and there was not a consistent correlation between seedling and mature plant responses within the Solanaceae accessions that we evaluated.

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Michelle L. Jones and William R. Woodson

In Dianthus caryophyllus flowers the pollinated stigma gives rise to signals that are translocated throughout the flower and ultimately result in corolla senescence. Pollination leads to a rapid increase in ethylene production by the pollinated styles followed by ethylene biosynthesis from the ovaries, the receptacle tissue, and lastly the petals. The accumulation of ACC in these floral tissues also correlates with the sequential pattern of ethylene production. Ethylene production by the pollinated style can be defined temporally by three distinct peaks, with the first peak detected as early as 1 hour after pollination. In a carnation flower with multiple styles it is also possible to detect ethylene production from an unpollinated style on a pollinated gynoecium by 1 hour after pollination. This finding provides evidence for very rapid post-pollination signaling between styles. ACC synthase expression is induced in pollinated styles as early as 1 hour after pollination, but no message is detected in pollinated ovaries. ACC synthase enzyme activity is also absent in the pollinated ovaries despite the accumulation of large amounts of ACC in the ovary after pollination. This indicates that ACC must be translocated between organs after pollination. When a pollinated styles is removed from the flower at least 12 hours after pollination the corolla will still senesce. This indicates that the pollination signal has exited the style by this time. Evidence in carnations suggests that ACC and ethylene may both be involved in aspects of post-pollination signaling.

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Nicole L. Waterland, John J. Finer and Michelle L. Jones

Drought stress during shipping and retailing reduces the postproduction quality and marketability of potted plants. Plants respond to drought stress by closing their stomata and reducing transpirational water loss. This stress response is mediated by the plant hormone abscisic acid (ABA). Exogenous applications of s-abscisic acid (s-ABA), the biologically active form of the hormone, can enhance drought tolerance and extend shelf life in a variety of bedding plants. However, little is known about the effectiveness of s-ABA at enhancing drought tolerance in perennial crops like chrysanthemum (Chrysanthemum ×morifolium). ‘Festive Ursula’ chrysanthemum plants were drenched (0, 125, 250, or 500 mg·L−1) or sprayed (0, 500, or 1000 mg·L−1) with s-ABA. All applications containing s-ABA effectively delayed wilting by reducing stomatal conductance (g S). Shelf life was extended from 1.2 to 4.0 days depending on the concentration of s-ABA. Spray applications of 500 mg·L−1 s-ABA to six additional chrysanthemum cultivars increased shelf life from 1.6 to 3.8 days following drought stress. s-ABA treatment also allowed severely drought-stressed chrysanthemums to recover and remain marketable after rewatering. Growers can treat chrysanthemums with s-ABA to reduce water use during shipping and to delay wilting if plants are not adequately watered during retailing.

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Nicole L. Waterland, John J. Finer and Michelle L. Jones

Drought stress during the shipping and retailing of floriculture crops can reduce postproduction shelf life and marketability. The plant hormone abscisic acid (ABA) mediates drought stress responses by closing stomata and reducing water loss. Applications of exogenous s-ABA effectively reduce water loss and allow a variety of species to survive temporary periods of drought stress. Unfortunately, s-ABA application can also lead to leaf chlorosis, which reduces the overall quality of economically important bedding plant species, including Viola ×wittrockiana (pansy). The goal of this research was to determine how to prevent s-ABA-induced leaf chlorosis in pansy and a closely related species, Viola cornuta (viola). All concentrations of both spray (250 or 500 mg·L−1) and drench (125 or 250 mg·L−1) s-ABA applications induced leaf yellowing. Young plants at the plug stage and 11-cm finished plants with one to two open flowers were further evaluated to determine if the developmental stage of the plants influenced s-ABA effectiveness or the development of negative side effects. Both plugs and finished pansies and violas developed leaf chlorosis after s-ABA applications, but symptoms were generally more severe in finished plants. The individual application of benzyladenine (BA), gibberellic acid (GA4+7), or the ethylene perception inhibitor, 1-methylcyclopropene, before s-ABA application had no effect on the development of s-ABA-induced leaf chlorosis. However, applications of 5 or 10 mg·L−1 BA and GA4+7 as a mixture (BA + GA4+7) before a drench or spray application of s-ABA prevented leaf chlorosis. The application of s-ABA and BA + GA4+7 would allow floriculture crops to tolerate temporary periods of drought stress without any loss of postproduction quality.

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Joyce C. Pennycooke, Ramarao Vepachedu, Cecil Stushnoff and Michelle L. Jones

Previous studies of plant tolerance to low temperature have focused primarily on the cold acclimation response, the process by which plants increase their tolerance to freezing in response to low nonfreezing temperatures, while studies on the deacclimation process have been largely neglected. In some plants, cold acclimation is accompanied by an increase in raffinose family oligosaccharides (RFO). The enzyme α-galactosidase (EC 3.2.1.22) breaks down RFO during deacclimation by hydrolyzing the terminal galactose moieties. Here we describe the isolation of PhGAL, an α-galactosidase cDNA clone from Petunia (Petunia ×hybrida `Mitchell'). The putative α-galactosidase cDNA has high nucleotide sequence homology (>80%) to other known plant α-galactosidases. PhGAL expression increased in response to increased temperature and there was no evidence of developmental regulation or tissue specific expression. Increases in α-galactosidase transcript 1 hour into deacclimation corresponded with increases in α-galactosidase activity and a concomitant decrease in raffinose content, suggesting that warm temperature may regulate RFO catabolism by increasing the transcription of the α-galactosidase gene. This information has potential practical applications whereby α-galactosidase may be targeted to modify endogenous raffinose accumulation in tissues needed for freezing stress tolerance.

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

Autophagy allows for the degradation and recycling of macromolecules and organelles. It plays a significant role in cellular homeostasis, nutrient remobilization during leaf senescence, and abiotic stress responses. Autophagosomes are the hallmark feature of autophagy, and their formation is regulated by the AuTophaGy-related (ATG) genes. The expression profiles of ATG genes have been reported in several agronomic and model plants. To gain insight into the role of autophagy in senescence and abiotic stress responses in floriculture crops, we investigated the regulation of petunia (Petunia ×hybrida) ATG genes (PhATG4, PhATG5, PhATG6, PhATG7, PhATG8a, and PhATG13) during flower senescence and in response to low fertility, nutrient deficiency (-N, -P, and -K), and chronic (weeks) or acute (hours) salt stress using quantitative polymerase chain reaction (PCR). Age-induced corolla wilting coincided with the increased expression of all ATG genes. Petunia ATG genes were upregulated by low fertility and N and P deficiency. Acute salt stress rapidly increased the expression of the petunia ATG genes, but chronic salt stress treatments did not. This project provides insight into the role of autophagy in flower senescence and abiotic stress responses in floriculture crops.

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

Metacaspases are cysteine proteases from plants, fungi, and protozoans that have structural similarity to metazoan caspases. They play a critical role in programmed cell death (PCD) induced by developmental cues and environmental signals. In this study, a type I metacaspase (PhMC1) was identified and characterized from Petunia ×hybrida ‘Mitchell Diploid’ (MD) (petunia). The recombinant PhMC1 had activity against the metacaspase substrate Boc-GRR-AMC (GRR). Activity was highest at pH 7–9 and was dependent on the active site C237. Quantitative polymerase chain reaction (qPCR) showed that PhMC1 transcripts increased at a later stage of petal development, when corollas were visibly senescent in both pollinated and unpollinated flowers. Gene expression patterns were similar to that of the senescence-related gene PhCP10, a homolog of Arabidopsis thaliana (arabidopsis) AtSAG12. PhMC1 transcripts were upregulated in the petals by ethylene treatment. This ethylene regulation did not require protein synthesis, indicating that PhMC1 is a primary ethylene response gene. Metacaspase-like activity against Boc-GRR-AMC increased in protein extracts from senescing petals. RNAi was used to knock down the expression of PhMC1. Transgenic PhMC1 petunias had no abnormal, vegetative growth phenotypes under normal greenhouse conditions, but flower senescence was accelerated by an average of 2 days.

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

Ethylene gas can cause extensive damage to bedding plants during production, shipping, and retailing. Seedlings exposed to ethylene exhibit the triple response, which includes an exaggerated apical hook, thickened hypocotyl, and reduced hypocotyl elongation. Our objective was to determine if the hypocotyl elongation component of the seedling triple response could be used to predict the sensitivity of mature plants at the marketable stage. Eighteen common bedding plants were evaluated. For the seedling hypocotyl elongation screen, seeds were germinated and grown in the dark on filter paper saturated with various concentrations of 1-aminocyclopropane-1-carboxylic acid (ACC; the immediate precursor to ethylene). The relative hypocotyl length at each ACC concentration was compared with untreated control (0 μM) seedlings. Mature plants, with at least four open flowers, were treated with ethylene (0, 0.01, 0.1, 1, or 10 μL·L−1) in the dark for 24 hours. Phenotypic responses to ethylene, including flower abscission, flower senescence, leaf abscission, leaf chlorosis, and epinasty, were rated on a scale of 0 to 5. Five species exhibited very little reduction in hypocotyl elongation when grown on ACC (low sensitivity). The remaining species were classified as medium or high ethylene sensitivity at the seedling stage. The most common symptoms of ethylene damage observed in mature plants were leaf epinasty, flower abscission, and flower senescence. The severity of these responses was used to identify plants with high, medium, or low sensitivity to ethylene. For six of the bedding plant species that were equally responsive at both developmental stages, the seedling hypocotyl elongation screen would provide a reliable means of predicting the ethylene sensitivity of mature plants.

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Emma L. Locke*, Cecil Stushnoff, Joyce C. Pennycooke and Michelle Jones

Salinity, drought and temperature frequently limit crop productivity. Transgenic Petunia ×hybrida cv. Mitchell with altered endogenous raffinose family oligosaccharides (RFO) due to over-expression (sense) or under-expression (antisense) of the tomato α-galactosidase gene show that antisense increases in RFO are associated with greater tolerance to freezing stress (Pennycooke et al., 2003). Because vegetative propagules of these antisense lines rooted and established more quickly than their sense counterparts, we hypothesized that antisense lines would also respond to salinity and wilting stress. Salinity treatment plants were exposed to 50-200 mm NaCl graduated 25 mm every 3 days and held at 200 mm for 13 days. Dry-down treatments were watered to pot capacity, then not watered until the onset of wilting. This was repeated in cycles for 26 days. Data were collected on plant growth, root/shoot ratios, and leaf water potential. Fresh and dry weights in four of the six antisense lines exceeded the wild type and sense lines. Osmotic potential for salinity and dry-down plants was 160% to 220% higher than control plants. Pearson correlations revealed that higher osmotic potential was partially associated with higher fresh weight (r = 0.7214, P = 0.02) and root/shoot ratios (r = -0.7414, P = 0.02) in salinity stressed plants. In the dry-down drought stressed plants, osmotic potential was not associated with fresh weight (r = 0.3364, ns) nor root/shoot ratio (r = -0.0431, ns). Salinity stress reduced root mass compared to control and dry down plants. Sense plants grew slowly and were highly variable.