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James D. Spiers, Fred T. Davies, Scott A. Finlayson, Chuanjiu He, Kevin M. Heinz, and Terri W. Starman

This research focused on the effects of nitrogen fertilization on jasmonic acid accumulation and total phenolic concentrations in gerbera. The phytohormone jasmonic acid is known to regulate many plant responses, including inducible defenses against insect herbivory. Phenolics are constitutive secondary metabolites that have been shown to negatively affect insect feeding. Gerbera jamesonii `Festival Salmon Rose' plants were grown in a growth chamber and subjected to either low fertilization (only supplied with initial fertilizer charge present in professional growing media) or high fertilization (recommended rate = 200 mg·L-1 N). Plants were fertilized with 200 mL of a 15N–7P–14K fertilizer at 0 or 200 mg·L-1 N at each watering (as needed). Treatments consisted of ±mechanical wounding with a hemostat to one physiologically mature leaf and the subsequent harvest of that leaf at specified time intervals for jasmonic acid quantification. Total phenolics were measured in physiologically mature and young leaves harvested 0 and 10 hours after ±mechanical wounding. Low-fertility plants had reduced aboveground dry mass, were deficient in nitrogen and phosphorus, and had about a 10× higher concentration of total phenolics when compared to high fertility plants. In low-fertility plants, young leaves had greater concentrations of phenolics compared to physiologically mature leaves. There were no differences in total phenolics due to wounding. The effect of nitrogen fertilization on jasmonic acid accumulation will also be discussed.

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William R. Woodson, Ky Young Park, Paul Larsen, and Hong Wang

The senescence of carnation (Dianthus caryophyllus L.) flower petals is associated with increased synthesis of the phytohormone ethylene. This ethylene serves to initiate and regulate the processes of programmed cell death. We are using molecular approaches to study the regulation of ethylene biosynthesis in various floral organs during development and senescence of flowers. We have isolated and cloned mRNAs which encode the ethylene biosynthetic pathway enzymes s-adenosylmethionine (SAM) synthetase, 1-aminocyclopropane-1-carboxylate (ACC) synthase and the ethylene forming enzyme (EFE) from carnation flower petals. These cDNAs have been used as molecular probes to determine the steady-state mRNA levels of these transcripts in senescing flowers. The increase in ethylene associated with petal senescence is accompanied by a dramatic increase in the abundance of transcripts for both ACC synthase and EFE. In striking contrast, the level of SAM synthetase mRNA decreases significantly with the onset of petal senescence. Genomic DNA Southern blots reveal both ACC synthase and EFE are encoded by multigene families. We have recently isolated several genomic clones from carnation which represent different ACC synthase genes. The structure and organization of these gene will be presented.

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Eva Bacaicoa, Ángel María Zamarreño, Diane Leménager, Roberto Baigorri, and José María García-Mina

Some studies suggest that iron (Fe) stress root responses are regulated by variations in specific plant hormones. However, this question remains unclear. A time-course experiment dealing with the relationship between the expression of the Fe-stress root responses at transcriptional (CsFRO1, CsIRT1, CsHA1, and CsHA2) and enzymatic levels [root Fe(III)-chelate reductase and plasma membrane H+-ATPase], and the variation of phytohormone concentrations in the shoot and root of Fe-starved plants have been studied in a Fe-efficient cucumber cultivar (Cucumis sativus L. cv. Ashley). The results indicate that the expression over time of the physiological Fe-stress root responses at transcriptional and enzyme activity levels are consistent with significant increases in indole-3-acetic acid root (transient) and shoot (sustained) concentrations. Fe-starvation also caused transient changes in the root concentration of abscisic acid and nitric oxide. Finally, an increase in root ethylene production and a decrease in the root concentration of some cytokinins were observed under Fe starvation, but they were not clearly timely coordinated with the expression of Fe physiological root responses.

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William R. Woodson

The senescence of carnation (Dianthus caryophylus) flower petals is regulated by the phytohormone ethylene and is associated with the expression of a number of senescence-related genes. These genes encode enzymes in the ethylene biosynthetic pathway, including both ACC synthase and ACC oxidase. Members of these gene families are differentially regulated in floral organs, with specific members responsible for the increase in ethylene biosynthesis that leads to petal senescence. Pollination often serves as the external signal to initiate the senescence cascade. Following pollination, a rapid increase in ethylene production by the pistal occurs, which is subsequently followed by increased ethylene in the petal. This response is mediated by pollen–pistil interaction(s) that occurs only in compatible pollinations. Recent data indicate that the signal transduction cascade following this cell-cell communication involves protein phosphorylation, as pollination-induced ethylene is sensitive to protein kinase and phosphatase inhibitors. To date, our lab has cloned and characterized a number of senescence-related genes that are believed to play a role in the process of senescence. These include genes that encode enzymes involved in cell wall dissolution (b-galactosidase), protein degradation (cysteine proteinase) and detoxification of breakdown products (glutathione s-transferase). Many of these senescence-related genes are under the transcriptional regulation of ethylene, which has been characterized at the molecular level. A number of biotechnology approaches to controlling the senescence of flowers have been explored. These include the down-regulation of ethylene biosynthetic genes, the expression of a dominant-negative mutation of the ethylene receptor gene, and the expression of genes that lead to increased cytokinin levels in tissues. These will be discussed in relation to the potential for delaying senescence through genetic engineering.

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Xunzhong Zhang, E.H. Ervin, and R.E. Schmidt

A variety of organic materials such as humic substances, seaweed extracts (SWE), organic matter, and amino acids are being used as fertilizer supplements in commercial turfgrass management. Among them, SWE and humic acid (HA) are widely used in various biostimulant product formulations. These compounds have been reported to contain phytohormones and osmoprotectants such as cytokinins, auxins, polyamines, and betaines. Manufacturer claims are that these products may supplement standard fertility programs by reducing mineral nutrient requirements while improving stress tolerance. There is a lack of season-long, field-based evidence to support these claims. This study was conducted to investigate the influence of monthly field applications of SWE, HA, and high and low seasonal fertilization regimes on the physiological health of fairway-height creeping bentgrass (Agrostis stolonifera L.). Plots were treated monthly with SWE at 16 mg·m-2 and HA (70% a.i.) at 38 mg·m-2 alone, or in combination, and were grown under low (20 kg·ha-1/month) or high nitrogen (50 kg·ha-1/month) fertilization regimes during 1996 and 1997. Endogenous antioxidant superoxide dismutase (SOD) activity, photochemical activity (PA), and turf quality were measured in July of each year. Superoxide dismutase activity was increased by 46% to 181%, accompanied by a PA increase of 9% to 18%, and improved visual quality of bentgrass in both years. There was no significant fertilization × supplement interaction. Although not part of our original objectives, it was noted that significantly less dollar spot (Sclerotinia homoeocarpa F.T. Bennett) disease incidence occurred in supplement-treated bentgrass. Our results indicate that increased SOD activity in July due to SWE and/or HA applications improved overall physiological health, irrespective of fertilization regime. This suggests that these compounds may be beneficial supplements for reducing standard fertilizer and fungicide inputs, while maintaining adequate creeping bentgrass health.

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Wei Li, Rongcai Yuan, Jacqueline K. Burns, L.W. Timmer, and Kuang-Ren Chung

Colletotrichum acutatum J. H. Simmonds infects citrus flower petals, causing brownish lesions, young fruit drop, production of persistent calyces, and leaf distortion. This suggests that hormones may be involved in symptom development. To identify the types of hormones, cDNA clones encoding proteins related to ethylene and jasmonate (JA) biosynthesis, indole-3-acetic acid (IAA) regulation, cell-wall modification, signal transduction, or fruit ripening were used to examine differential gene expressions in calamondin (Citrus madurensis Lour) and/or `Valencia' sweet orange (Citrus sinensis Osbeck) after C. acutatum infection. Northern-blot analyses revealed that the genes encoding 1-aminocyclopropane-1-carboxylate (ACC) oxidase and 12-oxophytodienoate required for ethylene and JA biosynthesis, respectively, were highly up-regulated in both citrus species. Both gene transcripts increased markedly in petals, young fruit and stigmas, but not in calyces. The transcripts of the genes encoding IAA glucose transferase and auxin-responsive GH3-like protein, but not IAA amino acid hydrolyase, also markedly increased in both species 5 days after inoculation. The expansin and chitinase genes were slightly up-regulated, whereas the senescence-induced nuclease and ß-galactosidase genes were down-regulated in calamondin. No differential expression of transcripts was detected for the genes encoding expansin, polygalacturonase, and serine-threonine kinase in sweet orange. As compared to the water controls, infection of C. acutatum increased ethylene and IAA levels by 3- and 140-fold. In contrast, abscisic acid (ABA) levels were not significantly changed. Collectively, the results indicate that infection by C. acutatum of citrus flowers triggered differential gene expressions, mainly associated with IAA, ethylene, and JA production and regulation, and increased hormone concentrations, consistent with the hypothesis of the involvement of phytohormones in postbloom fruit drop.

Open access

Yanxia Zhao, Guimei Qi, Fengshan Ren, Yongmei Wang, Pengfei Wang, and Xinying Wu

Abscisic acid (ABA) is an essential phytohormone that regulates plant growth and development, particularly in response to abiotic stress. The ABA receptor PYR/PYL/RCAR (PYL) family has been identified from some plant species. However, knowledge about the PYL family (VvPYLs) in grape (Vitis vinifera) is limited. This study aims to conduct genome-wide analyses of VvPYLs. We successfully identified eight PYL genes from the newest grape genome database. These VvPYLs could be divided into three subfamilies. Exon-intron structures were closely related to the phylogenetic relationship of the genes, and PYL genes that clustered in the same subfamily had a similar number of exons. VvPYL1, VvPYL2, VvPYL4, VvPYL7, and VvPYL8 were relatively highly expressed in roots. VvPYL1, VvPYL3, VvPYL7, and VvPYL8 were expressed in response to cold, salt, or polyethylene glycol stress. VvPYL6 was up-regulated by cold stress for 4 hours, and the expression of VvPYL2 was 1.74-fold greater than that of the control under cold stress. VvPYL8 was up-regulated 1.64-, 1.83-, and 1.90-fold compared with the control when treated with salt, PEG, or cold stress after 4 hours, respectively. Additionally, abiotic stress-inducible elements exist in VvPYL2, VvPYL3, VvPYL7, and VvPYL8, indicating that in these four genes, the response to abiotic stress may be regulated by cis-regulatory elements. The transcriptional levels of VvPYL1 and VvPYL8 significantly increased from fruit set to the ripening stage and decreased in the berry when treated by exogenous ABA. The eight VvPYL genes have diverse roles in grape stress responses, berry ripening, or development. This work provides insight into the role of VvPYL gene families in response to abiotic stress and berry ripening in grape.

Free access

Bruce W. Wood

one or more seed-associated phloem mobile phytohormones in regulation of floral initiation (i.e., the production of meristems of clearly recognizable flower primordia and includes all preceding reactions that are required if flowers are to be initiated

Free access

Norman Q. Arancon, Archana Pant, Theodore Radovich, Nguyen V. Hue, Jesse K. Potter, and Chad E. Converse

phytohormones [e.g., abscisic acid (ABA) and ABA metabolites, cytokinins, auxins, and gibberellins] of lyophilized compost tea samples were analyzed at the Plant Biotechnology Institute of the National Research Council of Canada (PBI-NRC Saskatoon, Saskatchewan

Free access

Yang Yang, Runfang Zhang, Pingsheng Leng, Zenghui Hu, and Man Shen

physiological and biochemical responses during cold acclimation, including the modification of membrane lipid composition, synthesis of protective proteins, increase of compatible compounds, and regulation of phytohormones ( Guy, 1990 ; Thomashow, 1999