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Philip J. Stewart, Ashley R. Winslow, and Kevin M. Folta

The transition from vegetative growth to reproductive growth is carefully controlled by a number of independent signal transduction systems, one of which interprets photoperiod. Photoperiodic control of flowering time has been well-described in Arabidopsis and rice, revealing the presence of a generally common network of regulatory proteins. Timely and appropriate progression to flowering is critical to profitable production of cultivated strawberry (Fragaria ×ananassa), a species that includes long-day, short-day, and day-neutral cultivars. In an effort to characterize the photoperiodic flowering control mechanism in strawberry, the Fragaria orthologs of the photoperiod pathway genes were cloned and sequenced. Strawberry versions of Constans, Constans-like, Leafy, Flowering Locus T, and Suppressor of Constans Overexpression 1 were identified by screening cDNA libraries and through degenerate PCR approaches. Expression of these transcripts in short-day and day-neutral cultivars was tested under long and short photoperiods. Functional complementation of Arabidopsis mutants was performed where appropriate, alleles were identified, genetic linkage was determined where possible, and relationships between the strawberry genes and homologs from other species were studied. These trials define the mechanistic elements of an agriculturally important pathway in this valuable crop, and lays the foundation for transgenic studies in strawberry to manipulate the floral transition.

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Yu Bai, Ying Zhou, Xiaoqing Tang, Yu Wang, Fangquan Wang, and Jie Yang

transition from vegetative growth to reproductive development ( Moon et al., 2005 ; Parcy, 2005 ). The genes involved in flowering control have been characterized in Arabidopsis thaliana and have been integrated into multiple flowering pathways, including

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Dipayan Sarkar, Prasanta C. Bhowmik, Young-In-Kwon, and Kalidas Shetty

phenylpropanoid pathway and the production of proline in plants during abiotic stress is well documented ( Christie et al., 1994 ; Dorffling et al., 1997 ). Studies in wheat indicated higher accumulation of proline during acclimation and its association in

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Yan Li, Hongyan Qi, Yazhong Jin, Xiaobin Tian, Linlin Sui, and Yan Qiu

aldehydes through β-oxidation, hydroperoxyacid cleavage, and the LOX pathways ( Schwab et al., 2008 ). Lipoxygenase and HPL are important enzymes produced by the LOX pathway, which is responsible for the synthesis of volatile compounds contributing to “green

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Thomas Ranney* and Thomas Eaker

Information on ploidy levels is extremely valuable for use in plant breeding programs. Fertility, crossability, and heritability of traits are all influenced by ploidy levels. Knowledge of reproductive pathways, including occurrence of apomixes, pseudogamy, and formation of unreduced gametes can also be important information for developing breeding strategies. Although ploidy level can be determined by counting chromosomes, flow cytometry provides a reliable and much faster means for determination of nuclear DNA content and associated ploidy level. Measurement of ploidy levels of seeds (embryo and endosperm) can also provide useful insights into reproductive pathways. The objective of this study was to determine the approximate genome size, estimated ploidy level, and range of reproductive pathways of a diverse collection of flowering crapbapples (Malus spp.). Genome sizes were calculated as nuclear DNA content for unreduced tissue (2C). Results from the taxa included in our survey showed DNA contents ranging from 1.52 to 1.82 for diploids, 2.40 to 2.62 for triploids, and 3.36 to 3.74 pg/2C for tetraploids. Based on these ranges, we identified 43 diploid, 10 triploid, and 4 tetraploid crabapple taxa in this collection. Results from open pollinated seeds and seedlings demonstrated a variety of reproductive pathways including apomixes and unreduced gametes. This research provides information on ploidy levels and reproductive pathways of flowering crabapples and will allow for more systematic and efficient progress in the development of improved cultivars.

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Jingyi Lv, Yonghong Ge, Canying Li, Mengyuan Zhang, and Jianrong Li

-isoleucine (JA-Ile) ( Wasternack, 2007 ). AOS is the first specific enzyme and the major control point of the JA biosynthesis pathway ( Laudert and Weiler, 1998 ). JA initiates its signaling process on the formation of a SCF COI1 -JA-Ile-JAZ [Skp

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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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Thomas O. Athoo, Andreas Winkler, and Moritz Knoche

about the mechanisms and pathways of water loss by a cherry fruit’s pedicel ( Linke et al., 2010 ; Smith and Whiting, 2011 ). The role played by the fruit in pedicel transpiration is not clear. Water loss from plant surfaces (including of fruit and

Open access

S.Y. Wang, G.L. Steffens, and M. Faust

Abstract

A cyanide-resistant alternative pathway was found to exist in root tissue of apple (Malus domestica Borkh.). In the absence of potassium cyanide (KCN), an inhibitor of cytochrome electron transport, the alternative pathway did not contribute to overall root respiration. However, in the presence of KCN or carbonyl cyanide m-chlorophenyl hydrazone (CCCP), an uncoupler, active participation of the alternative pathway was detected. Inhibition of O2 uptake by salicylhydroxamic acid (SHAM) was observed in the presence of antimycin A (AA) or sodium azide (NaN3), but to a lesser degree than when KCN was present. The degree of inhibition by SHAM was greatest in the presence of KCN, followed by AA and then NaN3. The antioxidant n-Propyl gallate (PG) was found to be an effective inhibitor of the alternative pathway. The site of inhibition in apple root tissue by PG is very similar to that of SHAM. Sodium benzoate, another antioxidant and free radical scavenger, and tetraethylthiuram disulfide (disulfiram), a copper chelator, did not inhibit the alternative pathway in apple root tissue.

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Gladys M. Nazario and Carol Lovatt

A study was undertaken to identify the pathway(s) leading to the synthesis of caffeine and theobromine in leaves of Coffea arabica. The relative contribution of purine nucleosidcs and bases to the biosynthesis of these alkaloids was assessed by measuring the incorporation of radiolabeled inosine, adenosine, adenine, hypoxanthine, and xanthine into caffeine and theobromine.

The results of this investigation suggest that caffeine and theobromine are end products of two distinctively different pathways. The incorporation of radiolabeled formate, adenosine, and xanthine was significantly greater into caffeine than into theobromine. Furthermore, exogenously supplied theobromine did not dilute the incorporation of [14C]formate, [14C]inosine, or [14C]xanthine into caffeine. In contrast, radiolabeled adenine was incorporated into theobromine but not into caffeine, and exogenously supplied adenine diluted the incorporation of [14 C]adenosine into theobromine, but not into caffeine.

Taken together, these results provide strong evidence that theobromine is not a precursor of caffeine biosynthesis in leaves of C. arabica.

Supported by the Citrus Research Center and Agricultural Experimental Station of the University of California, Riverside,