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Leslie D. Hintz, Renee R. Boyer, Monica A. Ponder, Robert C. Williams, and Steven L. Rideout

pathogen was not recovered from plant tissue ( Jablasone et al., 2004 ). Greenhouse tomato plants irrigated with S . Montevideo-contaminated water displayed no contamination in tomato fruits, but samples of roots exposed to four or more irrigation events

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R. Larry Peterson, Gregory T. Varney, and Shannon Binns

Primary and first-order lateral roots of Panax quinquefolius L. (American ginseng) were collected from plants in an experimental garden during their second year of growth and processed for light and transmission electron microscopy. Roots in primary growth had either a diarch or triarch primary xylem pattern, a pericycle, an endodermis with Casparian bands and subsequently a suberized cell wall, and a cortex of variable thickness with a suberized hypodermal layer. Both root types underwent rapid secondary growth and the primary root particularly formed a fleshy storage organ. The secondary phloem and secondary xylem had abundant parenchyma and few conducting elements. Secretory ducts differentiated in tissue derived from the pericycle and in the secondary phloem. Each schizogenous duct consisted of six to eight epithelial cells, which possessed dense, globular deposits but lacked starch. A phellogen, which produced several layers of suberized phellem, was initiated in the periphery of tissue derived from the pericycle. The results of this study clarify the anatomical localization of secretory duets in roots of this species.

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John A. McCallum, Meeghan Pither-Joyce, and Martin Shaw

Genetic and environmental factors affect onion (Allium cepa L.) pungency but the molecular basis for this variation is not understood. To initiate molecular analysis of onion sulfur metabolism we isolated cDNAs from onion associated with sulfur assimilation and compared gene expression and sulfur metabolism of mild and pungent onion cultivars. We isolated cDNAs encoding homologues of 5'adenosine-phosphosulfate (APS) reductase, γ-glutamylcysteine synthetase and serine acetyl transferase using a homology-based RT-PCR approach. Homologues of high-affinity sulfate transporters and sulfite reductase were isolated from an onion root differential cDNA library enriched for genes up-regulated by 48 hours sulfur deprivation. The influence of genotype and sulfur nutrition on root expression of selected genes was measured in an experiment in which a low pungency onion cultivar (`Houston Grano') and a high pungency cultivar (`Canterbury Longkeeper') were grown hydroponically in low (0.1 meq·L-1) or high (4.0 meq·L-1) sulfate medium and harvested before bulbing. `Canterbury Longkeeper' contained higher concentrations of (+)-S-methyl-L-cysteine sulfoxide in leaf and root than `Houston Grano' but cultivars did not differ in leaf trans-(+)-S-(1-propenyl)-L-cysteine sulfoxide concentrations. `Houston Grano' accumulated significantly higher concentrations of total N, nitrate, and basic amino acids in leaves and roots, suggesting these cultivars differ markedly in maintenance of S/N homeostasis. Steady-state transcript levels of APS reductase and high-affinity sulfate transporter in roots were significantly higher (2- to 3-fold) at low sulfate. By contrast, steady state levels of ATP sulfurylase transcript were significantly higher at high sulfate levels and in `Canterbury Longkeeper'. We conclude that differences in regulation of the sulfur assimilation pathway may underlie genetic differences in pungency.

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Jonathan P. Lynch

sulfur ( Bouranis et al., 2003 ; Drew et al., 1989 ; Fan et al., 2003 ; Konings and Verschuren, 1980 ). RCA is an important adaptation to soil flooding by facilitating oxygen movement to the roots. We hypothesized that RCA is also an adaptation to low

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Liang Cheng, Ning Zhang, and Bingru Huang

associated with salinity stress in leaves and roots of various plant species ( Arbona et al., 2003 ; Ghanem et al., 2008 ; Gómez-Cadenas et al., 1998 ; Kukreja et al., 2005 ; Zapata et al., 2004). Excessive ethylene in plants exposed to stresses, including

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Patrick E. McCullough, Ted Whitwell, Lambert B. McCarty, and Haibo Liu

further exacerbate root growth of these low-growing grasses ( White, 1998 ). Practices potentially injurious to dwarf-type bermudagrass roots such as preemergence herbicide applications may reduce turf vigor, inhibit recuperation from stress, and increase

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Gretchen B. North and Evan A. Baker

For desert succulents, and for several other plant species, older roots play a more active role in water uptake than is generally acknowledged. We suggest that older roots of most plants can and do take up water, and we discuss in more detail the

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Shixin Deng, Qun Yin, Shanshan Zhang, Kankan Shi, Zhongkui Jia, and Luyi Ma

. However, irrigation alters the water and nutrient status of the soil. Roots are the primary organ of plants that absorbs water and nutrients in the soil, and roots act as the dynamic interface between the plants and soil ( Gordon and Jackson, 2000 ). The

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Mordecai J. Jaffe and A. Carl Leopold

The autonomous movement of plant stems or bulbs down into the soil occurs through the contraction of roots. This type of movement was first noted by Theophrastus (≈300 BCE) and was described more recently by Tittmann (1819) in roots of Daucus

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Christine E.H. Coker, Gary Bachman, Chris Boyd, Pamela B. Blanchard, Ed Bush, and Mengmeng Gu

The Louisiana State University (LSU) Coastal Roots School Seedling Nursery Program for Habitat Restoration (Coastal Roots) was initiated in Jan. 2000 to assist students in Louisiana in developing an attitude of stewardship toward Louisiana's coastal