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Mordecai J. Jaffe and A. Carl Leopold

in cellular configuration occur as Easter lily root contraction advances. Dimensions are presented for endodermal cells (Endo), three levels of cortex cells (Crtx-1 to Crtx-3), exodermis cells (Exo), and epidermal cells (Epi) as contraction proceeds

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Bingru Huang and David M. Eissenstat

In Citrus L. sp., specific root length of whole root systems has been correlated positively with root hydraulic conductivity, but there is little mechanistic understanding of the causes for this association. The hydraulic conductivity of individual roots in relation to root anatomical characteristics in seedlings of three citrus rootstocks [sour orange (SO) (Citrus aurantium L.), trifoliate orange (TO) (Poncirus trifoliate (L.) Raf.), and Swingle citrumelo (SC) (C. paradisi Macf. × P. trifoliata)] that vary widely in specific root length (SRL) was measured. Among fibrous roots, first-order and secondorder laterals were examined. Relative differences among rootstocks in the overall hydraulic conductivity (LP) and radial conductivity (LR) for individual 1-month-old and 6-month-old second- and first-order roots generally were consistent with hydraulic conductivity determined previously for entire root systems. There were no significant differences in axial conductance per unit pressure (Kh) in either first- or second-order roots among the rootstocks. This was consistent with the similarity in number and diameter of xylem vessels. One-month-old second-order roots had no suberized exodermis but varied in cortical radius. Six-month-old second-order roots of TO, however, had more nonsuberized cells (passage cells) in the exodermis than roots of SC and SO, although the cortical radius of SC and SO roots were not different. Compared to 6-month-old second-order roots, 1-month-old second-order roots had much higher LP and LR but lower Kh. Differences in overall root hydraulic conductivity among the citrus rootstocks were mainly related to structural differences in the radial pathway for water movement, suggesting that radial hydraulic conductivity was the primary determining factor of water uptake in citrus rootstocks.

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Carlos H. Crisosto, R. Scott Johnson, Juvenal G. Luza, and Gayle M. Crisosto

The effect of irrigation management strategies on the quality and storage performance of `O'Henry' peaches [Prunus persica (L.) Batsch] was studied for two seasons. The deficit irrigation treatment induced a higher fruit soluble solids concentration and lower fruit weight. The excess irrigation treatment, compared to the optimum treatment, increased the rate of fruit water loss without altering fruit quality and storage performance. Scanning electron microscope observations indicated a higher density of trichomes on fruit from the deficit and optimum irrigation treatments than from the excess irrigation treatment. Light microscopy studies indicated that fruit from deficit and optimum irrigation had a continuous and much thicker cuticle than fruit from the excess irrigation treatment. These differences in exodermis structure may explain the high percentage of water loss from fruit from the excess irrigation treatment compared to the deficit and optimum irrigation treatments.

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C.S. Hew, L.Y. Lim, and C.M. Low

The uptake of nitrate and ammonium by a terrestial (Bromheadia finlaysonia) and an epiphytic (Dendrobium hybrid) orchid in solution culture has been studied. The rates of nitrate and ammonium were relatively linear, with higher rate of uptake for ammonium. The rates of nitrate uptake in terrestial and epiphytic orchids were 0.4 and 0.9 μmole gm fw-1 hr-1 respectively and they were considerably lower than those of most major crops. SEM studies show that the velamen of Bromheadia was 2 cells thick whereas that of Dendrobium was 8-10 cells thick. It is unlikely that the velamen is the major factor in restricting influx of nitrate or ammonium. Nitrate reductase (NR) and glutamine synthetase (GS) were present in roots and leaves of both orchids. NR was high in roots but low in leaves. The reverse was for GS. The activities of NR and GS was low but high enough to account for the rate of nitrate or ammonium uptake. It appears that the movement of ions across the transfer junction at the exodermis plays a major regulatory role in ion uptake by orchid root.

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Renata Goossen and Kimberly A. Williams

hybrids) are epiphytic, their roots have a unique absorptive complex of velamen and exodermis that, compared with the roots of other plant species, takes in moisture and mineral nutrients passively, and protects from dehydration and physical damage ( Bercu

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Sawyer N. Adams, Walter O. Ac-Pangan, and Lorenzo Rossi

with different environmental constraints (e.g., salinity, drought). Root performance in the presence of pollutants and toxic ions relies on the Casparian strip and suberin lamellae formed in the root rhizodermis and exodermis ( Chen et al., 2011 ; Kim

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Gretchen B. North and Evan A. Baker

hairs first appear ( Taiz and Zeiger, 2002 ). Further back from the tip, internal and external suberized cell layers (the endodermis and exodermis, respectively, and later the periderm) are said to make the root relatively impermeable to water ( Purves

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Wahiba Boutebtoub, Michel Chevalier, Jean-Claude Mauget, Monique Sigogne, Philippe Morel, and Gilles Galopin

's reagent Fig. 6 . Transverse section of a young root. Fig. 7 . Cortical tissue. ( A ) Exodermis; ( B ) parenchyma cells; ( C ) phloem; ( D ) xylem; ( E ) pericycle; ( F ) endodermis; ( G ) exodermis; ( H ) laticifer; arrow (▶): starch; Bar ( ): 100 μm

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Chun-hui Shi, Xiao-qing Wang, Xue-ying Zhang, Lian-ying Shen, Jun Luo, and Yu-xing Zhang

. Technol. 43 445 455 Meyer, C.J. Peterson, C.A. Bernards, M.A. 2011a Spatial and temporal deposition of suberin during maturation of the onion root exodermis Botany-botanique 89 119 131 Meyer, C.J. Peterson, C.A. Bernards, M.A. 2011b A comparison of suberin

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Maria A. Macias-Leon and Daniel I. Leskovar

.I. 1994 The plasmalemma surface area exposed to the soil solution is markedly reduced by maturation of the exodermis and death of the epidermis in onion roots Plant Cell Environ. 17 1183 1193 Kappler, R. Kristen, U. 1986 Exogenous cytokinins cause cell