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Michael A. Grusak and Kirk W. Pomper

Understanding the mechanisms that regulate xylem transport of calcium (Ca) to snap bean (Phaseolus vulgaris L.) pods could allow approaches to enhance pod Ca levels, and thereby improve the value of this food source for humans. Pods of greenhouse-grown plants of `Hystyle', `Labrador', `Tendergreen', `Green Crop', `BBL94', and `Gold Crop' were examined for stomatal density and rates of pod transpiration throughout pod development. Among pods ranging from 6 to 14 mm in diameter, Ca concentration and pod stomatal density varied inversely with increasing diameter in all cultivars; Ca concentration for pods of a given diameter also varied among cultivars. To assess the influence of pod stomatal density on pod transpiration, water loss was measured from detached pods of `Hystyle' and `Labrador', which have high and low pod stomatal densities, respectively. Pod transpiration rates were similar for the two cultivars, being ≈15% the rate measured in leaves under equivalent conditions, and comparable to rates of cuticular transpiration measured in leaves with closed stomates. These results suggest that pod stomates have no role, or have only a limited role, in pod transpiration. Pods of `Hystyle' and `Labrador' were placed in enclosures that maintained constant high- or low-humidity environments throughout pod development. For each cultivar, the high-humidity environment led to lower pod Ca concentrations, demonstrating that pod transpiration does have a significant impact on pod Ca accretion. However, `Hystyle' consistently exhibited higher pod Ca concentrations, relative to `Labrador', suggesting that differences in xylem sap Ca concentration may have been responsible for cultivar differences in pod Ca concentration.

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Moreno Toselli, James A. Flore and Bruno Marangoni

Low root-zone temperature is one of the potential causes of low rate of plant nutrient uptake in spring. In this period, fruit trees are frequently supplied with nitrogen and a delay in root absorption could lead to an increase of nitrate leaching. In this study we assessed the effect of low root temperature on kinetic of nitrogen absorption of apple trees. One-year-old rooted cuttings of `Mark' apple rootstocks were subjected to two root temperature: 8 ± 1°C (LT) and 23 ± 1°C (HT). Four days after treatment imposition, the potted plants were supplied with 20 mg of N as NH4N03, enriched with 10 atom% of 15N. One, 2, 4, and 8 days after fertilization, tree root system was inserted into a Sholander bomb where a 0.325-Mpa pressure was applied to collect the xylem sap from the stem cross section. The sap exudation rate was always depressed by low root temperature. Nitrogen flow through the xylem vessel was highest in HT plants the day after fertilization (10-fold higher than LT), then decreased constantly. In LT plants, N flow was low the first and the second day after fertilization then reached the maximum 4 days after fertilization, when it was significantly higher than in HT plants. The amount of fertilizer-N found in leaves reflected the different movement rate of N observed in the two treatments. In HT trees fertilizer-N reached a plateau 2 days after fertilization, while in LT it linearly increased over time. This results suggest that root zone temperature of 8°C, although causes a delay (2–4 days) in nitrogen uptake, does not represent a serious limiting factor for N nutrition of tested apple trees.

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Yong-Ping Gao, Hino Motosugi and Akira Sugiura

Ungrafted trees of seven apple rootstock cultivars, M.4, M.7, M.11, M.26, M.27, MM.106, and Maru. bakaidou (Malus prunifolia Borkh. var. ringo Asami; weeping type), and `Fuji' (Malus domestics Borkh.) trees grafted on these seven plus M.9 and M. 16 rootstock were grown in sand. They were regularly supplied with nutrient solutions of N as ammonium alone (A), nitrate alone (T), and both (AT). With both ungrafted and grafted trees, the shoot growth of six rootstock (M.11, M.4, M.7, MM.106, M.26, and M.27) was significantly less with A than with T. With `Fuji' trees grafted on the above six rootstock, the number of flowering buds and the ratios of flowering buds to total emerged buds were significantly enhanced by treatments A and AT, especially in the formation of axillary flowering buds. Flowering and shoot growth of `Fuji' trees grafted on M. prunifolia and M.16 were slightly affected by the form of supplied N. In the xylem sap, cytokinin-like activity was detected in a single zone in paper chromatography in all rootstock and `Fuji' trees. The activity in six ungrafted rootstock (M.4, M.7, M.11, M.26, M.27, and MM.106) and `Fuji' trees grafted on these plus M.9 rootstock were higher with A than with T. Gibberellin-like activity in the same sap was detected in two zones, Rfs 0.3 to 0.4 and Rfs 0.7 to 0.8 in paper chromatography. In the six ungrafted rootstock and in `Fuji' trees grafted on these plus M.9, A led to higher activity at Rfs 0.7 to 0.S, but T led to higher activity at Rfs 0.3 to 0.4. Cytokinin-like and gibberellin-like activities in ungrafted M. prunfolia and `Fuji' trees grafted on M. prunifolia or M.16 were not affected by the form of N.

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Allen V. Barker

days. The technique has been applied to assess nutritional deficiencies and toxicities in plant tissue and responses to abiotic stresses. Sampling and analysis of phloem and xylem sap are presented in Chapters 12 and 13. Procedures for collecting phloem

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Allen V. Barker

flow, and driving forces for water movement in the xylem. Also, this chapter covers the transport of nutrients, including mechanisms of xylem loading, xylem-sap composition, and xylem unloading in leaves. Chapter 10 is a rigorous one that covers solute

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Rangjian Qiu, Taisheng Du, Shaozhong Kang, Renqiang Chen and Laosheng Wu

was higher at the higher N application rate under higher water application treatment, but lower stem sap flow was observed at the higher N application rate if plants suffered water deficit. In a shrub ( Ligustrum ovalifolium ), the cumulative xylem sap

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Wenjing Guan, Xin Zhao, Richard Hassell and Judy Thies

concentration in xylem sap than that of self-rooted melon plants ( Salehi et al., 2010 ). In addition, foliar nitrate concentrations were lower in grafted watermelons and melons accompanied by higher nitrate reductase activities in comparison with self

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Anish Malladi and Jacqueline K. Burns

, phosphate, and nitrate from roots to shoots of flooded plants. Accounting for the effects of xylem sap flow rate on concentration and delivery Plant Physiol. 107 377 384 Ewing, E.E. Struik, P.C. 1992 Tuber formation in

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Pascal Nzokou and Bert M. Cregg

, or Mn contents ( Fig. 2 ). The reason for the significant effect on foliar Ca needs to be further investigated because Berger (1994) did not observe any change in Ca, K, or Mg concentration in xylem sap after mild or severe drought cycles. The

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Da Man, Yong-Xia Bao, Lie-Bao Han and Xunzhong Zhang

(zeatin riboside and zeatin ribotide–dihydrozeatin and isopentenyl adenine) are the most common naturally occurring cytokinins ( Strivastava, 2002 ). Bano et al. (1993) noted that cytokinin concentration in xylem sap declined after water deprivation and