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Bruce W. Wood

sap during the late winter to early spring transition period before and during budbreak likely influence floral initiation and evocation. Positive pressure within a tree’s above-ground stem structure leads to late winter xylem sap flow. This pressure

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Cheng Bai, Charles C. Reilly, and Bruce W. Wood

spring, this N pool, some of which is in soluble proteins that undergo enzymatic hydrolysis, is mobilized and translocated as reduced organic N moving in xylem sap to sinks in the canopy ( Ourry et al., 2001 ). Most of this translocating N is in the form

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Reza Salehi, Abdolkarim Kashi, Jung-Myung Lee, Mesbah Babalar, Mojtaba Delshad, Sang-Gyu Lee, and Yun-Chan Huh

calcium ions. Absorption and translocation of other micronutrients such as iron and boron are also influenced by the rootstock ( Rivero et al., 2004 ). Concentrations of nitrogen, phosphorus, calcium, and magnesium in xylem saps increased in grafted plants

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Robert C. Ebel, Xiangrong Duan, and Robert M. Augé

Mycorrhizal colonization can alter stomatal behavior of host leaves before or during soil drying, but the mechanism of influence is not always clear. We examined the possibility that mycorrhizal symbiosis might result in either altered stomatal sensitivity to abscisic acid (ABA) moving from roots to shoots in xylem sap, or altered movement of ABA in xylem as a function of soil water content (θ). Mycorrhizal colonization of Vigna unguiculata did not change the relationship between stomatal conductance (g s) and xylem [ABA] during drying of whole root systems. Stomatal conductance was higher in mycorrhizal than in similarly sized and similarly nourished nonmycorrhizal plants when soil moisture was relatively high, perhaps related to lower xylem [ABA] in mycorrhizal plants at high soil θ. Neither g s nor xylem [ABA] was affected by mycorrhizae at low soil θ. Higher g s in mycorrhizal plants was evidently not related to a mycorrhizal effect on leaf water status, as neither g s/shoot Ψ nor shoot Ψ/soil θ relationships were altered by the symbiosis. Stomatal conductance was much more closely correlated with xylem [ABA] than with soil θ or shoot Ψ. Decreased xylem [ABA] may explain why mycorrhizal colonization sometimes increases g s of unstressed mycorrhizal plants in the absence of mycorrhizae-induced changes in host nutrition. This work was supported by USDA NRICGP grant 91-37100-6723 (R.M.A).

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Seong-Hee Lee, Soon-Ho Ha, and Gap-Chae Chung

In order to diagnose the nutritional disorders caused by various environmental stress, biochemical test, xylem sap analysis and colorimetric petiole analysis were used to assay symptoms well before the severe development. Among the various enzymatic analysis, alkaline phosphatase activity was highly specific to calcium deficiency while in vivo nitrate reductase activity was not stable parameter in response to nitrogen deficiency. Determination of nitrogen, phosphorus and magnesium by colorimetric petiole analysis was sensitive to induced deficiencies. The status of potassium in the plant, however, could be better determined with the xylem sap analysis. Salinity stress induced by low osmotic potential of the nutrient solution increased the activity of alkaline phosphatase, showing similar results as calcium deficiency. Magnesium and phosphorous contents by the colorimetric petiole analysis were particularly low when the roots in anoxia.

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X. Deng, S.A. Weinbaum, T.M. DeJong, and T.T. Muraoka

Abortion of distillate flowers (PFA) in a protandrous cultivar of walnut (Juglans regia L. cv. Serr) was increased by N deficiency. Starch and N concentrations in wood of 2-year-old twigs decreased to minimal levels during abortion of distillate flowers. Nitrogen reserves in woody tissues were reduced by foliar N deficiency, as were concentrations of sugars and N in vacuum-extracted xylem sap. Abortive distillate flowers ceased growth before spur leaves reached 50% of full expansion. PFA may result from transient deficiencies of C and N during the spring flush of growth. Depletion of storage C and N was accentuated before maturation of distillate flowers in this cultivar by the metabolic demands of many catkins, spur growth, and leaf expansion.

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Eran Raveh

Chloride stress in commercial citrus is predominantly a result of increased osmotic pressure in the plant as a result of excess chloride. The source of the chloride is usually from the soil solution, where it is absorbed by the roots. After being absorbed, chloride flows through the xylem in the transpiration stream to the shoot, where it is accumulated by transpiring tissues such as leaves and fruit. Monitoring chloride concentration along any of these steps can be used to assess potential stress in the tree. Since some of these tissues tend to accumulate chloride (fruit and leaves) while others do not (root and xylem), analyses should be interpreted within the context of these differences. Having high chloride concentration in roots or xylem-water at a specific sampling time does not necessarily mean that leaves have already accumulated chloride to a toxic level, while having high chloride concentration in fruit or leaf analysis does not necessarily mean that the trees are still being exposed to high salinity in the soil solution. The advantages of the various analyses, as well as their difficulties, are discussed. It was concluded that a combination of xylem sap chloride analysis and leaf chloride analysis are the most useful tools for assessing potential chloride stress in citrus trees.

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Kyong Ju Choi, Gap Chae Chung, and Sung Ju Ahn

Cucumber (Cucumis sativus L.) seedlings were grafted onto cucumber-(CG) or figleaf gourd (FG, Cucurbita ficifolia Bouche) seedlings in order to determine the effect of solution temperature 12, 22, and 32C) on the mineral composition of xylem sap and plasma membrane K+–Mg++–ATPase activities of the roots. Low solution temperature (12C) lowered the concentration \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{H}_{2}\mathrm{PO}_{4}^{-}\) \end{document} in xylem sap of CG plants, but not of FG plants. Concentrations of K+, Ca++, and Mg++ in xylem sap were less affected than anions by solution temperature. The plasma membrane of FG plants grown in 12C solution temperature showed the highest K+–Mg++–ATPase activity at all ATP concentrations up to 3 mM and at low reaction temperature up to 12C, indicating resistance of figleaf gourd to low root temperature.

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Alexander Lang and Richard K. Volz

The effects of spur leaf removal on xylem sap flows and calcium accumulation in fruit of apple (Malus ×domestica Borkh. `Royal Gala') were determined 56 to 61 days after full bloom. Fruit calcium concentrations were reduced but fruit size was not influenced by partial spur defoliation at bloom. Apples exchanged xylem sap with the tree in daily cycles of flow reversal. The presence of local spur leaves promoted this exchange by accentuating the xylem sap drawn out of the fruit during the day, requiring more to flow back into the fruit at night to replace it. Calcium concentrations were lower in the xylem sap leaving the fruit than in that entering it. The reduced calcium accumulation in the fruit borne on defoliated spurs can therefore be attributed to the reduced volume of xylem sap exchanged between tree and fruit.

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Steven J. McArtney and David C. Ferree

Grapevines (Vitis vinifera L.) were covered with an 80% neutral shade cloth from flowering until harvest to investigate effects of shade on early season vegetative development in the year after treatment. Shading reduced root dry weight, the concentration of soluble sugars, and amino nitrogen in xylem sap at budbreak, and leaf area expansion in the following year. Dry weight of roots on both shaded and nonshaded vines declined by more than 50% in the first 3 weeks after budbreak and then began to increase, but still had not recovered to prebudbreak levels, 10 weeks after budbreak. Total leaf area per shoot was reduced in the year after shading due to both fewer and smaller leaves.