Transport and Energy Demand

Atpase Activity Plant

Intact membranes are effective barriers to the passage of ions and uncharged molecules. On the other hand, they are also the sites of selectivity and transport against the concentration gradient of solutes. In the experiment recorded in Table 2.2, for example, the potassium concentration in maize root press sap (which is approximately equal to the potassium concentration of the vacuoles) rose to 80 times the value of that in the external solution. In contrast, the sodium concentration in the...

Leaf maturation

Organic . . , structures Fig. 5.13 Schematic representation of the shift from import to export of assimilates and mineral nutrients during leaf maturation and the sink-source transition. also be caused by interruption of symplasmic phloem unloading Turgeon, 1989 . The photosynthetic capacity per se of a developing leaf is not a regulatory factor in sink-source transition. In developing sugar beet leaves grown in light or dark, photosynthate import 14C was markedly...

Mineral Nutrients of Low Phloem Mobility Example Calcium

Because of its low concentrations in the phloem sap Section 3.3.2 the import of calcium into growth sinks such as shoot apices, young leaves or fruits takes place nearly exclusively in the xylem, whereas the import in the phloem is negligible as shown for castor bean in Table 3.11. This is in marked contrast to potassium of which most terminal bud and at least half youngest leaves of the total net import takes place in the phloem. For magnesium phloem import contributes to 25 and 40 of the...

MM K mM Cf

Nyctinastic Symport

Schematic presentation of the system for measuring electropotentials in plant cells. B. Example of the calculation of ion distribution at chemical and electrochemical equilibrium assuming an electropotential of 59 mV. the membrane. To determine whether an ion is actively transported across a membrane, however, both the activity or concentration of the ion on either side of the membrane i.e., the chemical potential gradient and the electrical potential gradient i.e., differences in...

Factors Affecting Ion Release into the Xylem and Exudation Rate

The permeability of plant membranes to water is much higher than that to ions. Plant cells or roots therefore behave as osmometers. Ion release secretion, Section 2.8 into the apoplasm of the stele decreases both the osmotic potential and the water potential they become more negative , and a corresponding net flux of water from the external solution is induced. As a result of this water flux, the hydrostatic pressure increases. As the endodermis with the Casparian band 'seal' the apoplasm of...

Release of Ions into the Xylem

Root Apoplasm

After radial transport in the symplasm into the stele, most of the ions and organic solutes amino acids, organic acids are released into the xylem. This release into fully differentiated non-living xylem vessels therefore represents a retransfer from the symplasm into the apoplasm. Crafts and Broyer 1938 postulated uphill transport in the symplasm across the cortex to the endodermal cells and, in the stele, a 'leakage' into the xylem. The distinctly lower oxygen tension in the stele than in the...

B

Strategy Strategy Siderophore

Fig. 2.26 Model for circulation of mineral nutrients between shoots and roots as a mechanism for regulating uptake by roots. A Nutrients are uniformly mixed with the pool in the bulk tissue. B Only limited exchange of the cycling nutrients with the bulk tissue. Modified from Cooper corresponding fraction of the amino-N flux in the xylem was over 60 Cooper and Clarkson, 1989 . Drew and Saker 1984 proposed a model for the cycling of mineral nutrients in which potassium or phosphate delivered to...

General

The long-distance transport of water and solutes - mineral elements and low-molecular-weight organic compounds - takes place in the vascular system of xylem and phloem. Long-distance transport from the roots to the shoots occurs predominantly in the nonliving xylem vessels. Coniferous trees lack the continuous system of xylem vessels, and depend on tracheides which are non-living conducting cells ranging in length from 2 to 6 mm Tyree and Ewers, 1991 . In annual plant species too long-distance...

Exchange Adsorption and Resorption

Oxalic Acid Vacuole

The interactions between cations and the negatively charged groups in the cell walls of the xylem vessels and tracheides are similar to those in the AFS of the root cortex Fig. 2.2 . The long-distance transport of cations in the xylem can be compared with ion movement in a cation exchanger with a corresponding decline in the translocation rate of cations such as Ca2 Jacoby, 1967 and Cd2 Senden and Wolterbeek, 1990 , relative to that of water Thomas, 1967 or anions such as phosphate Ferguson and...

Uptake of Ions and Water Along the Root Axis

Growing roots vary both anatomically and physiologically along their longitudinal axes. This has to be borne in mind when models for mechanisms of 'the' behaviour of root tissue and root cells are based on uptake studies with isolated roots or roots of intact plants. In the apical zone nonvacuolated cells dominate. These cells differ in many respects from vacuolated cells in the basal zones. The apical root zones have higher respiration rates Thomson et al., 1989b which rapidly drop when...

Passage into the Cytoplasm and the Vacuole

Despite some selectivity for cation binding in the cell wall Section 2.2.1 , the main sites of selectivity in the uptake of cations and anions as well as solutes in general are located in the plasma membrane of individual cells. The plasma membrane is an effective barrier against the diffusion of solutes either from the apoplasm into the cytoplasm influx or from the cytoplasm into the apoplasm and the external solution efflux . The plasma membrane is also the principal site of active transport...

Characteristics of Ion Uptake by Roots

Before reaching the plasma membrane of root cells ions have to pass through the cell walls. In general, movement of ions and other low-molecular-weight solutes by diffusion or mass flow is not restricted to the external surface of the roots, that is the rhizodermal cells Fig. 2.1 . The cell walls and water-filled intercellular spaces of the root cortex are also, at least to a certain extent, accessible to these solutes from the external solution. The main barrier to solute flux in the apoplasm...

Radial Transport of Ions and Water Across the Root

Passage Water Through The Root

There are two parallel pathways or movement of ions solutes and water across the cortex towards the stele one passing through the apoplasm cell walls and intercellular Fig. 2.31 Part of transsection of a maize root showing the symplasmic A and apoplasmic B pathway of ion transport across the root. Fig. 2.31 Part of transsection of a maize root showing the symplasmic A and apoplasmic B pathway of ion transport across the root. spaces, Section 2.2.1 and another passing from cell to cell in the...

Xylem Transport

The composition and concentration of mineral elements and organic solutes in the xylem sap depend on factors such as plant species, mineral element supply to the roots, assimilation of mineral nutrients in the roots and nutrient recycling. Composition and particularly concentration of solutes are also strongly influenced by the degree of dilution by water Section 2.9 and are therefore dependent on the transpiration rate and the time of day. Composition and concentration of xylem sap also change...

Effect of Transpiration Rate on Distribution within the Shoot

The long-distance transport of a mineral element exclusively in the xylem should be expected to give a distinct distribution pattern in the shoot organs that depends on both transpiration rates e.g., ml g 1 dry weight each day and duration of transpiration e.g. age of the organ . This is true, for example, for manganese McCain and Markley, 1989 where at the same plant maple tree and similar leaf age the 'sun leaves' high transpiration rates have much higher manganese contents in their dry...

Principles of Transport and Phloem Anatomy

Long-distance transport in the phloem takes place in living cells, the sieve tubes Fig. 3.9 . The principles of the transport mechanism in the phloem were proposed as early as 1930 by Munch in a pressure flow hypothesis Druckstromtheorie based on the principle of the osmometer. This has already been discussed in Section 2.8 for the root pressure. Munch suggested that solutes such as sucrose are concentrated in the phloem of leaves Fig. 3.7 Boron toxicity in the leaves of lentil. Left control...

Transfer between the Xylem and Phloem

Xylem And Phloem Stranfer The Plants

In the vascular bundles, phloem and xylem are separated by only a few cells Fig. 3.9 . In the regulation of long-distance transport, exchange of solutes between the two conducting systems is very important. From the concentration differences shown in Table 3.8 it is evident that a transfer from phloem to xylem can occur downhill, through the plasma membrane of the sieve tubes, if an adequate concentration gradient exists. In contrast, for most organic and inorganic solutes a transfer from xylem...

Preface to Second Edition

As mentioned in the first edition the main aim of this textbook is to present the principles of the mineral nutrition of higher plants, based on current knowledge. This ambitious aim requires that the content of the book has to be updated regularly to take into account new developments in the subject as has been done in this second edition. The structure of the textbook has not been altered and the subject matter and number of chapters remains the same. The contents of the chapters, however,...

Structure and Composition of Membranes

Metabolism Polar Lipids

The capacity of plant cell membranes to regulate solute uptake has fascinated botanists since the nineteenth century. At that time the experimental techniques available limited the investigation of the process. Nevertheless, even by the early years of the twentieth century some basic facts of solute permeation across the plasma membrane and tonoplast had been established, as for example of the inverse relationship between membrane permeation and the diameter of uncharged molecules and the rates...

Mineral Nutrients with High Phloem Mobility

For mineral nutrients with high phloem mobility such as potassium, phosphorus or nitrogen as amino-N the relative importance of phloem and xylem transport into an organ mainly depends on the stage of development of the organ as shown in Table 3.10 for amino-N during the life of an individual leaf. Throughout the life of the leaf of the nitrate-fed castor bean plant, nitrogen import by the xylem sap was high and continued at a high rate and only declined at the onset of senescence. Additional...

Composition of the Phloem

Phloem sap has a high pH 7-8 and contains high concentrations of solutes, on average 15-25 dry matter. A comprehensive analysis of phloem sap composition is shown in Table 3.8. The main component is usually sucrose, which may comprise up to 90 of the solids. The proportion of sucrose to other solutes depends on the site of phloem sap collection, it is very high, for example near the ear of cereals Hayashi and Chino, 1990 Section 5.4 . In addition to sucrose, among the other organic solutes...

Ri

Gerendas Nutrition

Fig. 2.19 Model for internal pH stabilization and for charge compensation at different ratios of cation-anion uptake from the external solution. A. Excessive uptake of cations Cat when, for example, K2S04 is supplied. B. Excessive uptake of anions An when, for example, Ca N03 2 is supplied. For further details see Fig. 2.9. and the malic enzyme Fig. 2.20 . An increase in pH activates the enzyme PEP carboxylase reaction 1 , and both the rate of C02 fixation and the synthesis of oxaloacetate are...

Effect of Transpiration Rate on Uptake and Translocation

Mineral Passive Transport

The rate of water flux across the root short-distance transport and in the xylem vessels long-distance transport is determined by the root pressure and the rate of transpiration. An increase in the transpiration rate may, or may not, enhance the uptake and translocation of mineral elements in the xylem. Enhancement can be achieved in various ways, as shown in Fig. 3.5. Scheme A is true for mineral elements such as boron and silicon, except in the case of wetland rice Section 10.3.2 . Scheme C...

Introduction Definition and Classification of Mineral Nutrients

The beneficial effect of adding mineral elements e.g., plant ash or lime to soils to improve plant growth has been known in agriculture for more than 2000 years. Nevertheless, even 150 years ago it was still a matter of scientific controversy as to whether mineral elements function as nutrients for plant growth. It was mainly to the credit of Justus von Liebig 1803-1873 that the scattered information concerning the importance of mineral elements for plant growth was compiled and summarized and...

Influx into the Apoplasm

Fulvic Acid Diagram

Movement of low-molecular-weight solutes e.g. ions, organic acids, amino acids, sugars from the external solution into the cell walls of individual cells or roots the free Fig. 2.1 Cross section of two rhizodermal cells of a maize root. V, vacuole C, cytoplasm W, cell wall E, external solution. Courtesy of C. Hecht-Buchholz. Fig. 2.1 Cross section of two rhizodermal cells of a maize root. V, vacuole C, cytoplasm W, cell wall E, external solution. Courtesy of C. Hecht-Buchholz. space is a...

Yield and the Source Sink Relationships

Phaseolus Deficiency

More than 90 of plant dry matter consists of organic compounds such as cellulose, starch, lipids, and proteins. The total dry matter production of plants, the biological yield, is therefore in the first place directly related to photosynthesis, the primary process of synthesis of organic compounds in green plants. In crop plants, however, yield is usually defined by the dry matter production of those plant organs for which particular crops are cultivated and harvested e.g., grains and tubers ....

Uptake and Release of Gases and Other Volatile Compounds through Stomata

Silicon Deposition Epidermis Cuticle

In terrestrial plants the stomata Fig. 4.1 are the sites of exchange of gases mainly C02, 02 with the atmosphere. Their number per mm2 of leaf surface varies between Fig. 4.1 Scanning electron micrograph of lower abaxial leaf surfaces of Fagus sylvatica left and Puccinelliapeisonis right . Arrow stomata. Courtesy of R. Stelzer. Shoot Dry Weight, Nitrogen Content in the Dry Matter and Uptake of NH3-N from the Atmosphere in Italian Ryegrass Grown at Low Soil Nitrate Levels and Exposed to...

Y

Loading Sucrose

Fig. 5.10 Model for phloem loading of sucrose mediated by proton-sucrose cotransport, and for uniport of potassium and amino acids. Based on Baker, 1978 Giaquinta, 1980. pH 5.5-6.5 Sucrose low K low 5 -10 mM Fig. 5.10 Model for phloem loading of sucrose mediated by proton-sucrose cotransport, and for uniport of potassium and amino acids. Based on Baker, 1978 Giaquinta, 1980. described in Fig. 2.9 for the proton-anion cotransport at the plasma membrane of root cells. A range of evidence support...