[Investigations on the distribution and transport of ions in plant tissues with the X-Ray microanalyzer : I. Experiments on Vegetative Organs of Zea Mays]

Symplasmic and apoplasmic radial ion transport in plant roots : Cortical plasmalemmas lose absorption capacity during differentiation

The kinetics and localization of Rb(+) uptake by barley roots were studied as function of the water potential of the medium. At potentials causing plasmolysis, uptake is reduced and becomes restricted to the outer surface of the root. The conclusion is that, at least for Rb(+) in the range of low external concentrations (<1 mM), the mature root cortex has little if any primary absorption(1) capacity. Therefore, the apoplasmic pathway is of little or no significance for radial transport, which occurs by primary absorption at the epidermis and - perhaps - hypodermis followed by symplasmis transport to and through the cortex. Young cortex cells possess a primary absorption capacity comparable to that of the epidermis, but this feature is (largely) lost during differentiation.

Sodium and calcium localization in cells and tissues by precipitation with antimonate: a quantitative study

Komnick's antimonate technique, which was devised to localize Na+ in cells and tissues, was studied quantitatively. Some modifications, as well as its application to Ca2+ localization, were also investigated. We combined measurements of Na+ and Ca2+ retention in plant roots during the various procedures, electron microscopy, autoradiography, and semiquantitative X-ray microanalysis. We were able to show that (at least in barley roots) antimonate does not precipitate at all with Na+, irrespective of the Na+ content of the tissue or the method of antimonate application. (Even during precipitative freeze dissolution or after freeze drying, no Na+ is precipitated.) By means of Komnick's antimonate technique Ca2+ is trapped within the tissue, but only after serious dislocation. Perspectives for reliable localization of diffusible ions in cells and tissues, by precipitation simultaneously with conventional fixations, are bad.

In vivo measurement of cadmium ((115m)Cd) transport and accumulation in the stems of intact tomato plants (Lycopersicon esculentum, Mill.) : II. Lateral migration from the xylem and redistribution in the stem

The internal distribution processes of cadmium ((115m)Cd) in the stems of tomato plants have been investigated using in vivo β-spectrometric measurements with semiconductor detectors. The initial penetration into the xylem after root uptake and the subsequent lateral redistribution in the surrounding tissues were monitored continuously in each individual plant. The kinetics of the lateral migration toward the epidermis can be described by a diffusion process, characterized by an apparent diffusion coefficient of about 10(-8) cm(2) s(-1). After two days of cadmium supply this heavy metal is accumulated in relatively large amounts in the epidermal and cortical layers, from which it can be released only very slowly. On the contrary, the exchange processes with other divalent cations cause in the xylem a quick release, its rate being dependent on the duration of the preceding cadmium treatment.

[The role of inorganic phosphate in the regulation of the phosphoenolpyruvate carboxylase of Mesembryanthemum crystallinum L]

The activity of the phosphoenolpyruvate (PEP) carboxylase isolated from non-saline grown plants of the salt-tolerant plant Mesembryanthemum crystallinum is strongly inhibited by malate. This inhibition was found to depend on the pH (rising with increasing H(+)-concentrations) and on the concentration of malate used. The addition of inorganic phosphate (appropriate concentration 30 mM) to the in-vitro enzyme assay prior to malate addition results in a remarkable compensation of malate-caused inhibition of the enzyme activity. Again a dependency upon the pH can be observed. The ability of inorganic phosphate to restore malate-caused inhibition of the PEP-carboxylase increases with increasing pH.Another potent inhibitor of the PEP-carboxylase is NaCl, which shows a minimum inhibition at pH 7. At this pH a concentration of more than 60 mM NaCl is needed to reduce the activity of the enzyme below the control level with a 50% inhibition is reached at 150 mM. If the addition of NaCl is performed in the presence of 30 mM inorganic phosphate the inhibition is less pronounced. The enzyme now tolerates about 100 mM higher concentrations of NaCl without being inhibited.NaCl-treatment of Mesembryanthemum crystallinum plants results in an increase of inorganic phosphate in the cells with a concomitant establishment of a Crassulacean acid metabolism. The present results support evidence for a protective function of inorganic phosphate (compensation of NaCl-induced enzyme inhibition), possibly a commen reaction involved in the question of salt tolerance, and a more specific function (restriction of malatecaused inhibition of the PEP-carboxylase) providing the enzymatic background for the malate accumulation in Mesembryanthemum crystallinum.

Ultrastructure of xylem parenchyma cells of barley roots in relation to ion transport to the xylem

The structure of xylem parenchyma cells is examined in relation to transport of ions through the root. Measurement of uptake of (86)Rb(+) and its transport through the root at different distances from the apex show that this is a general activity along the length of the root and not confined to a limited region. Thus transport through the root is not stopped by removal of that part of the root tip containing metaxylem vessels with living contents. The structure of xylem parenchyma appears to be suitable for involvement in ion transport from the stele to the xylem. At 1 cm behind the tip, where metaxylem vessels have no living contents but ion uptake and transport are going on at high rates, xylem parenchyma cells are rich in cytoplasm with extensive rough endoplasmic reticulum and well-developed mitochondria. Their cell walls contain numerous plasmodesmata, establishing the possibility of a symplastic pathway across the stele up to the vessels. The results are discussed in relation to regulation of ion transport to the xylem vessels in roots.

Electron probe analysis of freeze-substituted, epoxy resin embedded tissue for ion transport studies in plants

A new technique is described to prepare plant material for electron probe analysis. Root segments 1 mm in length were frozen at-170°, freeze-substituted with anhydrous ether at-30° and infiltrated with Spurr's low-viscosity epoxy resin embedding medium at low temperatures. Sections 1 and 2μ thick were cut anhydrously using hexylene glycol in the ultramicrotome trough, mounted on the polished surface of a Be disc and vacuum coated with 150-200 Å aluminum.The new technique allows retention of water-soluble ions at the original sites in the tissue and is superior to cryostat sectioning in spatial resolution of electron probe analysis and in the preservation of cellular structures.The lateral transport of K(+) into the xylem of corn roots has been successfully studied by electron probe analysis of freeze-substituted, epoxy resin embedded material.

A histochemical study of adenosine triphosphatase and other nucleotide phosphatases in young root tips

The distribution of ATP-ase and other nucleotide phosphatases has been studied in young root tips of maize, barley and broad bean using frozen and paraffin sections stained by standard lead sulphide precipitation procedures. High ATP-ase activity was found at the root and cell surface which is in agreement with previous biochemical studies using excised roots and cell wall preparations. Staining was also found in the nuclei and at particulate sites in the cytoplasm. Differences were observed between the present work and the staining pattern obtained for β-glycerophosphatase, and between ATP-ase staining in the three roots studied. These results are discussed in relation to the possible physiological activity of the enzymes and to the differences found between earlier histochemical studies of ATP-ase activity.

[Investigations on the distribution and transport of ions in plant tissues with the electron probe X-ray micronalyser : II. Long-distance transport of ions to pea fruits]

Translocation and distribution of K, Ca, Sr and P in the fruit stalk and pods of Pisum sativum were studied by means of the electron probe X-ray micronalyser.Long-distance transport through the fruit stalk of K and P as well as of Ca and Sr takes mainly place in sieve tubes. Therefore the theory of MüNCH (1930) concerning the supply of substances via the phloem to seeds of weakly transpiring fruits is confirmed for several important ions. A fairly small Ca supply to the sieve tubes seems to be the reason that the transport of Ca in sieve tubes and its content in seeds are relatively low. Ca and Sr are also translocated in xylem vessels, mainly to the dorsal suture of the pods; there they accumulate as sulfate in the xylem tissues of the central vein.In addition to the longitudinal translocation there is also a lateral transport outwards from the conducting tissues. The heaviest depositions of minerals are located in the cell walls of sclerenchyma outside of the vascular bundles. These depositions consist mainly of Ca-Sr-phosphate in the fruit stalk and the dorsal suture and of Ca-Sr-sulfate as well as K-phosphate in the ventral suture. The cortical cells of the fruit stalk contain some crystals of Ca-Sr-oxalate.

Entry and distribution of aluminum in Zea mays : The mode of entry and distribution of aluminum in Zea mays: Electron microprobe X-ray analysis

The electron microprobe X-ray analyzer (microprobe) has been used to determine the mode of entry of aluminum (Al) and its distribution and localization in the corn plant. Microprobe analysis is a non-destructive method allowing for multiple element analysis in the same tissues, cells or cell organelles.Al was found to be precipitated on the surface of the epidermal cells of the root with no penetration into the cortex as long as the root surface remained intact. The root cap was freely permeable and contained the highest concentration of Al. The epidermal layer behind the root cap prevented movement into the cortex and conductive tissue.The penetration of a lateral root through the endodermis, cortex and epidermis provided a channel of entry for Al into the cortex and conducting tissues of both the lateral and main root. Essentially no Al was found in the transition zone and only small quantities were present in the above-ground plant parts.The localization of phosphorus was exactly the same as that of Al. This suggested that there was a precipitation of P by Al. A similar analysis for calcium and phosphorus on control plants did not reveal such a precipitation.The method of sample preparation was critical in retaining and localizing the elements in question and is discussed in that light.

[Investigations on the kinetics of ion uptake into the cytoplasm of mnium leaf cells by means of microautoradiography and electron probe X-ray microanalyser]

Methods of quantitative microautoradiography are described. The kinetics of ion uptake into the cytoplasm (including the plastids and other organelles) were investigated by means of microautoradiography and electron probe X-ray microanalyser.The results of microautoradiography show that under our experimental conditions at the end of the experiments the cytoplasm contains much more label per unit of volume than the vacuoles. The kinetics of this filling - up of the cytoplasm correspond to the system-1 isotherm of ion uptake. It must be concluded from the literature that system-1 reflects the process filling up the cytoplasm (=transport through the plasmalemma). The kinetic data reported here describe directly the actual filling - up of the cytoplasmic phase. For this reason the coincidence of kinetic features such as the hyperbolic shape of the rate versus concentration curves in both instances is of interest for the general model of ion uptake into cells of higher plants. The time course of the filling of the cytoplasm is dependent on the external concentration.Similar kinetic data are obtained with the electron probe X-ray microanalyser.The usefulness of a parallel application of microautoradiographic and electron probe X-ray microanalyser techniques in kinetic studies of transport is discussed.