Effects of Coupled Solute and Water Flow in Plant Roots with Special Reference to Brouwer's Experiment

This paper presents a further examination of the effects ofcoupled solute and water flow as it applies to plant roots.A cylindrical two-compartment membrane root model can accountfor many diverse root phenomena. Among these are (1) non-linearpressure flow, (2) interval osmotic dilution, (3) negative resistanceeffects, (4) non-osmotic water flux, and (5) the internal osmoticcompensation effect. In addition, we have now demonstrated thatthe same model is capable of reproducing the complex patternsof root resistance profile change noted by some workers. Innone of these instances is there need to invoke any change inthe hydraulic conductivity of the system to explain the observedeffects. The only features necessary to explain these phenomenaare a membrane-like structure and a mechanism for actively accumulatingsolutes.     

Passive and Active Components of Chloride Absorption in the Bark and the Wood of Citrus Roots

The characteristics of chloride absorption by the tap root of citrus (Citrus spp.) seedlings were compared in isolated disks of the bark and in segments of the wood. Analysis of elution curves of the isotope following saturation of the tissue shows that there are at least two components of the chloride absorption system: one typical of the free space (“passive”) and the other of the non-free space (“active”). These two components are present in the bark only, while the wood has essentially the characteristics of a free space absorption (the slow component of the efflux being less evident). The nature of the bark as an actively collecting tissue for chloride from 10 mM Na36Cl, in contrast to the wood, was established on the basis of uptake curves. Examination of the uptake in the bark of 3 citrus varieties revealed considerable differences with regard to the magnitude of the two components of chloride absorption. These findings are discussed in relation to the role of the cortex and the stele in the transport of ions.     

Isolation and Characterization of Components of the Lytic Compartment of Several Plant Tissues Including Separations with a Zonal Rotor

The ultrastructural localization of acid phosphatase in cellsof pea and mung bean root tips, wheat coleoptiles, cauliflowerflorets and potato shoots, occurred in association with theinner surface of membranes of vacuoles, within multivesicularbodies and in the Golgi stacks and associated vesicles. Tissue homogenization techniques were varied and behaviour ofcomponents of the lytic compartment in density gradients ofvarious types was systematically examined. A basic fractionationmethod, employing linear Ficoll density gradients, was developedand modified for routine use with the various plant tissues,and the results compared with those obtained on sucrose gradients.Two predominant bands of components of the lytic compartmentwere isolated; one of these equilibrated at a density of 1·06g cm^–3 and contained vacuoles and tonoplast components,the other band, with an isopycnic equilibrium density of 1·11g cm^–3, was rich in mitochondria, Golgi stacks and associatedvesicles. Sucrose gradients gave broadly similar separations,but of lower resolution, and with increased density of the components.Prior fractionation of homogenates by differential centrifugationgave poor subsequent separations of the lytic compartment indensity gradient ultracentrifugation. The bulk isolation of components of the lytic compartment frompotato shoots and cauliflower curd, using a zonal density gradienttechnique, is described and its possible applications are discussed. An improved method of rapid fixation of fractions enabled theuse of a modified Gomori lead-salt method for ultrastructurallocalization of ß-glycerophosphatase activity in isolatedelements of the lytic compartment. Lytic component, Golgi apparatus, density gradient fractionation, ultrastructure, acid hydrolases, ß-glycerophosphatase, Pisium sativum L., Phaseolus aureus L., Triticum aestivum L., Solanum tuberosum L., Brassica oleracea L.     

Experiments on Growth in Length of Plant Organs: I. A RECORDING AUXANOMETER

An auxanometer which records automatically growth incrementsof 0.0009 in. is described. With the instrument changes in therate of growth in response to changes in the gas compositionof the atmosphere have been observed in periods of 10 minutesor less.     

The Relation Between Ion Absorption and Protein Synthesis in Beet Disks

Disks of red beet storage tissue were incubated under asepticconditions permitting the development of various metabolic processescommonly associated with aged disks, and the effects of chloramphenicoland puromycin on protein synthesis, on the development of invertaseactivity and ion absorption capacity, and on ion absorptionper se were determined. Low concentrations of chloramphenicoland puromycin inhibit the development of ion absorption capacitybut stimulate invertase development and protein synthesis, whilehigher concentrations inhibit all three processes. In contrastion absorption itself is unaffected by puromycin, but is sensitiveto quite low concentrations of chloramphenicol The D-threo andL-threo isomers of chloramphenicol have sharply contrasted effectson the development, as distinct from the utilization, of ionabsorption capacity. The D isomer inhibits the development ofion absorption capacity more effectively than the L isomer whichin turn inhibits absorption more effectively than the D isomer. A reappraisal is made of the hypothesis that ion absorptionis directly linked with protein turnover and to account forthe results a model is proposed in which D-threo-chloramphenicolis active both as an uncoupler of oxidative phosphoryalationand as an inhibitor of protein synthesis, while L-threo-chloramphenicolacts only in the former capacity and puromycin only in the latter.It is concluded that the inhibition of ion uptake by chloramphenicolcannot be attributed to a contemporaneous effect on proteinsynthesis. However, the results are consistent with the involvementof ATPase proteins in ion uptake.     

Active and Passive Components of Sulfate Uptake in Sunflower Plants

The aim of the investigation was to identify components of active and passive ion uptake and transport in roots of plants and to assess their quantitative relations under different external and internal conditions. The uptake of radiosulfate and water by young sunflower plants from complete nutrient solutions labelled with ³⁵S was studied. The metabolism-linked nature of the sulfate uptake in the root following the passive migration into the apparent free space (AFS) was demonstrated by the addition of sodium. selenate, 2,4-dinitrophenol, potassium cyanide, and sodium azide to the nutrient solutions. The magnitude of the AFS measured on a root volume basis varied between 14 and 57 per cent depending on the pretreatment of the plants and the sulfate concentration of the nutrient solution. The variations were supposed to be due to different capacity to bind sulfate by exchange-adsorption within the AFS. The amounts of sulfate in different fractions of the total AFS-uptake were computed under certain theoretical assumptions. A quantitative connection was proposed between the magnitude of the adsorbed sulfate fraction in the AFS and the rate of active uptake into the symplasm. The exchange-adsorption probably constitutes the initial stage of active ion uptake. The stimulating effect by water on ion uptake would be an increase of the speed of transporting ions to, from, or along the adsorption sites in the AFS. Experiments conducted at temperatures in the nutrient solution between 5 and 35 C elucidated the multistep nature of ion transport within a root.     

Study of Effect of Autacoids on Water Absorption and Ion Transport by Skin of the Frog Rana temporaria

The experiments on the frog Rana temporaria isolated skin showed participation of autacoids in regulation of the epithelium water permeability and of the transepithelial ion transport. The removal of autacoids secreted by the cells into the Ringer solution at its internal surface with the aid of frequent replacements of this solution leads to an increased water permeability and to a decreased transepithelial potential difference. Inhibition of prostaglandin synthesis with 1 × 10^–5 M indomethacin produces the frog skin depolarization. Addition of prostaglandin E₂ to the Ringer solution at the internal surface of the frog skin is accompanied by a decrease of the osmotic permeability, hyperpolarization, and an increase of short-circuit current. The non-contradictory model is described of the role of autacoids in regulation of the frog skin functions connected with participation of the skin in the water–salt homeostasis.