Bacterial Infection and Ion Absorption Capacity in Beet Disks

The effect of bacterial contamination on the development ofa salt absorption capacity in disks of beetroot tissue has beeninvestigated. When disks are aged in water with adequate aerationat 25°C they develop a greatly increased capacity for saltabsorption. The development of this capacity is amenable toexperimental control and may be retarded by inhibitory compoundssuch as acriflavine, hibitane, and chlorocholine chloride. Acomparison of the rate of this development in disks aged understerile and non-sterile conditions has shown that non-sterileconditions retard development. Autoclaving the medium was moreeffective than sterilizing the tissue in eliminating the inhibitoryeffect. Attention is drawn to the risk of obtaining misleadingresults from a failure to take account of this factor.     

Ion Absorption and Retention by Chlorella Pyrenoidosa. II. Permeability of the Cell to Sodium and Rubidium

The Na and Rb permeability of Chlorella pyrenoidosa were estimated from the rates of radioisotope self-diffusion.

The isotopic exchange in absence of net ionic movements followed first order kinetics. This suggested that for sodium, which reached isotopic equilibrium in approximately 90 minutes, the cell behaved as 1 compartment with respect to isotopic exchange. Rubidium in 180 minutes approached isotopic equilibrium by 67%; thus, the existence of a single compartment for Rb has not been demonstrated. Net fluxes, calculated from the isotope exchange data, and expressed on a dry weight and surface area base showed that Na fluxes were approximately 7 times larger than Rb fluxes. Net Na fluxes of 90 milli-equivalents per 100 g dry weight per hour were far in excess of the observed maximum net accumulation of Na. However, Rb fluxes of 13 milliequivalents per 100 g dry weight per hour were of similar magnitude as the rate of Rb accumulation. Thus, permeability could be a limiting factor for Rb but not for Na accumulation. Sodium and Rb fluxes in absence of net ionic movements were inhibited by low temperature, dark air and dark N₂ conditions. This change in flux rates was explained mainly on the basis of metabolically dependent changes in the cell surface layers.

Isotope fluxes of Rb were drastically reduced in dark air and dark N₂ in the absence or presence of net cation movements. Dark N₂ essentially eliminated net cation accumulation, whereas dark air had relatively little effect on the net K and Rb accumulation by Chlorella. Thus the 2 major factors involved in net cation accumulation in the Chlorella cell, permeability and processes leading to cation retention, respond differently to metabolic inhibition permitting a separation of these 2 important aspects of cation accumulation.

     

Selective Inhibition of Absorption and Long Distance Transport in Relation to the Dual Mechanisms of Ion Absorption in Maize Seedlings

The influence of several uncouplers of oxidative phosphorylation and inhibitors of terminal electron transport was studied on absorption and long distance transport of both K and C1 at concentrations within each range of the dual isotherm typical of ion uptake by maize roots. At low concentrations in the range of system 1, the system considered to implement ion movement through the plasma membrane, root absorption and long distance transport are equally inhibited by a given inhibitor. In the high range of system 2, the system considered to mediate ion passage through the tonoplast, long distance transport is markedly less sensitive to inhibitors than is absorption. The observations are in accord with the hypothesis that only system 1 is involved in the uptake of ions from the external solution into the symplast, and hence into the xylem. At high concentrations, entrance into the symplasm is deemed to be largely by diffusion and therefore less inhibitor sensitive.With respect to absorption by the roots, the plasma membrane system is more inhibitor sensitive than is the tonoplast system. It is suggested that the difference in sensitivity is real, and not the consequence of an inequality of inhibitor concentration in the vicinity of the plasma membrane and tonoplast respectively.     

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.     

高压静电场促进植物吸收离子机理的初步探讨

高压静电场下盆栽水萝卜、使用含 ³²P培养液和由8种无机离子组成的培养液,测试 ³²P的放射强度分布和8种无机元素的分布,结果在土壤和培养液上层 ³²P的放射强度分别比对照高15.19%和63.73%,下层分别比对照低18.39%和29.05%.静电场下生长在含 ³²P土壤中的水萝卜叶片中 ³²P放射强度比对照高66.57%,而根部较对照低8.27%.在静电场作用下,培养液中无机离子向电场的正极方向移动(上层),而对照呈相反的分布趋势.这说明静电场促进植物对离子的吸收是与静电场作用下的离子移动有关.     

Ion Absorption and Retention by Chlorella pyrenoidosa. III. Selective Accumulation of Rubidium, Potassium and Sodium

The selective preference of Chlorella pyrenoidosa for alkali metal cations was found to have the order Rb > K > > > Na. It was demonstrated that a cation of higher preference can replace in the cell cations of lower preference by an ion interchange process.

The replacement of Na from the cell by K or Rb occurred against high external Na concentrations up to 450 meq/1 Na.

It is suggested that the structural selectivity of the Chlorella cell may be amplified by a chromatographic type repetitive selection process, driven by metabolically dependent unsymmetric shape changes of cellular membranes.