EFFECT OF ANTITRANSPIRANT SPRAY ON THE UPTAKE AND TRANSPORT OF RUBIDIUM BY PLANTS

Reducing rates of transpiration directly by antitranspirantsprays has obviated the need for drastically altering environmentalconditions in experiments that are designed to evaluate theeffects of transpiration. With this method a positive correlationbetween transpiration and translocation of rubidium was foundfor both sugar beet and bean plants. No correlation betweentotal rubidium uptake and transpiration was found in bean plants.Such correlation was found in sugar beets despite their havingbeen in a sugar rich status. ¹ This investigation was supported by a Samuel and Doris GouldScholarship. (Received May 18, 1963; )     

THE EFFECT OF GIBBERELLIC ACID ON THE ABSORPTION AND TRANSLOCATION OF PHOSPHORUS-32 BY BEAN PLANTS

Linck , A. J., and Theodore W. Sudia . (U. Minnesota, St. Paul.) The effect of gibberellic acid on the absorption and translocation of phosphorus-32 by bean plants. Amer. Jour. Bot. 47(2) : 101—105. Illus. 1960.–Plants of Phaseolus vulgaris, variety ‘Black Valentine,‘ treated with 1 p.p.m. gibberellic acid supplied to the roots for 4 hr. were compared with nontreated. plants for phosphorus-32 uptake. Plants treated with gibberellic acid where transpiration was either rapid or restricted absorbed more phosphorus-32 than those not treated. More phosphorus-32 was recovered from plants free to transpire than from plants in high humidity. In plants free to transpire, significantly more phosphorus was present in the treated plants after 28 hr. and significantly more phosphorus-32 accumulated in treated plants in those parts actively growing, i.e., stem apex, second internode and first trifoliate leaf, and in the roots. For plants in high humidity atmosphere significantly more phosphorus-32 was absorbed by the treated plants at the end of 4 hr. than in the non-treated plants and this difference was maintained throughout all times of harvest. For plants in high humidity atmosphere, significantly more phosphorus-32 accumulated in the lower portions, i.e., roots, hypocotyl, first internode and primary leaves, of treated plants than of non-treated plants, while the differences for the second internode, the first trifoliate leaf and the stem apex were not significant between treated and non-treated plants.     

EFFECT OF VARIOUS ANIONS ON THE TRANSPORT OF STRONTIUM WITHIN PLANTS

With a view to finding a means of reducing contamination offoods by radiostrontium, the inhibiting effects of various anionson the transport of strontium in plants are investigated. Pea and bean plants were pretreated with silicate, phosphateand nitrate ions, and the distribution of strontium in variousparts of the plants was examined.

1. In the case of pretreatment with silicate or phosphate ions,strontium absorption by the plant was decreased even if theseanions were absent in the culture solution at the time of applicationof ⁸⁹Sr.
2. The absorption of strontium by the plants pretreatedwith nitrateions was similar to that of the controls.
3. Strontiumabsorbed by the plants pretreated with silicate orphosphatewas found to be accumulated in the roots and its quantitytransportedto the aboveground parts was remarkably small; especiallyinthe case of application of silicate, no measurable amountofstrontium was transported to the upper parts of the plant.
4. Inthe control and nitrate-pretreated plants, strontium absorbedin the roots was readily transported to the aboveground parts.

(Received March 15, 1965; )     

THE TRANSPORT AND FUNCTION OF SILICON IN PLANTS

A number of lines of evidence (M_r, number of -OH groups, measured fluxes at inner mitochondrial membranes) suggest the intrinsic P_Si(OH)₄ of about 10^-10 m s^-1 in the plant cell plasmalemma. While relatively low, such a P_Si(OH)₄ could maintain the intracellular concentration of Si(OH)₄ equal to that in the medium for a phytoplankton cell of 5 μm radius growing with a generation time of 24 h. Such passive entry could not account for SiO, precipitation such as is required for scale (Chrysophyceae) or wall (Bacillariophyceae) production in terms of either the generation of a super-saturated solution or the quantity of SiO₂ required; active transport occurs at the plasmalemma (and possibly at an internal membrane) of such cells. The energy required for silicification, even in a diatom with an Si/C ratio of 0.25, is only some 2% of the total energy (as NADPH and ATP) needed for growth; the energy cost of leakage of Si(OH)₄ due to the intrinsic permeability of lipid bilayers to Si(OH)₄ is never more than 10% of the cost of silicification. In vascular land plants the entry of Si from the soil into the xylem can involve a flux ratio (mol Si/m³ water) that is less than (e.g. Leguminoseae) equal to (e.g. many Gramineae) or greater than (e.g. Oryza, Equisetum) the concentration (mol m^-3) in the bathing solution. Even the low influx of the Leguminoseae cannot be accounted for by the ‘lipid solution’ value of PS(OH)₄, but requires entry coupled (phenomenologically) to water influx with a reflexion coefficient of about 0.9. The situation in most Gramineae is described by such a coupling with a reflexion coefficient near O, while the accumulation of Si (relative to water) in Oryza and Equisetum involves an apparent reflexion coefficient which is negative, i.e. an active transport system stoichiometrically related to water flux. Even in Leguminoseae with a transpiration-stream concentration of Si(OH)₄ of only 20 mmol m^-3 (cf. the soil solution at 200 mmol m^-3), the fact that only I % of the water in the xylem is retained in the plant means that Si(OH)₄ at transpirational termini approaches saturation; super-saturation, and precipitation of SiO, occurs in Gramineae and Equisetum. SiO₂ precipitation occurs mainly near transpirational termini but can also occur in the xylem vessels and endodermis of roots, for example. Si(OH)₂ mobility in the phloem seems to be very restricted. The energy costs of SiO₂ relative to organic compounds as structural and defensive materials are in the ratio of 1:10-1:20 (on the basis of weight of material). The relative rarity of SiO₂ as a structural material is discussed in the context of the evolution of Si(OH)₄-transport mechanisms.     

镉离子对微管、管蛋白巯基和在体轴浆转运的作用

大鼠腹角注入~3H亮氨酸,3h后坐骨神经内注射 Cd~(2 )30μl,50mM Cd~(2 )轻度减小标记蛋白的轴浆转运距离,75或 100mM 阻断转运在注射点。巯基抑制剂马来酰胺与 50mM Cd~(2 )伍用的效应相加,使转运也阻断在注射点。巯基供应剂二巯基丁二钠则完全抵消100mMCd~(2 )对转运的阻断作用。Cd~(2 )还使坐骨神经匀浆上清液的巯基含量减少,马来酰胺与Cd~(2 )伍用则巯基进一步降低。自兔脑提取了微管的亚基管蛋白,Cd~(2 )降低管蛋白巯基的程度与其浓度呈线性关系。电镜的验证证明,Cd~(2 )使在体神经的微管解聚、微管减少或基本消失。由于巯基、微管和转运的变化程度均与Cd~(2 )的浓度大小有关,并且同一浓度的Cd~(2 )使微管和转运的受累程度相互对应,因此Cd~(2 )可能借络合管蛋白的巯基使微管解聚而阻断转运。实验进一步证明以前的论断,微管解聚可能是Cd~(2 )等药物阻断转运的一个中间环节,微管可能参与在体轴浆转运的机制。     

环糊精对绿豆下胚轴不定根形成的影响

10-3-10-2mol／β-环糊精能明显促进绿豆插条不定根根原基形成,增加不定根数目和总根长．10-4-10-2mol／Lβ-环糊精能提高不定根的鲜重、干重和可溶性蛋白质含量,降低IAA氧化酶活性,减少不定根的平均根长,但对下胚轴的鲜重和干重影响不明显．10－3mol／Lβ-环糊精能提高插条的不定根活力．