Acid-induced growth and the geotropic response of the wheat node

Summary Growth is initiated in segments of the leaf sheath base of Triticum aestivum by gravitational stimulation and by incubation in buffer solutions of pH 3. Both responses involve only an increase in segment length, are rapidly terminated on removal of the stimulus, have a similar Q₁₀ and are dependent upon cell turgor. They differ, however, in that the response to acid solutions is rapid and unaffected by anoxia. Acid-induced growth can be stopped and started repeatedly by changing the pH, an increase in pH from 3 to 5 or 7 being sufficient to terminate the response. The maximum growth induced by low pH is not increased by simultaneous stimulation by gravity.     

Spectral dependence of the light-induced geotropic response in Zea roots

The induction by light of geotropic responsiveness in the primary roots of Zea mays L. (cv. Golden Cross Bantam 70) was found to be governed by the all-or-none law. The response was induced by light energies above a threshold value, but the maximal curvature of geo-stimulated roots was constand irrespective of the light energy above that threshold. The action spectrum for this light effect showed a large peak at 650, a small peak at 410, and a shoulder at 663 nm. The effect of red light was not reversed by far-red light. Thus, the geotropic response in Zea roots may not be controlled by phytochrome.     

Inhibitors of the geotropic response in plants: A correlation of molecular structures

Selected compounds from several groups of chemicals known to affect the root geotropic response in plants have been assessed for their effects on both stem and root geotropism in cress seedlings in order to compare their relative activities. It is suggested that a class of compound which affects geotropism can be distinguished, and that the molecular requirements for its activity can be tentatively defined. It is suggested that an ortho carboxylic acid function attached to an aromatic ring, which is separated by a conjugated system of atoms from a second aromatic ring, is required for high activity. Substituents on the second aromatic ring increase activity if they assist in the achievement of a minimum molecular size.     

Phytotropins: Conformational requirements for the abolition of the root geotropic response

Compounds of the phytotropin class have been assessed for possible conformational requirements with respect to their ability to aftect the root geotropic response. It is shown that part of the molecule may need to adopt a planar configuration, and evidence is adduced which indicates that the remainder of the molecule may also have conformational requirements which need further definition. It is suggested that molecules which favour a conformation such that the aromatic ring which bears the carboxyl function is out of plane with the remainder of the molecule may have activity. Coplanarity of the carboxyl group with the ring to which it is attached is not a prerequisite for activity.     

Cell elongation in the grass pulvinus in response to geotropic stimulation and auxin application

Summary Horizontally-placed segments of Avena sativa L. shoots show a negative geotropic response after a period of 30 min. This response is based on cell elongation on the lower side of the leaf-sheath base (pulvinus). Triticum aestivum L., Hordeum vulgare L. and Secale cereale L. also show geotropic responses that are similar to those in Avena shoots. The pulvinus is a highly specialized organ with radial symmetry and is made up of epidermal, vascular, parenchymatous and collenchymatous tissues. Statoliths, which are confined to parenchyma cells around the vascular bundles, sediment towards the gravitational field within 10–15 min of geotropic stimulation. Collenchymatous cells occur as prominent bundle caps, and in Avena, they occupy about 30% of the volume of the pulvinus. Geotropic stimulation causes a 3- to 5-fold increase in the length of the cells on the side nearest to the center of the gravitational field. Growth can also be initiated in vertically-held pulvini by the application of indole-3-acetic acid, 1-naphthaleneacetic acid or 2.4-dichlorophenoxyacetic acid. 2.3.5.-triiodobenzoic acid interferes with growth response produced by geotropic stimulation as well as with the response caused by auxin application. Gibberellic acid and kinetin have no visible effect on the growth of the pulvinus. Polarization microscopy shows a unique, non-uniform stretching of the elongating collenchymatous cells. Nonelongated collenchymatous cells appear uniformally anisotropic. After geotropic stimulation or auxin application, they appear alternately anisotropic and almost isotropic. Such a pattern of cell elongation is also observed in collenchyma cells of geotropically-stimulated shoots of Rumex acetosa L., a dicotyledon.Abbreviations 2.4-D 2.4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - IAA indole-3-acetic acid - NAA l-naphthaleneacetic acid - TIBA 2.3.5-triiodobenzoic acid     

Ethylene and the geotropic response of lateral branches in peanuts (Arachis hypogaea L.)

The prostrate growth habit of runner-type peanut plants changedwhen treated with the ethylene-releasing compound CEPA: thehorizontal branches became plagiotropically oriented and theplant assumed a bushy form. Treatment with CEPA caused a markedincrease in ethylene evolution for about a week, which thendecreased to the level of the control. Nevertheless, the branchesmaintained their newly assumed plagiotropic orientation. Ethylene evolution from isolated branch tips correlated withtheir age and orientation, being highest in old plagiotropicand lowest in old diatropic branches. Light intensity and qualitywhich caused plagiotropic orientation of branches also causedan increase in ethylene evolution, while ethylene evolutionwas lowest under light conditions favouring diatropic orientation.Along with the changes to plagiotropic orientation by CEPA,an increase in GA-like substances and a decrease in growth inhibitorswas observed in extracts from treated plants. (Received October 7, 1975; )     

Variations in the geotropic sensitivity of germinating Funaria spores in response to some external influences

Experiments on the germination of the spores of Funaria have established the following.

• 1. 

  Some growth substances such as vitamins slightly promote the geotropic response of germinating spores in darkness.
• 2. 

  Glucose, even in concentrations as low as 10 mg./L, strongly stimulates the geotropic response.
• 3. 

  Light (at an intensity of 1000 lux and more) strongly inhibits the geotropic response. This effect is probably phototonic and can be partly counteracted by glucose.
• 4. 

  The nature of the phototropic and geotropic reactions of chloronema is variable, and depends to a certain extent on environmental influences.

     

Growth asymmetry precedes differential auxin response during apical hook initiation in Arabidopsis

The development of a hook-like structure at the apical part of the soil-emerging organs has fascinated botanists for centuries, but how it is initiated remains unclear. Here, we demonstrate with highthroughput infrared imaging and 2-D clinostat treatment that, when gravity-induced root bending is absent, apical hook formation still takes place.In such scenarios, hook formation begins with a de novo growth asymmetry at the apical part of a straightly elongating hypocotyl. Remarkably, suchde novo ...     

Growth response to subsurface soil acidity of wheat genotypes differing in aluminium tolerance

Subsurface soil acidity coupled with high levels of toxic Al is a major limiting factor in wheat production in many areas of the world. This study examined the effect of subsurface soil acidity on the growth and yield of two near-isogenic wheat genotypes differing in Al tolerance at a single genetic locus in reconstructed soil columns. In one experiment, plants were grown in columns with limed topsoil and limed or acidic subsurface soils, and received water only to the subsurface soil at a late part of the growth period. While shoot dry weight, ear number and grain yield of Al-tolerant genotype (ET8) were not affected by subsurface soil acidity, liming subsurface soil increased shoot weight and grain yield of Al-sensitive genotype (ES8) by 60% and ear number by 32%. Similarly, root length density of ET8 was the same in the limed and acidic subsurface soils, while the root length density of ES8 in the acidic subsurface soil was only half of that in the limed subsurface soil. In another experiment, plants were grown with limed topsoil and acidic subsurface soil under two watering regimes. Both genotypes supplied with water throughout the soil column produced almost twice the dry weight of those receiving water only in the subsurface soil. The tolerant genotype ET8 had shoot biomass and grain yield one-third higher than ES8 when supplied with water throughout the whole column, and had yield 11% higher when receiving water in the subsurface soil only. The tolerant genotype ET8 produced more than five times the root length in the acidic subsurface soil compared to ES8. Irrespective of watering regime, the amount of water added to maintain field capacity of the soil was up to 2-fold higher under ET8 than under ES8. The results suggest that the genotypic variation in growth and yield of wheat grown with subsurface soil acidity results from the difference in root proliferation in the subsurface soil and hence in utilizing nutrient and water reserves in the subsurface soil layer.     

Properties of the subunits of wheat germ initiation factor 3

Wheat germ initiation factor 3 (eukaryotic initiation factor 3, eIF-3) contains ten non-identical subunits (p116, p107, p87, p83, p56, p45, p41, p36, p34 and p28). Monoclonal antibodies to all except two of the subunits (p41 and p28) were obtained. None of the monoclonal antibodies react with more than one subunit, and only monoclonal antibodies to p36 inhibit the ability of eIF-3 to support initiation of polypeptide synthesis. Two of the subunits (p116 and p107) are highly basic polypeptides (pI greater than or equal to 8); five (p87, p56, p45, p34 and p28) are acidic polypeptides (pI = 5.4-6.1); and three (p83, p41 and p36) appear to exist in more than one isoelectric form. Eight of the subunits of eIF-3 are iodinated rapidly in vitro; the highest incorporation is into p56 and the lowest incorporation is into p28. No incorporation into p41 or p28 is observed. When eIF-3 is treated with N-[3H]ethylmaleimide, approx. 30 alkyl groups per eIF-3 are incorporated, and the eIF-3 is inactivated. No incorporation into p83 or p28 is observed; incorporation of the alkyl groups into the other eight subunits occurs at different rates. The rate of inactivation of eIF-3 by N-ethylmaleimide is slower than the overall rate of incorporation of alkyl groups. eIF-3 is stable between pH 5.5 and 10. Below pH 5.5, eIF-3 is inactivated and precipitation of protein occurs. Partial dissociation of the subunits and inactivation of eIF-3 is obtained by treatment with 2 M urea. Attempts to reassociate the subunits into an active particle were unsuccessful.     

The role of stretching the sinus node artery in initiation of atrial fibrillation

In anaesthetised dogs with open chest (n = 10), against the background of the Gd3+ (a blocking agent of mechano-sensitive ion channels), acetylcholine perfusion induced no significant changes either in probability of atrial fibrillation occurrence or in the paroxysm duration. The Gd3+ did not alter the deceleration of the sinus rhythm either. Therefore the mechanism of spontaneous occurrence of atrial cholinergic fibrillation seems not to be associated with the trigger activity induced by an increased blood pressure in the right atrium.     

characterization of wheat germ initiation factor eIF-2

The initiation factor eIF-2 that specifically binds Met-tRNA_f and GTP in ternary complex (eIF-2. GTP. Met-tRNA_f) has been purified to apparent homogeneity from wheat germ ribosomal salt wash. The purified factor exhibits a sedimentation coefficient of 5 · 5S and an aggregate molecular weight of 122000-daltons for the native protein.A preliminary account of this work was presented at the 66th Annual (1982) Meeting of the Federation of American Societies for Experimental Biology; Fed Proc 41, 1040.     

Lymph node accessory cells in the immune response

Summary The immune response in the rat parathymic lymph node was studied after administration of antigen into the peritoneal cavity. Special attention was paid to the accessory cells,which might induce the response. During the induction phase of the response a heterogeneous population of non-lymphoid mononuclear cells was present in the subcapsular sinus and the cortex of the node. These cells resemble veiled cells described in skin draining lymph and interdigitating cells in the paracortex of skin draining lymph nodes, but they do not contain Birbeck granules. It is concluded that the appearance of these granules depends on the site of the exudate provocation and that the presence of the organelles in these accessory cells is not obligatory for lymphocyte stimulation.     

Phosphorylation of wheat germ initiation factors and ribosomal proteins

The ability of the wheat germ initiation factors and ribosomes to serve as substrates for a wheat germ protein kinase (Yan and Tao 1982 J Biol Chem 257: 7037-7043) has been investigated. The wheat germ kinase catalyzes the phosphorylation of the 42,000 dalton subunit of eukaryotic initiation factor (eIF)-2 and the 107,000 dalton subunit of eIF-3. Other initiation factors, eIF-4B and eIF-4A, and elongation factors, EF-1 and EF-2, are not phosphorylated by the kinase. Quantitative analysis indicates that the kinase catalyzes the incorporation of about 0.5 to 0.6 mole of phosphate per mole of the 42,000 dalton subunit of eIF-2 and about 6 moles of phosphate per mole of the 107,000 dalton subunit of eIF-3. Three proteins (M_r = 38,000, 14,800, and 12,600) of the 60S ribosomal subunit are phosphorylated by the kinase, but none of the 40S ribosomal proteins are substrates of the kinase. No effects of phosphorylation on the activities of eIF-2, eIF-3, or 60S ribosomal subunits could be demonstrated in vitro.