Journal of Experimental Botany

WHEELER, A., W.

doi: 10.1093/jxb/17.4.621pmid: N/A

Abstract The growth of the primary leaf on intact plants was compared with that on plants from which the cotyledons, apical growing region, or trifoliate leaves had been removed. Removing the cotyledons early decreased the final area of the primary leaves, this response being partially accounted for by a decrease in their cell number, and increased the concentration (but not the quantity) of gibberellin and auxin in them. This response was not altered by applying any of several growth substances. Early removal of the apical growing region increased the final area of the primary leaves; it also increased the gibberellin content and concentration at Day 10 but did not influence the auxin content and concentration. Primary leaf expansion was affected less by detaching young trifoliate leaves than by removing the entire apical growing region. This content is only available as a PDF. © Oxford University Press

HOUSE, C., R.;FINDLAY,, NELE

doi: 10.1093/jxb/17.4.627pmid: N/A

Abstract It was found that the fluid exudation rate from isolated maize roots rapidly decreases when the external concentration of various solutes is increased; thereafter a relatively slow increase to a new value occurs. An analysis of this transient phenomenon has been achieved on the basis that there is an active transport of salt (KCl) into a compartment within the root. Further, it has been assumed that fluid exudation is created by a net osmotic water flow into this compartment. Our analysis of the experimental data indicates that the volume of the compartment has a similar magnitude to the estimated total volume of the xylem vessels in the root. The transient curve obtained with some solutes (methanol, magnesium sulphate, mannitol, and raffinose) were significantly different from the usual response. An attempt to apply an appropriate diffusion equation to the initial phase of the transient curves showed that the time course of this phase may be interpreted as being controlled by the rate of solute diffusion towards an osmotic barrier within the root. This content is only available as a PDF. Author notes 1Present address: School of Biological Sciences, University of Sydney, Australia. © Oxford University Press

SYRETT, P., J.

doi: 10.1093/jxb/17.4.641pmid: N/A

Abstract The addition of acetate to aerobic Chlorella pyrenoidosa in darkness was followed by the formations of isocitrate lyase actiity. After a lag period of 40 minutes the formation proceeded at a constant rate. By use of actylamide gel electrophoresis it was shown that the increase in enzyme activity was accompanied by the formation of a new protein which, after separation by electrophoresis, contained isocitrate lyase activity. The formation of isocitrate lyase was repressed by glucose; it was repressed by light in the presence of carbon dioxide, but not when DCMU was added. In light, plus DCMU, isocitrate lyase was formed anaerobically and the capacity for photo-formation of isocitrate lyase was saturated at 500 ergs/cm2/sec. In this respect the process resembled the photo-conversion of glucose to polysaccharide but differed from the photo-assimilation of carbon dioxide which became saturated at a heigher light intensity. Monochromatic light of 706 mμ wavelength supported both isocitrate layse formation and the conversion of glucose to polysaccharide but not carbon dioxide fixation. It is concluded that ATP generated by cyclic photophosphorylatin can provide the energy for isocitrate lyase synthesis in Chlorella. This content is only available as a PDF. © Oxford University Press

AVERY, D., J.

doi: 10.1093/jxb/17.4.655pmid: N/A

Abstract Factors affecting the supply of air to leaves enclosed in assimilation chambers have been studied using models and leaves of apple and plum. The rate of CO2 assimilation of a leaf does not increase linearly with increasing rate of air flow. Explanations of this and other observations are put forward in terms of the boundary-layer concept and diffusion paths. Comparisons are made with free-air conditions, and it is concluded that air should be supplied at the same rate (ml/min) for leaves of different size in the same chamber. Three cup designs were also studied. A method is described for making valid comparisons of assimilation rates per unit area by extrapolation to an infinitely high rate of air flow. Measurements of different sized leaves with chambers and cups can be compared in this way. Rates expressed per unit area can be correctly compared only if the resistance to diffusion outside the leaf is negligible, or under special conditions. Assimilation rates measured with rates of air flow giving CO2 availability equivalent to that occurring in static free air should be expressed per unit perimeter. Methods of correction of assimilation rates for the depletion of carbon dioxide from the air stream are considered. This content is only available as a PDF. © Oxford University Press

GOULDING, K., H.;MERRETT, M., J.

doi: 10.1093/jxb/17.4.678pmid: N/A

Abstract Chlorella pyrenoidosa can utilize sodium acetate as a carbon source for growth in the light. Growth proceeds under aerobic conditions both in the presence and in the absence of carbon dioxide, but under anaerobic conditions only in its presence. The assimilation of acetate does not result from oxidation to carbon dioxide followed by photosynthetic fixation because the products of 14C-acetate assimilation are different from the products of 14CO2 fixation in the presence of unlabelled acetate. In aerobic conditions 10-6 M DCMU induces a pattern of acetate assimilation in the light similar to that in the dark. Thus, in the presence of DCMU in the light, less acetate carbon is incorporated into cells, particularly into lipids, polysaccharide, and protein, and more is released as carbon dioxide than in its absence. The effect of 4 × 10-3 M MFA on acetate assimilation in the presence of 10-6 M DCMU is the same in light and dark. Acetate assimilation is unaffected by desaspidine and sodium bisulphite. The mean generation time of C. pyrenoidosa growing on acetate in the light under aerobic conditions is 20 hours. When 10-5 M DCMU is added the mean generation time is 60 hours, the same as that for Chlorella growing on acetate in the dark. The activity of the enzymes of the glyoxylate cycle, isocitrate lyase (E.C.4.1.3.1.) and malate synthetase (E.C.4.1.3.2.) is repressed in the light, but activity of both enzymes increases markedly when DCMU is added. This content is only available as a PDF. © Oxford University Press

HEATHCOTE, D., G.

doi: 10.1093/jxb/17.4.690pmid: N/A

Abstract A low amplitude oscillatory movement, distinct from the nutational movements occuring in the same plant, has been found to occur in seedling plants of runner bean. The frequency of the oscillation is between two and five cycles per hour, and appears to have a temperature coefficient of 2.24 in the range 15–25°C. The theoretical implication of this oscillation on the ‘geotropic hunting’ theory of nutation is discussed. This content is only available as a PDF. © Oxford University Press

EDELMAN,, J.;SINGH, S., P.

doi: 10.1093/jxb/17.4.696pmid: N/A

Abstract Analyses of the changes in starch and soluble sugars in sprouting potatoes show that when a single terminal sprout grows it draws upon the carbohydrates in every part of the tuber simultaneously; there appears to be no induced concentration gradients of these compounds through the tuber even though the starch content is eventually reduced to zero. This content is only available as a PDF. Author notes 1Permanent address: Division of Botany, I.A.R.I., New Delhi—12, India. © Oxford University Press

MACKLON, A. E., S.;MACDONALD, I., R.

doi: 10.1093/jxb/17.4.703pmid: N/A

Abstract Measurements have been made of the electrical potential difference between the vacuoles of single potato tuber cells and external Cl- solutions over the range 1–40 mM. With K+ as the counter-ion, the relationship between this transmembrane electrical potential and external Cl- concentration, for fresh cells at 20° C, was found to be one of decreasing negative polarity with increasing Cl- concentration (E at 1 mM Cl- external = – 81 m V; change in E for a 10-fold change in external concentration, ΔE10 = 46 m V). The linearity of this relationship, apparent on a semi-logarithmic plot, was virtually unaltered by low temperature (0.5–2.5° C) or by previous ageing of the cells for periods up to four days (indicating that metabolic ion absorption is not an electrogenic process). When the counter-ion was maintained at a constant high concentration (40 mM K+), the change in potential over the Cl- concentration range was only 4 m V, polarity becoming more negative with increasing Cl- concentration. With Ca++ as the counter-ion, the potential to external Cl- concentration relationship was similar to that found in KCl solutions, except that ΔE10 was only about 20 m V. Curves for the influx of C1- to be expected on the basis of these electrochemical data alone have been shown to run closely parallel to Cl– absorption isotherms previously determined experimentally. This confirms the opinion, already formed on the basis of theoretically derived values for passive Cl- influx, that Cl- uptake by both fresh and one-day-aged potato tissue, from KCl solutions and Cl- solutions with a fixed high K+ concentration, is rate-determined at o° C by passive movement across the plasmalemma. Uptake of Cl- by fresh tissue at 20° C appears to be similarly regulated. No such parallelism was found between observed and expected patterns of Cl- uptake from CaCl2 solutions, or from KCl by two-day-aged tissue, and here factors in addition to the electrochemical ones must determine low temperature Cl-uptake. This content is only available as a PDF. © Oxford University Press

DIGBY,, J.;WAREING, P., F.

doi: 10.1093/jxb/17.4.718pmid: N/A

Abstract The effects on cell division and cell size of indole-3-acetic acid (IAA), gibberellic acid (GA), and kinetin were studied in liquid suspension cultures of cambial cells derived from Acer pseudoplatanus. It was shown that all three hormones promote cell division and that the effects of both GA and kinetin are additive to those of IAA, but the effects of GA and kinetin together are not additive. Treatment with IAA resulted in an increase of mean cell size (indicating that cell expansion is promoted), but after GA or kinetin treatment the mean cell size was smaller, indicating that little cell expansion had taken place after each division. The results are discussed in relation to previous work on the effects of hormones in the intact cambium and to current theories on the interactions of growth hormones. This content is only available as a PDF. Author notes 1Present address: Department of Botany, University of Aberdeen, Aberdeen, Scotland. © Oxford University Press

STEWARD, F., C.;BIDWELL, R. G., S.

doi: 10.1093/jxb/17.4.726pmid: N/A

Abstract 14C-labelled sucrose, glutamine, and asparagine have been supplied to aseptically cultured carrot explants that either grew rapidly by cell division or, by contrast, only slowly by cell expansion. The radioactive substrates were supplied in a brief ‘pulse’ followed by a much longer period during which the tissues were supplied with 12C-substrates. The passage of 14C through the various soluble compounds of the tissue and into the protein was followed. Alternatively, the 14C-labelled compound was supplied throughout the entire period of an experiment while the tissue also received 12C-sucrose. The pulse-labelling experiments demonstrate turnover and the fate of the breakdown products, as well as the emphasis placed on this kind of metabolism by cells at different levels of activity in their growth. The long-term labelling experiments show the different ways in which carbon from various sources may be used and how these pathways are affected by growth. The amount of 14C present in the various free (ethanol soluble) and combined (ethanol insoluble, acid-hydrolysable compounds—proteins) was determined, as well as the specific activity of the carbon in each compound. The fate of 14C supplied as sucrose had much in common with 14C supplied as glutamine, with respect to the ease with which it entered both the protein being synthesized and the carbon dioxide evolved, but it was very different from 14C supplied as asparagine. To interpret these data, compartments or pools of metabolites are postulated in the organized cell; exogenous 14C-sucrose and 14C-glutamine readily furnish carbon for pools of amino-acids en route to protein, which are protected from both the stored compounds and those which arise after protein breakdown. However, exogenous 14C-asparagine enters, is accumulated, and persists in the pool of stored compounds which also receive the nitrogen-rich substances that arise from protein breakdown. The kinetic data and the specific activities of the carbon in its various forms require that protein breakdown and re-synthesis occur concomitantly, that the stimulus to grow, exerted by coconut milk, accentuates protein synthesis and also the pace of its turnover, that some respired carbon dioxide arises from protein, and that this moiety of the respiration is increased by the coconut-milk stimulus as it accentuates the pace of cyclical turnover. In similar experiments with free cells from different plants, the same general conclusions apply, but the rates of turnover of protein are greater in free cells than in tissue explants. Some specific differences, however, exist. Cells of Arachis, the only legume investigated, permit 14C-asparagine to contribute, like 14C-glutamine, to both protein synthesis and respired 14CO2; it is not merely segregated in a storage pool. Thus, by virtue of their organization, plant cells maintain the same substances simultaneously in distinct phases or compartments, where they play distinctive roles, without mingling. Genetics endows each cell with the information that makes its biochemical reactions feasible; the organization of the cells determines how far the feasible becomes practised in cells in any given situation. This content is only available as a PDF. Author notes 1Present address: Department of Biology, Western Reserve University, Cleveland, Ohio. © Oxford University Press