Journal of Experimental Botany

HANSEN, ALEXANDER, P.;PEOPLES, MARK, B.;GRESSHOFF, PETER, M.;ATKINS, CRAIG, A.;PATE, JOHN, S.;CARROLL, BERNARD, J.

doi: 10.1093/jxb/40.7.715pmid: N/A

Abstract Growth and symbiotic performance of soybean (Glycine max (L.) Merrill) cv. Bragg and three of its induced nodulation mutants (nod49, non-nodulating; ntsl 116, intermediate supernodulator; nts1007, extreme supernodulator) were compared throughout development under different nitrogen regimes (0, 2, 5 and 10 mol nitrate m−3). Nitrogen fixation was assessed using 15N-isotope dilution and xylem sap analysis for ureide content. Both techniques confirmed a complete lack of N2 fixation activity in nod49. Plant reliance on nitrogen fixation by the other genotypes was dependent on the nitrate regime and the developmental stage. The ntsl007 and ntsl 116 mutants fixed more nitrogen than the parent cultivar in the presence of 10 mol m−3 nitrate in the nutrient solution, but higher input of symbiotically derived nitrogen was still insufficient to offset the amount of nitrogen removed in the harvested seed. However, the mutants utilized less nitrate for growth than Bragg. Comparison of estimates of N2 fixation derived from the 15N-dilution technique with those based on relative ureide content of xylem sap indicated that the latter offered a simple and reliable procedure for evaluating the symbiotic performance of supernodulating plants. 15N-isotope dilution, supernodulation, ureides This content is only available as a PDF. Author notes 4 Present address: Institut fur Pflanzenernahrung, Universitat Hohenheim, Postfach 70 05 62, 7000 Stuttgart 70, FRG. 5 Present address: Plant Molecular Genetics, Institute of Agriculture, University of Tennessee, PO Box 1071, Knoxville, TN 37901-1071, USA. © Oxford University Press

BECANA,, MANUEL;SPRENT, JANET, I.

doi: 10.1093/jxb/40.7.725pmid: N/A

Abstract Multiple components of leghaemoglobins (Lbs) from several legume species have been separated by polyacrylamide gel electrophoresis (PAGE), and identified by densitometry at 405 nm, extraction from gels and formation of their respective CO-ferrous complexes. Components were numbered consecutively starting from the anode side, and their relative concentrations were calculated by densitometry in control and NO3- -treated nodules. The number of Lb components was five in Pisum sativum, four in Glycine max, at least two in Lupinus luteus and Trifolium repens, and two in Vigna radiata and V. unguiculata. Only one component was detected in fresh nodules of Phaseolus vulgaris. Nitrate significantly reduced the total content of Lb in all legumes, except Lupinus, the extent of reduction varying with the species. It also had a major effect on the proportions of components, causing an inversion in the relative abundance of Lb I and Lb II of V. radiata: the concentration of Lb I increased from 8% to 81% with NO3- application, while total Lb only decreased by 13%. Drastic changes in proportions of Lb components were not artifactual and cannot be attributed exclusively to different turnover rates. They should correspond to variations in biosynthesis of the various components, probably originating at the genetic level. Leghaemoglobin components, nitrate, nodule senescence This content is only available as a PDF. © Oxford University Press

RYLE, G. J., A.;POWELL, C., E.;TIMBRELL, M., K.;GORDON, A., J.

doi: 10.1093/jxb/40.7.733pmid: N/A

Abstract Single, clonal plants of white clover were grown without inorganic nitrogen in four contrasting day/night temperature regimes, with a 12 h photoperiod, in controlled environments. Root and nodule respiration and acetylene reduction activity were measured in a flow-through system during both day and night for plants acclimated to day/night regimes of 23/18, 15/10 and 10/5 °C. Similar measurements were made on plants acclimated to 20/15 °C and stepwise at temperatures from 4 to 33 °C. Peak rate of ethylene production, nitrogenase-linked respiration and basal root + nodule respiration increased approximately linearly from 5 to 23 °C both in temperature-acclimated plants and in plants exposed to varying measurement temperatures. The measured attributes did not vary significantly between day and night. Temperatures above 23–25 °C did not further enhance the rate of ethylene production, which remained essentially the same up to the maximum measured temperature of 33 °C. The measurements of nitrogenase-linked respiration between 5 and 23 °C, during both day and night, demonstrated a constant ‘energetic cost’ of acetylene reduction of 2.9 μmol CO2 μmol C2H4−1,. Over the same temperature range, the approximate activation energy of acetylene reduction was 60 kJ mol−1. The integrated day plus night nitrogenase-linked respiration accounted for 13.4–16% of the plant‘s net shoot photosynthesis in a single diurnal period: there was no significant effect of temperature between 5 and 23 °C. Trifolium repens, white clover, temperature, N2 fixation, respiration This content is only available as a PDF. Author notes " 2 Present address: AFRC Institute for Grassland and Animal Production, Welsh Plant Breeding Station, Aberystwyth, Dyfed SY23 3EB, UK. © Oxford University Press

LEE, R., B.;DREW, M., C.

doi: 10.1093/jxb/40.7.741pmid: N/A

Abstract The rate of influx of nitrate into the roots of intact barley plants was measured over a period of 3–5 min from external nitrate concentrations of 1–150 mmol m−3, using 13N-labelled nitrate as tracer. Ammonium at external concentrations of 0.005–50 mol m−3 inhibited nitrate influx in a manner which did not conform to a simple kinetic model but increased approximately as the logarithm of the ammonium concentration. At any particular ammonium concentration, inhibition of nitrate influx reached its full extent within 3 min of the ammonium being supplied and was not made more severe by up to 17 min pre-treatment with ammonium. On removing the external ammonium, nitrate influx returned to its original rate within about 3 min. Potassium at 0.005–50 mol m−3 did not reproduce the rapid effect of ammonium on nitrate influx. Net uptake of nitrate also decreased when ammonium was supplied, over a similar timescale and to a similar extent as nitrate influx. The decrease in nitrate influx caused by ammonium was sufficient to account for the observed reduction in net uptake, without necessitating any acceleration of nitrate efflux. Hordeum vulgare, roots, ion transport, short-lived isotopes, 13N This content is only available as a PDF. Author notes 2 Present address: Department of Horticultural Sciences, Texas A&M University, College Station, Texas 77843, USA. © Oxford University Press

COOPER, H., D.;CLARKSON, D., T.

doi: 10.1093/jxb/40.7.753pmid: N/A

Abstract A split root system was used to investigate the cycling of nitrogen between shoots and roots in young wheat and rye plants. 15N-nitrate was supplied to one part of the root system for various periods, at the end of which these roots were excised. Xylem sap was then collected from the other roots which had not been supplied directly with 15N-nitrate. 15N detected in the xylem sap indicated cycling of nitrogen between shoots and roots. Calculations showed that over 60% of the amino-N flux in the xylem was cycling. Thus nitrate assimilation in the root could account for only a minor part of amino-N in the xylem sap. The specific activity of 15N in the total N of xylem sap was higher than in the total N of roots and shoots through which it had cycled. This is because exchange between amino-N in the transport pools and bulk tissue N is limited. It is proposed that there is, in effect, a single regulatory pool of amino-N, common to shoots and roots, and that this pool may be a key element in the control of N uptake at the level of the whole plant. The likely energy costs of cycling and implications for the partitioning of N between shoots and roots are discussed. In further investigations the cycling of 42K-potassium and 32S-sulphur was demonstrated. Potassium, sulphur, transport, xylem This content is only available as a PDF. © Oxford University Press

TAYLOR, JOHN R., N.;EVANS, DAVID, J.

doi: 10.1093/jxb/40.7.763pmid: N/A

Abstract Protein bodies isolated from the starchy endosperm of ungerminated sorghum exhibited some autolytic activity but seemed incapable of significant self-hydrolysis. Enzyme assay, transmission electron microscopy, sodium dodecyl sulphate—polyacrylamide gel electrophoresis and amino acid analysis revealed that a proteinase extract from germinated sorghum could degrade the protein bodies in a manner resembling that which takes place in vivo. The protein bodies were degraded mainly from the periphery. Glutelin (matrix protein) was first hydrolysed, followed by the prolamin protein body protein. Proteinase extracts from both the germ and endosperm of germinated sorghum were capable of degrading the protein bodies. This finding is consistent with the concept that the proteinase is synthesized in the germ and then secreted into the starchy endosperm during germination. Sorghum bicolor, protein body degradation, proteinase. This content is only available as a PDF. Author notes 2 Present address: South African Breweries, Central Laboratory, P.O. Box 10, Isando 1600, South Africa. © Oxford University Press

OFFLER, C., E.;NERLICH, S., M.;PATRICK, J., W.

doi: 10.1093/jxb/40.7.769pmid: N/A

Abstract The seed coat vascular system of the developing seed of Vicia faba consists of a chalazal and two lateral veins. The veins are embedded in parenchymatous tissue which lies beneath the hypodermis and is divided into chlorenchyma, ground parenchyma and thin-walled parenchyma. The thin-walled parenchyma cells and, in old seed coats, the vascular parenchyma of the veins undergo additional secondary wall development to form transfer cells. Thus, transfer cells line the entire inner surface of the seed coat. Initial distribution of 14C-photosynthates and sodium fluorescein within the seed coat was in the vascular system. Subsequent transfer towards the embryo was either radially through vascular parenchyma and thin-walled parenchyma to thin-walled parenchyma/transfer cells, or by lateral spread within the ground and thin-walled parenchyma/transfer cells of the non-vascular region of the seed coat prior to radial transfer. One-third of the 14C-photosynthate delivered to the enclosed embryo was estimated to be transferred via the non-vascular region of the seed coat. The cotyledons consist of a single-layered epidermis enclosing storage parenchyma in which a differentiating reticulate vascular system is embedded. Epidermal cells juxtaposed to the seed coat develop wall ingrowths characteristic of transfer cells. Initial distribution of 14C-photosynthate within the cotyledons reflected the unequal delivery to the seed apoplast from the vascular and non-vascular regions of the seed coat. Subsequent even distribution of photosynthate within the cotyledons possibly occurred by transfer within their vascular system. Cellular pathway, photosynthate transfer, seed anatomy, transfer cell This content is only available as a PDF. © Oxford University Press

MINCHIN, P. E., H.;THORPE, M., R.

doi: 10.1093/jxb/40.7.781pmid: N/A

Abstract Continuous in vivo measurements of the partitioning of recently fixed photo-assimilate to individual ovules within a single pod of Pisum are reported. Also, partitioning to attached surgically modified ovules as well as partitioning to the solution bathing these ovules is described. Partitioning to whole ovules was found to vary up and down by about 10% over a time span of several hundred minutes, while that to surgically modified ovules continually fell and was reduced by about 65% 400 min post surgery. Partitioning from the seed coat to the bathing solution was reduced by 80%, so that partitioning of photo-assimilate from the pod to the bathing solution had been reduced by 93% and had virtually stopped. This observation throws some doubt upon the use of long-term (> 200 min) measurements of photo-assimilate efflux from attached seed coats in the study of photo-assimilate movement into ovules. This work is based upon a method of analysing carbon-11 tracer profiles which does not require that these profiles be corrected for radioactive decay, thus enabling this short-lived isotope to be used for quantitative studies of indefinite duration by continuous or multiple pulse labelling. Pea, ovules, carbon-11 This content is only available as a PDF. © Oxford University Press

BHADULA, S., K.;SAWHNEY, V., K.

doi: 10.1093/jxb/40.7.789pmid: N/A

Abstract The activity of amylases, and the level of starch and soluble sugar content were analysed in the normal (+/+), a ‘gibberellin-sensitive’ male sterile stamenless-2 (sl-2/sl-2) mutant, and GA3-reverted sl-2/sl-2 mutant stamens of tomato (Lycopersicon esculentum Mill.), at various stages of development. In the mutant stamens, amylolytic activity did not differ from that of the normal until the tetrad stage, but thereafter it was significantly lower than that of normal stamens. The starch content also did not differ in the two lines at early stages of development. However, at later stages it decreased in normal stamens, whereas it remained unchanged in the mutant. The soluble sugar content gradually increased during the development of normal stamens. But in mutant stamens, it remained the same throughout development and was significantly lower than the normal. In GA3-reverted mutant stamens, the amylolytic activity and the level of starch and soluble sugars were comparable to normal stamens. It is proposed that the sl-2/sl-2 mutation, through its effects on endogenous gibberellins, affects the activity of amylases which, in turn, result in lower sugar levels leading ultimately to abnormal pollen development. Amylases, male-sterility, tomato This content is only available as a PDF. Author notes 1 Present address: Department of Biochemistry, University of Saskatchewan, Saskatoon, SK S7N OWO, Canada. © Oxford University Press

BLACKWELL, J., R.;GILMOUR, D., J.

doi: 10.1093/jxb/40.7.795pmid: N/A

Abstract A method has been developed to measure the cell volume of the unicellular green alga Dunaliella parva 19/9 using Li+ measurements only. Concentrations of internal solutes can also be calculated if they are assayed in the same samples as Li+. We found that D. parva cells grown in 0.4 kmol m−3 NaCl have an average aqueous cell volume of 65.1 ±2.9 μm3, a K+ concentration of 126±6 mol m−3, a Na+ concentration of 11±11 mol m−3 and a glycerol concentration of 615±27 mol m−3 (n= 12). Algae grown in 1.5 kmol m−3 NaCl have an average aqueous cell volume of 131 ±7.5 μm3, a K+ concentration of 109±4 mol m−3, a Na+ concentration of 10±39 mol m−3 and a glycerol concentration of 1 425±59 mol m−3 (n = 12). These results indicate that D. parva cells adapted to high salinities have larger cell volumes than those adapted to lower salinities. However, there is no evidence for a significant difference in internal Na+ concentration, despite the almost 4-fold difference in the concentration of external NaCl. The intracellular glycerol concentration alone accounts for 65% and 54%, respectively, of the osmotic balance in low and high salt grown cells. Dunaliella, cell volume, intracellular solutes This content is only available as a PDF. © Oxford University Press