Journal of Experimental Botany

GORDON, A., J.

doi: 10.1093/jxb/42.8.961pmid: N/A

Abstract Analysis of the distribution of enzymes of carbohydrate, carboxylic acid and nitrogen metabolism in nodule tissues prepared by protoplast isolation techniques has led to some confusion about their whereabouts. In this study nodule cortical and central (infected) tissue was separated manually using a scalpel blade. Protein contents of whole nodules, central region and cortex were found to be 19, 25 and 5-0 mg g−1 fresh weight, respectively. Specific activities of glutamine synthetase (GS), phosphoenolpyruvate carboxylase (PEPC), invertase (INV) and sucrose synthase (SS) were higher in the central region than in the cortex. The reverse was true for UDP glucose pyrophosphorylase (UDPGPP), phosphoglucomutase (PGM) and phosphoglucose isomerase (PGI). The central (infected) region represented a minimum of 65% of the nodule fresh weight. Calculations based on this estimate and on the activities per gram fresh weight indicate that the bulk of the potential enzyme activity is located in the central region. This was particularly so for SS, INV and GS where greater than 96% of the relevant activity was located in the central region. Even the enzymes which had greater specific activities in the cortex (UDPGPP, PGM and PGI) were, in fact, predominantly found in the central region (86, 81, and 85%, respectively). The conclusion from this data must be that most metabolism in the nodule is likely to occur in the central region, although this does not negate the importance of the cortex in carbon and nitrogen flux. Glycine max, soybean, nodules, cortex, infected region, enzymes This content is only available as a PDF. © Oxford University Press

EGLI, MARGARET, A.;LARSON, RUBY, J.;HRUSCHKA, WILLIAM, R.;VANCE, CARROLL, P.

doi: 10.1093/jxb/42.8.969pmid: N/A

Abstract Root nodule development and function are accompanied by synthesis of numerous plant gene-encoded, nodule-specific (nodulin) and nodule-enhanced proteins. While bacterially-induced ineffective nodules have proven important in understanding nodulin synthesis, comparable information is lacking for plant gene-controlled ineffective nodules. Here, we compare synthesis of nodulins and nodule-enhanced proteins, including leghaemoglobin (Lb) and glutamine synthetase (GS), between effective alfalfa (Medicago sativa L. cv. Saranac) and two types of single gene recessive plant mutants (in tSa: early-senescing nodules and in3-3811: tumour-like nodules). Most nodulins were synthesized (in vitro) by nodule mRNA from in1Sa plants but at reduced amounts as compared to effective nodules. By contrast, in3-3811 nodules synthesized primarily a 30 kD nodulin. The proportion of acidic to basic Lbs was higher in young (day 7) non-N2-fixing ‘Saranac’ nodules than in mature (day 38) effective nodules. All Lbs were detected in mature in1Sa nodules but the ratio of acidic to basic Lb in vitro polypeptides resembled day 7 non-N2-fixing ‘Saranac’ nodules. Amounts of nodule-enhanced GS polypeptide were reduced in mature ineffective in1. and in3-3811 nodules as compared to ‘Saranac’. Amounts of Lb and GS mRNAs in both ‘Saranac’ and in1Sa increased during nodule development and decreased upon defoliation. Although in1Sa nodules contained less Lb and GS mRNA than did ‘Saranac’ nodules, differences between mRNA content were not as pronounced as differences in Lb and GS protein. These data suggest that expression of Lb and GS in in1Sa nodules is regulated by both transcriptional and post-transcriptional events. Medicago, N2-fixation, leghaemoglobin, glutamine synthetase, gene expression This content is only available as a PDF. © Oxford University Press

KAPPEN,, L.;HAEGER,, S.

doi: 10.1093/jxb/42.8.979pmid: N/A

Abstract Tradescantia albiflora has green variegated and white leaves. Its stomatal apparatus consists of the guard cells and two pairs of subsidiary cells. Investigations were carried out by observing the stomata microscopically by means of a video system in situ in a CO2 exchange chamber and by simultaneously measuring the gas exchange of the leaves. In response to air humidity changes, stomatal movements in T. albiflora begin, owing to turgor changes, in the polar and lateral subsidiary cells. The stomatal response of green leaves to changes of air humidity showed typical transient and oscillatory phases prior to steady-state reactions. In darkness, stomata closed when air humidity decreased; however, they did not reopen when air humidity was raised again. Stomata of illuminated white leaves responded like those of green leaves in darkness. With increasing soil water stress stomata responded to changing air humidity with reductions of the transient phases and a decreasing tendency to reopen when air humidity became high again. CO2 deficiency of the air caused the stomata to open in the dark, and interacted with the air humidity effect in such a way that stomata of green leaves responded to air humidity changes in darkness in a similar way as they did in light. Stomata, humidity response, green and white leaf areas, CO2 deficient air This content is only available as a PDF. © Oxford University Press

ATKINSON, C., J.

doi: 10.1093/jxb/42.8.987pmid: N/A

Abstract Inherent differences in the responses of stomata on abaxial and adaxial epidermal surfaces of leaves of Commelina communis have previously been suggested to be due to differences in the concentrations of apoplastic Ca. Adaxial stomata have also been reported to be more sensitive than abaxial stomata to applied abscisic acid (ABA). The aims of these experiments were to determine the validity of these conclusions and to see if xylem sap Ca has a role in determining the response of stomata to ABA. It can be shown from measurements of relative stomatal resistance (determined with a viscous flow porometer) and stomatal conductance that stomata were more open in plants grown on 8-0 mol m−3 Ca, than with those grown on 2-0 mol m−3 Ca. When attached leaves were fed with ABA via the transpiration stream neither the extent nor the rate with which conductance declined was dependent on Ca nutrition. The extent of Ca accumulation within both epidermes was related to the concentration of Ca in the rhizosphere and in the xylem sap. It did not, however, appear to reflect the apparent differences in the flux of the transpiration stream between the two epidermes. Plants growing at the lower Ca concentration accumulated proportionally more epidermal Ca relative to Ca in xylem sap. The evidence presented suggests that Ca movement from the xylem to the epidermis cannot be simply described by a mass flow model, and that the distribution of Ca is not an adequate explanation of the differences in the behaviour of adaxial and abaxial stomata. The potential role for changes in xylem sap Ca to act as a regulator of stomatal behaviour are discussed. Abscisic acid, calcium, Commelina communis L., stomatal conductance This content is only available as a PDF. © Oxford University Press

KUBÍNOVÁ,, LUCIE

doi: 10.1093/jxb/42.8.995pmid: N/A

Abstract The anatomical structure of the second leaf blade of barley {Hordeum vulgare L. cv. Koral) was studied in plants exposed to a photosynthetic photon flux density (PPFD) of 200 μmol m−2 s−1 compared with those grown under 25μmol m−2−11. Design-based stereological methods were used for the estimation of various leaf anatomical characteristics such as mesophyll volume, proportion of intercellular spaces, number of mesophyll cells, mean mesophyll cell volume, and internal leaf surface area. The structure of the mesophyll was more affected by different levels of PPFD than were the stomatal characteristics. Increased PPFD produced thicker leaves with a larger mesophyll volume having a higher number of less elongated mesophyll cells and a larger internal leaf surface area. Hordeum vulgare, light effect, mesophyll, stereology, stomata This content is only available as a PDF. © Oxford University Press

JACOB,, J.;LAWLOR, D., W.

doi: 10.1093/jxb/42.8.1003pmid: N/A

Abstract The effects of phosphate deficiency on the composition and photosynthetic CO2 assimilation rates of fully expanded leaves of sunflower, maize and wheat plants are described. The regulation of photosynthesis by stomatal and mesophyll characteristics of leaves of different phosphate status is analysed and related to structure. Phosphate deficient leaves had small concentrations of inorganic phosphate, Pi, in the tissue water. Rate of photosynthesis in leaves and stomatal conductance were smaller in plants grown with inadequate phosphate when measured under any given light intensity or CO2 partial pressure. Despite the decrease in stomatal conductance (and without evidence of patchy stomatal closure), the relative stomatal limitation of photosynthesis was similar in the plants grown with deficient or abundant phosphate. However, the mesophyll capacity for photosynthesis was greatly limited by phosphate deficiency. Leaves deficient in phosphate had larger numbers of small size cells per unit leaf area than leaves with adequate phosphate. The total soluble protein content of leaves decreased with phosphate deficiency in all three species; however, the leaf chlorophyll content was decreased only in sunflower and maize and not in wheat. These results suggest that stomatal conductance did not restrict the CO2 diffusion rate, rather the metabolism of the mesophyll was the limiting factor. This is shown by poor carboxylation efficiency and decreased apparent quantum yield for CO2 assimilation, both of which contributed to the increase in relative mesophyll limitation of photosynthesis in phosphate deficient plants. Apparent quantum yield, carboxylation efficiency, phosphate nutrition, photosynthesis, stomatal and mesophyll limitation This content is only available as a PDF. © Oxford University Press

WATSON, PATRICIA, A.;DUFFUS, CAROL, M.

doi: 10.1093/jxb/42.8.1013pmid: N/A

Abstract Immature detached caryopses from barley (Hordeum vulgare L. var. distichum cv. Midas) were shown to be capable of light-dependent retrieval of internally-produced CO2. In the first set of experiments, caryopses were radioactively labelled by supplying (U-14C)-sucrose to detached ears in liquid culture. Caryopses were then removed from the ear and given a 12 h chase of non-radioactive sucrose in either the light or dark. More 14C was recovered in the caryopses after the chase in the light than in the dark but the differences were not significant. In the second set of experiments, 14C-labelled caryopses obtained by a 15 min light incubation in 14CO2 were maintained in either the light or dark for 3 h and any redistribution of label between the tissues recorded. The results show that under these conditions, photosynthesis in the Chl-containing green layer of the pericarp can prevent losses of internally-produced CO2, since 3 times as much radiocarbon remained in the caryopses incubated in the light as in the dark. These differences were significant at P=0.001. Experiments with the mutant barley Albino lemma, which has no Chi in the pericarp, showed that there was little difference between light and dark treatments. This confirms the suggestion that photosynthesis in the pericarp of the normal cultivar Midas may be concerned in the refixation of CO2. Barley, pericarp, photosynthesis, carbon dioxide This content is only available as a PDF. © Oxford University Press

HERSCHBACH,, CORNELIA;RENNENBERG,, HEINZ

doi: 10.1093/jxb/42.8.1021pmid: N/A

Abstract In short-term experiments sulphate influx of excised tobacco roots {Nicotiana tabacum L. var. 'Samsun') followed monophasic Michaelis-Menten kinetics with an approximate Km of 12 ± 4 μM and vmax of 657 ± 211 nmol g−1 FW h−1. An inhibition of sulphate influx, xylem loading and exudation of more than 70% was achieved with 01 mM GSH within 1 h. Cysteine was two orders of magnitude more effective as an inhibitor than GSH. An inhibition of more than 75% was already obtained with 1.0μM cysteine. It may, therefore, be assumed that GSH is decomposed to yield cysteine concentrations that may inhibit sulphate influx, xylem loading and exudation. When BSO, a specific inhibitor of the initial step of GSH synthesis, was added, cysteine-mediated inhibition on sulphate influx, xylem loading and exudation was strongly diminished. Apparently, GSH synthesis is required to obtain inhibition of these processes by cysteine. The physiological mechanisms that may cause the inhibition of sulphate influx, xylem loading and exudation by glutathione are discussed. Sulphate transport, Nicotiana, Solanaceae, glutathione, cysteine, buthionine sulphoximine This content is only available as a PDF. © Oxford University Press

WHITE, PHILIP, J.;EARNSHAW, MICHAEL, J.;CLARKSON, DAVID, T.

doi: 10.1093/jxb/42.8.1031pmid: N/A

Abstract The effects of growth and assay temperature on unidirectional K+ fluxes in excised roots of rye (Secale cereale cv. Rheidol) were studied using 86Rb+ as a tracer. Both K+ influx to the vacuole, estimated as K+ uptake between 3 and 12 h after transfer of unlabelled roots to radioactive solution, and movement of K+ to the xylem were determined directly. Other fluxes were determined on excised roots of plants, which had been labelled with 86Rb+ since germination, by conventional triple exponential efflux analysis. When assayed at 20°C, roots of plants previously grown at 20°C(WG roots) had lower rates of net K+ uptake than roots of low temperature-acclimated plants, grown with a temperature diferential between roots (87°C) and shoots (20°C) either since germination (DG roots) or for 3 d prior to experiments (DT roots). This resulted from a greater unidirectional K+ efflux across the plasma membrane and a reduced K+ flux to the xylem in WG roots, compared to DG or DT roots, rather than a decrease in unidirectional K+ influx or a decrease in the net K+ flux to the vacuole. Indeed, although WG roots had lower rates of K+ influx and K+ efflux across the tonoplast at 20°C than DG or DT roots, roots of plants from all growth temperature treatments showed an equivalent net K+ flux to the vacuole. Although all unidirectional K+ fluxes in roots from plants grown under all temperature regimes were reduced by lowering the temperature of the root, these fluxes were differentially affected in roots of plants from contrasting growth temperature treatments. Rapid cooling to 8°C of WG roots resulted in a lower rate of K+ influx and a transient increase in K+ efflux across both the plasma membrane and tonoplast, compared to DG and DT roots. Furthermore, since the K+ flux to the xylem was lower in WG roots, the net K+ uptake at 8°C into WG roots was considerably reduced compared to DG and DT roots. These results suggest that low temperature-acclimation of K+ fluxes in rye roots may involve a reduction in the temperature sensitivity of K+ influx and a curtailment of K+ efflux across both the plasma membrane and tonoplast at low temperatures. K+influx, K+ efflux, low temperature, potassium, rye (Secale cereale cv. Rheidol) This content is only available as a PDF. © Oxford University Press

PRITCHARD,, J.;JONES, R. G., WYN;TOMOS, A., D.

doi: 10.1093/jxb/42.8.1043pmid: N/A

Abstract The growth rate of hydroponically grown wheat roots was reduced by mannitol solutions of various osmotic pressures. For example, following 24 h exposure to 0·96 MPa mannitol root elongation was reduced from 1· mm h−1 to 0·1 mm h−1 Mature cell length was reduced from 290 μm in unstressed roots to 100 μm in 0·96 MPa mannitol. This indicates a reduction in cell production rate from about 4 per h in the unstressed roots to 1 per h in the highest stress treatment. The growing zone extended over the apical 4·5 mm in unstressed roots but became shorter as growth ceased in the proximal regions at higher levels of osmotic stress. The turgor pressure along the apical 5·0 mm of unstressed roots was between 0·5 and 0·6 MPa but declined to 0·41 MPa over the next 50 mm. Following 24 h in 0·48 (200 mol m−3) or 0·72 MPa (300 mol m−) mannitol, turgor along the apical 50 mm was indistinguishable from that of unstressed roots but turgor declined more steeply in the region 5·10 mm from the tip. At the highest level of stress (0·96 MPa or 400 mol m−3 mannitol) turgor declined steeply within the apical 20 mm. Growth, turgor pressure, wall rheology, osmotic stress, osmotic adjustment This content is only available as a PDF. © Oxford University Press