Journal of Experimental Botany

LEE, R., B.;PURVES, J., V.;RATCLIFFE, R., G.;SAKER, L., R.

doi: 10.1093/jxb/43.11.1385pmid: N/A

Abstract Experimental treatments designed to affect the pathway of nitrogen assimilation were applied to the roots of intact maize plants growing with ammonium or nitrate as N-sources. The treatments comprised: external amino acid feeding; specific inhibitors of GS, GOGAT, and aminotransferases; and N-starvation. Their actions in vivo were confirmed by 14N- or 15N-NMR spectroscopy, or by HPLC analysis of tissue extracts. A strong correlation was noted between the levels of glutamine and asparagine in the roots. Rates of ammonium and nitrate absorption by the plants were then measured, over both short (5 min) and longer (1.5 h) periods. The results fell into two classes. After treatments which raised the intracellular concentrations of glutamine and/or asparagine, net uptake of N was suppressed, while conditions which decreased root glutamine and/or asparagine, stimulated net uptake of N. These findings are discussed in relation to the control of N-absorption during growth with differing levels of nitrogen supply. N-nutrition, 13N, 14N-NMR, 15N-NMR, barley, maize This content is only available as a PDF. Author notes 3On secondment to the Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK. © Oxford University Press

HASER,, ANNETTE;ROBINSON, DAVID, L.;DUC,, GERARD;VANCE, CARROLI, P.

doi: 10.1093/jxb/43.11.1397pmid: N/A

Abstract Although numerous reports have documented the effect of bacterially-induced ineffectiveness on root nodule structure, function, and plant gene expression, few studies have detailed the effect of the plant genome on similar parameters. In this report effective (N2-fixing) broadbean {Vicia faba L.) and plant-controlled ineffective (non-N2-fixing) broadbean recessive for the sym-1 gene were compared for nodule structure, developmental expression of nodule enzyme activities, enzyme proteins, and mRNAs involved in N assimilation, leghemoglobin (Lb) synthesis, and acetylene reduction activity (ARA). During development of effective wild-type nodules, glutamine synthetase (GS), aspartate aminotransferase (AAT), phosphoenolpyruvate carboxylase (PEPC) and NADH-glutamate synthase (GOGAT) activities and enzyme proteins increased coincident with nodule ARA. The increases in GS, AAT, and PEPC were associated with increased synthesis of mRNAs for these proteins. Synthesis of Lb polypeptides and mRNAs during development of effective nodules was similar to that of GS, AAT, and PEPC. By contrast, ineffective sym-1 nodules displayed little or no ARA and had neither the increases in enzyme activities nor enzyme proteins and mRNAs as seen for effective nodules. The effect of the sym-1 gene appeared to occur late in nodule development at either the stage of bacterial release from infection threads or differentiation of bacteria into bacteroids. High in vitro enzyme activities, enzyme polypeptides, and mRNA levels in parental effective nodules were dependent upon a signal associated with effective bacteroids that was lacking in sym-1 nodules. Nodule organogenesis did not appear to be a signal for the induction of GS, PEPC, AAT, and Lb expression in sym-1 nodules. Vicia faba, mutation, sym-1 gene, nodules This content is only available as a PDF. © Oxford University Press

TÉCSI, L., I.;WANG,, D;SMITH, A., M.;LEEGOOD, R, C.;MAULE, A., J.

doi: 10.1093/jxb/43.11.1409pmid: N/A

Abstract It has frequently been observed that starch accumulates in plant tissues after virus infection. In pea plants infected with red clover mottle comovirus, strain ‘O’, virus replicates in the inoculated leaves and at the shoot apex where it induces lethal top necrosis. Concomitant with the onset of top necrosis, starch accumulates in the intervening leaves which remain substantially virus-free. This pattern of starch accumulation can be mimicked by removal of the apex in uninfected plants. We conclude that in this plant-virus interaction starch accumulation is an indirect consequence of virus infection associated with the removal of the physiological sink for photosynthate. Pea, red clover mottle comovirus, starch accumulation, sink-source relationships This content is only available as a PDF. © Oxford University Press

KHEHRA, G., S.;MATHIAS, R., J.

doi: 10.1093/jxb/43.11.1413pmid: N/A

Abstract The relative importance of explant type, genotype and growth regulator regime in the determination of shoot regeneration frequencies from complex explants of Brassica napus L. has been evaluated. Cotyledon, hypocotyl and stem sections taken from one spring (Westar) and three winter (Ariana, Cobra, Libravo) varieties of B. napus were cultured on three different growth regulator regimes, 0.5 mg dm−3 NAA + 2.0mg dm−3 BAP, 0.5 mg dm−3 NAA + 4.0mg dm−3 BAP and 1.0mg dm−3 NAA + 4.0mg dm−3 BAP. The most significant effects on shoot regeneration were due to explant type and variety. The regeneration from stem segments was not only two to three times higher than from hypocotyls or cotyledons, in all varieties, but the response was also more uniform across the varieties. The explant effect accounted for 44–95% of the regeneration response. In contrast, the contribution of growth regulator regime was negligible. Although the growth regulator regime as an independent effect was unimportant, regeneration from both Ariana and Libravo was significantly affected by the interaction of genotype with growth regulator regime. The importance of both the high shoot regeneration frequency from stem segments and the relative uniformity of response across the four tested genotypes is discussed with respect to the potential benefits of using this explant source in Agrobacterium-based transformation experiments. Brassica napus, regeneration, genotype, tissue culture, complex explant This content is only available as a PDF. Author notes 1Present address: Department of Life Science, University of Nottingham, University Park, Nottingham NG7 2RD, UK. © Oxford University Press

MIEDZYBRODZKA, MARYSIA B, W.;YEOMAN, MICHAEL, M

doi: 10.1093/jxb/43.11.1419pmid: N/A

Abstract A comparison of morphology, trichome type and duvane accumulation of tobacco shoot cultures originating from seedlings, callus and cell suspension cultures incubated on a range of cytokinin concentrations is presented. A method for the extraction and HPLC analysis of duvatrienediols from cultures is described. Duvatrienediols (DVTs) were not detected in callus or cell suspension cultures and were only detected in seedling-denved shoot cultures. Shoot development was dependent on explant type probably as a result of pre-exposure of callus and suspension cells to high auxin concentrations. Low cytokinin levels promoted shoot development whilst high cytokinin levels increased the number of shoots regenerated but retarded their development. DVT accumulation occurred only in ‘normally’ developed shoots with trichomes. Growth of shoot cultures in liquid medium was inhibitory to the accumulation of DVTs. Optimum conditions for the accumulation of DVTs were shown to be incubation of seedling-derived shoot cultures on media containing 10−6 M BAP solidified with agar. The yield was 120 μg g−1 fr. wt. which is comparable to greenhouse-grown material. Both α and β-DVT were detected in a ratio of 5: 1. The relationship between tnchomes and DVT accumulation is discussed with reference to the roles of culture origin, cytokinin, trichome type and environmental effects. Tobacco, duvatrienediol, trichome, shoot culture This content is only available as a PDF. © Oxford University Press

MAUK, CRAIGHTON, S.;NOODÉN, LARRY, D.

doi: 10.1093/jxb/43.11.1429pmid: N/A

Abstract On the way from the roots to the seeds during reproductive development in soybean (Glycine max), a large proportion of the minerals pass through the leaves rather than travelling directly via the xylem. This direct and indirect movement of mineral nutrients has important implications for mineral redistribution, seed development and leaf senescence. Therefore, we have studied the role of cytokinin and mineral flux from the roots in regulating mineral redistribution from the leaves to the seeds using explants, i.e. a leaf, a pod and a subtending stem segment, with their bases immersed in treatment solutions. Thus, defined solutions containing cytokinin and/or minerals can be substituted for the roots. When explants (excised at early-mid podfill) are supplied H2O only, leaf N, P, K, Mo, Mg, Zn, Fe, B, Cu, Ca, and Mn decline, ranging from 93% for Mo to 38% for Fe. In explants on H2O, N, P, K, Mo, Mg, Zn, and Fe appear to be redistributed from the leaves to the seeds, while the B, Cu, Ca, and Mn lost from the leaves do not seem to move to the seeds. Although a mixture of minerals resembling xylem sap can delay net loss of these elements from the leaves, it does not prevent the decreases. The cytokinin zeatin (4.6 μM) inhibits the loss of N, IC, Mo, Mg, Zn, Fe, B, Cu, Ca, and Mn from the leaves, but not that of P. When combined with minerals, zeatin not only prevents the loss of the minerals from the leaves but may even greatly increase them with the possible exception of Zn, Fe, and Cu. Supplying the mineral nutrient mixture increases the quantities of N, P, K, Mg, Cu, and B in the seeds but not Zn, Fe, Mn, Ca, and Mo. For those minerals, especially N, where zeatin inhibits efflux from the leaves, it may reduce the amounts in the seeds, but it does not change P, K, Mg, and Ca. The accumulation and redistribution patterns of the different mineral nutrients show many dissimilarities thereby suggesting differences in the control of their distribution. Cytokinin, mineral transport, seed development, senescence This content is only available as a PDF. © Oxford University Press

HUANG,, BINGRU;NOBEL, PARK, S.

doi: 10.1093/jxb/43.11.1441pmid: N/A

Abstract Hydraulic conductivity (Lp), radial conductivity (LR), axial conductance (Kh), and related anatomical characteristics for lateral roots of Agave deserti were investigated during root growth and drought-induced abscission. The elongation rate of lateral roots averaged 5 mm d−1 under wet conditions and was reduced 95% by 17 d of drought (ψsoil−0.5 MPa); 46% of such roots abscised at 21 d of drought. Under wet conditions, Lp decreased with age up to 30 d, mainly reflecting suberization of endodermal cells. Lp and LR decreased basipetally along the roots under wet conditions and after 18 d of drought and were lower in the case of drought, both responses reflecting increases in the number of suberized endodermal cells. In contrast, Lp and LR increased basipetally along abscised roots at 35 d of drought, presumably due to the collapse of cortical cells. Kh increased with distance from the root tip; the greatest increase, which coincided with the loss of cross walls in late metaxylem vessels, occurred closer to the tip for roots from droughted plants compared with well-watered plants. Kh was reduced during drought by embolism of the xylem vessels, similar to the results for other studies. Drought, root age, water flow, xylem vessels This content is only available as a PDF. © Oxford University Press

PREMACHANDRA, GNANASIRI, S.;SANEOKA,, HIROHUMI;FUJITA,, KOUNOSUKE;OGATA,, SHOITSU

doi: 10.1093/jxb/43.11.1451pmid: N/A

Abstract A pot experiment was carried out using five maize {Zea mays L.) cultivars under three soil moisture levels (MPa 0 to −0.05, −0.3 to −0.9 and −1.2 to −1.5) to investigate the effects of water deficits on osmotic adjustment and stomatal conductance. The degree of leaf rolling and the sugar and nutrient concentrations in leaf cell sap were measured. Leaf water potential and osmotic potential decreased and stomatal conductance decreased with increasing water deficits. Stomatal conductance correlated positively with leaf water potential and osmotic potential. Degree of leaf rolling was lower in cultivars which maintained higher turgor. Osmotic adjustment of 0.08 to 0.43 MPa was found under the lowest soil moisture level in five cultivars used. Sugar and K were the major osmotic substances in the maize plant. Sugar, K and Mg concentrations increased under water deficit, and correlated negatively with a decrease in osmotic potential. Zea mays L., leaf water relations, leaf rolling, osmotic adjustment, stomatal conductance, water deficit This content is only available as a PDF. © Oxford University Press

TERRY, B., R.;FINDLAY, G., P.;TYERMAN, S, D.

doi: 10.1093/jxb/43.11.1457pmid: N/A

Abstract Ca2+-channel blockers at concentrations greater than 1 mmol m−3, directly affect the activity of K +selective channels in the plasma membrane of Amaranthus tricolor protoplasts. These effects are not mediated by the blockade of Ca2+ channels. Blockers tested included 1, 4-dihydropyridines (nifedipine, nicardipine), verapamil, bepridil, Gd3+ and La3+, applied to whole-cell and detached outside-out patches of plasma membrane at concentrations from 50μmol m−3 to 100 mmol m−3. For certain experiments the concentration of Ca2+ on the cytoplasmic side of the plasma membrane ([Ca2+]cyt) was buffered at either 50ftmol m−3 or 500 μmol m−3. The principal currents observed in whole-cells flowed through cation outward rectifier (OR) channels. Each blocker caused an immediate reduction of time-dependent outward currents at doses down to 1 mmol m−3 and produced a different, reversible, kinetic block of the outward current, independent of the level of [Ca2+]cyt. Verapamil also activated a sustained inward cation current at negative p.d. The same effects were found with individual channels in detached outside-out patches. Conductance and selectivity of the cation OR channels were unchanged by the drugs. [Ca2+]ex, was varied over a range from 0 to 10 mol m−3. Progressively lower [Ca2+]eI, increasingly enhanced the maximum amplitude of the time-dependent currents. Time-constants for decay of inward tail currents were increased at low [Ca2+]eit. These effects were rapidly reversible. Although there was no evidence that the cation ORs in plasma membrane of Amaranthus tricolor were dependent on [Ca2+]cyl for their activation, they were sensitive to the concentration of free Ca2+ in the extracellular medium. Verapamil, blocker, cation channels, Amaranthus, protoplasts This content is only available as a PDF. Author notes 1Present address. Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QJ, UK. © Oxford University Press

ROS,, ROC;COOK, DAVID, T.;MARTINEZ-CORTINA,, CARMEN;PICAZO,, ISABEL

doi: 10.1093/jxb/43.11.1475pmid: N/A

Abstract Six-day-old rice plants (Oryza sativa L. cv. Bahia) were grown in the presence of 0.5 mol m−3 Ni or Cd for 5 or 10 d. Five days after treatment, some plants were transferred to a medium containing no heavy metal for 5 or 10 d. Plasmalemma vesicles from shoots of treated, transferred (recovery experiments) and control plants were isolated, ATPase activity and proton-pumping were assessed, and free sterols and phospholipids determined. The ATPase hydrolytic activity was increased by 37% and 34% in 5 and 10 d Cd-treated plants, respectively; and by 66% in 5 and 10 d Ni-treated plants. However, neither the initial rate of H+ transport nor the proton-pumping rate at steady-state were significantly affected by the treatments. The relative proportion (%) of the plasmalemma sterols campesterol and Δ 5-avenasterol decreased while sitosterol increased during heavy metal treatment. The overall plasmalemma phospholipid fatty acyl chain length and degree of unsaturation were also reduced. In experiments where plants recovered from Cd and Ni treatment, differences between treated and control plants were reverted, particularly in 10 d Ni-recovered plants. The possible involvement of lipids in the regulation of the plasmalemma ATPase as well as the relationship between growth, ATPase and adaptations to stress conditions are discussed. Cadmium, nickel, sterols, phospholipids, ATPase This content is only available as a PDF. © Oxford University Press