Journal of Experimental Botany

Schönknecht, G.;Bauer, C.S.;Simonis, W.

doi: 10.1093/jxb/49.318.1pmid: N/A

Abstract The physiological function and the molecular mechanisms of Ca2+-mediated signal transduction processes were studied in the unicellular green alga Eremosphaera viridis by different electrophysiological and microfluorimetric techniques. A sudden blockage of photosynthetic electron transport by darkening or inhibitors causes a transient hyperpolarization of the plasma membrane. For the alga this transient hyperpolarization seems to be an important mechanism to release monovalent ions and to drive the uptake of divalent cations. The transient hyperpolarization is due to the opening of K+ channels and is caused by a rapid transient elevation of the cytosolic free Ca2+ concentration ([Ca2+]cy spike). Different agonists like caffeine or InsP3 which are known to release Ca2+ from internal stores in animal cells, also cause a transient hyperpolarization and a [Ca2+]cy spike, similar to darkening. In Eremosphaera the transient hyperpolarization can be used as an indicator for [Ca2+]cy spikes. The InsP3 gated and the ryanodine/cADPR gated Ca2+ channels which obviously both mediate Ca2+ release from internal stores in Eremosphaera do not seem to be involved in the dark-induced [Ca2+]cy spikes. Besides single [Ca2+]cy spikes, the addition of Sr2+ (or caffeine in the absence of divalent cations) causes repetitive [Ca2+]cy spikes which may last hours and resemble [Ca2+]cy oscillations observed in excitable animal cells. These observations suggest that some principal molecular mechanisms causing single or repetitive [Ca2+]cy spikes are conserved from animal to plant cells. Signal transduction, calcium, Eremosphaera viridis, calcium spikes, membrane potential © Oxford University Press 1998

Mimura, Tetsuro; Reid, Robert J.; Smith, F. Andrew

doi: 10.1093/jxb/49.318.13pmid: N/A

Abstract This paper examines the control of phosphate uptake into Chara corallina. Influxes of inorganic phosphate (Pi) into isolated single internodal cells were measured with 32Pi. Pretreatment of cells without Pi for up to 10 d increased Pi influx. However, during this starvation the concentrations of Pi in both the cytoplasm and the vacuole remained quite constant. When cells were pre-treated with 0.1 mM Pi, the subsequent influx of Pi was low. Under these conditions the Pi concentration in the cytoplasm was almost the same as that of Pi-starved cells, but vacuolar Pi increased with time. Transfer of cells from medium containing 0.1 mM Pi to Pi-free medium induced an increase of Pi influx within 3 d irrespective of the concentration of Pi in the vacuole.p ]During Pi starvation, neither the membrane potential nor the cytoplasmic pH changed. Manipulation of the cytoplasmic pH by weak acids or ammonium decreased the Pi influx slightly.p ]Pi efflux was also measured, using cells loaded with 32Pi. Addition of a low concentration of Pi in the rinsing medium rapidly and temporarily induced an increase in the efflux.p ]The results show that Pi influx is controlled by factors other than simple feedback from cytoplasmic or vacuolar Pi concentrations or thermodynamic driving forces for H+-coupled Pi uptake. It is suggested that uptake of Pi is controlled via the concentration of Pi in the external medium, through induction or repression of two types of plasma membrane Pi transporters. Chara corallina, membrane transport, phosphate influx, phosphate starvation This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Tourmente, S.; Lazreg, A.; Lafleuriel, J.; Tutois, S.; Cuvillier, C.; Espagnol, M.C.; Picard, G.

doi: 10.1093/jxb/49.318.21pmid: N/A

Abstract In order to characterize new GC-rich minisatellites present in the Arabidopsis thaliana genome, a genomic library was screened at low stringency with a probe containing nine repeated-units of a minisatellite (CMs1) previously identified. Both minisatellites and minisatellite-like elements were identified. The minisatellites, with a tandemly-repeated structure, all contain the Arabidopsis thaliana-core sequence previously defined (Tourmente et al., 1994). Both minisatellite and minisatellite-like sequences occur in the Arabidopsis genome in low copy and are weakly polymorphic between ecotypes. The genetic mapping of these markers has shown that they are dispersed on the genome. YACs clones of the CIC library carrying these minisatellites and minisatellite-like sequences were identified. Arabidopsis thaliana, minisatellites, polymorphism 1 EMBL accession nos. U 52954-52956; AF016274-77. This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Metodiev, M.V.

doi: 10.1093/jxb/49.318.27pmid: N/A

Abstract Venom of Vespa crabro induced in barley an abundant expression of at least five polypeptides, having the same apparent molecular masses as the jasmonate induced polypeptides. Treatment of venom by trypsin, as well as addition of indomethacin prevented the appearance of the polypeptides. Separation of the venom by gel-filtration chromatography showed that the fraction containing phospholipase activity was able to induce expression of the 23 kDa polypeptide as revealed by 2-D electrophoresis, but the induction was much stronger when this fraction was applied together with the fraction of the low molecular weight peptides. The treatment by venom did not promote senescence of the detached leaves as the jasmonate did and kept the photosynthesis, transpiration, protein content, and the intensity of labelled amino acid incorporation into proteins near the control values. Jasmonate-induced proteins, hornet venom, phospholipase, barley © Oxford University Press 1998

Weselake, Randall J.; Byers, Susan D.; Davoren, Jon M.; Laroche, André; Hodges, D. Mark; Pomeroy, M. Keith; Furukawa-Stoffer, Tara L.

doi: 10.1093/jxb/49.318.33pmid: N/A

Abstract The effect of sucrose concentration on triacylglycerol biosynthesis and associated gene expression was examined in a microspore-derived cell suspension culture of oilseed rape (Brassica napus L. cv. Jet Neuf). The triacylglycerol content of the cells increased about 5-fold on a fresh weight basis when the sucrose concentration in the growth medium was raised from 2% to 22% (w/v). The specific activity of microsomal diacylglycerol acyltransferase (EC 2.3.1.20) and its activity per unit fresh weight increased about 2.5-fold and 6-fold, respectively, when sucrose concentration was increased from 2% to 14%. mRNA encoding the major oleosin also appeared to increase in abundance over the 2–14% sucrose concentration range when RNA fractions were analysed by the reverse transcription-polymerase chain reaction. The sucrose-mediated increases in diacylglycerol acyltransferase activity and oleosin mRNA indicated that the cell suspension could be a useful research tool for the identification of cDNAs encoding triacylglycerol biosynthetic enzymes and associated proteins. Triacylglycerol, Brassica, sucrose, acyltransferase, differential display This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Arrese-Igor{, Cesar;Gordon{, Anthony J.;Minchin{, Frank R.;Denison, R. Ford

doi: 10.1093/jxb/49.318.41pmid: N/A

Abstract The entry of nitrate into the infected region of soybean nodules and the possibility of a subsequent nitrite accumulation was studied. Nitrate was observed to gain access to the infected region in the short-term and significant amounts could be measured within 2 d of nitrate supply. The availability of nitrate in the bacteroid-containing region did not cause free-nitrite accumulation for at least 8 d. However, to avoid the artefactual production of nitrite during extraction it was necessary to disrupt nodules in the presence of zinc acetate and ethanol, to prevent bacteroid nitrate reductase activity. Nitrite rapidly accumulated if nodules were extracted without prior enzyme-inactivation, or if bacteroids were allowed access to nitrate, or, more significantly, if nodules were not extracted immediately following detachment. Nitrate accumulation in detached nodules was mediated by oxygen concentration within the nodule; in the presence of pure N2 gas, nitrite accumulation was three times greater than in air and, conversely, it was prevented by exposure to pure O2. Furthermore, nitrite produced in detached nodules under atmospheric conditions was scavenged by transfering these nodules into 100% oxygen. However, measurements of apparent functional leghaemoglobin, using a nodule oximeter, suggested that after 8 d nitrate exposure up to 83% of Lb activity was lost, possibly due to interactions with nitrite produced in the nodule interior leading to the formation of nitrosylleghaemoglobin. Glycine max, cortex, infected region, leghaemoglobin, nitrate, nitrite, nodules, soybean © Oxford University Press 1998

Gary, Christian; Bertin, Nadia; Frossard, Jean-Sylvain; Le Bot, Jacques

doi: 10.1093/jxb/49.318.49pmid: N/A

Abstract The construction cost of plant tissues is used in crop models to convert the products of photosynthesis intobiomass. As for other greenhouse crops, tomato tissues are specific in that they have a high mineral content. The consequences of this accumulation of minerals on the construction cost of the tissues and the possible interactions with the physiological age of the organs and with the CO2 concentration in the atmosphere was examined. For that purpose, threemethods of estimating the construction cost were used and compared. Large quantities of minerals accumulated in the tissues of tomato plants (ranging from 0.05 in fruits to 0.26 g g-1 DM in leaves). The subsequent dilution of the organic matter explained why the estimated construction cost of the dry matter (organic matter+minerals) was fairly low in comparison to that of other crop species. The construction cost was higher in fruits than in vegetative organs, partly because of a lower mineral content. It decreased by 7–12% from top to bottom of the canopy, following the increase in the physiological age of the tissues. This ontogenic drift was partly explained by the accumulation of minerals in the older organs. In the conditions of CO2 enrichment of a commercial greenhouse, no effect of CO2 concentration on the mineral content and on the construction cost of tissues was observed. Such a variability of the construction cost of tomato plant tissues due to the accumulation of minerals or to the ontogeny questions the use of standard values in crop models. Lycopersicon esculentum Mill., construction cost, heat of combustion, elemental composition, mineral content This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Gary, Christian;Bot, Jacques Le;Frossard, Jean-Sylvain;Andriolo, Jerônimo Luiz

doi: 10.1093/jxb/49.318.59pmid: N/A

Abstract The construction cost of a plant tissue, i.e. the amount of photoassimilates used in the synthesis of a unit weight, varies with its biochemical composition. Crop modellers use standard values published for a few groups of cultivated species. Yet, there are also intraspecific variations in the construction cost in relation with the development of the plant or organ. This research aimed at analysing the ontogenic changes in the construction cost of leaves, stems, roots, and fruits of tomato plants and the specific contribution of the mineral content to these changes. For that purpose, samples were harvested from the vegetative phase to the beginning of fruit production. The estimation of the construction cost was based on the contents of carbon, nitrogen and ash. In leaves, the construction cost decreased with the physiological age whereas, in stem internodes, it varied with the sympod number. These ontogenic changes could partly be explained by different accumulations of minerals. In contrast, the construction cost and the mineral content of fruits and roots remained fairly stable. On a whole plant basis, the construction cost of the bulk of each category of organs varied much less. Most of the increase in the mean construction cost of the whole plant during the experiment was due to changes in the allocation ratio between the vegetative parts and the fruits. Attention of crop modellers is drawn to the importance of a precise estimation of the construction cost and to the existence of ontogenic changes at the whole plant and organ levels. Lycopersicon esculentum Mill., construction cost, mineral content, ontogeny, carbon content © Oxford University Press 1998

Meuser, Julia; Frensch, Jürgen

doi: 10.1093/jxb/49.318.69pmid: N/A

Abstract A new approach to study dynamic interactions between transpiration and xylem pressure in intact plants is presented. Pressure probe measurements were performed in living (immature) late metaxylem of maize roots rather than in adjacent mature xylem. This eliminated technical limitations related to the measurement of negative pressures. Water relations of single cells showed that turgor and volumetric elastic modulus were significantly larger in living metaxylem than in cortical cells; hydraulic conductivity was similar in both types of root cells. Increasing transpiration induced an immediate decrease of xylem pressure, and vice versa. Turgor in the living metaxylem could be continuously recorded for more than 1 h. The relationship between xylem pressure and transpiration yielded a root hydraulic resistance of 1.3×109 MPa s m−3. Control experiments indicated that the response of living xylem in the positive pressure range essentially paralleled that of mature root xylem in the negative range. In mature xylem, pressures as low as −0.55 MPa were recorded for short periods (several minutes). Several tests verified that the pressure probe was in contact with mature xylem during the measurements of tensions. The results demonstrate convincingly that transpiration generates an effective driving force for water uptake in roots, a central feature of the cohesion theory. Hydraulic conductivity, negative pressure, root development, turgor, water transport, Zea mays This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Woodall, G.S.;Dodd, I.C.;Stewart, G.R.

doi: 10.1093/jxb/49.318.79pmid: N/A

Abstract Leaf developmental patterns were characterized in four rainforest tree species of Syzygium. Leaf optical properties, pigment changes, expansion characteristics, stomatal development, and photosynthetic rates were studied. In both S. luehmannii and S. wilsonii photosynthetic development was delayed until after full leaf expansion. Rates of O2 evolution were negative during expansion of S. luehmannii and S. wilsonii leaves and stomatal conductance was 10–20 mmol m-2 s-1 lower than for corresponding leaves of S. moorei. Stomatal conductance data and scanning electron microscopy showed that the development of functional stomata was delayed until after full leaf expansion in S. luehmannii and S. wilsonii, however, low stomatal conductance was not responsible for the lack of photosynthetic potential during leaf expansion in these species. Leaves of S. luehmannii and S. wilsonii required less than 10 d for full leaf expansion and contained anthocyanin during expansion. In contrast, leaves of S. moorei and S. corynanthum expanded slowly (20–40 d required for full leaf expansion), exhibited positive rates of O2 evolution and did not accumulate anthocyanin. In S. luehmannii and S. wilsonii anthocyanin was located in the vacuole of distinct cell layers just below the upper epidermis and the possible functions of anthocyanin accumulation are discussed. This is the first report where such variation in leaf development has been characterized in the one genus. Anthocyanin, leaf expansion, photosynthetic development, delayed leaf greening, stomatal development © Oxford University Press 1998