Journal of Experimental Botany

Noctor, Graham;Arisi, Ana-Carolina M.;Jouanin, Lise;Kunert, Karl J.;Rennenberg, Heinz;Foyer, Christine H.

doi: 10.1093/jxb/49.321.623pmid: N/A

Abstract Crucial roles in sulphur metabolism and plant defence have been described in recent years for the tripeptide thiol glutathione. In spite of this, the metabolism of glutathione and its response to stress conditions remained only partly understood. In many plants, one of the major difficulties in studying the control of glutathione synthesis is the low extractable activities of the enzymes involved. Consequently, several groups have exploited transformation technology using genes for the enzymes of glutathione synthesis or reduction. This approach has allowed the production of plants with systematically enhanced levels of glutathione (up to 4-fold higher than untransformed controls) and has permitted numerous insights into the control of glutathione synthesis or reduction state and its interaction with other areas of primary or defensive metabolism. Oxidative stress, photorespiration, glutathione, ascorbate, poplar © Oxford University Press 1998

May, Mike J.;Vernoux, Teva;Leaver, Chris;Van Montagu, Marc;Inzé, Dirk

doi: 10.1093/jxb/49.321.649pmid: N/A

Abstract Glutathione (GSH; γ-glutamylcysteinyl glycine) is an abundant and ubiquitous thiol with proposed roles in the storage and transport of reduced sulphur, the synthesis of proteins and nucleic acids and as a modulator of enzyme activity. The level of glutathione has also been shown to correlate with the adaptation of plants to extremes of temperature, in the tolerance of plants to xenobiotics and to biotic and abiotic environmental stresses. In addition, the size of the reduced glutathione pool shows marked alterations in response to a number of environmental conditions. Taken together, these findings have prompted intense efforts to characterize in detail the mechanisms underlying glutathione homeostasis in plants and to elucidate the role of these responses in the strategies plants have evolved to adapt to environmental stresses. The aim of this review is to assess recent biochemical, molecular, genetic, and physiological advances which are increasing our understanding of the mechanisms by which plant glutathione homeostasis is controlled and the role of glutathione in the integration of cellular processes with plant growth and development under stress. Glutathione, cloning, mutant, spatial mapping, plant development, stress © Oxford University Press 1998

Signora, Laurent;Galtier, Nathalie;Skøt, Leif;Lucas, Hélène;Foyer, Christine H.

doi: 10.1093/jxb/49.321.669pmid: N/A

Abstract Arabidopsis thaliana ecotype Columbia was transformed with a maize sucrose phosphate synthase (SPS) cDNA under the control of the promoter for the small subunit of ribulose-1,5-bisphosphate carboxylase from tobacco (rbcS). The effects of SPS over-expression were compared in plants of the T2 and T3 generations grown either in air or with CO2 enrichment (700 μl l−1) for either 4 or 10 weeks. Maximal extractable foliar SPS activities were three times those of the untransformed controls in the highest rbcS-SPS expressing line. In untransformed Arabidopsis leaves SPS activity was not subject to light/dark regulation, but was modified by incubation with either the inhibitor, orthophosphate, or the activator, mannose. Photosynthesis (Amax) values were similar in all lines grown in air. After 10 weeks of CO2 enrichment a decrease in Amax in the untransformed controls, but not in the high SPS expressors, was observed. There was a strong correlation between the sucrose-tostarch ratio of the leaves and their SPS activity in both growth conditions. The total foliar carbohydrate contents of 4-week-old plants was similar in all lines whether plants were grown in air or with CO2 enrichment. After 10 weeks growth the leaves of the high rbcS-SPS expressors accumulated much less total carbohydrate than untransformed control leaves in both growth conditions. It was concluded that SPS overexpression causes increased foliar sucrose/starch ratios in Arabidopsis leaves and favours decreased foliar carbohydrate contents when plants are grown for long periods with CO2 enrichment. Arabidopsis, sucrose, starch, photosynthesis, carbon partitioning, CO2 enrichment © Oxford University Press 1998

Büker, Mareike; Schünemann, Danja; Borchert, Sieglinde

doi: 10.1093/jxb/49.321.681pmid: N/A

Abstract To characterize the developmental stage of tomato fruits, chlorophyll content, photosynthetic O2 evolution and CO2 fixation of pericarp slices were determined. During the first developmental stages a higher expression level of the triose phosphate translocator was detected. Transport measurements revealed that both the hexose phosphate and the triose phosphate translocator are very likely to be active at this time. Plastidic and cytosolic fructose-1,6-bisphosphatase are active in green fruit pericarp, whereas in red pericarp only the cytosolic form is present. Tomato fruit chloroplasts are able to synthesize starch from GIc6P. Starch synthesis is strongly dependent on the addition of 3PGA and ATP and on plastid illumination. Fruit chloroplasts exhibit very low CO2 fixation rates and so the capacities of green pericarp slices were investigated. In relation to chlorophyll content, pericarp slices show the same capacity of starch synthesis as spinach or potato leaves. To investigate the presence of further reactions consuming the products of photosynthetic electron transport, the GOGAT activity was measured. In the light, glutamane/2-oxoglutarate-dependent formation of glutamate occurred with a high activity. In the presence of Glc6P only 18% of the light activity was obtained. Since the Glc6P-dependent activity is rather low, the release of 14CO2 from labelled [1-14C]-Glc6P was also measured. In the dark, the formation of glutamate and oxidation of Glc6P are very tightly coupled to each other in fruit chloroplasts. Tomato fruit, chloroplast, plastid development, starch svnthesis alutamate svnthase This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Lovisolo, Claudio;Schubert, Andrea

doi: 10.1093/jxb/49.321.693pmid: N/A

Abstract Modifications of vessel size and of shoot hydraulic conductivity induced by different water availability levels (ψleaf −0.35 MPa, −0.6 MPa and −0.8 MPa, respectively) were investigated in container-grown grapevine plants. Plant water loss, measured as xylem sap flow and as leaf transpiration, was lower in waterstressed plants. Morphometric measurements on xylem showed that vessels of water-stressed plants had lower transectional areas. Shoot hydraulic conductivity (kh), shoot specific conductivity (ks) and leaf specific conductivity (kl) were lower in water-stressed plants. When conductivities were measured on shoot portions, differences between treatments were particularly high at the basal internodes. At the lower stress level no embolism was detected, and reduced conductivity could be explained by the reduction of vessel diameter, according to the Poiseuille equation. At the higher stress level kh was further reduced by formation of vessel embolisms. The tension gradient along the shoot increased only at the higher stress level. Stomatal conductance was linearly correlated with kl at low stress levels, suggesting a concerted regulation of water flow, while at higher stress levels stomatal conductance decreased with no changes of kl. Reduced development of xylem vessels in grapevines subjected to moderate water stress may contribute to the control of water flow and to a reduction in vulnerability to xylem embolism. Sap flow rate, transpiration, stomatal conductance, xylem vessel anatomy, vessel embolism © Oxford University Press 1998

Cutillas-Iturralde, Antonio;Fulton2, Daniel C.;Fry, Stephen C.;Lorences, Ester P.

doi: 10.1093/jxb/49.321.701pmid: N/A

Abstract In this work the effect of injection of xyloglucanderived oligosaccharides (XGOs) into whole persimmon (Diospyros kaki L.) fruits on ethylene biosynthesis was investigated. Fruits collected during different ripening stages produced low levels of ethylene without a climacteric-like peak. Pretreatment of these fruits with 10 cm3 C2H4 m−3 for 8 h stimulated little or no endogenous ethylene production. However, when persimmon fruits were injected with a mixture of XGOs a burst in ethylene production was observed compared with water-injected control fruits or fruits injected with different monosaccharide solutions. In order to study the influence of oligosaccharide structure and fruit ripening stage on the ability of XGOs to induce ethylene synthesis, fucosylated and non-fucosylated XGOs were injected into persimmon fruits harvested at two different ripening stages. Both oligosaccharide structures were able to induce ethylene production. Induction of ethylene by XGOs was much more evident in fruits harvested later in time, indicating that the process is developmentally regulated. The levels of 1-aminocyclopropane-l-carboxylic acid (ACC) in injected persimmon fruits were also examined. This study showed that the increase in the rate of ethylene biosynthesis induced by XGOs was accompanied by the accumulation of its metabolic precursor ACC. Diospyros kaki, xyloglucan oligosaccharides, ethylene © Oxford University Press 1998

Müller, J.; Dulieu, H.

doi: 10.1093/jxb/49.321.707pmid: N/A

Abstract The symbiosis between higher plants and arbuscular mycorrhizal fungi (AMF) is generally thought to improve the mineral nutrition of many plants. Moreover, AMF seem to play a role in transferring assimilated carbon between plants. To answer the question whether this carbon transfer could be sufficient to enhance the growth of non-assimilating plants, tobacco wild-type plants and non-photosynthesizing mutants were co-cultivated in the presence and absence of a mycorrhizal inoculum. Newly formed leaves were counted and biomass was determined at the final harvest. The mycorrhizal infection was determined in the roots. When the mutants were co-cultivated with a wild-type plant in the presence of a mycorrhizal inoculum, leaf number and the shoot biomass were significantly higher than in etiolated plants co-cultivated with wildtype plants without AMF or with etiolated plants alone. Arbuscular mycorrhiza, carbon transfer, growth enhancement, symbiosis This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Lopez-Delgado, Humberto; Dat, James F.; Foyer, Christine H.; Scott, Ian M.

doi: 10.1093/jxb/49.321.713pmid: N/A

Abstract Potato microplants propagated as nodal explants were subjected to heat treatments in vitro similar to those employed in the thermotherapy step of virus eradication procedures. Low concentrations (10−6–10−5 M) of acetylsalicylic acid (ASA) in the culture medium improved (by 3.7-fold) tolerance of a 5-week hightemperature (35°C) treatment. Furthermore, tissues subcultured on to ASA-free medium following several weeks of growth on ASA were more thermotolerant (by 3.8-fold) of a 7 week 35°C treatment, and (by 38-fold) of a 15h 42°C heat-shock. Stems of microplants grown on ASA contained significantly less catalase activity and higher levels of H2O2 than controls. Explanting and heat treatment, however, reduced catalase activity to similar levels in ASA-treated and control microplant tissues. To investigate whether H2O2 could be involved in signal transduction during the induction of thermotolerance, nodal explants were incubated for 1 h in H2O2 (0.1–50 mM), and then cultured under standard conditions. The microplants that grew from the H2O2-treated explants showed concentrationdependent decreases in stem height, but were significantly more thermotolerant than controls, more than 1 month after the H2O2 treatment. Thus, thermotolerance induced in these conditions was extremely stable. It is concluded that both salicylate and H2O2 treatments can induce thermotolerance in this system. Acetylsalicylic acid, heat-shock, hydrogen peroxide, potato, microplant, thermotolerance This content is only available as a PDF. Author notes 3 Present address: Programa de Papa, Instituto Nacional de Investigaciones Forestales y Agropecuarias (INIFAP), Metepec, Mex. 2142, A.P. 1-2, Mexico. © Oxford University Press 1998 © Oxford University Press 1998

Cárdenas-Navarro, Raúl; Adamowicz, Stéphane; Robin, Paul

doi: 10.1093/jxb/49.321.721pmid: N/A

Abstract A simple model is proposed to describe diurnal net nitrate uptake rate patterns observed experimentally on young plants grown under constant non-limiting nutrition. It rests on two hypotheses: net uptake rate is under negative feedback control by internal plant nitrate content, and nitrogen metabolism occurs only during the light period. The model parameters were determined from the results of three independent experiments performed under non-disturbing conditions in a growth room at constant air and solution temperatures. Net hourly nitrate uptake rate was measured through a diurnal cycle and after an extended 28 h period of darkness. It increased continuously during the light period and decreased during the dark period. Under prolonged darkness, net uptake declined to an asymptotic positive uptake rate of about 10−5 mol h−1 g−1 total plant dry weight. The measured hourly nitrate uptake rate values were consistent with independent determinations of long-term nitrate and total N accumulations in the plant. Realistic simulations of experimental data are achieved with the proposed model. Furthermore, the maintenance of a positive net uptake rate, measured in non-growing plants subjected to prolonged darkness, is explained in the model by the continuous increase of plant water content. The importance of the diurnal variations of plant water content for nitrate uptake rate is emphasized and gives consistency to the homeostasis hypothesis of the model. The diurnal changes in nitrate uptake predicted by the model are strongly dependent on the assumption made for diurnal changes in nitrate assimilation. While the purely photosynthetic assumption is convenient, a more realistic metabolism submodel is needed. Light/dark cycles, day, night, water content, nitrogen, hydroponic This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998

Cecchini, Edi; Al-Kaff, Nadia S.; Bannister, Andrew; Giannakou, Maria E.; McCallum, Don G.; Maule, Andrew J.; Milner, Joel J.; Covey, Simon N.

doi: 10.1093/jxb/49.321.731pmid: N/A

Abstract Pathogenic interactions between genetic variants of cauliflower mosaic virus (CaMV) and Arabidopsis thaliana were characterized to identify combinations potentially useful in molecular genetic analysis. Infections of a glabrous mutant (gl1) of Arabidopsis ecotype Columbia (Col-O gl1) by 30 CaMV isolates were assessed by recording symptom character. Thirteen isolates failed to cause symptoms; the remainder induced symptoms that varied between mild and very severe. Some CaMV isolates produced symptoms in Arabidopsis that differed significantly in severity or character from those produced in a standard host Brassica rapa (turnip). A greater variety of symptom types was observed in a single Arabidopsis ecotype infected with a range of CaMV isolates than was found in a range of Arabidopsis ecotypes infected with a single, typical CaMV isolate (Cabb B-JI). One isolate, Bari-1, that was asymptomatic but accumulated virus in Arabidopsis ecotype Col-O gl1, caused mild symptoms in ecotype Ler gl1. A hybrid virus constructed from CaMV isolates Cabb B-JI and Bari-1 produced symptoms in Arabidopsis variants that were more severe than in either parental isolate. From a screen of EMS-mutagenized Arabidopsis, one mutant (Col-O dv1) with a pale-green, dark-vein phenotype which had an altered symptom response to CaMV, was isolated. From this, a phenotypically near-normal revertant (Col-O dv1R) spontaneously arose, but which showed altered responses to CaMV. Infection of Col-O dv1R by CaMV isolate Bari-1 elicited symptoms unlike the parent Arabidopsis ecotype (Col-O gl1). Also, Col-O dv1 and Col-O dv1R expressed an uncharacteristic necrotic reaction to CaMV. Caulimovirus, Cruciferae, plant mutants, symptom expression This content is only available as a PDF. © Oxford University Press 1998 © Oxford University Press 1998