摘要:

ABSTRACTThese experiments investigate events involved in triggering sugar accumulation in the cold in tubers ofSolanum tuberosumL. cv. Desirée. Sugar content,14C‐glucose metabolism, metabolite levels and activities of sucrose phosphate synthase (SPS) and starch‐degrading enzymes were followed after transfer to 4°C. (i)Netsucrose accumulation began between 2 and 4 d. By 10 d, reducing sugars were also increasing. From 20 d onwards, sugar accumulation slowed. Sucrose fell, but reducing sugars continued to increase. (ii) To measureunidirectionalsucrose synthesis, U‐[14C]glucose was injected into tubers after various times at 4°C. The tubers were then incubated for 6 h. After 1 d at 4°C, both the absolute and the relative (expressed as a percentage of the metabolized label) rates of sucrose synthesis decreased compared to those at 20°C. Between 2 and 4 d at 4°C, labelling of sucrose increased 3‐fold, to over 60% of the metabolized label. This high rate was maintained for up to 50 d in cold storage. When tissue slices were incubated with 2.5 mol m−3U‐[14C]glucose, the rate of labelling of sucrose in slices from 6 d cold‐stored material was higher than in slices from warm‐stored material, irrespective of whether the incubation occurred at 4°C or at 20°C. (iii) Hexose‐phosphates increased during the first day after transfer to 4°C. Their levels fell during the next 3 d, as sucrose synthesis increased. They then rose (until 20 d) and fell, in parallel with the rise and decline of sucrose levels. UDPglucose remained unaltered during the first 4 d, and then increased and decreased in parallel with sucrose. (iv) SPS activity assayed in optimal conditions and the total amount of SPS protein did not change. However, when assayed in the presence of phosphate and limiting substrate concentrations, activity rose 3–5‐fold between 2 and 4 d. (v) Amylases and phosphorylases were investigated using zymograms to separate isoforms. Phosphorylases did not change. Between 2 and 4 d at 4°C, a new amylolytic activity appeared. (vi) Estimates of the specific activity of the phosphorylated intermediates and the absolute rate of sucrose synthesis (calculated from the14C‐labelling data and metabolite analysis) showed that changed kinetic properties of SPS and decreased levels of hexose‐phosphate are accompanied by a 6–8‐fold stimulation of sucrose synthesis. They also show that the final level of sugar is partly determined by a cycle of sugar synthesis and degradation. (vii) It is concluded that the onset of sugar accumulation in cold‐stored tubers is initiated by a change in the kinetic properties of SPS and the appearance of a new amylolytic activity. It is discussed how other factors, including hexose‐phosphate levels and subcellular compartmentalization, could also influence the final levels of sugars by altering the ba

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00001.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe influence of irradiance on photosynthesis under natural conditions was studied in aseasonal Singapore using threeHeliconiataxa:H. rostrata, H. psittacorum × H. spathocircinatacv. Golden Torch andH. psittacorumcv. Tay. When grown under full sunlight, all three heliconias exhibited reduced phatosynthetic capacities and lowered chlorophyll content per leaf area as compared with those grown under intermediate and deep shade. A marked decrease in the chlorophyll fluorescenceFv/Fmratio and an increase in photochemical quenching (1‐qp) and non‐photochemical quenching (qN) were observed in upper leaves of plants grown under full sunlight. Increases inqNsuggest that ‘photoinhibition’ (decreases inFv/Fm) inHeliconiagrown under natural tropical conditions are probably due to photoprotective energy dissipation processes. The quantum yield, the maximum photosynthetic rate,Fv/Fmand the chlorophyll content of upper leaves were lower than those of lower leaves on the same plants grown under full sunlight. Similarly, lower values were obtained for the tip (sun) portion than for the base (shaded) portion of the leaves. The changes inFv/Fmand in the levels of (1 –qp) in leaves grown under intermediate and deep shade were negligible in plants during the course of day. However, there was a steep decrease inFv/Fmand an increase in the levels of (1 –qp), along with an increase in incident light in the sun leaves. The lowestFv/Fmand the highest level of (1 –qp) indicated minimum PSII efficiency at midday in full sun. These results indicate that, inHeliconia, the top leaves (particularly leaf tips) experienced sustained decreases in PSII efficiency upon exposure to full sunlight. Although all three taxa exhibited sustained decreases in photosynthetic capacity in full sunlight, the sun leaves of ‘Tay’ showed higher photosynthetic capacity than those of the other two taxa. This could be due, at least in part, to the vertical leaf angle and smaller lamina area. When the upright leaves of ‘Tay’ were constrained to a horizontal angle, they exhibited lower PSII efficiency (FvIFmratio), while horizontal leaves of ‘Rostrata’ and ‘Golden Torch’ inclined lo near‐vertical angles showed increased efficiency. Thus, an increase in leaf angle helps to achieve a reduction in the sustained decrease in PSII efficiency by decreasing the levels of incident sunlight and s

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00002.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWe investigated the synthesis and translocation of amino compounds inParasponia, a genus of the Ulmaceae that represents the only non‐legumes known to form a root nodule symbiosis with rhizohia. In the xylem sap ofP.andersoniiwe identified asparagine. aspartate. glutamine, glutamated significant quantities of a non‐protein amino acid. 4‐methylglutamte(2‐amino‐4‐methylpentanedioic acid). This identification was confirmed by two methods, capillary gas chromatography (GC) electron ionization (El) mass spectrometry (MS) and reverse phase high pressure liquid chromatography (HPLC) analysis of derivatized compounds. In leaf, root and nodule samples fromP. andersoniiandP. parviflorawe also identified the related compounds 4‐methyleneglutamate and 4‐methyleneglulamine. Using15N2labelling and GC‐Ms analysis of root nodule extracts we followed N2fixation and ammonia assimilation inP.andersonii root nodules and observed Label initially in glutamine and subsequently in glutamate, suggesting operation of the glutamine synthetase/glutamine:2‐oxoglutarate aminotransferase (GS/GOGAT) pathway. Importantly, we observed the incorporation of significant quantities of15N into 4‐methylglutamate in nodules, demonstrating thede novasynthesis of this non protein amino acid and suggesting a role in the translation of N i

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00003.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTChlorophyll fluorescence and internal patterns of14CO2fixation were measured in sun and shade leaves of spinach after treatment with various light intensities. When sun leaves were irradiated with 2000μmol m−2s−1for 2h,FV/FMdecreased by about 15%, but14CO2fixation was unaffected, whereas shade leaves exhibited a 21% decrease inFv/FMand a 25% decrease in14CO2fixation. Irradiation of sun and shade leaves with 4000μmol m−1for 4 h decreased FV/FMby 30% in sun leaves and 40% in shade leaves, while total14CO2fixation decreased by 41% in sun leaves and 55% in shade leaves. After light treatment, gradients of CO2fixation across leaves were determined by measuring14CO2fixed in paradermal leaf sections after a 10s pulse of14CO2. Gradients of14CO2fixation in control sun and shade leaves were identified when expressed on a relative basis and normalized for leaf depth. Treatment of leaves with 2000 μmol PAR m−2s−1for 2h did not after patterns of carbon fixation across sun leaves, but slightly altered the pattern in shade leaves. In contrast, treatment of sun and shade leaves with 4000μmol m−2s−1for 4h decreased carbon fixation more in the palisade mesophyll cells than in the spongy mesophyll cells of sun and shade leaves, and fixation in medial tissue of shade leaves was dramatically decreased compared to the adaxial and abaxial tissue. The interaction between leaf anatomy and biochemical parameters involved in tolerance to photoinhibition in spi

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00004.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe response curves of leaf photosynthesis to varying light, temperature and leaf‐to‐air vapour pressure deficit were measured in the C3plantsFlaveria pringleiandOryza sativain normal air with a computerized open infrared gas analysis (IRGA) system, and the photochemical efficiency of photosystem II, described as (1–F,/F′m) after Genty. Briantais&Baker (1989,Biochimica et Biophysica Acta990, 87–92), was simultaneously measured with a modulated fluorometer. A model was written for rates of CO2fixation as a function of the true rate of O2evolution measured by fluorescene analysis (Jo2), mesophyll conductance and intercellular CO2partial pressure. A second model was developed for rates of CO2fixation as a function of Jo2, mesophyll conductance and stomatal conductance. In the latter case, leaf stomatal conductance was simulated using the stomatal model proposed by Leuning (1995,Plant, Cell and Environment18, 339–355). The rates of CO2fixation predicted from the models were similar to rates measured by IRGA. The results indicate that there is potential to measure CO2fixation in C3plants by combining the non‐invasive measurement of Jo2by chlorophyll fluorescence analysis with the stomatal cond

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00005.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTPlant growth rate has frequently been associated with herbivore defence: a large investment in quantitative defence compounds occurs at the expense of growth. We tested whether such a relationship also holds for growth rate and pathogen resistance. For 15 radish (Raphanus sativusL.) cultivars, we determined the potential growth rate and the resistance to fungal wilt disease caused byFusarium oxysporum.We subsequently aimed to explain a putative negative relationship between growth rate and resistance based on plant chemical composition. Both growth rate and resistance level varied greatly among cultivars. Moreover, there was a strong negative correlation between growth rate and resistance, i.e. there are costs associated with a high resistance level. Roots of slow‐growing, resistant cultivars have a higher biomass density. Using pyrolysis mass spectrometry. we part1y explained variation in both growth rate and resistance in terms of the same change in chemical composition. Leaves of slow‐growing, resistant cultivars contained more cell wall material. Surprisingly, roots of slow‐growing, highly resistant cultivars contained significantly less cell wall material, and more cytoplasmic elements (proteins). We speculate that this higher protein concentration is related to high construction and turn‐over costs and high metabolic activity. The latter in turn is thought to be responsible for a rapid and adequate resistance reaction, in which phenols may be i

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00006.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTCytosolic Ca2+· ([Ca2+]i, and elongation growth were measured in the roots ofArabidopsis thaliana. Exposure of plant tissues to high NaCl and abscisic acid (ABA) concentrations results in a reduction in the rate of growth, but the mechanism by which growth is inhibited is not understood. Both NaCl and ABA treatments are known to influence [Ca2+]i, and in this study we measured the effects of salinity and ABA on [Ca2+]iin cells from the meristematic region ofArabidopsisroots. The Ca2+‐sensitive dye Fura‐2 and ratiometric techniques were used to measure [Ca2+]iin cells of the root meristem region. Resting [Ca2+]iwas found to be between 100 and 200 μmol m−3in roots of untreated plants. Resting [Ca2+]ichanged in response to changes in the [Ca2+] surrounding growing roots. An increase of external [Ca2+] increased [Ca2+]i; conversely, a decrease of external [Ca2+] decreased [Ca2+]i. Exposure of roots to NaCl caused a rapid reduction of [Ca2+]i, a response that was proportional to the external NaCl concentration. Thus, as the NaCl concentration was increased, [Ca2+]iin root meristematic cells decreased. Root elongation was also inhibited in proportion to the external NaCl concentration, with maximal inhibition occurring at 120 mol m−3NaCl. The [Ca2+]iof root meristem cells also changed in response to ABA, and the magnitude of the effect of ABA was dependent upon ABA concentration. Treatment with 0.2 mmol m−3ABA caused a momentary increase in [Ca2+]ifollowed by a decrease after 15 min, but 10 mmol m−3ABA caused an immediate decline in [Ca2+]i. There was a strong positive correlation between [Ca2+]iand root elongation rates. Experiments with the ABA‐deficientArabidopsismutantaba‐3indicated that the reduction in [Ca2+]ibrought about by NaCl was unlikely to be mediated via changes in endogenous ABA. Experiments with solutes such as sorbitol, KCl and NaNO3indicated that the effects of NaCl could be mimicked by other solutes and was not

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00007.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe NH3compensation point (χNH3) inHordeum vulgarecvs Golf and Laevigatum was determined at different growth stages under controlled environmental conditions. The plants were grown to maturity in hydroponics under N limitation. When plants were exposed to NH3at realistic ambient levels ranging from 0 to 25 nmol NH3mol−1air at an air temperature of 20°C, a significant (P<0.001) linear correlation between the NH3flux and the atmospheric NH3mole fraction was observed, showing a constant conductivity to NH3exchange irrespective of the NH3level. For both cultivars a marked decrease in χNH3was observed in the period from tillering to anthesis. In cv. Golf, χNH3decreased from 6.4 ± 1.1 to 3.0 ± 0.4 nmol NH3mol−1air, while χNH3in cv. Laevigatum dropped from 4.2 ± 0.3 nmol NH3mol−1air to below the detection limit (<0.9 nmol NH3mol−1air). The NH3compensation points increased again during senescence, peaking at 5.3 ± 0.8 nmol NH3mol−1air for cv. Laevigatum. The modern and high‐yielding cv. Golf had significantly higher (P<0.01) NH3compensation points than the old and primitive cv. Laevigatum. Golf also had higher shoot NH4+and total nitrogen concentrations than Laevigatum. During generative growth the ratio between NH3and water vapour conductivities increased 10‐fold, suggesting a shortening of the diffusive path length for NH3compared to H2O

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00008.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTSynechococcus R‐2(PCC 1942) actively accumulates sulphate in the light and dark. Intracellular sulphate was 1.35 ± 0.23 mol m−3(light) and 0.894 ± 0.152 mol m−3(dark) under control conditions (BG‐11 media: pHo, 7.5; [SO42−]o, 0.304 mol m−3). The sulphate transporter is different from that found in higher plants: it appears to be an ATP‐driven pump transporting one SO42−/ATP [ΔμSO42−i,o=+ 27.7 ± 0.24 kJ mol−1(light) and + 24 ± 0.34 kj mol−1(dark)]. The rate of metabolism of SO42−at pHo, 7.5 was 150 ± 28 pmol m−2s−1(n = 185) in the light but only 12.8 ± 3.6 pmol m−2s−1(n = 61) in the dark. Light‐driven sulphate uptake is partially inhibited by DCMU and chloramphenicol. Sulphate uptake is not linked to potassium, proton, sodium or chloride transport. The alga has a constitutive over‐capacity for sulphate uptake [light (n= 105):Km= 0.3 ± 0.1 mmol m−3,Vmax, = 1.8 ± 0.6 nmol m−2s−1; dark (n= 56):Km= 1.4 ± 0.4 mmol m−3,Vmax= 41 ± 22 pmol m−2s−1]. Sulphite (SO32−) was a competitive inhibitor of sulp

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00009.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTStudies that quantify plant δ15N often assume that fractionation during nitrogen uptake and intra‐plant variation in δ15N are minimal. We tested both assumptions by growing tomato (Lycopersicon esculetumMill. cv. T‐5) at NH4+or NO−3concentrations typical of those found in the soil. Fractionation did not occur with uptake; whole‐plant δ15N was not significantly different from source δ15N for plants grown on either nitrogen form. No intra‐plant variation in δ15N was observed for plants grown with NH+4. In contrast. δ15N of leaves was as much as 5.8% greater than that of roots for plants grown with NO−3. The contrasting patterns of intra‐plant variation are probably caused by different assimilation patterns. NH+4is assimilated immediately in the root, so organic nitrogen in the shoot and root is the product of a single assimilation event. NO−3assimilation can occur in shoots and roots. Fractionation during assimilation caused the δ15N of NO−3to become enriched relative to organic nitrogen; the δ15N of NO−3was 11.1 and 12.9% greater than the δ15N of organic nitrogen in leaves and roots, respectively. Leaf δ15N may therefore be greater than that of roots because the NO−3available for assimilation in leaves originates from a NO−3pool that was previously exposed to

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00010.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY