摘要:

Restriction fragment analysis revealed differences in mitochondrial DNA (mtDNA) between adult and juvenile coastal redwood,Sequoia sempervirens(D. Don) Endl. Thus, for example, juvenile shoots contained 4.0‐ and 3.6‐kbBamHI], restricted fragments that were absent in adult material. Rejuvenation by 5 repetitive graftings onto juvenile rootstocks resulted in the same 4.0‐ and 3.6‐kb fragments as were present in the juvenile material. The similarities in mtDNA fragments of juvenile and rejuvenated. shoots, as well as their distinction from adult shoots, were confirmed by double digestion, Southern hybridization and DNA seq

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00942.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

In vivo15N and14N nuclear magnetic resonance spectroscopy was used to investigate the assimilation of nitrate and ammonium in seedlings of Norway spruce (Picea abies[L.] Karst.). The main objective was to study accumulation of free NH+4and examine to what extent the nitrogen source affects the composition of the free amino acid pools in roots, stems and needles. NH+4concentrations in plants growing in the presence of 0.5–50 mMammonium were quantified using14N NMR. The NH+4values in tissues ranged from 6 to 46 μmol (g fresh weight)−1. with highest concentrations in roots and needles. The tissue NH+4peaked at 5.0 mMNH+4in the medium. and failed to increase when NH+4in the medium was increased to 50 mM, indicating metabolic control of the concentration of this cation in tissues. The14N NMR spectra were used to estimate pH of the NH+4storage pools. Based on the pH sensitivity of the quintet of14NH+4resonance, we suggest that the pH of the ammonium storage compartments in the roots and stems should be 3.7–3.8, and in needles 3.4–3.5, representing extremely low pH values of the tissue.15N from nitrate or ammonium was first incorporated into the amide group of glutamine and then into α‐amino groups, confirming that the glutamine synthetase/ glutamate synthase cycle is the major route of nitrogen assimilation into amino acids and thus plays a role in lowering the levels of NH+4in the cytoplasm. NH+4can also be assimilated in roots in plants growing in darkness. The main15N‐labelled amino acids were glutamine. arginine and alanine. Almost no15N signals from needles were observed. Double labelling (δN + w, wN) of arginine is consistent with the operation of the ornithine cycle, and enrichment indicates that this cycle is a major sink of newly assimilated nitrogen. Nitrogen assimilation in roots in the presence of added methionine sulphoximine and glutamate indicated the catabolic action of glutamate dehydrogenase. The15N NMR spectra of plants grown on15N‐urea showed a marked increase in the labelling of ammonium and glutamine. indicating high urease activity. Amino acids were also quantified using high pressure liquid chromatography. Arginine was found to be an important transport form of nitr

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00943.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The pattern and sequence of cellular degradation during the course of leaf senescence remains obscure and the nature of the trigger that induces cell senescence is unknown. In order to probe the pre‐mortem phase of senescence temporal changes in cell ultrastucture were studied in aging leaves of light‐grown achlorophyllousHordeum vulgareL. cv. Dyan mutant seedlings. Electron microscope examination of the ultrastructure of mesophyll cell plastids revealed the absence of ribosomes and a highly disorganized prolamellar body. Both the number and size of plastoglobuli increased with aging and this change coincided with depletion of starch grains and dilation of lamellar membranes. Aging of mesophyll cells occurred coincident with a decline in ribosome content of the cytoplasm and loss of matrix granularity. Loss of ribosomes associated with the outer nuclear envelope membrane and a reduction in chromatin were also apparent. Only after 10 days was there evidence of loss of internal membrane integrity and swelling of mitochondrial cristae. Compartmentation was thus maintained during the aging process with membrane dissolution occurring late in senescence. These results suggest that an inability to produce chlorophyll and carotenoids and form thylakoid stacks due to the absence of plastid ribosomes, contributes to the rapid onset of senescence in light‐grown achlorophyllous seedlings. Furthermore, disruption of chloroplast ribosome synthesis/assembly may constitute part of the plastid signal involved in triggering cell senes

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00944.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Tonoplast vesicles were isolated from tomato (Lycopersicon esculentumMill.) fruit pericarp and purified on a discontinuous sucrose gradient. ATPase activity was inhibited by nitrate and bafilomycin A1but was insensitive to vanadate and azide. PPase hydrolytic activity was inhibited by NaF but was insensitive to nitrate, bafilomycin A1vanadate and azide. Kimetic studies of PPase activity gave an apparent Km, for PP3of 18 μM. Identical distributions of bafilomycin‐ and NO3‐sensitive ATPase activities within continuous sucrose density gradients, confirmed that bafilomycin‐sensitive ATPase activity is a suitable marker for the tonoplast. By comparing the distribution of bafilomycin‐sensitive ATPase activity with that of PPase activity, it was possible to locate the PPase enzyme exclusively at the tonoplast. The apparent density of the tonoplast did not change during fruit development. Measurements of tonoplast PPase and ATPase activities during fruit development over a 35‐day period revealed an 80% reduction in PPase specific activity and a small decrease in ATPase specific activity. ATP‐ and PP1‐dependent ΔpH generation was measured by the quenching of quinacrine fluorescence in tonoplast vesicles prepared on a discontinuous Dextran gradient. No H+efflux was detected on the addition of sucrose to energized vesicles. Therefore a H+/sucrose antiport may not be the mechanism of sucrose uptake at the tomato fruit tonoplast. Similar results were obtained with glucose, fructose and sorbitol. The lack of ATP (or PP1) stimulation of [14C]‐sucrose uptake also suggested that an antiport was not involved. Initial uptake rates of radiolabelled glucose and fructose were almost double that for sucrose. The inhibition of hexose uptake byp‐chloromercuribenzene sulphonate (PCMBS) implicated the involvement of a carrier. Therefore storage of hexose in the tomato fruit vacuole and maintenance of a downhill sucrose concentration gradient into sink cells is likely to be regulated by the activity of sucrose metabolizing enzymes, rather than by energy‐requiring uptake mechan

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00945.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Calcium ions play an important role in the regulation of stomatal movement and the mechanism underlying this action is yet to be determined. It is suggested that guard cell plasma membrane ATPase is a target for calcium action and that this effect is mediated by calmodulin. In this study, the effects of calcium and two calmodulin antagonists on ATPase activity in a crude homogenate ofCommelina communisL. guard cell protoplasts were examined. The homogenate contained Mg2+‐dependent, K+‐simulated ATPase activity, which was inhibited by CaCl2while stimulated by the calmodulin antagonists, compound 48/80 and chlorpromazine. The calmodulin antagonists partially reversed the inhibitory effect of calcium ions. The results support the possibility of calmodulin involvement in the regulation of guard cell ATPase activity by calcium i

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00946.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

As the autoclaving of a sugar together with other nutrient components enhances its degradation with the associated formation of toxic products, it is advisable to autoclave it separately from other medium components. In such cases, and to prepare growth media of consistent quality, it may also be necessary to adjust the duration of autoclaving according to the volume of the sugar solution. The results of an attempt to fine‐adjust the autoclaving procedure are presented.Glucose, used as model sugar in this investigation, was autoclaved for 20,32 or 44 min in volumes of 0.25. 1.2 and 5 1. The rise in temperature of the solutions was monitored by thermocouples. Glucose degradation was estimated by the rate of cyanide‐initiated oxygen consumption. The rates were found to be inversely proportional to the volumes in a semilogarithmic plot. The T‐t (temperature‐time) value, the area under the solution temperature vs time curve, was found to be an independent variable from which the extent of glucose degradation could be deduced. For a chosen level of thermodegradation of glucose, the duration of autoclaving for solutions of different volumes could be determined graphically from a T‐t value vs

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00947.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

In a plastid‐free assay, Mg‐chelatase from pea (Pisum sativumL. cv. Spring) and cucumber (Cucumis sativusL. cv. Sumter) chloroplasts is inhibited to equal extents by the mercurial reagents.p‐chloromercuribenzoate (PCMB) andp‐chloromercuribenzene sulfonate (PCMBS). However, in intact chloroplasts PCMB inhibits Mg‐chelatase fourfold more strongly than does PCMBS. Since PCMBS cannot penetrate membranes as readily as PCMB, Mg‐chelatase may be localized interior to the inner chloroplast envelope. When Mg‐chelatase is assayed with photosynthetically generated ATP, the presence of an external ATP trap does not inhibit activity, suggesting that the enzyme is not located in the interenvelope space. None of the components of Mg‐chelatase are integral membrane proteins: Mg‐chelatase activity is readily solubilized by washing the total chloroplast membranes in buffers of low MgCl2content. This precludes localization by purifying individual thylakoid and envelope membranes which requires low Mg

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00948.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Our previous work indicated that salinity caused a shift in the predominant site of nitrate reduction and assimilation from the shoot to the root in tomato plants. In the present work we tested whether an enhanced supply of dissolved inorganic carbon (DIC, CO2+ HCO3) to the root solution could increase anaplerotic provision of carbon compounds for the increased nitrogen assimilation in the root ofsalinity‐stressed Lycopersicon esculentum(L.) Mill. cv. F144. The seedlings were grown in hydroponic culture with 0 or 100mMNaCl and aeration of the root solution with either ambient or CO2‐enriched air (5000 μmol mol−1). The salinity‐treated plants accumulated more dry weight and higher total N when the roots were supplied with CO2‐enriched aeration than when aerated with ambient air. Plants grown with salinity and enriched DIC also had higher rates of NO−3uptake and translocated more NO−3and reduced N in the xylem sap than did equivalent plants grown with ambient DIC. Incorporation of DIC was measured by supplying a 1 ‐h pulse of H14CO−3to the roots followed by extraction with 80% ethanol. Enriched DIC increased root incorporation of DIC 10‐fold in both salinized and non‐salinized plants. In salinity‐stressed plants, the products of dissolved inorganic14C were preferentially diverted into amino acid synthesis to a greater extent than in non‐salinized plants in which label was accumulated in organic acids. It was concluded that enriched DIC can increase the supply of N and anaplerotic carbon for amino acid synthesis in roots of salinized plants. Thus enriched DIC could relieve the limitation of carbon supply for ammonium assimilation and thus ameliorate the influence of salinity on NO−3uptake and assimilatio

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00949.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

We compared photosynthetic and UV‐B‐absorbing pigment concentrations, gas‐exchange rates and photosystem II (PSII) electron transport rates in leaves of pea (Pisum sativummutant Argenteum) grown without UV‐B or under an enhanced UV‐B treatment (18 kJ m−2biologically effective daily dose) in a greenhouse. We also compared the distribution of chlorophyll by depth within leaves of each treatment by using image analysis of chlorophyll autofluorescence. Ultraviolet‐B treatment elicited putative protective responses such as an 80% increase in UV‐B‐absorbing compound concentrations (leaf‐area basis), and a slight increase in mesophyll thickness (178 in controls compared to 191 μm in UV‐B‐treated leaves). However, photosynthetic rates of UV‐B‐treated leaves were only 80% of those of controls. This was paralleled by reductions in leaf conductance to water vapor (50% of controls) and intercellular CO2concentrations, suggesting that stomatal limitations were at least partly responsible for lower photosynthetic rates under the UV‐B treatment. Total chlorophyll concentrations (leaf‐area basis) in UV‐B‐treated leaves were only 70% of controls, and there was a shift in the relative distribution of chlorophyll with depth in UV‐B‐treated leaves. In control leaves chlorophyll concentrations were highest near the adaxial surface of the upper palisade, dropped with depth and then increased slightly in the bottom of the spongy mesophyll nearest the abaxial surface. In contrast, in UV‐B‐treated leaves chlorophyll concentrations were lowest at the adaxial surface of the upper palisade and increased with depth through the leaf. The most notable treatment difference in chlorophyll concentrations was in the upper palisade near the adaxial surface of leaves, where we estimate that chlorophyll concentrations in each 1‐μm‐thick paradermal layer were about 50% lower in UV‐B‐treated leaves than in controls. We found reduced electron transport capacity in UV‐B‐treated leaves, based on lower maximum fluorescence (Fm), variable to maximum fluorescence ratios (F,/Fm) and quantum yield of PSII electron transport (Y). However, the above were assessed from fluorometer measurements on the adaxial leaf surface and may reflect the markedly lower chlorophyll co

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00950.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Hydration offers an effective means for raising seed performance in many crop species. The objective of this study was to evaluate the effect of vermiculite hydration on germinability and several physiological activities related to vigor in artificially aged watermelon seeds differing in ploidy. Aging was achieved by incubating the seeds at 45°C and 79% relative humidity for 6 days, then the seeds were air‐dried to their original moisture level (4.7%). Hydration was achieved by mixing the untreated and aged seeds with moist vermiculite No. 3 at 25°C for 24 h. The partially hydrated seeds were air‐dried at 25°C for 36 h to 4.7% moisture level. Significant differences existed between unaged and aged seeds, with lower germination percentage and slower germination speed in the latter. Aging also increased lipid peroxidation and reduced the activity of peroxide‐scavenging enzymes. The germinability of aged watermelon seed was restored partially by vermiculite hydration. The activities of protein synthesis and peroxide‐scavenging enzymes in axis and cotyledon portions of the seeds were also increased by hydration treatment. The changes in germination and related physiological responses in relation to aging and hydration are similar in seeds differing in ploidy, despite differences in their germination performance, seed leakage, extent of lipid peroxidation and activities of peroxide‐scaven

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb00951.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY