摘要:

Leaf senescence and ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1.1.39) degradation in orange [Citrus sinensis(L.) Osbeck cv. Washington Navel] explants have been investigated. Explants consisted of a segment of stem (ca 15 cm) and 5 mature leaves. In vitro RuBP carboxylase degradation was determined by culturing the explants in water for different periods of time (3 days usually) and quantifying the two RuBP carboxylase subunits in the extracts following sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE). In vitro RuBP carboxylase degradation was estimated by autodigestion of leaf extracts and SDS‐PAGE. The extent of in vivo RuBP carboxylase degradation in explants cultured under 16 h light/8 h dark photoperiod varied throughout the year and showed a cyclic behaviour correlated with the growth cycle ofCitrus.The highest proteolytic activity both in vivo and in vitro was found in explants made from April to August coinciding with the maximum vegetative growth period of the tree.Leaf senescence and abscission could be retarded significantly at any time of the year by maintaining the explants continuously in the dark. Treatment of the explants in the dark with a continuous flow of ethylene enhanced both leaf abscission and rate of RuBP carboxylase degradation, proportionally to ethylene concentration (0.1‐0.6 ppm). Ethylene‐induced senescence ofCitrusleaf explants in the dark appears to be a convenient model system to study the regulation of the proteolytic degradation of RuB

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb09184.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Chlorophyll‐free plasma membranes of the unicellular green algaChlamydomonas reinhardtiiDangeard were purified from a microsomal fraction using an aqueous polymer two‐phase system of 6.5% (w/w) dextran T500, 6·5% (w/w) polyethylene glycol 3350, 60 mMNaCI, 0 33Msucrose and 5 mMpotassium phosphate (pH 7·8). The plasma membrane fraction contained only 2·4% of the microsomal membrane protein. Specific activity of the plasma membrane marker enzyme, K*, Mg2+‐ATPase (EC 3.6.1.3). was enriched 9‐fold over the microsomal fraction, and 22% of total activity was recovered in the upper, polyethylene glycol‐rich phase.Contamination from intracellular membranes was minimal. K*, Mg2+‐ATPase showed a pH optimum at about 6·5, and addition of 0·05% (w/v) Triton X‐100 stimulated the activity 3‐fold. [3H]‐Nimodipinc was employed to characterize 1,4‐dihydropyridine‐specific membrane receptors. Two apparent binding sites with different affinities to nimodipine were found in the crude microsomal fraction. The separation of plasma membranes from intracellular membranes revealed that one binding site with higher affinity (KD= 9 nM) was located on the plasma membrane and a second binding site with lower affinity (KD= 36 nM) on an intracellular membrane The apparent dissociation constants determined from the association and dissociation rate constants in kinetic experiments were comparable to those determined by equilibrium experiments. The maximum number of binding sites of the plasma membrane fraction and the intracellular membrane fraction was Bmax= 440 and 470 fmol (mg protein)‐1, respectively. [3H]‐Nimodipinc binding was inhibited by (±) verapamil and stimulated by D‐cis‐diltiazem in both fractions. Moreover, ethyle‐neglycol‐bis(2‐aminoethylcther)‐N, N'‐tetraacctic acid (EGTA) inhibited [3H]‐nimo‐dipinc binding in the plasma membrane fraction but not in the intracellular membrane fraction T

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb09185.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The dormancy‐breaking effect of several known germination promoters was studied in 9 genetically pure lines ofAvena fatuaL. during a period of controlled after‐ripening. Changes in the germination response show at least two dormancy states in the caryopses of these lines. The first state is overcome by a short period of after‐ripening and is insensitive to nitrate and azide, while the second state is more persistent and is sensitive to nitrate and azide. Both states are sensitive to gibberellic acid (OA,) and ethanol. In the most dormant lines a third ethanol‐insensitive dormancy state is present. The duration of both major dormancy states was related to several environmental factors influencing plant growth and seed storage. Duration was increased in caryopses produced from plants matured under low temperatures (15°C) and decreased in caryopses produced from plants matured under high temperatures (25°C). Duration was increased in caryopses after‐ripened under low temperatures (4°C) and decreased in caryopses after‐ripened under high temperatures (45°C). Dehulling the seeds prior to after‐ripening reduced the duration of both major dormancy states. The multiple state dormancy system and its environmentally induced plasticity are discussed with reference to previous explanations of the dormancy mecha

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb09186.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Fructose 1,6‐bisphosphatase (α‐D‐fructose 1,6‐bisphosphate 1‐phosphohydrolase, EC 3.1.3.11; FBPase) from immature wheat endosperm has been resolved into two forms, FBPase‐I and FBPase‐II. Their specific activities over crude homogenate increased 47‐ and 77‐fold, respectively, by using ammonium sulfate fractionation, DEAE‐cellulose chromatography and gel filtration through Sephadex G‐200. The pH optimum was 7.6 for FBPase‐I and 8.4 for FBPase‐II. The two forms were highly specific for the substrate FBP with Kmvalues of 0.17 and 0.08 mM, respectively, for FBPase‐I and FBPase‐II at their respective pH optimum and saturating Mg2+concentration. pH had no effect on the Kmvalue for FBPase‐I, but that for FBPase‐II increased below optimum pH. Neither of the forms had an absolute requirement for Mg2+, although it was essential for maximum activity. Mg2+could not be replaced by Cu2+, Ca2+, Ba2+, Co2+or Ni2+. Sulfhydryl reagents inactivated both FBPase‐I and FBPase‐II. Of the metabolites, only 6‐phosphogluconate was inhibitory with 50% inhibition at 2 and 4 mM

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb09187.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Maize seedlings (Zea maysL. cv. DK 246) grown for 1–4 days in the presence of abscisic acid (ABA) or triadimefon (a fungicide) demonstrated an enhanced ability to withstand the effects of a 3‐h sub‐lethal (40°C) or lethal (45°C) heat shock. Both the ABA and triadimefon treatments were applied solely to the roots of seedlings; however, the ability to withstand a heat shock was induced in both the root and the shoot. The level of protection provided by these agents was dependent upon the time that plants were exposed to them; prolonged exposure reduced tolerance to subsequent

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb09188.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The aim of this study was to investigate the extent to which fully developed leaves ofHedera helixL. are capable of acclimating to new light conditions and how this ability is determined by the life phase of the plant. To this end juvenile and adult plants were transferred from a low (L) to a moderately high (H) light regime and vice versa and changes of photosynthetic gas exchange, RuBP carboxylase (EC 4.1.1.39) activity and specific anatomy were monitored in leaves that were fully developed prior to the transfer.Immediately after transfer from L to H there was a decrease in the rate of net photosynthesis (Fn). This photoinhibition was particularly pronounced in leaves of the adult life phase. Fnrecovered after 10 to 20 days at H, and 40 to 65 days after transfer the rate exceeded that of control plants by about 20% in leaves of the adult life phase and by about 50% in leaves of the juvenile life phase. If H plants were transferred to L, Fnhad declined only slightly after 30 to 40 days and regained its initial level within a few days, when the plants were returned to the original high light regime.The increased rates of Fnper unit leaf area in leaves transferred from L to H were associated with higher light levels necessary to saturate Fn, higher carboxylation efficiencies, higher contents of soluble protein and higher activities of RuBP carboxylase, whereas the quantum yield did not change. Although fully differentiated before transfer, the leaves had formed a further cell layer in the palisade parenchyma. Related to leaf volume there was no increase in Fn.Our results indicate that in the adult life phase of ivy phenotypie light acclimation occurs mainly during leaf development, whereas in juvenile plants fully expanded leaves still possess a rather wide modulativc acclimation plasticity.

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb09189.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Barley (Hordeum vulgare, cv. Triumph), wheat (Triticum aestivum, cv. Kleiber) and oat (Avena sativa, cv. Tarok) were grown until day 20 in nitrate‐containing solutions or in nitrogen‐free solutions for periods up to 8 days immediately prior to day 20. They then were exposed for 4 h to complete, nitrate‐free solutions containing 0.5 or 2.0 mM ammonium (98 atom%15N). In all 3 species in 2 experiments, net ammonium uptake was low in plants grown continuously in nitrate, and increased 3 to 4‐fold with increasing nitrogen deprivation. Charge balance during net ammonium uptake was largely maintained by the sum of net potassium and net proton efflux. Variations in root ammonium concentration at the time of exposure to the ammonium solutions revealed no consistent pattern with net ammonium uptake, implying that a product of ammonium assimilation may serve as a negative effector for the uptake process. In nitrogen‐replete plants, and in those deprived of nitrogen for 2 days, the amounts of endogenous14N‐ammonium recovered in the ambient15N‐ammonium solution during the 4‐h uptake period were greater than the initial amounts of14N‐ammonium present in the root tissue. Significant generation of14N‐ammonium from endogenous organic nitrogen sources was thus evide

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb09190.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Net photosynthesis, concurrent carbon export and starch, sucrose and inorganic phosphorus concentrations were measured in leaves of white clover (Trifolium repensL. cv. Grasslands Huia) grown at four levels of phosphorus supply in the presence or absence of mineral nitrogen. The nitrogen treatments had no effect on growth, photosyntheis or carbon export. At the three higher levels of phosphorus supply, the amount of carbon exported was about 77% of net fixation. Photosynthesis and export per leaf decreased with phosphorus supply, primarily through the effect of phosphorus supply on leaf area. The rate of photosynthesis was reduced only at the lowest level of phosphorus supply.Inorganic phosphorus rose with phosphorus supply but starch concentration was unaffected. Sucrose was reduced at the lowest level of phosphorus supply but not significantly affected at higher levels. The ratio between starch and sucrose concentration was also unaffected at the higher levels, but was increased at the lowest level of supply. There thus appeared to be direct effects of phosphorus supply on photosynthesis, partitioning of carbon to carbohydrates and, by implication, export, only at the lowest level of phosphorus supply. As leaf area and plant growth were affected over the whole range of phosphorus supply, factors other than photosynthesis per se must have determined the response of growth to phosphorus supply.

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb09191.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Bulbs from three species of the plant family Amaryllidaceae (Narcissus pseudonurcissusL.,Leucojum aestivumL. andLeucojum vernumL.) were found to contain mannose‐specific lectins. These lectins were serologically identical to a previously reported Amaryllidaceae lectin fromGalanthus nivalisL. bulbs, but had a different molecular structure. The lectins described in this paper are dimeric proteins composed of subunits of 13 kDa, which are not held together by disulphide bridges. In hapten‐inhibition assays Amaryllidaceae lectins exhibited exclusive specificity towards mannose. Furthermore, they all had a high specific agglutination activity with trypsin‐treated rabbit erythrocytes, whereas human red blood cells were not aggluti

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb09192.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Ethylene production was induced in Valencia oranges [Citrus sinensis(L.) Osbcck] by injection of the fungal enzyme mixture Pectolyase (Aspergillus japonicus) which contains pectolytic enzymes into the peel. The mixture also stimulated production of 1‐aminocyclopropane‐1‐carboxylic acid (ACC). Cycloheximide partially inhibited the Pectolyase‐induced ethylene response. Pectin fragments, resulting from partial acid hydrolysis or Pectolyase digestion, caused an increase in ethylene production when injected into the peel of intact orange fruits. Pectic fragments produced by fungal enzymes are known to be elicitors of phytoalexins and in this study are shown to elicit ethylene in

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb09193.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY