摘要:

A strong approach to understanding the regulation of enzymes in metabolic pathways, such as those responsible for amino acid biosynthesis, is to follow enzyme levels throughout the growth curve of higher plant cells in suspension culture. The rise and fall of enzyme levels can be traced as a function of physiological stage of growth Subculturing, as typically carried out by low‐factor dilution of stationary phase cells, yields a system suitable for the study of changes in enzyme and metabolite levels that accompany the transition from stationary‐phase physiology to exponential‐phase physiology. However, the short duration of exponential growth in such subculture protocols is inadequate to avoid carryover effects from previous stationary‐phase physiology. Suspension cultures ofNicotiana silvestrisSpeg, et Comes (2N = 24) were used to demonstrate substantial carryover levels of acid phosphatase, alkaline phosphatase and protease activities. A subculture routine is described for maintaining cell populations in exponential phase indefinitely. About 10 generations of sustained exponential growth is required to approach a true balanced state of exponential growth. Such exponential phase populations consist of cells termed EE cells. EE‐cell populations were similar to cells that have been in exponential phase for only a few generations (E cells), with respect to doubling time (about 40 h) and to minimal density of diluted populations able to resume growth (about 500 cells ml−1). EE cells possess a high content of soluble protein; they are smaller and more aggregated than are E cells. Upon dilution into fresh medium, EE cells resume exponential growth without a lag. In contrast to E cells, EE cells exhibit properties of balanced growth, since proportionate increases in cell number, dry weight, wet weight and packed‐cell volume were observed. E cells, sampled at different elapsed times of growth, are likely to differ in metabolite, enzyme and cell properties, whereas EE cells exhibit near‐cons

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb04933.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Plasma membrane vesicles were purified from 8‐day‐old oat (Avena sativaL. cv. Brighton) roots in an aqueous polymer two‐phase system. The plasma membranes possessed high specific ATPase activity [ca 4 μmol P1(mg protein)−1min−1at 37°C]. Addition of lysophosphatidylcholine (lyso‐PC) produced a 2–3 fold activation of the plasma membrane ATPase, an effect due both to exposure of latent ATP binding sites and to a true activation of the enzyme. Lipid activation increased the affinity for ATP and caused a shift of the pH optimum of the H+‐ATPase activity to 6.75 as compared to pH 6.45 for the negative H+‐ATPase. Activation was dependent on the chain length of the acyl group of the lyso‐PC, with maximal activition obtained by palmitoyl lyso‐PC. Free fatty acids also activated the membrane‐bound H+‐ATPase. This activation was also dependent on chain length and to the degree of unsaturation, with linolenic and arachidonic acid as the most efficient fatty acids. Exogenously added PC was hydrolyzed to lyso‐PC and free fatty acids by an enzyme in the plasma membrane preparation, presumably of the phospholipase A type. Both lyso‐PC and free fatty acids are products of phospholipase A2(EC 3.1.1.4) action, and addition of phospholipase A2from animal sources increased the H+‐ATPase activity within seconds. Interaction with lipids and fatty acids could thus be part of the regulatory system for H+‐ATPase activity in vivo, and the endogenous phospholipase may be involved in the regulation of the H+‐AT

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb04934.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Plasma membrane vesicles with H+‐ATPase activity were purified from 8‐day‐old oat (Avena sativaL. cv. Brighton) roots using an aqueous polymer two‐phase system. Of several detergents tested, only lysophosphatidylcholine solubilized the H+‐ATPase in an active form. Solubilization of the H+‐ATPase with lysophosphatidylcholine was possible in the absence of glycerol, but the ATPase activity decreased about 4–5 times as rapidly in the absence as in the presence of 30% (w/v) glycerol. The solubilized enzyme was further stabilized by ATP and protons. Addition of 1 mMATP to the plasma membranes halted inactivation of the H+‐ATPase. Even in the absence of polyol compounds and ATP, the enzyme was stable for hours at relatively low pH with an optimum around pH 6.7 at room temperature. The curve for the stability of soluble H+‐ATPase as a function of pH closely resembles the pH curve for the activity of the H+‐ATPase. This suggests that binding of protons to transport sites may stabilize the soluble H+‐ATPase in an enzy

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb04935.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

In a study of the plant communities of two Australian rainforests, it was found that pioner species had high levels of nitrate reductase (EC 1.6.6.1) and were predominantly leaf nitrate assimilators. Under‐ and over‐storey species had low levels of shoot and root nitrate reductase activity, and many of them showed little capacity for nitrate reduction even when nitrate ions were freely available. Although closed‐forest species have lower levels of nitrate reductase than those of gaps and forest margins, their total nitrogen contents were similar, suggesting the former utilize nitrogen sources other than nitrate ions. Glutamine synthetase (EC 6.3.1.2) was present in the leaves of all species examined. In the leaves of pioneer species the chloroplastic isoform of glutamine synthetase predominted, while in most of the species typical of closed‐forest the cytosolic isoform accounted for at least 40% of total leaf activity. Low levels of chloroplastic glutamine synthetase were correlated with a low capacity for leaf nitrate reduction, and both are characteristic of many species that regenerate and grow for some time in shade. Low levels of chloroplastic glutamine synthetase imply that, in some of these woody plants, photorespiratory ammonia is re‐assimilated via cytosolic glutamine s

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb04936.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The epidermis ofArgenteummutant ofPisum sativumL. andVicia fabaL. was shown to be effective in protecting mesophyll photosynthesis from UV‐C irradiation (peak 254 nm; 1.5 W m−2). These plants were chosen because it is easy to peel the epidermis from both sides of the leaf inArgenteumand the abaxial side inVicia. Chlorophyllafluorescence induction was decreased to the same extent by UV‐C radiation in both leaf sides when the epidermis was removed. The fluorescence from the leaf with the epidermis inact was not affected. With irradiation of leaves with higher intensity (3.4 W m−2) of UV‐C, the variable fluorescence was decreased by UV‐C impinging on the abaxial side, but not the adaxial side in either of the plant species. A methanol extract from the mutantPisumepidermis had a high absorbance in the UV region, and the absorbance was more than two‐fold larger in adaxial epidermis than in abaxial epidermis. These results indicate that the epidermal layer, which contains substances that have high UV absorbance, protects mesophyll photosynthesis against

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb04937.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Scions of a southern (59° 40’N Lat.) and a northern (69° 39’N Lat.) ecotype ofSalix pentandraL. were grafted on clonal rootstocks of the same ecotypes. Effects of photoperiod on elongation growth of the 4 combinations (south/south, south/north, north/south and north/north) were studied in a phytotron at 18° and 15°C. The photoperiodic response was primarily dependent on the ecotype of the scion, but this response was significantly modified by the rootstock. Cessation of apical growth was advanced by a northern clone and delayed by a southern clone as a rootstock. The results indicate that the critical photoperiod for cessation of apical growth could be slightly decreased by a northern and increased by a southern ro

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb04938.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Membrane lipids and steady‐state CO2fixation rates were studied in moss protonemata in order to evaluate separately the effects of growth temperature, freezing stress and the achievement of frost hardiness. Protonemata ofCeratodon purpureus(Hedw.) Brid, were grown at 20 and 4°C and parts of both materials were then hardened. The low growth temperature increased the content and unsaturation level of membrane lipids significantly. This did not, however, cause a noticeable increase in the frost hardiness. Nor was the achievement of frost hardiness in this material accompanied by further changes in the amount or unsaturtion level of any membrane lipid class. Cytoplasmic membranes were abundant in both unhardened and hardened materials grown at 4°C, which agreed with the high phospholipid content of these protonemata. The only significant difference in membrane lipids between unhardened and hardened materials was a 50% lower level oftrans16:1 fatty acid in the phosphatidylglycerol fraction of hardened protonemata.In hardened protonemata monogalactosyldiacylglycerol (MGDG) was the membrane lipid most liable to decrease during the freeze‐thaw cycle. The loss of MGDG was accompanied by partial inhibition of CO2fixation. Provided the content of phospholipids remained unchanged (freeze‐thaw cycle with – 10°C in hardened protonemata), this inhibition was mostly reversible. If loss of the phospholipids also had occurred during the freeze‐thaw cycle, as was the case in unhardened material at or below ‐10°C, CO2fixation was severely and nearly irreversibly inhibite

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb04939.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Ethylene production and overall levels of free and conjugated 1‐aminocyclopropane‐1‐carboxylic acid (ACC) were studied in parenchymatous tissues, excised from clmacteric apples (Malus domesticaBorkh. cv. Granny Smith) and infiltrated with an incubation medium containing 0, 1, 10 or 100 mMCa2+, with or without exogenous ACC (2 mM). Irrespective of whether exogenous ACC was applied or not, ethylene production was inhibited to the same extent (40%) by an apoplastic effect of 100 mMCa2+. In the absence of external ACC, the inhibition was associated with an increase in total endogenous ACC and may be related to a reduction in the rate of the last step of ethylene pathway. This suggests that the ethylene‐forming enzyme (EFE) is localized in the plasma membrane. Low Ca2+concentrations (1 mM) enhanced basal ethylene synthesis due to influx of Ca2+into the cytosol, while overall concentrations of ACC in the tissue decreased. However, 1 mMCa2+did not stimulate ACC‐dependent ethylene formation. Thus, Ca2+influx may stimulate the translocation of endogenous ACC from synthesis or storage compartment (s) to reactive site(s) of the plasma membrane. The concentration of 10 mMCa2+had no effect on basal ethylene production and appears to represent a balance point between the stimulating and inhibiting effects of 1 and 100 mMCa2+, respectively, Furthermore, the charge‐times of exogenous ACC observed with 0, 1 and 10 mMCa2+suggest that EFE is located on the inner side of the plas

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb04940.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Levels of soluble and bound invertases and amylases were studied in relation to the changes in the free sugars and the accumulation of starch in the developing sorghum [Sorghum bicolor(L.) Moench, cv. spv. 351] caryopsis and its associated bractspedicel. Besides sucrose, glucose and fructose as the principal sugars, small amounts of sugars of the raffinose series were detected in the developing caryopsis. Through out the period of caryopsis development, the amount of reducing sugars was higher than that of sucrose. With the advancement in the development of the caryopsis, the contents and levels of sucrose rose with a concomitant fall in the activity of soluble acid (pH 4.8) invertase (EC 3.2.1.26) in the endosperm. In the pericarp‐aleurone layer, the activity of soluble acid invertase predominated over soluble neutral (pH 7.5) invertase (EC 3.2.1.27). The activity of bound acid invertase declined with the ageing of the caryopsis. In bracts‐pedicel, the activity of bound invertase and the levels of reducing sugars peaked around 18 days post anthesis. In these organs, the level of starch gradually decreased concomitantly with an increase in its level in the developing caryopsis. Amylases (EC 3.2.1.1 and 3.2.1.2) are distributed in the endosperm as well as in the pericarp‐aleurone layer. On culturing detached ears in [U‐14C]‐sucrose solution for 6 h in the dark at 25°C, 80–90% of the14C of extracted major sugars (i.e. sucrose + glucose + fructose) of the caryopsis appeared in sucrose alone. In comparison with the effects of glucose or fructose, transport into the caryopsis of14C from [U‐14C]‐sucrose supplied to detached ears was promoted by the addition to the radiolabelled sucrose solution of 1% unlabelled sucrose. Addition to the [U‐14C]‐sucrose solution fed to the detached ears of 20 mMNaN3or HgCl2or galactose, lowered the amount of14C in the free sugars and sta

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb04941.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The effects of nitrate on nitrogenase (EC 1.18.2.1) activity of soybean (Glycine max[L.] Merr) cv. Bragg and its supernodulating mutant derivative, nts382, were compared. A short‐term nitrate treatment was used to allow effects on nitrogenase activity to be studied in the absence of effects on nodule growth and a low inoculum dose, which prevented supernodulation of nts382, was employed to test for any interaction between supernodulation and the magnitude of the effect of nitrate on nitrogenase activity. At the usual inoculum dose, nitrogenase activity, per g nocule, of nts382 was lower than that of Bragg and was proportionally less affected by nitrate. Decreasing the inoculum dose increased nitrogenase activity of nts382 and also the proportional decline in response to nitrate. The decline in the ureide conentration in xylem exudate in response to nitrate was proportionally similar to the decline in nitrogenase activity per plant. However, although nitrogenase activity per plant of nts382 was several‐fold less than that of Bragg, the ureide flux rate (ureide concentration x xylem sap exudation rate), was not different. At the usual inodulum dose, the ureide content of the nocules, stems plus petioles and leaves of nts382 was greater than that of Bragg. Decreasing the inoculum dose reduced the ureide content of the nodules of nts382 but not of Bragg. Ureide degradative capacity of the leaves was the same for Bragg and nts382. Low activities of 5‐phosphoribosyl pyrophosphate amidotransferase (EC 2.4.2.14) and glutamine synthetase (EC 6.3.1.2) in the nodules reflected the low nitrogenase activity of n

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1988.tb04942.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY