摘要:

Spring barley (Hordeum vulgareL. cv. Golf) was grown at different nitrate supply rates, controlled by using the relative addition rate technique, in order to elucidate the relationship between nitrate‐N supply and root and shoot levels of abscisic acid (ABA). The plants were maintained as (1) standard cultures where nitrate was supplied at relative addition rates (RAs) of 0.03, 0.09 and 0.18 day−1, and (2) split‐root cultures at RA 0.09 day−1but with the nitrate distributed between the two root parts in ratios of 100:0, 80:20 and 60:40. Time‐dependent changes in root and shoot concentrations of ABA (determined by radioimmunoassay using a monoclonal antibody) were observed in both standard and split‐root cultures during 12 days of acclimation to the different nitrate regimes. However, the ABA responses were similar at all nitrate supply rates. Further experiments were performed with split‐root cultures where the distribution of nitrate between the two root parts was reversed from 80:20 to 20:80 so that short‐term effects to local perturbations of nitrate supply could be studied without altering whole‐plant N absorption. Transient increases in ABA concentrations (maximum of 25 to 40% after 3 to 4 h) were observed in both subroot parts, as well as in xylem sap and shoot tissue. By pruning the root system it was demonstrated that the change in ABA had its origin in the subroot part receiving the increased nitrate supply (i.e. switched from 20 to 80% of the total nitrate supply). The data indicate that ABA responses are easily transmitted between different organs, including transmission from one set of seminal roots to another via the shoot. The data do not provide any indication that long‐term nitrate supplies or general nitrogen status of barley plants affect, or are otherwise related to, the average tissue ABA concentrations

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb05515.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The expression of cytosolic and plastid pyruvate kinase (PK; E.C. 2.7.1.40) in various tissues of tobacco (Nicotiana tabacumcv. Petit Havana SR1) was investigated. To facilitate this study, a cDNA clone for cytosolic pyruvate kinase (PKc) was isolated from a tobacco seed cDNA expression library. This cDNA has an open reading frame capable of encoding a 508‐amino acid polypeptide with a predicted molecular mass of 55.1 kDa. The deduced amino acid sequence has 76% identity with the sequence of potato PKc. Southern blot analysis shows thatN. tabacumcontains two copies of the PKcgene, each derived from the single gene found in its progenitors,N. tomentosiformisandN. sylvestris. Northern blots detected a 1.9‐kb band in flower, seed, root, stem and leaf tissues ofN. tabacum. Immunoblotting using anti‐[castor oil seed (COS) PKc]‐immunoglobulin G (IgG) detected 58‐ and 56‐kDa polypeptides in all tobacco tissues examined. In developing seeds, mRNA levels were low except for a peak at 8 days post anthesis (dpa), whereas the highest level of the PKcpolypeptides was detected 10–16 dpa. The persistence of PKcwell after the peak in mRNA levels suggests that PKcis stable in developing seeds. Our previous studies have shown that leucoplast PK (PKp) mRNA could be detected throughout tobacco seed development as well as in somatic tissues. In developing seeds, steady state PKcmRNA levels showed a broad peak of accumulation from 8–20 dpa, reaching maximum levels at 16 dpa. In the present study, polypeptides of 63 and 60 kDa were detected on immunoblots probed with anti‐(COS PKp)IgG in developing tobacco seeds 10–20 dpa. The observed pattern of PKpprotein accumulation closely correlated with the profile of steady state mRNA levels suggesting that this isoenzyme has a much greater rate of turnover than that of PKc. In contrast to PKc, there was no detectable accumulation of PKpprotein at other times during seed development or in somatic tissues even though significant levels of PKpmRNA could be detected. The differences in the protein accumulation and mRNA expression patterns of PKcand PKpsuggest that the tissue‐specific and developmental expression of these isoenzymes in tobacco may be controlled by independent transcriptional and post‐tra

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb05516.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Circadian rhythms are characteristic of many physiological and biochemical processes in the freshwater flagellateEuglena gracilis. Earlier, we found that the rhythms of photosynthesis, phototaxis and cell shape followed the same pattern in control organisms, but were differently affected by stress such as UV‐B irradiation and nitrogen deficiency. Here we extend our studies to use isolated plasma membranes to characterize the rhythms of some plasma membrane‐bound enzymes. Also, we wanted to see whether stress‐induced changes of these rhythms could be detected at the subcellular level and possibly be coupled to the changes seen in photosynthesis, phototaxis and cell shape. The isolation of plasma membranes using aqueous polymer two‐phase partitioning was successful, as judged by the large enrichment of the plasma membrane‐marker 5′‐nucleotidase, and the difference in the polypeptide pattern compared with the microsomal fraction from which it was prepared.Two other enzymes were analyzed, K+, Mg2+‐ATPase, and adenylyl cyclase. The specific activities of all three enzymes were decreased by UV‐B radiation by ca 30–50%, compared with the control cultures. On the other hand, nitrogen deficiency not only reduced the activity of the K+.Mg2+‐ATPase but also increased the activities of the 5′‐nucleotidase and adenylyl cyclase. The different treatments also resulted in differences in polypeptide pattern, e.g., a polypeptide around 30 kDa seemed to be specific to plasma membranes of nitrogen‐deficient cultures and one at 39 kDa for the UV‐B radiated ones.All three enzymes showed diurnal rhythms that were affected by UV‐B radiation. The peak in the rhythm of the ATPase was shifted by UV‐B radiation, the rhythm of the 5′‐nucleotidase nearly eliminated. The first peak of adenylyl cyclase activity was delayed, so that it looked more like a broad peak between 2 and 11 h after the onset of light. The rhythm of ATPase activity could be correlated with that of photosynthesis in both control and UV‐B irradiated cultures. Also, the rhythms of adenylyl cyclase activity and cell

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb05517.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The contribution of individual plant mitochondrial respiratory pathways to total respiration is commonly assessed by titration with specific inhibitors of different components in the branched electron transport chain. A pathway's contribution is equal to the activity when the other branch is blocked by an inhibitor multiplied by the degree (0‐1.0) to which this activity is engaged when both pathways are operating. According to Bahr and Bonner (1973. J. Biol. Chem. 218: 3441–3445) the plot of the activities of identical titrations, one performed in the absence and the other in the presence of a specific inhibitor of the other branch of the respiratory chain, yields a straight line whose slope indicates the engagement of the titrated pathway during uninhibited respiration. An initial slope of zero may occur if electron flux is diverted between pathways during titrations. However, beyond the breakpoint (representing the point of pathway saturation), a straight line is obtained with a slope representing engagement. This technique assumes that the kinetics of inhibiting a specific component of the respiratory chain are independent of the absolute rate of electron flux through the total pathway. To test this assumption, the activity of respiratory pathways in isolated soybean (Glycine max[L]. Merr. cv. Stevens) mitochondria was titrated with specific inhibitors of the cytochrome and alternative oxidases. Under these conditions, the electron flux through a given pathway was manipulated by poising the rate of succinate oxidation with the succinate dehydrogenase inhibitor malonate. Construction of activity plots in the presence versus absence of malonate failed to result in straight lines for either KCN (when titrating the cytochrome pathway) or salicylhydroxamic acid (when titrating the alternative pathway). Rather, the resultant plots were always curvilinear whenever the activity in the presence of malonate divided by the activity in the absence of malonate was less than 1.0. In no case could the real engagement of the pathway be precisely estimated from the titration data. Titrations of cytochrome pathway activity in isolated potato tuber (Solanum tuberosumL. cv. Sabago and Canabex) mitochondria (which lack the alternative oxidase) showed that as the inhibitor concentration was increased, so did the reduction status of the ubiquinone pool, to a new steady state. The dependence of inhibition kinetics on the rate of flux through the pathway, and the increase in ubiquinone pool reduction upon KCN addition, are explained in terms of the elasticity of component enzymes as outlined in the theory of metabolic control analysis. The implications of this finding for the use of titrations to estimate engagement of plant respiratory pathways are discus

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb05518.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

No straightforward method exists for separating the proportion of ion exchange and respiration due to rhizoplane microbial organisms from that of root ion exchange and respiration. We examined several antibiotics that might be used for the temporary elimination of rhizoplane bacteria from hydroponically grown wheat roots (Triticum aestivumcv. Veery 10). Each antibiotic was tested for herbicidal activity and plate counts were used to enumerate bacteria and evaluate antibiotic kinetics. Only ‐lactam antibiotics (penicillins and cephalosporins) did not reduce wheat growth rates. Aminoglycosides, the pyrimidine trimethoprim, colistin and rifampicin reduced growth rates substantially. Antibiotics acted slowly, with maximum reductions in rhizoplane bacteria occurring after more that 48 h of exposure. Combinations of nonphytotoxic antibiotics reduced platable rhizoplane bacteria by as much as 98%; however, this was generally a reduction from about 109to 106colony forming units per gram of dry root mass, so that many viable bacteria remained on root surfaces. We present evidence which suggests that insufficient bacterial biomass exists on root surfaces of nonstressed plants grown under well‐aerated conditions to quantitatively interfere with root nitrogen absorption measureme

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb05519.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

From an analytical model it was shown that for a given total amount of nitrogen in the canopy, there exists an optimal leaf area index (LAI), and therefore an optimal average leaf introgen content, at which canopy photosynthesis is maximal. If the LAI is increased above this optimum, increased light interception will not compensate for reduction in photosynthetic capacity of the canopy resulting from reduced leaf nitrogen contents. It was further derived from the model that the value of the optimal LAI increases with the photosynthetic nitrogen use efficiency (PNUE) and decreases with the canopy extinction coefficient for light (KL) and incident photon flux density (PFD) at the top of the canopy. These hypotheses were tested on dense stands of species with different photosynthetic modes and different architectures. A garden experiment was carried out with the C4monocot sorghum (Sorghum bicolor[L.] Moensch cv. Pioneer), the C3monocot rice (Oryza sativaL. cv. Araure 4), the C4dicot amaranth (Amaranthus cruentusL. cv. K113) and the C3dicot soybean (Glycine max[L.] Merr. cv. Williams) at two levels of nitrogen availability.The C4species had higher PNUEs than the C3species while the dicots formed stands with higher extinction coefficients for light and had lower PNUEs than the monocots. The C4and monocot species were found to have formed more leaf area per unit leaf nitrogen (i.e., had lower leaf nitrogen contents) than the C3and dicot species, respectively. These results indicate that the PNUE and the extinction coefficient for light are important factors determining the amount of leaf area produced per unit nitrogen as was predicted by the model.

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb05520.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Oleic acid is incorporated into an insoluble fraction left over after lipid extraction inScenedesmus acutus. This incorporation is extremely sensitive to the chloroacetamide herbicide, metazachlor (I50= ca 20 nM). Therefore, factors influencing the incorporation of radioactivity from oleic acid into this non‐lipid fraction were investigated.S. acutuscells were cultivated under various conditions with or without inhibitors and [14C]‐oleic acid was supplied to the algae; the lipids were extracted and the radioactivity incorporated in the remaining fraction monitored. The inhibition seemed specific for chloroacetamides and related classes since it was also observed with alachlor, dimethenamid and mefenacet (an oxyacetamide). In contrast, it could not be found with diuron, oryzalin, nor could it be observed with a non‐herbicidal metazachlor derivative or iodoacetamide. Incorporation of oleic acid into that fraction required meta‐bolically active cells and was stimulated by light. Other fatty acids (16:0, 18:2, and 18:3) were also incorporated into the non‐lipid fraction but their incorporation was not inhibited by metazachlor. Among other components, the fraction contains proteins. However, a possible specific effect of chloroacetamides on the binding of oleic acid to proteins or on the in vitro activity of lipid transfer proteins could not be detected. Not much is known yet about mechanism and chemistry of oleic acid incorporation but this finding opens a new path for investigations towards the primary target of these h

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb05521.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The intracellular location of sucrose‐phosphate phosphatase (SPP; EC 3.1, 3.24) was investigated by comparing the ratios of SPP to vacuolar and cytosolic markers in protoplasts and vacuoles from storage tissues of red beet (Beta vulgaris) and turnip (Brassica rapaL. var.rapa) hypocotyl, and carrot (Daucus carota) root. In all three instances, SPP activity was found not to be associated with vacuolar markers ß‐acetyl‐glucosaminidase and α‐mannosidase, but proportionally associated with the cytosolic marker alcohol dehydrogenase. It was determined that in storage cells of red beet and turnip hypocotyl, as well as in carrot root, SPP is located in the cytoplasm. Discrepancies with earlier reports indicating SPP of vacuolar origin are

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb05522.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

In conifers such as Norway spruce, the extent of shoot growth is predetermined by the size and number of embryonal organs of the buds laid down the previous year. As it is known that cytokinins have a key role in bud development a possible hypothesis is that the level of cytokinin in the buds during their formation determines their size and complexity. As a first step to test this hypothesis we compared cytokinin levels in buds of different size of annual shoots from 15‐ to 20‐year‐old trees ofPicea abies(L.) Karst. Apical buds from the leaders, and from branches in lower parts of the trees, were collected in April, July and August. The difference in size of the buds and the shoots growing from them was considerable in these three positions. Extracts were purified by immunoaffinity columns, and the retained compounds were separated by high‐performance liquid chromatography (HPLC). Quantification was made by enzyme‐linked immunosorbent assay (ELISA), and the accuracy of this method was checked by measurements with liquid chromatography‐mass spectrometry (LC‐MS) and UV absorption. Zeatin riboside (ZR) was the most abundant cytokinin, but isopentenyladenosine (iPA) was also present in all samples. The large apical bud of the leader contained much higher cytokinin concentrations than the considerably smaller buds from lower positions, and during the period of secondary growth in July, similar relationships were found for annual stem tissue from different positions. The possible role of ZR as a controlling factor in bud development and apical control is discussed. Our conclusion is that the level of zeatin‐type cytokinins appears to play an important role in the establishment of differences in bud size and, thereby, the architecture of

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb05523.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

The induction of the phenylpropanoid pathway and of tyramine metabolism was monitored in cell suspension cultures ofNicotiana tabacumtreated with cell wall‐degrading enzymes, in an attempt to correlate the synthesis of hydroxycinnamic acid amides of tyramine with the formation of wall‐bound phenolic polymers. Treatment with commercial pectinase (fromPenicilium occitanis) induced a rapid rise in phenylalanine ammonia‐lyase (EC 4.3.1.5), 4‐coumarate:CoA ligase (EC 6.2.1.12), tyramine hydroxycinnamoyltransferase (EC 2.3.1.110) and peroxidase (EC 1.11.1.7) activities, and a concomitant decline in cinnamyl alcohol dehydrogenase (EC 1.1.1.195) activity. The induction of the phenylpropanoid pathway and of the synthesis of cinnamoyl‐tyramines preceded the death of a large proportion of the elicited cells. When the cultures were treated with pronase (fromStreptomyces griseus), most cells remained alive and the induction of enzymes of the phenylpropanoid pathway lasted for several days, resulting in an accumulation of cinnamoyltyramines in the cells and in the culture medium. Treatment with pronase induced an increase in the activity of moderately anionic isoperoxidases which were also induced in pectinase‐treated cells. Cinnamyl alcohol dehydrogenase activity remained stable in pronase‐elicited cells, which rapidly accumulated thioglycolic acid‐extractable phenolic polymers in their cell walls. The accumulation of these polymers coincided with the induction of 4‐coumarate:CoA ligase but preceded the rise in tyramine hydroxycinnamoyltransferase and pero

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1995.tb05524.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY