Showing papers in "Planta in 1980"
TL;DR: Various aspects of the biochemistry of photosynthetic carbon assimilation in C3 plants are integrated into a form compatible with studies of gas exchange in leaves.
Abstract: Various aspects of the biochemistry of photosynthetic carbon assimilation in C3 plants are integrated into a form compatible with studies of gas exchange in leaves. These aspects include the kinetic properties of ribulose bisphosphate carboxylase-oxygenase; the requirements of the photosynthetic carbon reduction and photorespiratory carbon oxidation cycles for reduced pyridine nucleotides; the dependence of electron transport on photon flux and the presence of a temperature dependent upper limit to electron transport. The measurements of gas exchange with which the model outputs may be compared include those of the temperature and partial pressure of CO2(p(CO2)) dependencies of quantum yield, the variation of compensation point with temperature and partial pressure of O2(p(O2)), the dependence of net CO2 assimilation rate on p(CO2) and irradiance, and the influence of p(CO2) and irradiance on the temperature dependence of assimilation rate.
7,312 citations
TL;DR: Measurements of the kinetics of Cinorg transport indicate that the affinity of the transport mechanism for CInorg is similar in both high- and low-CO2-grown cells, however, Vmax is 10-fold higher in the latter case, and it is suggested that this higher Vmax for transport is the basis of the superior capability to accumulate Cinorge and the higher apparent photosynthetic affinity for external Cinborg in low- CO2- grown Anabaena.
Abstract: The apparent photosynthetic affinity of A. variabilis to CO2 is greatly affected by the CO2 concentration in the medium during growth. Halfmaximal rate of photosynthetic O2 evolution is achieved at 10 μM and 100 μM inorganic carbon (Cinorg) in cells grown at low-CO2 (air) and high CO2 (5% v/v CO2 in air), respectively, whilst the maximum rate of photosynthesis is similar in both cases. Both high- and low-CO2-grown Anabaena accumulate Cinorg within the cell; however, the rate of accumulation and the steady-state internal Cinorg concentration reached is much higher in low as compared with high-CO2-grown cells. It is suggested that Anabaena cells actively accumulate Cinorg. Measurements of the kinetics of Cinorg transport indicate that the affinity of the transport mechanism for Cinorg is similar (Km(Cinorg(≃150 μM) in both high- and low-CO2-grown cells. However, Vmax is 10-fold higher in the latter case. It is suggested that this higher Vmax for transport is the basis of the superior capability to accumulate Cinorg and the higher apparent photosynthetic affinity for external Cinorg in low-CO2-grown Anabaena. Carbonic anhydrase activity was not detectable in Anabaena, yet both photosynthetic affinity to Cinorg in the medium (but not Vmax) and the rate of accumulation of Cinorg were inhibited by the carbonic-anhydrase inhibitor ethoxyzolamide.
285 citations
TL;DR: It is suggested that turgor is the critical parameter of plant water relations which controls ABA production in water-stressed leaves and requires a lower water potential in order to accumulate ABA than did leaves from previously unstressed plants.
Abstract: Mature leaves of Phaseolus vulgaris L (red kidney bean), Xanthium strumarium L (cocklebur), and Gossypium hirsutum L (cotton) were used to study accumulation of abscisic acid (ABA) during water stress The water status of individual, detached leaves was monitored while the leaves slowly wilted, and samples were cut from the leaves as they lost water The leaf sections were incubated at their respecitive water contents to allow ABA to build up or not At least 8 h were required for a new steady-state level of ABA to be established The samples from any one leaf covered a range of known water potentials (ψ), osmotic pressures (π), and turgor pressures (p) The π and p values were calculated from “pressure-volume curves”, using a pressure bomb to measure the water potentials Decreasing water potential had little effect on ABA levels in leaves at high turgor Sensitivity of the production of ABA to changes in ψ progressively increased as turgor approached zero At p=1 bar, ABA content averaged 4 times the level found in fully turgid samples Below p=1 bar, ABA content increased sharply to as much as 40 times the level found in unstressed samples ABA levels rose steeply at different water potentials for different leaves, according to the ψ at which turgor became zero These differences were caused by the different osmotic pressures of the leaves that were used; ψ must cqual -π for turgor to be zero Leaves vary in π, not only among species, but also between plants of one and the same species depending on the growing conditions A difference of 6 bars (calculated at ψ=0) was found between the osmotic pressures of leaves from two groups of G hirsutum plants; one group had previously experienced periodic water stress, and the other group had never been stressed When individual leaves were subsequently wilted, the leaves from stress-conditioned plants required a lower water potential in order to accumulate ABA than did leaves from previously unstressed plants On the basis of these results we suggest that turgor is the critical parameter of plant water relations which controls ABA production in water-stressed leaves
259 citations
TL;DR: The amino-acid contents of chloroplasts prepared from leaves and from leaf protoplasts have been determined and γ-aminobutyric acid accumulates to high levels, while homoserine and glutamic acid decrease, during protoplast formation and breakage.
Abstract: A procedure is described for the rapid ( 240 nmol/mg chl), even thought it is proportionately lower in the chloroplast relative to the rest of the cell. The chloroplasts contain about 20% of many of the amino acids of the cell, but for individual amino acids the percentage in the chloroplast ranges from 8 to 40% of the cell total. Glutamic acid, glutamine and aspartic acid are enriched in the chloroplasts, while asparagine, homoserine and β-(isoxazolin-5-one-2-yl)-alanine are relatively lower. Leakage of amino acids from the chloroplast during preparation or repeated washing was ca. 20%. Some differences exist between the amino-acid composition of chloroplasts isolated from intact leaves and from protoplasts. In particular, γ-aminobutyric acid accumulates to high levels, while homoserine and glutamic acid decrease, during protoplast formation and breakage.
238 citations
TL;DR: Levels of free ABA, as determined by radioimmunoassay (RIA), correlated well with those reported in the literature and evidence was obtained for the presence of ABA conjugates other than the glucose ester in some plants.
Abstract: Two radioimmunoassays have been developed which allow the parallel quantitation of free as well as conjugated natural (+)-abscisic acid (ABA) directly and separately, in unpurified plant extracts. The differential specificity of antisera has been achieved by coupling ABA through C1 (for total ABA determination) or C4 (for free ABA determination), respectively, to proteins to obtain the immunogenic conjugates. Compounds structurally related to ABA, such as, dihydrophaseic acid or phaseic acid, do not interfere with either of the assays, even when present in more than ten-fold excess. Other related compounds, such as, violaxanthin or xanthoxin, do not cross react at all. Both antisera respond to (+)-ABA but show very low immunoreactivity with (-)-ABA. As little as 27 pg of ABA (serum for free ABA) or 47 pg (serum for total ABA) may be detected and the measuring ranges are from 0.2–8 and 0.2–30 pmol, respectively. Average recoveries are greater than 99%. Using these assays, more than 100 samples can be assayed for free and conjugated ABA per day. Levels of free ABA, as determined by radioimmunoassay (RIA), correlated well with those reported in the literature. Levels of conjugated ABA were found to be generally higher than previously reported for ABA after alkaline hydrolysis of the extracts. Conjugated ABA accumulates during aging of leaves and levels of conjugated ABA up to 17-fold higher than those of free ABA have been detected in senescent leaves of Hyoscyamus niger L. Evidence was obtained for the presence of ABA conjugates other than the glucose ester in some plants.
203 citations
TL;DR: Chlorophyll a formation seems to be a light-dependent step which is required for the stabilization of the LHCP and might be explained by the deficiency of chlorophyll in the red light-treated plants.
Abstract: The effect of light on the biosynthesis of the light-harvesting chlorophyll a/b protein (LHCP) is investigated in wild-type barley (Hordeum vulgare L.) and in the chlorophyll b-less mutant chlorina f2. In dark-grown plants a short red light pulse triggers the appearance of mRNA activity for the LHCP. While the accumulation of this mRNA is controlled by phytochrome (Apel (1979) Eur. J. Biochem. 97, 183–188), the red light treatment is not sufficient to induce the appearance of the LHCP within the membrane. Thus, at least one of the subsequent steps in the biosynthetic pathway leading to the assembly of the LHCP is controlled by light. The red light-induced mRNA is taken up into the polysomes during the subsequent dark period and is translated in vitro in a cell-free protein synthesizing system. However, an accumulation of the freshly synthesized polypeptide within the plant is not observed. The apparent instability of the polypeptide might be explained by the deficiency of chlorophyll in the red light-treated plants. In the chlorophyll b-less barley mutant chlorina f2 an accumulation of the freshly synthesized apoprotein of the LHCP can be observed in the light. Thus, chlorophyll a formation seems to be a light-dependent step which is required for the stabilization of the LHCP.
160 citations
TL;DR: A simple minimal medium which supports the growth of these haploid cells with a plating efficiency of 30–40%, independent of the cell density in the range of 1–4 to 3·104 cells ml-1, has been established.
Abstract: Preliminary attempts to define a completely synthetic medium able to support divisions of haploid tobacco mesophyll protoplasts at low initial densities have failed. High protoplast concentrations together with large amounts of naphtaleneacetic acid in the medium (3 mg l-1 NAA) were required for maximal induction of protoplast division. However, cell suspensions derived from haploid protoplasts after four days of preculture at high initial cell densities could be diluted to densities as low as 1–4 cells ml-1, provided the concentration of NAA in the medium was lowered to below 0.3 mg l-1. The optimal NAA supply for low cell density growth was affected by the nature of the nitrogen source. A simple minimal medium which supports the growth of these haploid cells with a plating efficiency of 30–40%, independent of the cell density in the range of 1–4 to 3·104 cells ml-1, has been established. In this medium inositol was the only vitamin stringently required for growth. Growth of cells at low densities was also possible in a medium initially containing 3 mg l-1 NAA, provided it was conditioned by the growth of protoplasts at high densities. Preliminary experiments with [14C]NAA showed that the amount of free NAA remaining in the medium after preincubation at high densities was drastically reduced. Simultaneously, NAA conjugates accumulated in the medium. The implications of these results are discussed.
155 citations
TL;DR: Using somatic hybrid cell lines Arabidopsis thaliana+Brassica campestris, obtained by cloning individual protoplast-fusion products as starting material, shoots and flowering plants have been regenerated, representing the first case of intergeneric-intertribal hybridization of flowering plants.
Abstract: Using somatic hybrid cell lines Arabidopsis thaliana+Brassica campestris, obtained by cloning individual protoplast-fusion products as starting material, shoots and flowering plants have been regenerated. Cytological, biochemical, and morphological analyses indicate that genetic material of both species is present in the resultant plants. Shoots and plants obtained from different lines and different regeneration events differed morphologically and genetically. Most regenerants show morphological abnormalities and unusual organizational patterns. Flowering forms have so far been sterile. "Asymmetric" hybrids (i.e., hybrids bearing most genetic material of one of the parent species and only few chromosomes of the other) were more regular in morphology. The results represent the first case of intergeneric-intertribal hybridization of flowering plants.
152 citations
TL;DR: The activity of a range of endo- and exopeptidase enzymes have been measured in the glumes, flag leaf and stem during the period of grain development in wheat and show a sequential pattern of appearance with activity peaks occurring at a number of intervals from anthesis until just prior to the cessation of grain growth.
Abstract: The activity of a range of endo- and exopeptidase enzymes have been measured in the glumes, flag leaf and stem during the period of grain development in wheat. The enzymes show a sequential pattern of appearance with activity peaks occurring at a number of intervals from anthesis until just prior to the cessation of grain growth. Of the enzymes studied only the haemoglobin- and casein-degrading activity and alanylglycine-dipeptidase activity increased during the period of rapid protein loss, while aminopeptidase, carboxypeptidase and leucyltyrosine dipeptidase reached maximum activity prior to this period.
138 citations
TL;DR: It was found that development of the phloem commenced before that of the xylem, and it was proposed thatphloem is formed in response to auxin, whilexylem is formedIn response to Auxin together with some added factor which reaches it from the Phloem.
Abstract: The differentiation of sieve and tracheary elements was studied in callus culture of Daucus carota L., Syringa vulgaris L., Glycine max (L.) Merr., Helianthus annuus L., Hibiscus cannabinus L. and Pisum sativum L. By the lacmoid clearing technique it was found that development of the phloem commenced before that of the xylem. In not one of the calluses was differentiation of tracheary elements observed in the absence of sieve elements. The influence of indole-3-acetic acid (IAA) and sucrose was evaluated quantitatively in callus of Syringa, Daucus and Glycine. Low IAA levels resulted in the differentiation of sieve elements with no tracheary cells. High levels resulted in that of both phloem and xylem. IAA thus controlled the number of sieve and tracheary elements, increase in auxin concentration boosting the number of both cell types. Changes in sucrose concentration, while the IAA concentration was kept constant, did not have a specific effect on either sieve element differentiation, or on the ratio between phloem and xylem. Sucrose did, however, affect the quantity of callose deposited on the sieve plates, because increase in the sucrose concentration resulted in an increase in the amount of callose. It is proposed that phloem is formed in response to auxin, while xylem is formed in response to auxin together with some added factor which reaches it from the phloem.
133 citations
TL;DR: Observations are discussed in relation to the fact that Helianthus, as an “iron efficient” plant, responds physiologically to iron deficiency by extrusion of H+, production of reducing substances, and a steep increase in the uptake efficiency of Fe.
Abstract: Helianthus annuus L. responds to iron deficiency by forming a thickened cortex and abundant root hairs in a zone near the root apex that corresponds to the primary developmental stage. Cytological investigations revealed that within 24 to 48 h of iron deficiency most of the peripheral cells differentiate into transfer cells. The wall labyrinth is always situated on the peripheral walls that face the external medium. The cytoplasm of these cells is characterized by numerous mitochondria, extensive rough endoplasmic reticulum, and large leucoplasts containing protein bodies. These observations are discussed in relation to the fact that Helianthus, as an “iron efficient” plant, responds physiologically to iron deficiency by extrusion of H+, production of reducing substances, and a steep increase in the uptake efficiency of Fe.
TL;DR: The effects of hyper- and hypo-saline stresses on the levels of various inorganic and organic solutes in Ulva lactuca have been recorded and the possibility that tertiary sulphonium dipolar ions have an analogous role in some algae to glycinebetaine and possibly other quaternary nitrogen compounds in higher plants as cytoplasmic osmotica is discussed briefly.
Abstract: The effects of hyper- and hypo-saline stresses on the levels of various inorganic and organic solutes inUlva lactuca have been recorded. Hypoosmotic stress decreased the tissue concentration of K+, Na+ and Cl- while hyper-osmotic stress caused a transient increase in Na+ and a stable accumulation of K+ and Cl-. The tissue content of β-dimethylsulphoniopropionate (β-dimethylpropiothetin) responded to changes in salinity. The time course of hypersaline stress showed the β-dimethylsulophoniopropionate concentration rose as the Na+ level fell. The levels of free sugars and amino acids, including proline, were relatively low in this alga and did not appear to be important in osmotic adjustment. The possibility that tertiary sulphonium dipolar ions have an analogous role in some algae to glycinebetaine and possibly other quaternary nitrogen compounds in higher plants as cytoplasmic osmotica is discussed briefly.
TL;DR: The flag leaf of wheat was examined for changes in quantity and activity of ribulose-bisphosphate carboxylase, in the proteolytic degradation of RuBPCase and other native proteins, and in the ultrastructure of the leaf cells during grain development.
Abstract: The flag leaf of wheat was examined for changes in quantity and activity of ribulose-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39), in the proteolytic degradation of RuBPCase and other native proteins, and in the ultrastructure of the leaf cells during grain development. Proteolytic degradation of RuBPCase at pH 4.8 increased until 8-10 d after anthesis, then declined, and increased again 16-18 d after anthesis. The second peak coincided with the onset of a preferential loss of immunologically recognizable RuBPCase. The specific activity and number of active sites per molecule of RuBPCase did not change during senescence. Examination of ultrastructure with the electron microscope showed little change in the appearance of the mitochondria as the flag leaf aged. Prominent cristae were still evident 35 d after anthesis. In contrast, the chloroplasts showed a progressive disruption of the thylakoid structure and an increasing number of osmiophilic glubules. The double membrane envelope surrounding the chloroplast appeared intact until at least 20 d after anthesis. The tonoplast also appeared intact up to 20 d. At later stages of senescence of the leaf the outer membrane of the chloroplast adjacent to the tonoplast appeared to break but the inner membrane of the envelope appeared intact until at least 35 d after anthesis.
TL;DR: Three peroxidase isoenzyme-groups found in cell walls of tobacco were tested for their capacity to form H2O2 and Isoenzyme-group GI showed the highest Kapp-value, i.e., maximal H1O2-formation was received for group GIII which is ionically bound to the cell wall, while GI yields maximal polymerization rates for coniferyl- and p-coumarylalcohol.
Abstract: Three peroxidase isoenzyme-groups found in cell walls of tobacco were tested for their capacity to form H2O2. Isoenzyme-group GI, located only in cell walls (GII and GIII are also found in protoplasts) showed the highest Kapp-value for H2O2-formation. The lowest Kapp-value, i.e., maximal H2O2-formation was received for group GIII which is ionically bound to the cell wall. As shown before, GI yields maximal polymerization rates for coniferyl- and p-coumarylalcohol. These facts indicate that each of the peroxidase isoenzyme groups of the cell wall is involved with different catalytic functions within the same pathways of H2O2-formation and succeeding lignification. H2O2-formation catalyzed by all 3 groups was increased by very low concentrations of Mn2+-ions. The required amount of Mn2+ leading to maximal stimulation was in each case dependent on the basic rate of H2O2-formation. Maximal stimulation of H2O2-formation by phenolic compounds was achieved by coniferylalcohol at a concentration of 10-4M for all groups. Stimulation by p-coumaryl-and by sinapylalcohol was not as significant.
TL;DR: The observations are best explained by a model in which hooped bundles of microtubules—which are directly or indirectly associated with molecules involved with cellulose biosynthesis at the cell surface—act as an essential template or scaffolding for the orientated deposition of cellulose.
Abstract: Indirect immunofluorescence has been used to study the function of cytoplasmic microtubules in controlling the shape of elongated carrot cells in culture. Using a purified wall-degrading preparation, the elongated cells are converted to spherical protoplasts and the transverse hoops of bundled microtubules are disorganised but not depolymerised in the process. Since microtubules remain attached to fragments of protoplast membrane adhering to coverslips and are still seen to be organised laterally in bundles, it would appear that re-orientation of the transverse bundles is due to loss of cell wall and not to the cleavage of microtubule bridges. After 24 h treatment in 10-3 M colchicine, microtubules are depolymerised in elongated cells but, at this time, the cells retain their elongated shape. This suggests that wall which was organised in the presence of transverse microtubule bundles can retain asymmetric shape for short periods in the absence of those tubules. However, after longer periods of time the cells become spherical in colchicine. Neither wall nor tubules therefore exert individual control on continued cellular elongation and so we emphasize the fundamental nature of wall/microtubule interactions in shape control. It is concluded that the observations are best explained by a model in which hooped bundles of microtubules—which are directly or indirectly associated with molecules involved with cellulose biosynthesis at the cell surface—act as an essential template or scaffolding for the orientated deposition of cellulose.
TL;DR: Radioimmunoassays for the quantitation of trans-zeatin and related cytokinins have been developed and, due to the high specificity of this assay, crude extracts may be used for analysis.
Abstract: Radioimmunoassays for the quantitation of trans-zeatin and related cytokinins have been developed. Antisera produced against bovine serum albumin conjugates of trans-zeatinriboside have a high affinity (Ka=2.4.10-11 M) for zeatinriboside and for zeatin, but show a negligible cross reaction to isopentenyladenosine (0.1%) and cis-zeatinriboside (0.4%), only a slight cross reaction to dihydrozeatin (1.7%), and no cross reaction at all to other purines, such as adenosine and related, compounds, was observed. The assays are sensitive and measuring ranges extend from 0.06–30 pmol (0.02–10 ng) of zeatinriboside. This has been achieved by employing as tracers immunoreactive zeatin derivatives with high-specific activity, (tritiated zeatinriboside-dialcohol: 8.37.1011 Bq mmol-1 and zeatinribosyl-[125I]tyramine: ca. 1.9.1013 Bq mmol-1. The detection limit is 40 fmol (15pg) for the assay employing the tritiated tracer, and assay reproducibility is high (variation coefficients of triplicates less than 5%). Several hundred assays can be completed in one day, and, due to the high specificity of this assay, crude extracts may be used for analysis. The course of zeatin levels in developing fruits of Lycopersicon esculentum cv. Moneymaker is given.
TL;DR: The increase in extension rate induced by supplementary FR is reversed by an increase in the fluence rate of red light (R), which indicates that the response is controlled by phytochrome photoequilibrium.
Abstract: Treatment of the whole of aSinapis alba plant with supplementary far-red light (FR), in back-ground white light (WL), induces a rapid increase in stem extension rate. This rapid increase is regulated by the light environment of the stem itself. Supplementary FR to the stem increases extension rate after a lag period of 10–15 min. A lag period of 3–4 h follows FR irradiation of the leaf, before an increase in extension rate is detectable. When the stem is given supplementary FR, the change in extension rate which is induced increases with increasing FR fluence rate, and with decreasing phytochrome photoequilibrium. There is no difference between the effects of supplementary FR λmax 719 nm and supplementary FR λmax 739 nm for these relationships. The increase in extension rate induced by supplementary FR is reversed by an increase in the fluence rate of red light (R). These data indicate that the response is controlled by phytochrome photoequilibrium.
TL;DR: The interrelationship between the peripheral cytoplasm and the nucleus and the role of microtubules in maintaining and reestablishing cell polarity are discussed.
Abstract: In the caulonema tip cells of Funaria hygrometrica, chloroplasts, mitochondria, and dictyosomes have differences in structure which are determined by cell polarity. In contrast to the slowly growing chloronema tip cells the apical cell of the caulonema contains a tip body. Colchicine stops tip growth; it causes the formation of subapical cell protrusions, redistribution of the plastids, and a loss of their polar differentiation. Cytochalasin B inhibits growth and affects the position of cell organelles. After treatment with ionophore A23 187, growth is slower and shorter and wider cells are formed. D2O causes a transient reversion of organelle distribution but premitotic nuclei are not dislocated. In some tip cells the reversion of polarity persists; they continue to grow with a new tip at their base. During centrifugation, colchicine has only a slight influence on the stability of organelle anchorage. The former polar organization of most cells is restored within a few hours after centrifugation, and the cells resume normal growth. In premitotic cells the nucleus and other organelles cannot be retransported, they often continue to grow with reversed polarity. Colchicine retards the redistribution of organelles generally and increases the number of cells that form a basal outgrowth. The interrelationship between the peripheral cytoplasm and the nucleus and the role of microtubules in maintaining and reestablishing cell polarity are discussed.
TL;DR: Evidence is presented to show that legumin, the major storage protein in Pisum, is synthesised in vitro by the wheat germ and reticulocyte lysate systems, from polyribosomes and mRNA isolated from developing pea seeds.
Abstract: Polypeptide material has been immunoprecipitated by antivicilin antibodies from translation products of polyribosomes and poly(A)-rich RNA isolated from developing seeds of Pisum sativum in the wheat germ and reticulocyte lysate cell-free synthesis systems. Analysis of this material by SDS-PAGE shows it to consist of three bands, of molecular weights 70,000, 50,000 and 47,000. The in vitro vicilin polypeptides of 70,000 and 50,000 mol. wt. have been shown to be very similar to the 70,000 and 50,000 mol. wt. subunits of vicilin by specific immunoprecipitation, and behaviour on treatment with cyanogen bromide and trypsin. The 50,000 mol. wt. in vitro vicilin polypeptide contains no significant extra sequence compared to the 50,000 mol. wt. vicilin subunit. The 47,000 mol. wt. in vitro vicilin polypeptide has no corresponding subunit in vicilin from mature seeds, but a 47,000 mol. wt. subunit is present in vicilin isolated from developing seeds. Comparison of translation products from polysomes isolated from seeds at middle and late stages of development shows that synthesis of the 50,000 and 47,000 mol. wt., but not 70,000 mol. wt. polypeptides is very much reduced at late stages of development. These results are discussed with reference to the nature of the vicilin fraction.
TL;DR: In the intact attached root and calculated on a protein basis NR, GOGAT, and GS are found to have slightly higher specific activities in the apical 5 mm than in more mature regions of theRoot ofea mays L. GDH and AS, on the other hand, are much more active in extracts prepared from mature areas of the root than in theApical region.
Abstract: The enzymes nitrate reductase (NR), glutamate dehydrogenase (GDH), glutamate synthase (GOGAT), glutamine synthetase (GS) and asparagine synthetase (AS) have been assayed in various regions along the seedling root ofZea mays L. In the intact attached root and calculated on a protein basis NR, GOGAT, and GS are found to have slightly higher specific activities in the apical 5 mm than in more mature regions of the root. GDH and AS, on the other hand, are much more active in extracts prepared from mature regions of the root than in the apical region. In excised root tips incubated in the presence of NH4 (+) and NO3 (-) there was a marked increase in GDH and AS, and a slight decrease in GOGAT and GS. Additions of NO3 (-) are required for NR activity but neither NO3 (-) nor NH4 (+) additions altered the activity levels of the other four enzymes. Additions of glucose to the medium inhibited the development of AS and GDH activities and resulted in higher activity levels of NR, GS and GOGAT. Glucose additions also enhanced the incorporation of acetate-(14)C and leucine-(14)C into protein. Additions of cycloheximide inhibit the development of NR, AS and GDH activities and also the incorporation of acetate-(14)C and leucine into protein.
TL;DR: Two analogs of DCB, 2-chloro-6-fluorobenzonitrile and 2,6-dichlorobenzene carbothiamide, were as specific and nearly as effective as DCB with respect to their effects on cellulose synthesis.
Abstract: Several compounds were tested for their ability to inhibit the in-vivo synthesis of cellulose and other cell-wall polysaccharides in fibers of cotton (Gossypium hirsutum L.) developing on in-vitro cultured ovules. Inhibitory effects were measured by the ability of the compounds to inhibit the incorporation of radioactivity from [U-14C]glucose into these cell-wall polymers. Of the compounds surveyed, 2,6-dichlorobenzonitrile (DCB) was the most effective and specific one for its effects on cellulose synthesis when compared to its effect on the synthesis of other cell-wall components. At 10 μM DCB caused 80% inhibition of cellulose synthesis, and the effect was reversed upon removal of the DCB, with recovery to 90% of the control rate. Two analogs of DCB, 2-chloro-6-fluorobenzonitrile and 2,6-dichlorobenzene carbothiamide, were as specific and nearly as effective as DCB with respect to their effects on cellulose synthesis. Coumarin, generally regarded as an inhibitor of cellulose synthesis in other plant systems, was effective in cotton fibers in millimolar concentrations and, like DCB, was relatively specific with regard to its effect on cellulose synthesis. DCB and coumarin inhibited the synthesis of both primary and secondary wall cellulose. Bacitracin, an inhibitor of the cycling of phosphorylated polyprenols involved in cell-wall synthesis in bacteria, and ethylenediaminetetracetic acid (EDTA) and ethyleneglycol-bis-(β-amino-ethylether)-N,N′-tetracetic acid (EGTA), chelators of civalent cations, were also effective, although only at relatively high concentrations, in inhibiting incorporation of radioactivity into cellulose.
TL;DR: Evidence is presented which shows that this photorespiratory N cycle in Chlamydomonas derives its N from protein rather than from freshly synthesised glutamate, suggesting that previous estimates of the amount of N recycled in photorespiration may have been too high.
Abstract: Work demonstrating the operation of a photorespiratory N cycle in Chlamydomonas is described. NH3 release by this process is light dependent, sensitive to changes in pO2 and pCO2, and abolished by a photosystem II inhibitor. Evidence is presented which shows that this NH3 derives its N from protein rather than from freshly synthesised glutamate. Protein turnover is shown to provide amino-N at a rate sufficient to account for the highest photorespiratory N excretion observed suggesting that changes in excretion can be accounted for by increased catabolism of normally recirculating amino acids. It is equally possible however that a direct link between photorespiration and protein turnover exists, increased NH3 excretion resulting from enhanced protein turnover. The data suggest that if similar mechanisms operate in higher plants, previous estimates of the amount of N recycled in photorespiration may have been too high.
TL;DR: The results indicate that the Mg2+-dependent, KCl-stimulated ATPase activity is not exclusively associated with vacuoles and may be different enzymes.
Abstract: Phosphatase activities were measured in preparations of vacuoles isolated from storage roots of red beet (Beta vulgaris L.). The vacuoles possessed both acid phosphatase and ATPase activities which could be distinguished by their susceptibility to inhibition by low concentrations of ammonium molybdate [(NH4)6Mo7O24·4H2O]. The acid phosphatase was completely inhibited by 100 μM ammonium molybdate but the ATPase was unaffected. The acid phosphatase was a soluble enzyme which hydrolysed a large number of phosphate esters and had a pH optimum of 5.5. In contrast, the ATPase was partially membrane-bound, had a pH optimum of 8.0 and hydrolysed ATP preferentially, although it was also active agianst PPi, GTP and GDP. At pH 8.0 both the ATPase and PPase activities were Mg2+-dependent and were further stimulated by KCl. The ATPase and PPase activities at pH 8.0 may be different enzymes. The recovery and purification of the ATPase during vacuole isolation were determined. The results indicate that the Mg2+-dependent, KCl-stimulated ATPase activity is not exclusively associated with vacuoles.
TL;DR: It was found that the rearrangement of the cortical MTs to approximate a series of concentric circles on the residual meristem occurred before the emergence of leaf primordia, indicating a coordinated reorientation of the two structures.
Abstract: In the “regeneration” of a shoot from a leaf of the succulent, Graptopetalum paraguayense E. Walther the first new organs are leaf primordia. The original arrangement of cellulose microfibrils and of microtubules (MTs) in the epidermis of the leaf-forming site is one of parallel, straight lines. In the new primordium both structures still have a congruent arrangement but it is roughly in the form of concentric circles that surround the new cylindrical organ. The regions which undergo the greatest shift in orientation (90°) were studied in detail. Departures from the original cellulose alignment are detected in changes in the polarized-light image. Departures from the original cortical MT arrangement are detected using electron microscopy. The over-all reorganization of the MT pattern is followed by the tally of MT profiles, the various regions being studied in two perpendicular planes of section. This corrects for the difference in efficiency in counting transverse versus longitudinal profiles of MTs. Reorientation takes place sporadically, cell by cell, for both the cellulose microfibrils and the MTs, indicating a coordinated reorientation of the two structures. That MTs and cellulose microfibrils reorient jointly in individual cells was shown by reconstruction of the arrays of cortical MTs in paradermal sections of individual cells whose recent change in the orientation of cellulose deposition had been detected with polarized light. Closeness of the two alignments was also indicated by images where the MT and microfibril alignments co-varied within a single cell. The change-over in alignment of the MTs appears to involve stages where arrays of contrasting orientation co-exist to give a criss-cross image. During this critical reorganization, the frequency of the MTs is high. It falls during subsequent enlargement of the organ. It was found that the rearrangement of the cortical MTs to approximate a series of concentric circles on the residual meristem occurred before the emergence of leaf primordia. Through their apparent influence on microfibril alignments, the changes in MT disposition, described here, have the potential to generate major biophysical changes that accompany organogenesis.
TL;DR: The rise in ethylene production accompanying the respiration climacteric and senescence of cut carnation flowers was associated with a 30-fold increase in the concentration of 1-aminocyclopropane-1-carboxylic acid in the petals, and addition of aminoxyacetic acid to the solution in which the flowers were kept completely inhibited accumulation of ACC in all flower parts.
Abstract: The rise in ethylene production accompanying the respiration climacteric and senescence of cut carnation flowers (Dianthus caryophyllus L. cv. White Sim) was associated with a 30-fold increase in the concentration of 1-aminocyclopropane-1-carboxylic acid (ACC) in the petals (initial content 0.3 nmol/g fresh weight). Pretreatment of the flowers with silver thiosulfate (STS) retarded flower senescence and prevented the increase in ACC concentration in the petals. An increase in ACC in the remaining flower parts, which appeared to precede the increase in the petals, was only partially prevented by the STS pretreatment. Addition of aminoxyacetic acid (2 mM) to the solution in which the flowers were kept completely inhibited accumulation of ACC in all flower parts.
TL;DR: Evidence including the stability of resistance in the cultures, the resistance of cultures initiated from regenerated plants, the altered feedback regulation, and the increased free amino acids, indicates a mutational origin for these traits in line D33.
Abstract: Tissue culture selection techniques were used to isolate a maize (Zea mays L.) variant D33, in which the aspartate family pathway was less sensitive to feedback inhibition by lysine. D33 was recovered by successively subculturing cultures originally derived from immature embryos on MS medium containing growth-inhibitory levels of lysine+threonine. The ability of D33 to grow vigorously on lysine+ threonine medium was retained after growth for 12 months on nonselection medium. New cultures initiated from shoot tissues of plants regenerated from D33 also were resistant to lysine+threonine inhibition. The Ki of aspartokinase for its feedback inhibitor, lysine, was about 9-fold higher in D33 than for the enzyme from unselected cultures. The free pools of lysine, threonine, isoleucine and methionine were increased 2–9-fold in D33 cultures. This was consistent with the observed change in feedback regulation of aspartokinase, the first enzyme common to the biosynthesis of these amino acids in the aspartate pathway. The accumulated evidence including the stability of resistance in the cultures, the resistance of cultures initiated from regenerated plants, the altered feedback regulation, and the increased free amino acids, indicates a mutational origin for these traits in line D33.
TL;DR: The results indicate that the changes in the ability of cells to accumulate anthocyanin involve no qualitative change in the genetic information of the cells, i.e., the changes are not the consequence of mutations.
Abstract: The accumulation of anthocyanin by clones and subclones from a cell suspension culture of wild carrot (Daucus carota L) has been measured under standard conditions Clones which accumulate low amounts of anthocyanin were shown, by recloning after maintenance by serial passage, to have become heterogenous and to contain cells with increased accumulation of anthocyanin There appears to be a maximum amount of anthocyanin that clones can accumulate Clones which accumulate the maximum amount of anthocyanin were shown by recloning after maintenance by serial passaging, to have become heterogenous and to contain many cells which accumulate less than the maximum possible amount of anthocyanin When clones which accumulate the maximum amount of anthocyanin are maintained by serial passage, the decline in anthocyanin accumulation is different in different media The results indicate that the changes in the ability of cells to accumulate anthocyanin involve no qualitative change in the genetic information of the cells, ie, the changes are not the consequence of mutations
TL;DR: Intactness and the oxidative and phosphorylative properties of the mitochondria remained unchanged during this time period and Na+ and Mg2+ do not induce Ca2+ release from mitochondria.
Abstract: Mitochondria from etiolated corn possess a much greater Ca2+ uptake capacity per mg protein than microsomes from the same source. Differences in energy requirements, sensitivity to specific inhibitors, and sedimentation properties enabled us to study both Ca2+ uptake mechanisms without mutual contamination. The microsomal Ca2+ uptake does not vary much among different plants as compared to the mitochondrial Ca2+ uptake; this is also true for different organs of the same plant. Mitochondrial Ca2+ uptake is more dependent on the age of the seedlings than microsomal uptake, because of changes in active Ca2+ uptake activity rather than of changes in efflux. Intactness and the oxidative and phosphorylative properties of the mitochondria remained unchanged during this time period. Na+ and Mg2+ do not induce Ca2+ release from mitochondria.
TL;DR: The increase in K+ levels in the phloem in darkness is interpreted as an osmoregulatory response to conditions of restricted solute availability, and can be explained on the basis of the sucrose-H+ co-transport mechanism ofphloem loading.
Abstract: Phloem-sap composition was studied in plants of Ricinus communis L. grown on a waterculture medium. The sap possessed a relatively high K+:Na+ ratio and low levels of Ca2+ and free H+. Sucrose and K+ (together with its associated anions) accounted for 75% of the phloem-sap solute potential (Ψs). In plants kept in continuous darkness, a decrease in phloem-sap sucrose levels over 24h was accompanied by an increase in K+ levels. Measurements of phloem-sap Ψs and xylem water potential (Ψ) indicated that this resulted in a partial maintenance of phloem turgor pressure Ψp. In darkness there was also a marked decrease in the malate content of the leaf tissue, and it is possible that organic carbon from this source was mobilized for export in the phloem. The results support the concept of the phloem sap as a symplastic phase. We interpret the increase in K+ levels in the phloem in darkness as an osmoregulatory response to conditions of restricted solute availability. This reponse can be explained on the basis of the sucrose-H+ co-transport mechanism of phloem loading.
TL;DR: The results suggest that gibberellins and ABA may exert a major regulatory control in natural fruit-set and Peas can be used for the assay of fructigenic activity.
Abstract: The development of parthenocarpic fruits of Pisum sativum L. cv. Alaska was induced by the application of different plant-growth regulators in aqueous solution to the emasculated ovaries in untopped plants. At least one compound in each of the groups of auxins (2,4-dichlorophenoxyacetic acid), cytokinins (benzyladenine), and gibberellins (gibberellic acid) was found active. Gibberellic acid (GA3), however, was the only substance which produced pods similar to those of fruits with seeds. The length of the pods obtained by GA3 was a linear function of the logarithm of the concentration of GA3 in the solution. The effect of GA3 (at a concentration which produced 50% of the maximum pod length) was enhanced by a simultaneous application of 2,4-dichlorophenoxyacetic acid. Abscisic acid (ABA) counteracted the effect of GA3 and of topping. The results suggest that gibberellins and ABA may exert a major regulatory control in natural fruit-set. Peas can be used for the assay of fructigenic activity and is an advantageous material for the study of the mode of action of gibberellins on fruit-set.