Sugar-Starvation-Induced Changes of Carbon Metabolism in Excised Maize Root Tips

Excised maize (Zea mays L.) root tips were used to study the early metabolic effects of glucose (Glc) starvation. Root tips were prelabeled with [1-13C]Glc so that carbohydrates and metabolic intermediates were close to steady-state labeling, but lipids and proteins were scarcely labeled. They were then incubated in a sugar-deprived medium for carbon starvation. Changes in the level of soluble sugars, the respiratory quotient, and the 13C enrichment of intermediates, as measured by 13C and 1H nuclear magnetic resonance, were studied to detect changes in carbon fluxes through glycolysis and the tricarboxylic acid cycle. Labeling of glutamate carbons revealed two major changes in carbon input into the tricarboxylic acid cycle: (a) the phosphoenolpyruvate carboxylase flux stopped early after the start of Glc starvation, and (b) the contribution of glycolysis as the source of acetyl-coenzyme A for respiration decreased progressively, indicating an increasing contribution of the catabolism of protein amino acids, fatty acids, or both. The enrichment of glutamate carbons gave no evidence for proteolysis in the early steps of starvation, indicating that the catabolism of proteins was delayed compared with that of fatty acids. Labeling of carbohydrates showed that sucrose turnover continues during sugar starvation, but gave no indication for any significant flux through gluconeogenesis.     

Intracellular Levels of Cyclic Nucleotides during Cell Enlargement and Cell Division in Excised Tobacco Pith Tissues

Two lines of evidence, one of which is based on the radioimmunoassay and the other on adenosine 3', 5'-cyclic monophosphate (cyclic AMP)-dependent histone phosphorylation, are presented to demonstrate the presence of cyclic AMP in excised tissues of higher plant species. Intracellular levels of this cyclic nucleotide appear to be determined by auxin and a positive correlation has been found to exist between cell enlargement and chromosomal DNA replication, both auxin-dependent processes, and the level of cyclic AMP in tobacco pith cells. Intracellular guanosine 3', 5'-cyclic monophosphate (cyclic GMP) levels, while measurable, did not appear to be affected by either auxin or kinetin, or both, during the cell enlargement or cell division phases of the cell cycle in the tobacco pith system.     

Changes in Respiratory Metabolism during Callus Growth and Adventitious Root Formation in Jerusalem Artichoke Tuber Tissues

The CN-resistant alternative oxidase pathway was examined inrelation to the formation of callus and adventitious roots ofJerusalem artichoke tuber tissues. During the early stage ofincubation at 28?C, respiration was significantly activatedand the O₂-uptake rate via the Cyt pathway increased 2.5–2.6times by the second day of culture regardless of the presenceof 2,4-D. However, further increases and preservation of highlevels of Cyt pathway activities were observed only in the callusformingtissues. The capacity of the alternative pathway also increased,but the actually operating fraction was very small (0–4%of total respiration). On the other hand, during the later stagesof culture in which adventitious roots emerged from the callus,activation of the alternative pathway was observed. These resultssuggested that the alternative pathway was not involved in callusgrowth but was related to root formation in callus tissues ofJerusalem artichoke tubers. (Received October 29, 1986; Accepted April 20, 1987)     

Hormonal Control of Nuclease Level in Excised Avena Leaf Tissues1

In excised Avena leaves, kinetin and benzyladenine decreased,while abscisic acid and benzimidazole increased the over-allnuclease level. Significant effects were observed as early as2 h after treatment. Not all the nucleases of the Avena leafwere affected by the growth regulators. Changes in over-allnuclease activity were accounted for almost entirely by changesin the amount of a relatively purine-specific endo-ribonuclease,which produces 2',3'-cyclic phosphates as breakdown products.Slight changes induced by the growth regulators were also detectedin the amount of a sugar non-specific endo-nuclease which produces5'-nucleotides and has a relative specificity for adenylic acid.The level of an alkaline phosphodiesterase, an exo-nucleasewhich produces 5'-nucleotides, was not affected by any of thegrowth regulators tested. Gibberellic acid and indol-3yl-aceticacid did not influence the level of Avena nucleases.     

Structural Changes and Aluminium Distribution in Maize Root Tissues

Growth and structural responses of primary roots of Zea mays L. to aluminium chloride were studied. The treatment of seedlings with 50 μM AlCl₃ resulted in high accumulation of Al, partial inhibition of root growth, occurrence of surface lesions in peripheral tissues, root thickening caused by expansion of inner cortical cells, reduced root cap length, extensive vacuolation, cell distortion, and increased synthesis of callose within 24 h. This revised version was published online in July 2006 with corrections to the Cover Date.     

Root Growth Activity of Barban in Relation to Auxin and Other Growth Factors

The effect of barban (4-Cl-2-butynyl-N-3-Cl-phenylcarbamate) on the growth of roots of wheat seedlings has been studied. In concentrations of 10^?7 to 5 · 10^?7M barban causes rapid inhibitions of cytokineses and cell elongation, the effects of which are spontaneously reversible. The reversion of the meristem inhibition is enhanced by thymidylic acid and indole-3-acetic acid (IAA). Initiation of cell elongation is slowed down or ceases during cytostasis; its reversal, on the other hand, is promoted by IAA and kinetin but inhibited by Fe. The final cell elongation attained is strongly reduced by barban and reversed under transient aberrant elongation. This inhibition and the recovery appear both to be additive to cell elongation actions of auxin and antiauxin but reversed by nucleic acid components. The inhibition of elongation is increased by Fe. The following explanation for this phenomenon is suggested: the primary effect of barban is known to be the blocking of metaphases under anaesthesis; this blocking then leads to reduced activation of IAA, kinetin and other metabolites. Auxin is required for cell divisions and initiation of elongation: the apical root growth equals in this respect that of shoot apices and lateral meristems. Initiation of cell elongation is closely dependent upon metabolites produced in dividing meristematic cells, whereas the limitation of cell stretching is independent of the meristem activity. No explanation is offered for the role of Fe.     

Absence of a Causal Relationship between Auxin-Induced Growth and Changes in the Content of Ascorbic and Dehydroascorbic Acids in Excised Plant Tissues

The data reported indicate that the oxidation-reduction balance of the ascorbic acid system is not causally related to the auxin-regulation of cell elongation. There was no shift in the ascorbic acid (AA) to dehydroascorbic acid (DHA) ratio with growth-promoting concentration of auxin in several plant tissues. The AA to DHA ratio was experimentally increased without altering the growth rate. Inhibition of growth by supra-optimal auxin was associated with a decrease in the AA to DHA ratio. Since the AA to DHA ratio was lowered by EDTA treatment without altering growth, it seems unlikely that the decrease in the AA to DHA ratio related to the inhibition of growth by high levels of auxin.     

Cortical Cell Fluxes of Phosphate in Excised Root Segments of Allium cepa L.

Compartmental analysis was used to study content and transmembranefluxes of phosphate in excised root segments in a nutrient solutioncontaining 1.0 mol phosphate m^–3, at pH 5.6. The resultingradioactivity content versus time curve deviated from the criteriadetermining a relationship conforming to first order kinetics,since the final rate constant was an order of magnitude lowerthan that exhibited by the curve for efflux versus time. Thedata were manipulated so as to bring about conformation to theappropriate criteria, revealing a large, slowly exchanging poolthat is considered to represent assimilated phosphate or storedpolyphosphate. Subsequent calculations, using the modified data,suggested that H₂PO₄ was absorbed by a phosphate pump at theplasmalemma, but was actively extruded from the vacuole afterpassive entry. The consequences of pH effects in the cell wall,cytoplasm and vacuole in determining the concentration of H₂PO^–₄in each phase are discussed. Key words: Phosphate compartmentation, pH, efflux     

Transformation of Nicotine to Nornicotine in Excised Tobacco Root Culture

Two kinds of fluorescent compounds were isolated in crystalline forms, by silica gel column chromatography, from Japanese chestnuts stored in cold. They had bluish violet and greenish blue fluorescence, and were identified as 6, 7-dimethoxycoumarin and scopoletin, respectively.     

Cowpea Root Rot Severity and Metabolic Changes in Relation to Manganese Application

Severity of root rot (Rhizoctonia solani and Rhizoctonia bataticola) of cowpea (Vigna unguiculata L.) was reduced by 42.7 and 42.0%, respectively over control following the application of 10 μg/g Mn as manganese sulphate. Reduction in disease incidence was associated with increased levels of polyphenol oxidase (PPO), peroxidase (PO) and total phenols. PO activity was several times more as compared with PPO‐specific activity and increased markedly after infection either with R. solani or R. bataticola. Contrary to PPO and PO, the specific activity of catalase declined sharply. Infection also caused an increase in the content of reducing sugars, Cu, Zn and Mn but a decrease in o‐dihydric phenols, flavanols, total soluble sugars, non‐reducing sugars and Fe contents. It is suggested that Mn at the rate of 10 μg/g soil can be used to manage the root rot of cowpea.     

Regulators of Cell Division in Plant Tissues XII. A Cytokinin Bioassay Using Excised Radish Cotyledons

A rapid bioassay for cytokinins is described. This is based on the ability of these compounds to promote markedly the expansion of radish cotyledons excised soon after seed germination. The response, which is due largely to a promotion of cell enlargement, is inhibited by abscisic acid. Gibberellins, certain amino acids and calcium salts, naturally occurring substances without cytokinin activity, induce small growth increments in the assay. Cytokinin structure-activity relationships observed for the assay are very similar to those which apply in the tobacco-pith tissue culture assay.     

Purification and Characterization of a Ferredoxin-NADP Oxidoreductase-Like Enzyme from Radish Root Tissues

An enzyme able to reduce cytochrome c via ferredoxin in the presence of NADPH, was isolated, purified from radish (Raphanus sativus var acanthiformis cultivar miyashige) roots and characterized. The enzyme was purified by DEAE-cellulose, Blue-Cellulofine, Ferredoxin-Sepharose 4B, and Sephadex G-100 column chromatography. Molecular mass of the enzyme was estimated to be 33,000 and 35,000 daltons by Sephadex G-100 gel filtration and SDS-PAGE, respectively. Its absorption spectrum suggested that the enzyme contains flavin as a prosthetic group. The K_m values for NADPH and ferredoxin were calculated to be 9.2 and 1.2 micromolar, respectively. The enzyme required NADPH and did not use NADH as an electron donor. The optimal pH was 8.4. The enzyme also catalyzed the photoreduction of NADP⁺ in the spinach leaf thylakoid membranes depleted of ferredoxin and ferredoxin-NADP⁺ oxidoreductase. The effect of NaCl and MgCl₂ concentration on the activity and amino acid composition of the enzyme were demonstrated. The results suggest that the enzyme is similar to ferredoxin-NADP⁺ oxidoreductase from chloroplasts and cyanobacteria and is the key enzyme catalyzing the electron transport between NADPH, generated by the pentose phosphate pathway, and ferredoxin in plastids of plant heterotrophic tissues.     

葡萄贮藏过程中落粒与离区酶活性变化及植物生长调节物质的关系

研究了无核白葡萄(Vitis vinifera L.)采后贮藏过程中离区纤维素酶、果胶酯酶(Pectinesterase,PE)、多聚半乳糖醛酸酶(polygalacturonase,PG)、脂氧合酶(lipoxygenase,LOX)和过氧化物酶(peroxidase,POD)活性的变化与落粒的关系及植物生长调节物质对其的影响。结果表明,葡萄在贮藏过程中,伴随浆果落粒的增加,离区纤维素酶、PG、LOX、POD活性升高,PE活性下降。离区纤维素酶、PG、LOX等酶的活性与葡萄落粒程度之间呈显著正相关。外源ABA和CEPA处理能增强离区纤维素酶、PG、LOX活性,促进落粒;GA3,IAA处理则能抑制离区纤维素酶、PG、LOX活性,减轻落粒。ABA对落粒的促进效应及GA3对纤维素酶活性和落粒的抑制效应尤为明显,表明GA3与ABA比值在葡萄采后落粒过程中起重要的作用。     

Dependence of Root Cell Growth and Division on Root Diameter

Primary roots of 98 species from different families of monocotyledonous and dicotyledonous plants and adventitious roots obtained from bulbs and rhizomes of 24 monocot species were studied. Root growth rate, root diameter, length of the meristem and elongation zones, number of meristematic cells in a file of cortical cells, and length of fully elongated cells were evaluated in each species after the onset of steady growth. The mitotic cycle duration and relative cell elongation rate were calculated. In all species, the meristem length was approximately equal to two root diameters. When comparing different species, the rate of root growth increased with a larger root diameter. This was due to an increase in the number of meristematic cells in a row and, to a lesser degree, to a greater length of fully elongated cells. The duration of the mitotic cycle and the relative cell elongation rate did not correlate with the root diameter. It is suggested that the meristem size depends on the level of nutrient inflow from upper tissues, and is thereby controlled during further growth.     

Gradient of Growth, Spontaneous Changes in Growth Rate and Response to Auxin of Excised Hypocotyl Segments of Phaseolus aureus

Spontaneous growth was studied in excised mung bean (Phaseolus aureus Roxb.) hypocotyl segments. Measurements were made with a growth-recording apparatus using displacement transducers on single 5- to 6-millimeter samples excised from the growth zone immediately below the hook.