The control of bud dormancy in potato tubers

Potato (Solanum tuberosum L.) tuber buds normally remain dormant through the growing season until several weeks after harvest. In the cultivar Majestic, this innate dormancy persisted for 9 to 12 weeks in storage at 10° C, but only 3 to 4 weeks when the tubers were stored at 2° C. At certain stages, supplying cytokinins to tubers with innately dormant buds induced sprout growth within 2 d. The growth rate was comparable to that of buds whose innate dormancy had been lost naturally. Cytokinin-treatment did not accelerate the rates of cell division and cell expansion in buds whose innate dormancy had already broken naturally. Gibberellic acid did not induce sprout growth in buds with innate dormancy. We conclude that cytokinins may well be the primary factor in the switch from innate dormancy to the non-dormant state in potato tuber buds, but probably do not control the subsequent sprout growth.Abbreviations tio ⁶ade 6-(4-hydroxy-3-methylbut-trans-2-enyl amino)purine, zeatin - tio⁶ado 6-(4-hydroxy-3-methylbut-trans-2-enyl amino)-9--D-ribofuranosyl purine, zeatin riboside     

Calcium-binding and its effect on circular dichroism of plant calmodulin

The Ca²⁺-binding properties of calmodulin purified from zucchini (Cucurbita pepo L.) has been determined. A value of 3.3 mol Ca²⁺ per mol of zucchini calmodulin was measured at pH 7.5 by equilibrium chromatography. The far-and near-UV circular-dichroic spectra of the Ca²⁺-and Mg²⁺-saturated as well as from the metal-free forms of zucchini calmodulin reveal that upon Ca²⁺-binding the -helix content increases. A comparison with the spectra of vertebrate calmodulin indicates that both calmodulin have a similar secondary structure, similar Ca²⁺-induced conformational changes and the same number of Ca²⁺-binding sites.Abbreviations CAPP 10-(3-aminopropyl)-2-chloro-phenothiazine - EGTA ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - EDTA ethylenediaminetetraacetic acid Dedicated to Prof. Dr. Karl Decker on the occasion of his 60th birthday     

Phosphorylation of chloroplast membrane proteins partially protects against photoinhibition

Thylakoids isolated from peas (Pisum sativum cv. Kelvedon Wonder) and phosphorylated by incubation with ATP have been compared with non-phosphorylated thylakoids in their sensitivity to photoinhibition by exposure to illumination in vitro. Assays of the kinetics of fluorescence induction at 20° C and the fluorescence emission spectra at-196° C indicate a proportionally larger decrease in fluorescence as a result of photoinhibitory treatment of non-phosphorylated compared with phosphorylated thylakoids. It is concluded that protein phosphorylation can afford partial protection to thylakoids exposed to photoinhibitory conditions.Abbreviations and symbols DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - F ₀ Level of chlorophyll fluorescence when photosystem 2 traps are open - F _m Level of chlorphyll fluorescence when photosystem 2 traps are closed - P Maximum level of fluorescence reached in the absence of DCMU - PSI (II) photosystem I(II)     

The control of bud dormancy in potato tubers. Measurement of the seasonal pattern of changing concentrations of zeatin-cytokinins

A radioimmunoassay, combined with high-performance liquid chromatography, has been used to analyse the zeatin-type cytokinins of potato (Solanum tuberosum L. cv. Majestic) tubers and tuber buds throughout growth and storage. During tuber growth, zeatin riboside was the predominant cytokinin detected in all tissues. Immediately after harvest, the total cytokinin concentration fell dramatically in the storage tissue, largely as a consequence of the disappearance of zeatin riboside. During storage, levels of cytokinins in the storage tissue remained relatively constant, but increased in the tuber buds. In the buds of tubers stored at 2°C there was a 20-to 50-fold increase in total cytokinin over six weeks, coinciding with the natural break of innate dormancy. At 10°C the rise in the level of bud cytokinins was slower, correlating with the longer duration of innate dormancy. Injecting unlabelled cytokinins into tubers in amounts known to induce sprouting gave rise to increases in cytokinin concentrations in the buds of the same order as the increase associated with the natural break of dormancy. Metabolism of injected cytokinins was greater in non-dormant than in dormant tubers. The roles of cytokinin concentration and the sensitivity of the buds to cytokinin in the control of dormancy are discussed.Abbreviations CK cytokinin - FW fresh weight - HPLC high-performance liquid chromatography - RIA radioimmunoassay - tio⁶ade 6-(4-hydroxy-3-methylbut-trans-2-enylamino)-purine=zeatin - tio⁶adeglc⁹ 6-(4-hydroxy-3-methylbut-trans-2-enylamino)-9--D-glucopyranosyl purine=zeatin-9-glucoside - tio⁶ado 6-(4-hydroxy-3-methylbut-trans-2-enylamino)-9--D-ribofuranosyl purine=zeatin riboside - tio⁶ado-[³H]-diol a radioactive derivative of zeatin riboside, synthesised by periodate-oxidation followed by [³H]NaBH₄-reduction - tio⁶AMP 6-(4-hydroxy-3-methylbut-trans-2-enylamino)-9--D-5-phosphoribofuranosyl purine=zeatin riboside 5-monophosphate - t(ioglc⁴)⁶ade 6-(4-O--D-glucopyranosyl-3-methylbut-trans-2-enylamino)-purine=zeatin-O-glucoside     

Amino-acid-transport mutant of Nicotiana tabacum L.

The structure of spinach ribulose 1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) has been investigated by tilted-view electron microscopy of negatively stained monolayer crystals and image processing. The structure determined consists of a cylinder of octagonal cross-section with a large central hole. Based on this and other available evidence a model for the arrangement of the large and small subunits is suggested with the eight small subunits arranged equatorially around the core of eight large subunits.Abbreviations LS large subunit - Rubisco ribulose 1,5-bisphosphate carboxylase/oxygenase - SS small subunit     

Induction of de-novo synthesis of tryptophan decarboxylase in cell suspensions of Catharanthus roseus

Tryptophan decarboxylase (EC 4.2.1.27) is synthesized de-novo by Catharanthus roseus cells shortly after the cells have been transferred into culture medium in which monoterpenoid indole alkaloids are formed. The enzyme production, monitored by in-vivo labelling with [³⁵S]methionine and immunoprecipitation, precedes the apparent maximal enzyme activity by 10–12 h. From the time course of the descending enzyme activity after induction, a half-life of 21 h for tryptophan decarboxylase in C. roseus cell suspensions is calculated. A comparison of the polyadenylated-RNA preparations from C. roseus cells indicates that mRNA activity for tryptophan decarboxylase is only detected in cells grown in the production medium. The importance of tryptophan decarboxylase induction with respect to the accumulation of th corresponding alkaloids is discussed.Abbreviation TDC tryptophan decarboxylase     

Photoacoustic and fluorescence measurements of the chilling response and their relationship to carbon dioxide uptake in tomato plants

The response of tomato plants to various chilling treatments was studied using two approaches for the measurement of photosynthetic activity. One involved the use of a portable fluorometer for the measurement of in-vivo chlorophyll fluorescence, while the other employed a newly introduced photoacoustic system which allowed changes in oxygen evolution to be followed in a leaf disc. A strong correlation was found between results obtained by each system and those obtained by a conventional open gas-exchange system for the determination of CO₂ uptake. Both systems of measurements could readily distinguish between the effects of chilling in the dark (at 3° C for 18 h) and chilling at high photon flux density (2000 mol m^-2 s^-1 for 5h at 5° C). Chilling in the dark had practically no effect on the quantum yield of oxygen evolution, chlorophyll fluorescence or CO₂ uptake, while chilling at excessively high photon flux density resulted in a sharp reduction (50–70%) in the quantum yields obtained. The results support the view that photosystem II cannot be the primary site of damage by chilling in the dark, although it is significantly affected by chilling at high light intensity.Abbreviations DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - PA photoacoustic - PFD photon flux density - PSII photosystem II     

Subcellular localization of the common shikimate-pathway enzymes in Pisum sativum L.

5-Enolpyruvylshikimate 3-phosphate (EPSP) synthase (3-phosphoshikimate 1-carboxyvinyltransferase; EC 2.5.1.19), 3-dehydroquinate dehydratase (EC 4.2.1.10) and shikimate: NADP⁺ oxidoreductase (EC 1.1.1.25) were present in intact chloroplasts and root plastids isolated from pea seedling extracts by sucrose and modified-silica density gradient centrifugation. In young (approx. 10-d-old) seedling shoots the enzymes were predominantly chloroplastic; high-performance anion-exchange chromatography resolved minor isoenzymic activities not observed in density-gradientpurified chloroplasts. The initial enzyme of the shikimate pathway, 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase (EC 4.1.2.15) was also associated with intact density-gradient-purified chloroplasts. 3-Dehydroquinate synthase (EC 4.6.1.3) and shikimate kinase (EC 2.7.1.71) were detected together with the other pathway enzymes in stromal preparations from washed chloroplasts. Plastidic EPSP synthase was inhibited by micromolar concentrations of the herbicide glyphosate.Abbreviations DAHP 3-deoxy-d-arabino-heptulosonate 7-phosphate - DEAE diethylaminoethyl - DHQase 3-dehydroquinate dehydratase - DTT dithiothreitol - EPSP 5-enolpyruvylshikimate 3-phosphate - SORase shikimate:NADP⁺ oxidoreductase     

A light-enhanced metabolism of sulfite in cells of Cucumis sativus L. cotyledons

The effects of light and several photosynthetic inhibitors on the rate of sulfite metabolism in cells obtained from Cucumis sativus L. cotyledons was studied. The cells were treated with 200 M Na₂SO₃ and the disappearance of sulfite was monitored using either dithiobisnitrobenzoic acid or fuchsin. The rate of sulfite disappearance in light was double the dark rate. Disalicylidene propanediamine at 1 mM increased this light-enhanced metabolism approx. 50%; neither 1 M 3,4-dichlorophenyl-N,N-dimethylurea nor 0.1 mM cyanazine, which completely inhibited CO₂-dependent oxygen evolution, affected the rate of sulfite metabolism. Addition of 200 M Na₂SO₃ to the cells partially inhibited ¹⁴CO₂ fixation. The rate of sulfite consumption by the cells did not affect this inhibition. We conclude that light-dependent sulfite metabolism is cucumber cells may utilize reduced ferredoxin generated as a result of photosynthetic electron transport. An injurious interaction between CO₂ fixation and sulfite appears to occur independently of the sulfite-metabolism process.Abbreviations DCMU 3,4-dichlorophenyl-N,N-dimethylurea - DSPD disalicylidene propanediamine - DTNB 5,5-dithiobis-(2-nitrobenzoic acid)     

Plastid changes during the conversion of chloroplasts to chromoplasts in ripening tomatoes

Methods were developed for the isolation of plastids from mature green and ripening tomatoes (Lycopersicon esculentum Mill.) and purification by sucrose or Percoll density-gradient centrifugation. Assessment of the purity of preparations involved phase-contrast and electron microscopy, assays for marker enzymes and RNA extraction and analysis. Proteins were extracted from isolated plastids at different ripening stages and separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The profiles obtained from chloroplasts and chromoplasts showed many qualitative and quantitative differences. Labelling of proteins with [³⁵S]methionine in vivo showed that there was active protein synthesis throughout ripening, but there was a change in the plastid proteins made as ripening proceeded. The cellular location of synthesis of specific proteins has yet to be established.Abbreviations CS citrate synthase - EDTA ethylenediaminetetraacetic acid,-acetate - GAPDH NADP⁺-glyceraldehyde-3-phosphate dehydrogenase - rRNA ribosomal RNA - SDS sodium dodecyl sulphate - SDS-PAGE SDS-polyacrylamide gel electrophoresis - Tris 2-amino-2(hydroxymethyl)-1,3-propanediol