Calcium requirement of phytochrome-mediated fern-spore germination: No direct phytochrome-calcium interaction in the phytochrome-initiated transduction chain

Phytochrome-mediated germination of fern spores of Dryopteris paleacea Sw. was initiated by a saturating red-light (R) irradiation after 20 h of imbibition. For its realization external Ca²⁺ was required, with a threshold at a submicromolar concentration, and an optimum was reached around 10^-4 M. At concentrations 10^-1 M only a reduced response was obtained, based probably on an unspecific osmotic or ionic effect. The germination response was inhibited by La³⁺, an antagonist of Ca²⁺. From these results it is concluded that Ca²⁺ influx from the medium into the spores may be an important event in phytochrome-mediated germination. In the absence of Ca²⁺ the R-stimulated system remained capable of responding to Ca²⁺, added as late as 40 h after R. Moreover, Ca²⁺ was effective even if added after the active form of phytochrome, Pfr, had been abolished by far-red (FR) 24 h after R. Thus, the primary effect of Pfr, that initiates the transduction chain, does not require calcium. Coupling of Pfr to subsequent dark reactions has been investigated by R-FR irradiations with various dark intervals. The resulting escape kinetics were characterized by a lag phase (6 h) and half-maximal escape from FR reversibility (19 h). These kinetics were not significantly changed by the presence or absence of calcium. Thus, direct interaction of Pfr and calcium is not a step in the transduction chain initiated by the active form of photochrome.Abbreviations EGTA ethyleneglycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid - FR far-red light - Pr red-light-absorbing form of phytochrome - Pfr far red-light-absorbing form of phytochrome - Pipes piperazine-1,4-bis(2-ethanesulfonic acid) - R red light A preliminary report of this work was presented at the XIV Int. Bot. Congr., Berlin (West), Germany, Book of Abstracts, 2-116a-5 (1987)     

Heat shock proteins in Sorghum bicolor and Pennisetum americanum I. genotypic and developmental variation during seed germination

Abstract The capacity to synthesize heat shock proteins (HSPs) during seed germination of sorghum (Sorghum bicolor) and pearl millet (Pennisetum americanum) has been examined. HSP synthesis is detectable in a thermotolerant genotype of sorghum during the first hour of imbibition of the seed under high temperature stress. A non-coordinate control of HSP synthesis during germination was revealed. Genotypic differences were manifest in the stage of germination at which the ability to synthesize HSPs was first apparent and this related to the thermosensitivity of that genotype.     

A stochastic model for the membrane potential of a stimulated neuron

We present a simple model describing the transition between the prefiring, firing and postfiring phases of a single neuron in a large neural net. Using typical values for the physiological parameters that enter the model, we find average interspike times that are close to those reported in experimental measurements.     

In vitro culture of embryos of Cucumis spp.: heart-stage embryos have a higher ability of direct plant formation than advanced-stage embryos

Summary The ability of embryos at different developmental stages to form plants in vitro has been studied in cultivated Cucumis sativus L. and in the wild species C. zeyheri 2 x Sond. and C. metuliferus Naud. On MS medium containing 3.5% sucrose, 0.1 mg 1^–1 kinetin (Kn) and 0.01 mg 1^–1 indoleacetic acid (IAA), proembryos (0.03–0.05 mm) and early globular embryos (0.05–0.08 mm) from the wild species developed into plants in low frequencies of 8% and 21%, respectively. These embryos should be surrounded by the embryo sac tissue. On the same medium late globular (0.08–0.1 mm) and early heart-stage embryos (0.1–0.3 mm) developed into plants in moderately high and high frequencies of 48% and 83%, respectively. The presence of the embryo sac at these stages was still beneficial, but no longer a prerequisite. Late heart-stage embryos (0.3–0.8 mm) also showed high frequencies of plant formation, 63%, if Kn was applied at a concentration of 1 mg 1^–1. From the early cotyledon stage onwards, the frequency of plant formation gradually decreased, reaching a minimum at the late cotyledon stage. Subsequently it began to increase again up to the late maturation stage. The poor plant formation shown by the intermediate-aged embryos could be improved slightly by lowering the sucrose concentration to 0.5% and by increasing the Kn concentration to 10 mg 1^–1. Relative to the wild species, embryos of C. sativus showed lower percentages of plant formation. The optimum sucrose concentration was 2% for the heart-stage C. sativus embryos. In all three species the ability to form plants strongly decreased with increasing embryo age, from early to late cotyledon. This is thought to be caused by the increasing tendency of the embryos at these stages to continue in vitro the normal embryo development.     

Anisotropy decay of fluorescence as an experimental approach to protein dynamics

This minireview makes an initial assessment of the progress made using anisotropy decay measurements for investigating the conformational changes and molecular dynamics in soluble systems. A critical analysis of available data is presented. The anisotropy decays of the tryptophan fluorescence of staphylococcal nuclease, adrenocorticotropin, melittin and of labeled transfer RNA were studied for investigating the functional conformational changes of these systems. The emissions of variously labeled immunoglobulins have been used to elucidate the conformations of these proteins before and after the binding of specific antibodies. Labeled myosin and its fragments have given information on the functional motions of the protein domains. The anisotropy decays of labeled and natural hemoglobin systems have been utilized for exploring the allosteric behavior of these molecules. The data suggest a wide applicability of this technique to the study of protein dynamics and conformational changes of macromolecules.     

Synchrotron-excited time-resolved fluorescence spectroscopy of adenosine,protonated adenosine and 6N, 6N-dimethyladenosine in aqueous solution at room temperature

The fluorescence behavior of adenosine in neutral solution has been studied by time-resolved spectroscopy using synchrotron excitation and timecorrelated single photon counting, and by decay time measurements. Three emissions have been identified and correlated with three excitation spectra. The assignment of these transitions has been made by comparison with similar measurements on ⁶N, ⁶N-dimethyladenosine (6 DMA), and on adenosine in acid solution (ADO H⁺). It is proposed that two of the transitions of adenosine which correlate with 6DMA originate from coplanar and orthogonal rotational conformers of the amino group. The other transition, correlating with ADO H⁺ may originate either from the ³H-imino tautomer, or from a differently solvated rotational conformer.A partial presentation of this work has been made at the Second Congress of the European Society for Photobiology Padova, Italy, 6–10 September 1987     

Overwintering and growth regulator treatment effects on celery (Apium graveolens L.) flowering and seed production

Celery (Apium graveolens L.) plants cv. Jason overwintered in a polythene tunnel flowered earlier and grew taller than similar plants given a 10-week cold-treatment at 5°C prior to transplanting in the same tunnel in mid-February. However, there was no significant difference in the yield of seeds obtained from both treatments, plants grown at a density of 4m^-2 yielded less seeds than those at 2m^-2, though the yield per unit area was slightly higher from the high density treatment. Treatment with 100 mgl^-1 GA₃ applied twice just prior to flowering and during anthesis increased flower stalk, flower pedicel and stamen length but delayed flower opening and seed ripening and decreased seed set and seed yield. Treatment with a mixture of 1000 mgl^-1 GA₄ and GA₇ plus 1000 mgl^-1 ethephon on three occasions during seed ripening decreased seed yield and reduced seed germination though those seeds capable of germinating were less dormant than seeds from untreated plants. The size distribution of seeds was unaffected by any treatment other than the preseeding spray with GA₃ which reduced the percentage of medium-size seeds.     

Reversing the inhibitory effect of paclobutrazol on seed germination of Amaranthus paniculatus by GA3, ethephon or ACC

The germination of Amaranthus paniculatus seeds was inhibited by applying paclobutrazol, a specific inhibitor of gibberellin biosynthesis. This inhibition was markedly counteracted by gibberellin A₃ (GA₃), suggesting that endogenous gibberellins are required for germination in this species. The inhibitory effect of paclobutrazol was also overcome by ethephon (2-chloroethylphosphonic acid) or the precursor of ethylene biosynthesis, ACC (1-aminocyclopropane-l-carboxylic acid). Thus the physiological effect of gibberellin can be mimicked by ethylene released from ethephon or synthesised from exogenous ACC. It is suggested, that endogenous gibberellins are involved in germination of Amaranthus paniculatus seeds and that action of GA₃ can be substituted by ethylene.Abbreviations ACC 1-aminocyclopropane-l-carboxylic acid - AMO-1618 (2-isopropyl-5methyl-4-trimethylammoniumchloride)-phenyl-l-piperidinium-carboxylate - ancymidol -cyclopropyl--(4-methoxyphenyl)-5-pyrimidine methanol - chloromequat chloride (2-chloroethyl)trimethylammoniumchloride - ethephon 2-chloroethylphosphonic acid - GA gibberellin A₃ - paclobutrazol (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-lyl)pentan-3-ol - Phosphon D 2,4,dichlorobenzyl-tributhylphosphoniumchloride - tetcyclacis 5,(4-chlorophenyl)-3,4,5,9,10-pentaaza-tetracyclo)5,4,1,0,Z,6,0^8,11 dodeca-3,9-diene