Variation within teosinte. I. Numerical analysis of morphological data

Principal components analysis of 27 morphological characters for 18 accessions of teosinte and 3 accessions of maize separated teosinte into 6 phenetic groups which showed broad agreement with previous taxonomic groupings. Tests for regression suggested significant linear relationships with altitude; teosintes from higher elevations are generally more maize-like for a combination of characters. Introgression from maize may have blurred racial identities within teosinte, but variation among current teosinte accessions cannot be satisfactorily explained solely on the basis of known maize introgression. It appears instead that racial differentiation in teosinte was well established by the time of the domestication of maize. While current racial classification of teosinte is quite useful, it does not adequately reflect the amount of genetic variation, nor does it accurately portray many of the relationships within teosinte.     

A covalently bound photoisomerizable agonist. Comparison with reversibly bound agonists at electrophorus electroplaques

After disulphide bonds are reduced with dithiothreitol, trans-3- (α-bromomethyl)-3’-[α- (trimethylammonium)methyl]azobenzene (trans-QBr) alkylates a sulfhydryl group on receptors. The membrane conductance induced by this “tethered agonist” shares many properties with that induced by reversible agonists. Equilibrium conductance increases as the membrane potential is made more negative; the voltage sensitivity resembles that seen with 50 [mu]M carbachol. Voltage- jump relaxations follow an exponential time-course; the rate constants are about twice as large as those seen with 50 μM carbachol and have the same voltage and temperature sensitivity. With reversible agonists, the rate of channel opening increases with the frequency of agonist-receptor collisions: with tethered trans-Qbr, this rate depends only on intramolecular events. In comparison to the conductance induced by reversible agonists, the QBr-induced conductance is at least 10-fold less sensitive to competitive blockade by tubocurarine and roughly as sensitive to “open-channel blockade” bu QX-222. Light-flash experiments with tethered QBr resemble those with the reversible photoisomerizable agonist, 3,3’,bis-[α-(trimethylammonium)methyl]azobenzene (Bis-Q): the conductance is increased by cis {arrow} trans photoisomerizations and decreased by trans {arrow} cis photoisomerizations. As with Bis-Q, ligh-flash relaxations have the same rate constant as voltage-jump relaxations. Receptors with tethered trans isomer. By comparing the agonist-induced conductance with the cis/tans ratio, we conclude that each channel’s activation is determined by the configuration of a single tethered QBr molecule. The QBr-induced conductance shows slow decreases (time constant, several hundred milliseconds), which can be partially reversed by flashes. The similarities suggest that the same rate-limiting step governs the opening and closing of channels for both reversible and tethered agonists. Therefore, this step is probably not the initial encounter between agonist and receptor molecules.     

Heterogeneity of human alpha-fetoprotein as revealed by isoelectric focusing in urea-containing gels.

The heterogeneity of human alpha-fetoprotein has been studied by analytical isoelectric focusing in polyacrylamide gel slabs in the presence of 8 M urea. Six major isoelectric variants could be identified over a pH range of 6.0--6.2. Verification of their identity was achieved by crossed immunoelectrophoresis into agarose gel containing monospecific antiserum to human alpha-fetoprotein. Complete desialylation of the protein did not abolish the heterogeneity; a complex pattern of major alpha-fetoprotein bands persisted over a more alkaline pH range. We have been able to correlate the pattern of alpha-fetoprotein heterogeneity seen following extended agarose gel electrophoresis with that obtained during isoelectric focusing in the presence of urea. The quantity of certain alpha-fetoprotein charge isomers in various alpha-fetoprotein isolates may be important in considering certain biological functions of this protein.     

Role of voltage-sensitive receptors in nicotinic transmission.

This paper compares the conductance induced by bath-applied acetyl-choline (ACh) and by the same transmitter released from nerve terminals at Electrophorus electroplaques. For the former case, dose-response relations are characterized by the maximal agonist-induced conductance, rgamma (130 mmho/cm2), and by the concentration which induces half this conductance; this concentration is termed Kapp and equals 50 micron at -85 mV. For the latter case, neurally evoked postsynaptic currents (PSCs) are characterized by the peak conductance during strongly facilitated release, gPSC, and by the rate constant for decay, alpha. Since gPSC roughly equals rgamma, it is concluded that the PSC activates nearly all available receptor channels. These and other data agree with recent estimates that during the growth phase of the quantal response, (a) the ACh concentration is at least several hundred micromolar; and (b) most nearby channels are activated. However both alpha and Kapp increase during depolarization, at a rate of about e-fold per 86 mV. These observations on voltage sensitivity suggest that a suprathreshold synaptic event is rapidly terminated because the action potential abruptly releases ACh molecules from receptors.     

Response of acetylcholine receptors to photoisomerizations of bound agonist molecules.

In these experiments, agonist-induced conductance is measured while a sudden perturbation is produced at the agonist-receptor binding site. A voltage-clamped Electrophorus electroplaque is exposed to trans-Bis-Q, a potent agonist. Some channels are open; these receptors have bound agonist molecules. A light flash isomerizes 3(-35)% of the trans-Bis-Q molecules to their cis form, a far poorer agonist. This causes a rapid decrease of membrane conductance (phase 1), followed by a slower increase (phase 2). Phase 1 has the amplitude and wavelength dependence expected if the channel closes within 100 mus after a single bound trans-Bis-Q is isomerized, and if the photochemistry of bound Bis-Q resembles that in solution. Therefore, the receptor channel responds rapidly, and with a hundred-fold greater closing rate, after this change in the structure of a bound ligand. Phase 2 (the conductance increase) seems to represent the relaxation back toward equilibrium after phase 1, because (a) phase 2 has the same time constant (1(-5) ms) as a voltage- or concentration-jump relaxation under identical conditions; and (b) phase 2 is smaller if the flash has led to a net decrease in (trans-Bis-Q). Still slower signals follow: phase 3, a decrease of conductance (time constant 5(-10 ms); and phase 4, an equal and opposite increase (several seconds). Phase 3 is abolished by curare and does not depend on the history of the membrane voltage. We consider several mechanisms for phases 3 and 4.     

Unimodality,symmetry and the step-state hypothesis of electrophoretic variation in natural populations

Summary The population frequency distributions of electromorphs of polymorphic loci, when ordered by electrophoretic mobility, tend strongly and significantly to be both unimodal and symmetrical. Such distributions are predicted by all step-change models and their generality in published data can be construed as supportive of the step-change hypothesis. On the other hand, unimodality and symmetry might also be due to artifactual unit perception biases that affect the interpretation and reporting of electro-phoretic data. In any case, it appears that perceived electromorphs are highly heterogeneous.This work was supported by PHS Grant RO 1 GM 21283-O1 GEN.     

The isolation and identification of the female sex pheromones of the red bollworm moth, Diparopsis castanea

The female sex pheromones of the red bollworm moth, Diparopsis castanea, were isolated by solvent extraction of the terminal abdominal segments of the female moth followed by purification of the solvent extract by liquid-solid and gas chromatography. The pheromones were identified by gas chromatographic analysis, micro-ozonolysis, infra-red and mass spectroscopy, and comparison with synthetic material. The major pheromone was 9,11-dodecadien-1-yl acetate (80 : 20 trans : cis). Minor components identified were trans 9-dodecen-1-yl acetate, 11-dodecen-1-yl acetate, and dodecan-1-yl acetate.