Growth-regulator Interactions in the Growth of the Shoot System of Avena sativa Seedlings: I. THE GROWTH OF THE FIRST INTERNODE

1. Segments, 3.5 mm. long, cut from the first internode of Avenasativa seedlings grown in complete darkness respond to bothauxins and gibberellic acid by accelerated extension. 2. The optimum concentration of indole-3-acetic acid (IAA) is10 p.p.m. and of gibberellic acid (GA) is 0.1 p.p.m. 3. The degree of stimulation relative to the growth of controlsegments is affected by the inclusion in the segement of thenode between the internode and coleoptile. Thus the gibberellineffect is greatly increased while the IAA effect is decreased.The optimal concentrations are not affected by inclusion ofthe node. 4. These results can best be explained in terms of the supplyby the node tissue of an endogenous auxin which is necessaryfor the expression of GA action. 5. Numerous factorial experiments demonstrated that there isno detectable interaction between applied IAA and GA in thepromotion of first-internode extension. This implies that thepostulated endogenous auxin which synergized GAA action in (4)is either an active form of IAA produced only in the node tissueor is a completely different auxin. 6. No synergism of growth-promotive action can be detected betweenGA and the two synthetic auxins I-naphthylacetic acid and 2,4-dichlorophenoxyaceticacid. 7. p-chlorophenoxy-iso-butyric acid (PCIB) anc 2,4,6-trichlorophenoxyaceticacid (2,4,6-T) act as weak auxins and thus antagonize competitivelythe promotive action of GA. 8. The anti-auxin -(I-naphythyl-methyl-sulphide)propionic acid(NMSP) antagonizes competitively the promotive action of bothIAA and GA. 9. The facts under (5)–(8) suggest that auxins and GAare acting at the same growth-promotion centres and may competefor them. 10. Growth inhibitions are induced by high concentrations ofPCIB, 2,4,6-T and NMSP. The inhibitions produced by PCIB and2,4,6-T are both synergized by supra-optimal concentrationsof IAA while that of NMSP is synergized by supra-optimal concentrationsof both IAA and GA. This similarity of the effects of IAA andGA suggests that their inhibition actions also are of a closelysimilar nature.     

The conversion of pyridoxine phosphate into pyridoxal phosphate in Escherichia coli

1. Evidence is presented for the presence of pyridoxine phosphate oxidase in aqueous extracts of Escherichia coli. Some comparison is made with pyridoxamine phosphate oxidase. 2. Isoniazid and iproniazid were found to combine with pyridoxal phosphate, but isoniazid did not combine with either pyridoxamine phosphate or pyridoxine phosphate. Both oxidase activities were somewhat inhibited by benzylamine and putrescine, but not by phenethylamine or cadaverine. 3. The significance of pyridoxine phosphate oxidase in cell metabolism is discussed.     

Cytidine Analogues and Stomatogenic Recovery in Amicronucleate Paramecium tetraurelia and Paramecium jenningsi

Removal of the micronuclei of Paramecium tetraurelia and Paramecium jenningsi by micropipetting generates amicronucleate cell lines. These cell lines go through a period of growth depression for several dozen fissions, but they gradually recover. Amicronucleate cells in the depression period characteristically exhibit abnormal oral development, particularly reduction in the length of the buccal cavity and an abnormal pattern of the oral membranelles. To test the notion that the macronucleus is involved in the recovery of amicronucleate cell lines, DNA demethylation drugs were administered to amicronucleates in the depression period. After at least 4 fissions, the treated amicronucleates were assessed for their progress in recovery by scoring the proportion of cells with normal oral membranelles. Cvtidine analogues which demethylate cytosine specifically at the 5 position, namely 5-azacytidine, 5-aza-2'- deoxycytidine and 5-fluoro-2'-deoxycytidine. promoted recovery of the amicronucleates. Cytidine, 6-azacytidine, 2'-fluoro-2'-deoxy-cytidine and cytosine-β-D-arabinofuranoside did not. These results suggest that (i) 5-methylcytosine is present in the macronucleus of these Paramecium species, probably in small amounts and (ii) recovery of amicronucleates involves demethylation of macronuclear DNA. This implies that in normal cells the micronuclei are involved in maintaining the macronuclear DNA in a methylated state and hence the inactivation of the macronuclear sequences that are to be employed for stomatogenic recovery. A general mechanism for the control of gene expression may therefore be employed for the regulation of specific sequences.     

Differential responses of expiratory muscles to chemical stimuli in awake dogs

We assessed respiratory muscle response patterns to chemoreceptor stimuli (hypercapnia, hypoxia, normocapnic hypoxia, almitrine, and almitrine + CO2) in six awake dogs. Mean electromyogram (EMG) activities were measured in the crural (CR) diaphragm, triangularis sterni (TS), and transversus abdominis (TA). Hypercapnia and normocapnic hypoxia caused mild to marked hyperpnea [2-5 times control inspiratory flow (VI)] and increased activity in CR diaphragm, TS, and TA. When hypocapnia was permitted to develop during hypoxia and almitrine-induced moderate hyperpnea, CR diaphragm activity increased, whereas TS and TA activities usually did not change or were reduced below control. Over time in hypercapnia, CR diaphragm, TS, and TA were augmented and maintained at these levels over many minutes; with hypoxic hyperventilation CR diaphragm, TS, and TA were first augmented but then CR diaphragm remained augmented while TS and, less consistently, TA were inhibited over time. Marked hyperpnea (4-5 times control) due to carotid body stimulation increased TA and TS EMG activity despite an accompanying hypocapnia. We conclude that in the intact awake dog 1) carotid body stimulation augments the activity of both inspiratory and expiratory muscles; 2) hypocapnia overrides the augmenting effect of carotid body stimulation on expiratory muscles during moderate hyperpnea, usually resulting in either no change or inhibition; 3) at higher levels of hyperpnea both chemoreceptor stimulation and stimulatory effects secondary to a high ventilatory output favor expiratory muscle activation; these effects override any inhibitory effects of a coincident hypocapnia; and 4) expiratory muscles of the rib cage/abdomen may be augmented/inhibited independently of one another.     

A synthesis of acylphosphonic acids and of 1-aminoalkylphosphonic acids: the action of pyruvate dehydrogenase and lactate dehydrogenase on acetylphosphonic acid.

Acylphosphonic acids, R-CO-PO(OH)2, have been synthesized by the steps [formula: see text] of which the last is new and provides a mild method for de-esterifying acylphosphonic acids. Their reductive amination gives a simple way of making 1-aminoalkylphosphonic acids. Acetylphosphonic acid inhibited NAD+ reduction by pyruvate with the pyruvate dehydrogenases from Escherichia coli and Bacillus stearothermophilus. The inhibition was competitive with pyruvate, with Ki of 6 microM for the E. coli enzyme (pyruvate Km 0.5 mM) and one of 0.4 mM of the B. stearothermophilus enzyme (pyruvate Km 0.1 mM). Acetylphosphonate and its monomethyl ester are substates for pig heart lactate dehydrogenase, with Km values of 15 mM and 10 mM respectively (pyruvate Km 0.05 mM) and specificity constants one thousandth that for pyruvate.     

A comparison of the effects of chromate,molybdate and cadmium oxide on respiration in the yeastSaccharomyces cerevisiae

Summary Growth ofSaccharomyces cerevisiae on non-fermentable medium was more sensitive to inhibition by chromate than growth on fermentable medium. Chromate was selectively toxic against oxygen uptake in cells grown in non-fermentable medium and also inducedpetite mutations. CdO demonstrated similar but lesser effects on growth and respiration. However, molybdate had little toxicity to yeast non-fermentable growth and stimulated oxygen uptake in cells grown in fermentable and non-fermentable media. These results suggest that chromate, a carcinogen, may act more directly against the mitochondria ofS. cerevisiae than related chemical species, CdO and molybdate.     

Noninfectious human immunodeficiency virus type 1 mutants deficient in genomic RNA.

All retroviruses contain, in the nucleocapsid domain of the Gag protein, one or two copies of the sequence Cys-X2-Cys-X4-His-X4-Cys. We have generated a series of mutants in the two copies of this motif present in human immunodeficiency virus type 1. These mutants encoded virus particles that were apparently composed of the normal complement of viral proteins but contained only 2 to 20% of the normal level of genomic RNA. No infectivity could be detected in the mutant particles, while 10(5) infectious U were present in an equivalent amount of wild-type particles. Thus, the mutants have another defect in addition to the inefficiency with which they encapsidate genomic RNA. Our results show that both copies of the motif are required for normal RNA packaging and for infectivity. Mutants of this type may have important applications, including nonhazardous materials for research, immunogens in vaccine and immunotherapy studies, and diagnostic reagents.