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.     

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.     

Effect of scatter factor on motility of epithelial cells and fibroblasts

The scatter factor is a protein released by fibroblasts that causes dispersal of epithelial cell colonies and disruption of intercellular junctions, as well as an alteration of morphology with ruffling and rapid extension and movement of pseudopodia. To find out if the scatter factor has a direct effect on cell migration, the Boyden chamber assay was used to determine the effect of partially purified factor on the migration of cells through 8 microns pore size filters. The results showed that the mobility of Madin-Darby canine kidney (MDCK) cells was stimulated, and usually maximal at 100 ng per ml, which is equivalent to 100 to 200 units of activity in the standard assay based on the morphology and arrangement of cells. The migration was due to chemotaxis and chemokinesis. A keratinocyte cell line was also sensitive as were, to a lesser extent, BSCl monkey kidney cells. The motility of freshly isolated fibroblasts and fibroblast cell lines, however, was not significantly affected. The results confirm the cell specificity and paracrine role of the scatter factor and show that this fibroblast-derived molecule can directly stimulate the movement of epithelial cells.     

An Ultrastructural Investigation of 180°-Rotated Ciliary Meridians in Tetrahymena pyriformis*

SYNOPSIS. An ultrastructural investigation has been carried out on 180°-rotated ciliary meridians (inverted meridians) in Tetrahymena pyriformis temperature-sensitive mutant (mol^b/mol^b), syngen 1, strain B. The longitudinal, transverse and postciliary microtubular bands, the kinetodesmal fiber, and the parasomal sac, are shown to be disposed at a 180° angle to their normal positions or orientations. Other abnormalities are as folows: the first 2 basal bodies of the inverted meridian fail to organize into “couplets” and the inverted meridian intrudes into the anterior pole region; an extra longitudinal microtubular band is found in one of the cell lines.     

Commitment to the First Cortical Reorganization During Conjugation in Stylonychia mytilus: An Argument for Homology with Cortical Development During Binary Fission

The asexual nature of the first cortical reorganization of conjugation in Stylonychia was analyzed by comparing the effect of amputation performed at different stages of early conjugation to that performed on vegetative cells at different stages of the cell cycle. Amputation of vegetative cells delineated a point of commitment to binary fission at 0.51–0.57 of the cell cycle. Cells amputated before this point were induced to undergo the regenerative mode of asexual development, but those amputated after this point continued with binary fission. In parallel, during conjugation a similar commitment was made around the time of formation of tight mating-pairs: early conjugants amputated around this time might undergo regeneration, and those operated on after this stage continued with the first cortical reorganization as in typical conjugants. The two mates of a pair might differ in their response to amputation, suggesting that the timing of commitment to the first cortical reorganization is not related to the events of conjugation, but rather is individually determined in the vegetative cycle of the cells before they pair up in mating. These observations provide support for the notion that the first cortical reorganization of conjugants is homologous to the asexual mode of cortical development in dividers, according to the theory of developmental heterochrony in the sexual reproduction of hypotrichs. The timing of commitment to the first cortical reorganization was found to temporally correlate with the entrance of the micronuclei into meiosis. Since the first cortical reorganization can proceed without the micronucleus, this raises the possibility that initiation of micronuclear meiosis is closely coupled with, and may be determined by, the commitment to the first cortical reorganization.