A re-evaluation of polypodium bradeorum and P. Colysoides

During field studies on the pteridophytes of Costa Rica, a peculiarly dimorphic polypodioid fern was found in the rain-forests of the Atlantic lowlands near Puerto Viejo. The variation in the fertile frond, ranging from simple and short petiolate to pinnatisect and long petiolate, coupled with peculiarly elongate and irregular sori, prompted further investigations. Additional herbarium specimens from localities in Mexico, British Honduras, Nicaragua, and Costa Rica showed intermixed variations between plants with all leaves simple (typified byPolypodium bradeorum Rosenstock) to plants with all leaves lobed or pinnatisect (typified byP. colysoides Maxon & Copeland). Other characters were judged sufficiently homogeneous to consider these individuals as conspecific underP. bradeorum. Morphological studies indicate parallel evolution of several characters in the Asiatic generaColysis, Microsorium, andLeptochilus on the one hand and the New World members ofMicro gramma, Pleopeltis, andPolypodium bradeorum on the other     

Six new species of Elaphoglossum (Elaphoglossaceae)

The fern genusElaphoglossum is well represented in wet, mountainous regions of Latin America, from which many species have recently been described. Six more new species ofElaphoglossum are reported:E. bryogenes from Ecuador andE. caudulatum, E. diminutum, E. delasotae, E. lellingeri, E. subcordatum, andE. xiphiophorum from Colombia.     

Calcium content and distribution as a function of growth and transformation in the mouse 3T3 cell

Total Ca content and that fraction of Ca sensitive to removal by the chelator ethylene glycol-bis(β-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA) have been investigated in the mouse 3T3 cell as a function of growth stage, transformation with SV40 virus, and serum levels of the media. Cells were allowed to grow through several doublings in media containing (45)Ca. The cellular content of (45)Ca was used to access total cell Ca. That fraction of (45)Ca removed by EGTA was presumed to represent primarily surface-localized Ca. The data are expressed on a per cell volume basis to compensate for size differences as a function of growth stage and transformation. During exponential growth phase, the 3T3 cell contains 525pmol Ca/μl cell volume. Of this, approx. 457 pmol/μl is not removable by EGTA and, presumably, is cytoplasmically located. This value is in close agreement with previous studies on the HeLa cell (470 pmol Ca/μl cell water after the removal of the surface Ca). The low level of EGTA- removable Ca present in the 3T3 cell during early exponential growth (68 pmol Ca/μl cell volume) increases progressively with increasing cell density, and upon quiescence it is sevenfold greater. In contrast, SV40- transformed 3T3 cells growing exponentially possess total levels of Ca which are approximately two-thirds the levels of the normal 3T3 cell. However, their EGTA-sensitive Ca is not significantly different from that of exponentially growing, normal 3T3 cells. As the transformed cells continue to grow at high density, their total ca and their sensitivity to EGTA do not change, in contrast to the normal 3T3 cell. Thus, an increase in Ca associated with the cell surface appears to be correlated with growth inhibition. This has been investigated further by regulating growth of the normal and transformed cell with alterations in the serum level of the media. In 4 percent calf serum the normal cell is stopped from continued proliferation. Growth stoppage under these conditions is characterized by a nearly fourfold increase in EGTA-removable Ca, similar to the increase observed upon quiescence in depleted 10 percent serum. Similar treatment of the transformed cell does not reduce its growth rate, nor does it significantly alter Ca distribution. However, at 0.5 percent medium serum levels, the SV40 3T3 growth rate is substantially reduced and, under these conditions, EGTA-removable Ca increases twofold.     

Unidirectional replication in Escherichia coli of three small plasmids derived from R factor R12

Replicating molecules of three small plasmids, pSM1, pSM2, and pSM3, were isolated from a CsCl density gradient containing ethidium bromide. These plasmids are all derived from R12, a mutant of NR1 (same as R100). By means of pulse-labeling experiments, the replicating forms were located at buoyant densities intermediate between those of the closed circular and open circular DNA bands. These molecules were analyzed by electron microscopy following digestion with restriction endonucleases. Digestion of pSM2 with EcoR1 and with HindIII revealed the presence of a single origin of replication located 1.72 kilobases (kb) from the EcoR1 cutting site (2.04 kb from the HindIII cutting site). These experiments also demonstrated that replication occurs in a unidirectional mode from the origin. Analysis of EcoR1-cleaved replicating molecules of pSM1 and pSM3, which carry common sequences completely or partly homologous to pSM2, provides further evidence for the unidirectional replication of these plasmids from a common origin. The site of the origin of replication was fixed at 85.5 on the kilobase map of R100. This origin, which is located in the RTF region, probably corresponds to one of the replication origins of R100.     

Physical properties and gel electrophoresis behavior of R12-derived plasmid DNAs.

A series of closed circular (I) plasmid DNAs has been derived from drug resistance factor R12, and the nicked circular (II) and linear (III) derivatives of these molecules prepared by irradiation in the presence of ethidium bromide and by treatment with restriction enzyme EcoRI, respectively. These DNAs encompass the molecular weight range 3.6 to 61 megadaltons. The base compositions range from 45% to 51% (GC) as estimated by buoyant density determinations. The smaller plasmids are significantly less supercoiled (9-10%) than are the larger (12-13%). The gel electrophoretic behavior of the three DNA structural forms was determined as a function of molecular weight in agarose gels of concentrations ranging from 0.7% to 1.6% and at electrophoresis salt concentrations from 0.02 M to 0.08 M sodium acetate. The mobilities of DNAs I and III undergo a reversal relative to each other at a molecular weight which decreases with increasing agarose gel concentration. The molecular weight at which DNA II fails to enter a gel depends upon the ionic strength during electrophoresis but not upon the gel concentration.     

A SURVEY FOR 1,3,6,7-TETRAHYDROXY-C-GLYCOSYLXANTHONES EMPHASIZING THE “PRIMITIVE” LEPTOSPORANGIATE FERNS AND THEIR ALLIES

A survey for 1,3,6,7-tetrahydroxy-C-glycosylxanthones of representative species within the primitive vascular plants, emphasizing the leptosporangiate ferns, has indicated a limited distribution of these compounds within three leptosporangiate families: Hymenophyllaceae, Aspleniaceae and Marsileaceae. In the Hymenophyllaceae the distribution of these compounds appears to be a useful criterion for segregating species of Mecodium from other species of Hymenophyllum (sensu lato) and suggests that the tubulate vs. the valvate indusial condition may not be an ideal character for separating all species of Hymenophyllum (s.l.) from those of Trichomanes (s.l.). These compounds appear useful for delimiting several species of Elaphoglossum section Pachyglossa and support a relationship among the Aspleniaceae, Athyriaceae, and Elaphoglossaceae. Their presence in Marsilea also raises questions as to the origin of this group of plants.     

Nine new elaphoglossums (Elaphoglossaceae) from Mexico

Nine new species ofElaphoglossum are described from southern and western México:E. alan-smithii, E. decursivum, E. dissitifrons, E. leonardii. E. lepidopodum, E. mcvaughii, E. parduei, E. rzedowskii, andE. seminudum.