THE ZOOSPORE OF CHLOROKYBUS ATMOPHYTICUS,A CHAROPHYTE WITH SARCINOID GROWTH HABIT

Chlorokybus atmophyticus has a sarcinoid growth habit and produces scale-covered zoospores. Flagella are laterally inserted and attached internally to a multilayered structure characteristic of the Charophyceae. There are two kinds of pyrenoid in each cell, a feature previously observed in only one scaly green flagellate. C. atmophyticus demonstrates that the sarcinoid growth habit arose independently at least twice in the green algae and cannot be used to define taxonomic groups unless combined with other criteria. It is further concluded that C. atmophyticus should be classified in a separate family Chlorokybaceae and a separate order Chloroky bales.     

CONDITIONS OF ILLUMINATION AND ZOOSPOROGENESIS IN KLEBSORMIDIUM FLACCIDUM1

The filamentous green alga Klebsormidium flaccidum will produce zoospores when cultured on a diurnal regime of 8-hr light and 16-hr dark. Zoosporogenesis is inhibited by interruption of the dark period with light of sufficient intensity and duration. The relationship between intensity and maximum time of interruption before total inhibition of zoosporogenesis is nonlinear.     

A heparin sulfate-regulated human keratinocyte autocrine factor is similar or identical to amphiregulin.

A novel human keratinocyte-derived autocrine factor (KAF) was purified from conditioned medium by using heparin affinity chromatography as the first step. Purified KAF stimulated the growth of normal human keratinocytes, mouse AKR-2B cells, and a mouse keratinocyte cell line (BALB/MK). Heparin sulfate inhibited KAF mitogenic activity on all cell types tested and inhibited the ability of KAF to compete with epidermal growth factor for cell surface binding. Interestingly, KAF stimulated the growth of BALB/MK cells at high cell density but failed to stimulate these cells at clonal density. Protein microsequencing of the first 20 NH2-terminal amino acid residues of purified KAF revealed identity to the NH2 terminus of human amphiregulin (AR). Northern (RNA) blot analysis with AR-specific cRNA demonstrated that human keratinocytes, as well as mammary epithelial cell cultures, expressed high levels of AR mRNA. In contrast, AR mRNA was not detected in normal human fibroblasts or melanocytes and was present at reduced levels in several mammary tumor cell lines. The mitogenic activity of purified AR was also shown to be inhibited by heparin sulfate, and an AR-specific enzyme-linked immunosorbent assay (ELISA) revealed that KAF and AR are antigenically related. We have previously shown that human keratinocytes can grow in an autocrine manner. Our present study demonstrates that one of the growth factors responsible for this autocrine growth (KAF) is similar or identical to AR and that KAF and AR bioactivity can be negatively regulated by heparin sulfate.     

The case for a polyphyletic origin of mitochondria: Morphological and molecular comparisons

The comparative morphology and pigmentation of protists suggest that those with tubular mitochondrial cristae belong to a different lineage than those with lamellar cristae and that the evolutionary divergence might have been very early. We propose that the difference in cristal morphology is the result of separate origins of the mitochondria from endosymbionts related to the Rhodospirillaceae (purple nonsulfur bacteria) but differing in the morphology of their internal membranes. Comparisons of the cytochromes c of protists and the Rhodospirillaceae and of 16s rRNA T1 oligonucleotide catalogs in the Rhodospirillaceae do not contradict, and in fact provide support for, the idea. More extensive evidence may be lacking simply because cytochromes c have been studied in very few protists with tubular mitochondrial cristae.     

CYTOKINESIS AND PLASMODESMATA IN ULOTHRIX1

Cytokinesis essentially similar to that of vascular plants occurs in Ulothrix, an unbranched filamentous green alga. Plasmodesmata, similar to those of vascular plants, but different from those of many other algae, are also present. Cell plate formation and plasmodesmata also occur in Stigeoclonium, a branched green alga.     

LIGHT-HARVESTING PIGMENT-PROTEIN COMPLEXES OF THE ULVOPHYCEAE (CHLOROPHYTA):CHARACTERIZATION AND PHYLOGENETIC SIGNIFICANCE1

Photosystem II light-harvesting complexes were isolated from a number of ulvophycean algae. Some of these light-harvesting complexes displayed unusual features, most notably a high apparent molecular weight (ca. 58,000) when isolated by lithium doderyl sulfate polyarrylamide gel electrophoresis. Other ulvophycean light-harvesting complexes had a low-molecular weight (ca. 30,000). The distribution of the high-molecular weight complex was limited to certain members of the Caulerpales and Blastophysa rhizopus (Siphanocladales). Within the Caulerpales, there were also spectral differences between the high-molecular weight and low-molecular weight light-harvesting complex types. The differences in light-harvesting complexes in the Ulvophyceae suggest that there are two lines of evolution in the Caulerpales and that Blastophysa may be an intermediate between the Siphon-ocladales and the Caulerpales.     

Isolation and characterization of the Beadex locus of Drosophila melanogaster: a putative cis-acting negative regulatory element for the heldup-a gene.

We isolated recombinant lambda phage clones spanning 49 kilobases of DNA which contain the Beadex and heldup-a loci of Drosophila melanogaster. These cloned DNAs were used to analyze the structure of eight dominant mutant alleles of the Beadex locus which show increased gene activity. A region, only 700 base pairs in length, is altered in each of these mutants. Six of the mutations have DNA insertions within this segment. Most of these insertions resemble retrovirus-like transposable elements. In one case (Beadex2) the inserted sequences are homologous to the gypsy transposon family. The other two Beadex alleles were induced by hybrid dysgenesis and suffered deletions which included at least part of the 700-base-pair segment. These deletions appear to have resulted from imprecise excision or deletion of a nearby P element found in the wild-type parental strain. Analysis of one heldup-a allele (heldup-aD30r) indicates that a similar P element-mediated event is responsible for this lesion. In this mutant, deletion of sequences no more than 1,600 base pairs from the Beadex locus accompanies the loss of heldup-a function. The deleted sequences in heldup-aD30r include the entire 700-base-pair segment within which at least part of the Beadex locus resides, yet these flies have no Beadex phenotype. This indicates that a functional heldup-a gene is necessary for expression of the Beadex phenotype. Together, these results suggest that the Beadex functional domain is contained within a short segment of DNA near the heldup-a gene and support the hypothesis that the Beadex locus functions as a cis-acting negative regulatory element for the heldup-a gene.     

Studies on the size,location and turnover of calcium pools accessible to growing Tetrahymena cells

Tetrahymena pyriformis cells in the logarithmic phase of growth accumulate 2.5–3.75 times as much calcium per unit volume as is present in the growth medium. It appears that most of this calcium is stored in a non-ionic form, with approximately 30% existing in the cilia, near its site of action in effecting ciliary reversal. The exchange of extracellular ⁴⁵Ca²⁺ with the major internal pools is extremely rapid, exhibiting a $\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of less than 0.5 h. Sites located on the cilia are responsible for 35–50% of Ca²⁺ influx, with the remainder entering through other positions on the cell surface.