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R C Starr

Publications and source records attributed to R C Starr.

9 recordsLinked to original sources
PubMed1996

The lurlenes, a new class of plastoquinone-related mating pheromones from Chlamydomonas allensworthii (Chlorophyceae).

Chlamydomonas allensworthii is a recently described species, which differs phenotypically and in its reproductive behaviour from other members of this genus of flagellated green protists. Its female cells temporarily or constantly excrete a luring signal into the medium to attract the male cells for mating. The sperm is susceptible to the pheromone either all the time or only after a maturation process. Maturation in this species is accompanied with a colour shift from green to khaki (strain from Lemon cove CA) or to olive (strain from Catarina TX), apparently due to degradation of chloroplast material. In the bioassay with polyacrylamide beads (plain or DEAE-substituted) to which the lures are bound, acting as mock females, Catarina-strain males are only attracted to Catarina strain lures, whereas Lemon-Cove-strain males are attracted to Lemon-Cove-strain lures and to a lesser extent, to Catarina-strain lures. Being amphiphilic acid, Lemon-Cove-strain lure is more tightly bound to DEAE beads. Catarina-strain lure is an uncharged amphiphile. The two signal compounds have been isolated and identified by chemical analysis and mass and NMR spectroscopies as O(5)-beta-D-xylosylated degradation products of the chloroplast electron transporter hydroplastoquinone, its polyprenoid side chain being oxidatively cleaved at the fourth double bond. Lurlenic acid (lurlene L) is the resulting acid and lurlenol (lurlene C) the corresponding alcohol. The pheromonal activities of both compounds have a threshold at 1 pM, and are destroyed by deglycosylation and subsequent oxidation to the quinonoid aglycon. This class of amphiphilic lures, having the same basic glycosylated hydroquinone structure, is named lurlenes.

Animals↗
PubMed1995

Chemoattraction of male gametes by a pheromone produced by female gametes of Chlamydomonas.

In isogamous species of Chlamydomonas, such as Chlamydomonas reinhardtii and Chlamydomonas eugametos, the sexual process involves the use of flagella agglutinins by which the gametes of compatible strains adhere through chance encounter and ultimately pair and fuse to form zygotes. In a newly described heterogamous species, Chlamydomonas allensworthii, the sexual process is initiated by the chemoattraction of small sperm to a sexually competent female gamete, which continues to secrete the pheromone until it has fused with one of the sperm so attracted. From bacteria-free female strains of C. allensworthii, the chemoat-tractant has been isolated and identified as a pentosylated hydroquinone (Mr = 532) whose spectral, chemical, and physical properties are in accord with the structure of a 2,3-dimethyl-5-(triprenylcarboxymethyl)-1,4-benzohydroquinone-1-(beta-xyloside). A rapid bioassay of the pheromone uses DEAE-Toyopearl 650M beads to which the pheromone adsorbs. When such activated beads are placed in a suspension of sperm, they act as surrogate females and attract the small motile sperm. The purified pheromone shows activity at a concentration as low as 1 pM.

Journal Article↗
PubMed1980

L-Glutamic acid as a mediator of sexual morphogenesis in Volvox capensis.

In Volvox capensis the development of sexual individuals is in response to low concentrations (68 nM) of L-glutamic acid rather than to such species-specific glycoproteins as have been isolated in Volvox carteri or are believed to exist in a number of other species. V. capensis grows equally as well in light and in darkness in a medium supplemented with sodium acetate; however, L-glutamic acid is active as an inducer of the sexual form only in populations grown in the light. The site of action of L-glutamic acid and its biochemical role in the sexual response are unknown. Attempts to induce the sexual response by using the other L-amino acids, various analogs of glutamic acid, compounds of similar structure (e.g., gamma-aminobutyric acid), and intermediates of biochemical pathways known to involve L-glutamic acid (e.g., alpha-ketoglutarate or pyroglutamic acid) have been unsuccessful. L-Glutamic acid is produced by V. capensis as a natural product of the digestion of the glycoproteinaceous parental matrix at the time young spheroids escape. As a population increases, so does the level of L-glutamic acid produced at each succeeding generation until the threshold of sensitivity is reached and the induction of sexual forms is effected. This serves as a mechanism for ensuring the production of sexual spheroids and their zygotes, the only phase in the life cycle resistant to drying. Thus, Volvox is especially adapted to an existence in ephemeral pools of water resulting from seasonal rains.

Journal Article↗
PubMed1974

Purification and characterization of the hormone initiating sexual morphogenesis in Volvox carteri f. nagariensis Iyengar.

In Volvox carteri f. nagariensis male spheroids secrete into the medium a sexual hormone which controls the initiation of the developmental pathway leading to the formation of sexual embryos. In the absence of the hormone asexual embryos are formed. Analysis of the highly purified hormone indicates that it is a glycoprotein of 27,500-30,000 daltons, composed of one peptide chain, which has a typical composition except for a relatively low content of tryptophan. The glycosidic moiety, which accounts for about 45% of the weight of the molecule, consists of pentoses, hexoses, and amino hexoses. In the bioassay the highly purified hormone stimulates 100% formation of sexual embryos at a concentration of 10(-10) g/liter and 14.4% sexual embryos at 10(-11) g/liter (3 x 10(-16) M). The activity is remarkably thermostable and resistant to different denaturing procedures.

Amino Acids↗