Strigol: biogenesis and physiological activity

The role played by molecules of the strigolactone family in stimulating the germination of seeds of parasitic weeds of the genera Striga, Orobanche and Alectra has never been clearly elucidated. The biogenesis of these unusual terpenoid lactones, originally identified in minute quantities in the root exudates of a small number of host plants and two or three "false hosts", also remains obscure. These lactones, as the chemical signals which initiate the life cycle of Striga, are consequently at the forefront of the Striga research effort. This paper reviews recent key discoveries relating to the biosynthesis and mode of action of strigolactones, and summarises the evidence suggesting that these molecules may be far more widely distributed and have a greater physiological significance than has hitherto been appreciated.     

Identification and cardiotropic actions of brain/gut-derived tachykinin-related peptides (TRPs) from the American lobster Homarus americanus

Two tachykinin-related peptides (TRPs) are known in decapods, APSGFLGMRamide and TPSGFLGMRamide. The former peptide appears to be ubiquitously conserved in members of this taxon, while the latter has been suggested to be a genus (Cancer)- or infraorder (Brachyura)-specific isoform. Here, we characterized a cDNA from the American lobster Homarus americanus (infraorder Astacidea) that encodes both TRPs: six copies of APSGFLGMRamide and one of TPSGFLGMRamide. Mass spectral analyses of the H. americanus supraoesophageal ganglion (brain) and commissural ganglia confirmed the presence of both peptides in these neural tissues; both isoforms were also detected in the midgut. Physiological experiments showed that both APSGFLGMRamide and TPSGFLGMRamide are cardioactive in H. americanus, eliciting identical increases in both heart contraction frequency and amplitude. Collectively, our data represent the first genetic confirmation of TRPs in H. americanus and of TPSGFLGMRamide in any species, demonstrate that TPSGFLGMRamide is not restricted to brachyurans, and show that both this peptide and APSGFLGMRamide are brain-gut isoforms, the first peptides thus far confirmed to possess this dual tissue distribution in H. americanus. Our data also suggest a possible role for TRPs in modulating the output of the lobster heart.     

Localization of the Thy-1 antigen to the surfaces of rat retinal ganglion cells

Indirect immunofluorescence has been used to localize the Thy-1 antigen to ganglion cell axons, the ganglion cell layer and the inner plexiform layer in cryostat sections of adult and neonatal rat retina. In similar immunofluorescence experiments monoclonal antibodies raised against the 200,000 molecular weight neurofilament polypeptide bound only to ganglion cell axons and processes in the outer plexiform layer.Less than 1% of cells dissociated from 8 day postnatal rat retina had superficial Thy-1 antigen demonstrable by immunofluorescence; these cells were generally large and their size spectrum was similar to that of ganglion cells $\text{in}$$\text{situ}$. After culture for 1 day many of these Thy-1 positive cells had generated neurofilament antigen.We conclude that Thy-1 is found chiefly or exclusively on ganglion cells of eight day retina, and may be useful in the identification and isolation of these cells by immunoselection procedures.     

Enzymatic conversion of glutamate to delta-aminolevulinic acid in soluble extracts of Euglena gracilis

Glutamate was converted to the chlorophyll and heme precursor delta-aminolevulinic acid in soluble extracts of Euglena gracilis. delta-Aminolevulinic acid-forming activity depended on the presence of native enzyme, glutamate, ATP, Mg2+, NADPH or NADH, and RNA. The requirement for reduced pyridine nucleotide was observed only if, prior to incubation, the enzyme extract was filtered through activated carbon to remove firmly bound reductant. Dithiothreitol was also required for activity after carbon treatment. delta-Aminolevulinic acid formation was stimulated by RNA from various plant tissues and algal cells, including greening barley leaves and members of the algal groups Chlorophyta (Chlorella vulgaris, Chlamydomonas reinhardtii), Rhodophyta (Cyanidium caldarium), Cyanophyta (Anacystis nidulans, Synechocystis sp. PCC 6803), and Prochlorophyta (Prochlorothrix hollandica), but not by RNA derived from Escherichia coli, yeast, wheat germ, bovine liver, and Methanobacterium thermoautotrophicum. E. coli glutamate-specific tRNA was inhibitory. Several of the RNAs that did not stimulate delta-aminolevulinic acid formation nevertheless became acylated when incubated with glutamate in the presence of Euglena enzyme extract. RNA extracted from nongreen dark-grown wild-type Euglena cells was about half as stimulatory as that from chlorophyllous light-grown cells, and RNA from aplastidic mutant cells stimulated only slightly. delta-Aminolevulinic acid-forming enzyme activity was present in extracts of light-grown wild-type cells, but undetectable in extracts of aplastidic mutant and dark-grown wild-type cells. Gabaculine inhibited delta-aminolevulinic acid formation at submicromolar concentration. Heme inhibited 50% at 25 microM, but protoporphyrin IX, Mg-protoporphyrin IX, and protochlorophyllide inhibited only slightly at this concentration.     

Future directions in plant hormone research

Future directions in plant hormone research are discussed, with particular reference to the regulation of hormone biosynthesis, hormone perception, and signal transduction.