“Self” and “Non-Self” in the Control of Phytoalexin Biosynthesis: Plant Phospholipases A2 with Alkaloid-Specific Molecular Fingerprints

The overproduction of specialized metabolites requires plants to manage the inherent burdens, including the risk of self-intoxication. We present a control mechanism that stops the expression of phytoalexin biosynthetic enzymes by blocking the antecedent signal transduction cascade. Cultured cells of Eschscholzia californica (Papaveraceae) and Catharanthus roseus (Apocynaceae) overproduce benzophenanthridine alkaloids and monoterpenoid indole alkaloids, respectively, in response to microbial elicitors. In both plants, an elicitor-responsive phospholipase A2 (PLA2) at the plasma membrane generates signal molecules that initiate the induction of biosynthetic enzymes. The final alkaloids produced in the respective plant inhibit the respective PLA, a negative feedback that prevents continuous overexpression. The selective inhibition by alkaloids from the class produced in the “self” plant could be transferred to leaves of Nicotiana benthamiana via recombinant expression of PLA2. The 3D homology model of each PLA2 displays a binding pocket that specifically accommodates alkaloids of the class produced by the same plant, but not of the other class; for example, C. roseus PLA2 only accommodates C. roseus alkaloids. The interaction energies of docked alkaloids correlate with their selective inhibition of PLA2 activity. The existence in two evolutionary distant plants of phospholipases A2 that discriminate “self-made” from “foreign” alkaloids reveals molecular fingerprints left in signal enzymes during the evolution of species-specific, cytotoxic phytoalexins.     

Ants adjust their pheromone deposition to a changing environment and their probability of making errors

Animals must contend with an ever-changing environment. Social animals, especially eusocial insects such as ants and bees, rely heavily on communication for their success. However, in a changing environment, communicated information can become rapidly outdated. This is a particular problem for pheromone trail using ants, as once deposited pheromones cannot be removed. Here, we study the response of ant foragers to an environmental change. Ants were trained to one feeder location, and the feeder was then moved to a different location. We found that ants responded to an environmental change by strongly upregulating pheromone deposition immediately after experiencing the change. This may help maintain the colony''s foraging flexibility, and allow multiple food locations to be exploited simultaneously. Our treatment also caused uncertainty in the foragers, by making their memories less reliable. Ants which had made an error but eventually found the food source upregulated pheromone deposition when returning to the nest. Intriguingly, ants on their way towards the food source downregulated pheromone deposition if they were going to make an error. This may suggest that individual ants can measure the reliability of their own memories and respond appropriately.     

Microgeographic genetic structure and intraspecific parasitism in the ant Leptothorax nylanderi

1. Genetic colony structure of the small central European ant Leptothorax nylanderi is affected strongly by ecological constraints such as nest site availability and intraspecific social parasitism. 2. Although L. nylanderi is generally monogynous and monandrous, more than a quarter of all nests collected in a dense population near Würzburg, Germany, contained several matrilines. As shown by microsatellite analysis, the average nest‐mate relatedness in these nests was 0.20. Genetically heterogeneous nests arise from nest take‐over by alien colonies or founding queens, a result of severe competition for nest sites. 3. In summer, more than one‐third of all colonies inhabited several nest sites at a time. Polydomy appears to be rather limited, with two or three nests belonging to a single polydomous colony. 4. Queens appear to dominate male production; only a small fraction (8%) of males was definitively not progeny of the queen present but might have been worker progeny or offspring of another queen. 5. Strong evidence for heterozygote deficiency was found and a total of nine diploid males was discovered in two colonies. These findings suggest deviation from random mating through small, localised nuptial flights.     

A phase I/II study of recombinant interferon alpha 2a and hydroxyurea for chronic myelocytic leukemia

Nine previously untreated patients with Philadelphia chromosome-positive chronic myelocytic leukemia (CML) were treated with recombinant interferon alpha 2a (rIFN-alpha 2a) and hydroxyurea. Patients received 6 X 10(6) U rIFN-alpha 2a daily for the first week and 3 X 10(6) U rIFN-alpha 2a daily for the second week. As maintenance treatment starting on day 15, patients received 3 X 10(6) U rIFN-alpha 2a 3 times a week. Simultaneously, hydroxyurea was given, starting at a dose of 40 mg/kg on day one. The maintenance dosage was adjusted to the white blood cell count. Two patients responded with complete hematological remissions but without cytogenetic and molecular-genetic improvements. Seven patients responded with partial hematological remissions. Response to therapy was rapid; normal white blood cell counts were reached after a median of 12 days. The doses of rIFN-alpha 2a and hydroxyurea needed to keep the leucocyte count in the normal range were low (3 X 10(6) U rIFN-alpha 2a 3 times per week, 0.5-1.5 g hydroxyurea/day). Acute toxicity of the combination therapy consisted of fever (9 of 9 patients), flulike symptoms (7 of 9 patients), pruritus and/or rash (3 of 9 patients) and evidence of a tumor cell lysis syndrome (1 of 9 patients). The side effects were not dose-limiting. Combination therapy with rIFN-alpha 2a and hydroxyurea for CML is well tolerated and allows quick and effective hematological control of the disease.     

Molecular cloning of a pea mRNA encoding an early light induced,nuclear coded chloroplast protein

Summary cDNA clones were isolated for a chloroplast protein, the mRNA of which is induced to maximum levels within 2–4 h after onset of illumination in five day old, etiolated pea seedlings. The cDNA library was constructed from poly(A)⁺-mRNA which was isolated from 4 h illuminated seedlings. The extremely short induction period of the early light induced protein(ELIP)-mRNA established the basis of our screening procedure. Colony hybridization experiments were performed with³²P-labelled cDNA probes, synthesized from RNA of seedlings which had been exposed to different programs of illumination. Plasmid DNAs were isolated from colonies showing strong hybridization signals exclusively with cDNA corresponding to the 4 h-mRNA. Hybrid released translation of preselected plasmids p 17/C2 and p17/C4 revealed a peptide of M_r 24 000. After posttranslational importin vitro, the processed product of M_r 17 000 appears in the chloroplast. Using these clones, the expression of the ELIP-mRNA was investigated by DOT-hybridization. The ELIP-mRNA reaches maximum levels within 2–4 hours after onset of illumination. Our results correspond precisely to thein vivo characteristics and indicate positive identification of the sought clones.     

Reproductive Hierarchies Among Workers of the Slave-making Ant,Chalepoxenus muellerianus

In queenright colonies of the slave-making ant, Chalepoxenus muellerianus, workers formed dominance hierarchies through ritualized food begging and antennation bouts, but did not lay eggs. Within a few hours of the experimental removal of the queen, the frequency of dominance displays increased drastically and the interactions became considerably more violent. During the observation period, the dominant workers almost incessantly attacked subordinate slave-makers and slaves by antennation and biting. The aggression rate decreased after approximately 3–4 wk. Within a single colony, several high-ranking workers were observed laying eggs, although typically only one or a few top-ranking individuals became fully fertile Directly after eclosion, young workers engaged in aggressive interactions with other young workers and high-ranking old workers, but did not dominate the top-ranking egg-layers. Callows achieved ranks immediately below the top-ranking worker.     

RAPD reactions from crude plant DNA

As opposed to standard polymerase chain reaction (PCR) using specific primers, genome analysis involving short random primers, for example RAPD, may yield inconsistent results if crude plant DNA preparations are used as the template. When RNase A, a thermostable enzyme, was added to such reactions, highly repeatable banding patterns were obtained from crude plant DNA, thus speeding up analyses substantially.     

Reproductive Competition in Colonies of the Ant Leptothorax gredleri

Colonies of the ant, Leptothorax (s. str.) gredleri may contain several inseminated female reproductives of which typically only one is laying eggs. Observations suggest that “functional monogyny” is caused by aggressive interactions among nestmate queens. Only the most dominant queen reproduces. Subordinate queens either leave the colony to found their own nests solitarily or by budding, or stay in the nest without reproducing, but may eventually replace the dominant queen. The interrelations of life history of L. gredleri, population structure and habitat characteristics are examined.