Alterations of auxin perception in rolB-transformed tobacco protoplasts. Time course of rolB mRNA expression and increase in auxin sensitivity reveal multiple control by auxin.

Expression and physiological effects of the root-inducing rolB gene of Agrobacterium rhizogenes T-DNA were studied simultaneously in tobacco (Nicotiana tabacum) mesophyll protoplasts. The kinetic study of the expression of rolB mRNA following exogenous auxin application showed that auxin transiently stimulated rolB expression, with mRNA levels starting to accumulate 6 to 9 h after auxin was supplied and increasing 300-fold after 12 to 18 h. The parallel study of the auxin sensitivity of rolB-transformed protoplasts, as assayed by their electrical response to the hormone, showed that the auxin treatment generated an increase in sensitivity by a factor of up to 100,000, whereas in untransformed protoplasts the same auxin treatment induced an increase in auxin sensitivity that never exceeded 30- to 50-fold. This reflects a strong cooperative effect of auxin and rolB in transformed protoplasts. Surprisingly, the maximal increase in sensitivity was observed several hours before the maximal accumulation of rolB mRNA, suggesting that the dramatic control of auxin sensitivity by auxin in rolB-transformed protoplasts requires only low levels of rolB expression. Antibodies directed against ZmER-abp1, the major auxin-binding protein from maize, differentially altered the auxin sensitivity of the electrical response of rolB-transformed and normal protoplasts. This suggests that alterations of the auxin reception-transduction pathway at the plasma membrane of rolB-transformed protoplasts may account for their increased auxin sensitivity.     

Activation of formylmethanofuran synthesis in cell extracts of Methanobacterium thermoautotrophicum.

In cell extracts of Methanobacterium thermoautotrophicum, formylmethanofuran (formyl-MFR) synthesis (an essential CO2 fixation reaction that is an early step in CO2 reduction to methane) is subject to a complex activation that involves a heterodisulfide of coenzyme M and N-(7-mercaptoheptanoyl)threonine O3-phosphate (CoM-S-S-HTP). In this paper we report that titanium(III) citrate, a low-potential reducing agent, stimulated CO2 reduction to methane and activated formyl-MFR synthesis in cell extracts. Titanium(III) citrate functioned as the sole source of electrons for formyl-MFR synthesis and enabled this reaction to occur independently of CoM-S-S-HTP. In addition, CoM-S-S-HTP was found to activate an unknown electron carrier that reduced metronidazole. The activation of formyl-MFR synthesis by CoM-S-S-HTP may involve the activation of a low-potential electron carrier.     

Larvae of Maculinea rebeli, a large-blue butterfly, and their Myrmica host ants: wild adoption and behaviour in ant-nests

The behavioural interactions between caterpillars of Maculinea rebeli Hir. and their Myrmica ant hosts were studied, both in the wild at the time of adoption, and inside captive nests of six Myrmica species.
In the wild, freshly moulted, final instar caterpillars left their food-plants at a time of day that coincided with the peak foraging activity of Myrmica (18:00-20:00 h). Once on the ground, caterpillars made no attempt to search for Myrmica but settled and waited for foraging ants to find them, which took up to 1.5 h. There was no adoption ritual: foragers of any Myrmica species picked up the caterpillars within 1–4 sec of discovery, and carried them directly to their nests.
Caterpillars grew from < 2 mg to 110 mg in laboratory ant-nests. About 60 mg was gained in autumn but 40% of this was lost during the winter, while the temperature was < 14 °C. Although caterpillars survived best with their normal host, Myrmica schencki , they could also survive in the nests of other Myrmica species. The presence of queen ants had no effect upon survival. The behaviour of the caterpillars was described and illustrated: this included the production of secretions that were drunk by the ants, begging for food and direct feeding by ants. The preferred solid food was ant eggs.
The results are discussed in terms of the social biology of Myrmica ants. It is hypothesized that Maculinea rebeli caterpillars mimic the touch pheromones of ant worker-larvae. This would explain the inability of ants to recognize caterpillars before touching them, their immediate adoption by any Myrmica species after discovery, host specificity inside wild ant-nests, the absence of queen-effect and the intimate attention of host workers.