Isolation of cell cycle mutants of Physarum polycephalum

Summary Asynchronous amoebal cultures of temperature-sensitive mutants of Physarum polycephalum were examined cytologically, and two cell cycle mutants were identified. Genetic analysis indicated that each mutant carried a single mutation that was expressed in both amoebal and plasmodial phases. Thus it is possible to isolate cell cycle mutations expressed in plasmodia by initial isolation and analysis of amoebal mutants, a quicker procedure than the alternative of isolating plasmodial mutants directly. The two mutants were studied further by measuring nuclear DNA contents and synthesis of macromolecules. Both mutants gave results consistent with a block in nuclear division.     

The messenger matters: Pollinator functional group influences mating system dynamics

The incredible diversity of plant mating systems has fuelled research in evolutionary biology for over a century. Currently, there is broad concern about the impact of rapidly changing pollinator communities on plant populations. Very few studies, however, examine patterns and mechanisms associated with multiple paternity from cross‐pollen loads. Often, foraging pollinators collect a mixed pollen load that may result in the deposition of pollen from different sires to receptive stigmas. Coincident deposition of self‐ and cross‐pollen leads to interesting mating system dynamics and has been investigated in numerous species. But, mixed pollen loads often consist of a diversity of cross‐pollen and result in multiple sires of seeds within a fruit. In this issue of Molecular Ecology, Rhodes, Fant, and Skogen ( 2017 ) examine how pollinator identity and spatial isolation influence multiple paternity within fruits of a self‐incompatible evening primrose. The authors demonstrate that pollen pool diversity varies between two pollinator types, hawkmoths and diurnal solitary bees. Further, progeny from more isolated plants were less likely to have multiple sires regardless of the pollinator type. Moving forward, studies of mating system dynamics should consider the implications of multiple paternity and move beyond the self‐ and cross‐pollination paradigm. Rhodes et al. ( 2017 ) demonstrate the importance of understanding the roles that functionally diverse pollinators play in mating system dynamics.     

Agrarian Reform and Class Consciousness in Nicaragua

Agrarian Reform and Class Consciousness in Nicaragua. Laura J. Enriquez. Gainesville: University Press of Florida, 1997.206 pp.     

Caffeine Junkie: an Unprecedented Glutathione S-Transferase-Dependent Oxygenase Required for Caffeine Degradation by Pseudomonas putida CBB5

Caffeine and other N-methylated xanthines are natural products found in many foods, beverages, and pharmaceuticals. Therefore, it is not surprising that bacteria have evolved to live on caffeine as a sole carbon and nitrogen source. The caffeine degradation pathway of Pseudomonas putida CBB5 utilizes an unprecedented glutathione-S-transferase-dependent Rieske oxygenase for demethylation of 7-methylxanthine to xanthine, the final step in caffeine N-demethylation. The gene coding this function is unusual, in that the iron-sulfur and non-heme iron domains that compose the normally functional Rieske oxygenase (RO) are encoded by separate proteins. The non-heme iron domain is located in the monooxygenase, ndmC, while the Rieske [2Fe-2S] domain is fused to the RO reductase gene, ndmD. This fusion, however, does not interfere with the interaction of the reductase with N₁- and N₃-demethylase RO oxygenases, which are involved in the initial reactions of caffeine degradation. We demonstrate that the N₇-demethylation reaction absolutely requires a unique, tightly bound protein complex composed of NdmC, NdmD, and NdmE, a novel glutathione-S-transferase (GST). NdmE is proposed to function as a noncatalytic subunit that serves a structural role in the complexation of the oxygenase (NdmC) and Rieske domains (NdmD). Genome analyses found this gene organization of a split RO and GST gene cluster to occur more broadly, implying a larger function for RO-GST protein partners.     

Increased Atmospheric SO2 Detected from Changes in Leaf Physiognomy across the Triassic–Jurassic Boundary Interval of East Greenland

The Triassic–Jurassic boundary (Tr–J; ∼201 Ma) is marked by a doubling in the concentration of atmospheric CO₂, rising temperatures, and ecosystem instability. This appears to have been driven by a major perturbation in the global carbon cycle due to massive volcanism in the Central Atlantic Magmatic Province. It is hypothesized that this volcanism also likely delivered sulphur dioxide (SO₂) to the atmosphere. The role that SO₂ may have played in leading to ecosystem instability at the time has not received much attention. To date, little direct evidence has been presented from the fossil record capable of implicating SO₂ as a cause of plant extinctions at this time. In order to address this, we performed a physiognomic leaf analysis on well-preserved fossil leaves, including Ginkgoales, bennettites, and conifers from nine plant beds that span the Tr–J boundary at Astartekløft, East Greenland. The physiognomic responses of fossil taxa were compared to the leaf size and shape variations observed in nearest living equivalent taxa exposed to simulated palaeoatmospheric treatments in controlled environment chambers. The modern taxa showed a statistically significant increase in leaf roundness when fumigated with SO₂. A similar increase in leaf roundness was also observed in the Tr–J fossil taxa immediately prior to a sudden decrease in their relative abundances at Astartekløft. This research reveals that increases in atmospheric SO₂ can likely be traced in the fossil record by analyzing physiognomic changes in fossil leaves. A pattern of relative abundance decline following increased leaf roundness for all six fossil taxa investigated supports the hypothesis that SO₂ had a significant role in Tr–J plant extinctions. This finding highlights that the role of SO₂ in plant biodiversity declines across other major geological boundaries coinciding with global scale volcanism should be further explored using leaf physiognomy.