BICARBONATE STIMULATION OF CALCIFICATION AND PHOTOSYNTHESIS IN TWO HERMATYPIC CORALS1

A wide range of bicarbonate concentrations was used to monitor the kinetics of bicarbonate (HCO₃^?) use in both photosynthesis and calcification in two reef‐building corals, Porites porites and Acropora sp. Experiments carried out close to the P. porites collection site in Barbados showed that additions of NaHCO₃ to synthetic seawater proportionally increased the calcification rate of this coral until the concentration exceeded three times that of seawater (6 mM). Photosynthetic rates were also stimulated by HCO₃^? addition, but these became saturated at a lower concentration (4 mM). Similar experiments on aquarium‐acclimated colonies of Indo‐Pacific Acropora sp. showed that calcification and photosynthesis in this coral were enhanced to an even greater extent than P. porites, with calcification continuing to increase above 8 mM HCO₃^?, and photosynthesis saturating at 6 mM. Calcification rates of Acropora sp. were also monitored in the dark, and, although these were lower than in the light for a given HCO₃^? concentration, they still increased dramatically with HCO₃^? addition, showing that calcification in this coral is light stimulated but not light dependent.     

Parasite age-intensity relationships in red-spotted newts: does immune memory influence salamander disease dynamics?

Acquired immune memory in vertebrates influences transmission and persistence of infections, with consequences for parasite dynamics at both the individual and population levels. The potential impact of acquired immunity is of particular interest for salamanders, whose acquired immune systems are thought to be less effective than those of frogs and other tetrapods. One way to examine the importance of acquired immunity to parasite dynamics at the population level is by examining the relationship between host age and parasite infection intensity. Acquired immunity reduces infection rates in older animals, causing decreased parasite intensity in older age classes and leading to curvilinear age-intensity relationships for persistent parasites and convex age-intensity relationships for transient parasites. We used age-intensity relationships to look for the signature of acquired immunity for 12 parasite taxa of red-spotted newts (Notophthalmus viridescens), using data from a 2-year parasitological survey of six newt populations. We estimated ages from snout-vent length (SVL) based on the relationship between SVL and skeletochronologically-derived ages in a subset of newts. We found evidence of acquired immunity to two parasite taxa, bacterial pathogens and the protist Amphibiocystidium viridescens, whose convex age-intensity relationships could not be easily explained by alternative mechanisms. Our results suggest that the acquired immune response of newts is sufficient to influence the dynamics of at least some parasites.     

The maize floury1 gene encodes a novel endoplasmic reticulum protein involved in zein protein body formation

The maize (Zea mays) floury1 (fl1) mutant was first reported almost 100 years ago, but its molecular identity has remained unknown. We report the cloning of Fl1, which encodes a novel zein protein body membrane protein with three predicted transmembrane domains and a C-terminal plant-specific domain of unknown function (DUF593). In wild-type endosperm, the FL1 protein accumulates at a high level during the period of zein synthesis and protein body development and declines to a low level at kernel maturity. Immunogold labeling showed that FL1 resides in the endoplasmic reticulum surrounding the protein body. Zein protein bodies in fl1 mutants are of normal size, shape, and abundance. However, mutant protein bodies ectopically accumulate 22-kD alpha-zeins in the gamma-zein-rich periphery and center of the core, rather than their normal discrete location in a ring at outer edge of the core. The 19-kD alpha-zein is uniformly distributed throughout the core in wild-type protein bodies, and this distribution is unaffected in fl1 mutants. Pairwise yeast two-hybrid experiments showed that FL1 DUF593 interacts with the 22-kD alpha-zein. Results of these studies suggest that FL1 participates in protein body formation by facilitating the localization of 22-kD alpha-zein and that this is essential for the formation of vitreous endosperm.     

Interaction of the Saccharomyces cerevisiae cortical actin patch protein Rvs167p with proteins involved in ER to Golgi vesicle trafficking

We have used affinity chromatography to identify two proteins that bind to the SH3 domain of the actin cytoskeleton protein Rvs167p: Gyp5p and Gyl1p. Gyp5p has been shown to be a GTPase activating protein (GAP) for Ypt1p, a Rab GTPase involved in ER to Golgi trafficking; Gyl1p is a protein that resembles Gyp5p and has recently been shown to colocalize with and belong to the same protein complex as Gyp5p. We show that Gyl1p and Gyp5p interact directly with each other, likely through their carboxy-terminal coiled-coil regions. In assays of GAP activity, Gyp5p had GAP activity toward Ypt1p and we found that this activity was stimulated by the addition of Gyl1p. Gyl1p had no GAP activity toward Ypt1p. Genetic experiments suggest a role for Gyp5p and Gyl1p in ER to Golgi trafficking, consistent with their biochemical role. Since Rvs167p has a previously characterized role in endocytosis and we have shown here that it interacts with proteins involved in Golgi vesicle trafficking, we suggest that Rvs167p may have a general role in vesicle trafficking.     

Sequence-specific interaction between mitochondrial Fe-S scaffold protein Isu and Hsp70 Ssq1 is essential for their in vivo function

Isu, the scaffold for assembly of Fe-S clusters in the yeast mitochondrial matrix, is a substrate protein for the Hsp70 Ssq1 and the J-protein Jac1 in vitro. As expected for an Hsp70-substrate interaction, the formation of a stable complex between Isu and Ssq1 requires Jac1 in the presence of ATP. Here we report that a conserved tripeptide, PVK, of Isu is critical for interaction with Ssq1 because amino acid substitutions in this tripeptide inhibit both the formation of the Isu-Ssq1 complex and the ability of Isu to stimulate the ATPase activity of Ssq1. These biochemical defects correlate well with the growth defects of cells expressing mutant Isu proteins. We conclude that the Ssq1-Isu substrate interaction is critical for Fe-S cluster biogenesis in vivo. The ability of Jac1 and mutant Isu proteins to cooperatively stimulate the ATPase activity of Ssq1 was also measured. Increasing the concentration of Jac1 and mutant Isu together but not individually partially overcame the effect of the reduced affinity of the Isu mutant proteins for Ssq1. These results, along with the observation that overexpression of Jac1 was able to suppress the growth defect of an ISU mutant, support the hypothesis that Isu is "targeted" to Ssq1 by Jac1, with a preformed Jac1-Isu complex interacting with Ssq1.     

Rapid increase in southern elephant seal genetic diversity after a founder event

Genetic diversity provides the raw material for populations to respond to changing environmental conditions. The evolution of diversity within populations is based on the accumulation of mutations and their retention or loss through selection and genetic drift, while migration can also introduce new variation. However, the extent to which population growth and sustained large population size can lead to rapid and significant increases in diversity has not been widely investigated. Here, we assess this empirically by applying approximate Bayesian computation to a novel ancient DNA dataset that spans the life of a southern elephant seal (Mirounga leonina) population, from initial founding approximately 7000 years ago to eventual extinction within the past millennium. We find that rapid population growth and sustained large population size can explain substantial increases in population genetic diversity over a period of several hundred generations, subsequently lost when the population went to extinction. Results suggest that the impact of diversity introduced through migration was relatively minor. We thus demonstrate, by examining genetic diversity across the life of a population, that environmental change could generate the raw material for adaptive evolution over a very short evolutionary time scale through rapid establishment of a large, stable population.     

Ecosystem Responses to Nitrogen Deposition in the Colorado Front Range

We asked whether 3–5 kg N y⁻¹ atmospheric N deposition was sufficient to have influenced natural, otherwise undisturbed, terrestrial and aquatic ecosystems of the Colorado Front Range by comparing ecosystem processes and properties east and west of the Continental Divide. The eastern side receives elevated N deposition from urban, agricultural, and industrial sources, compared with 1–2 kg N y⁻¹ on the western side. Foliage of east side old-growth Englemann spruce forests have significantly lower C:N and lignin:N ratios and greater N:Mg and N:P ratios. Soil % N is higher, and C:N ratios lower in the east side stands, and potential net N mineralization rates are greater. Lake NO₃ concentrations are significantly higher in eastern lakes than western lakes. Two east side lakes studied paleolimnologically revealed rapid changes in diatom community composition and increased biovolumes and cell concentrations. The diatom flora is now representative of increased disturbance or eutrophication. Sediment nitrogen isotopic ratios have become progressively lighter over the past 50 years, coincident with the change in algal flora, possibly from an influx of isotopically light N volatilized from agricultural fields and feedlots. Seventy-five percent of the increased east side soil N pool can be accounted for by increased N deposition commensurate with human settlement. Nitrogen emissions from fixed, mobile, and agricultural sources have increased dramatically since approximately 1950 to the east of the Colorado Front Range, as they have in many parts of the world. Our findings indicate even slight increases in atmospheric deposition lead to measurable changes in ecosystem properties. Received 16 November 1999; accepted 8 February 2000.