The hypothesis that biotic interactions are stronger at lower relative to higher latitudes has a rich history, drawing from ecological and evolutionary theory. While this hypothesis suggests that stronger interactions at lower latitudes may contribute to the maintenance of contemporary patterns of diversity, there remain few standardized biogeographic comparisons of community effects of species interactions. Using marine seagrasses as a focal ecosystem of conservation importance and sessile marine invertebrates as model prey, we tested the hypothesis that predation is stronger at lower latitudes and can shape contemporary patterns of prey diversity. To further advance understanding beyond prior studies, we also explored mechanisms that likely underlie a change in interaction outcomes with latitude. Multiple observational and experimental approaches were employed to test for effects of predators, and the mechanisms that may underlie these effects, in seagrass ecosystems of the western Atlantic Ocean spanning 30° of latitude from the temperate zone to the tropics. In predator exclusion experiments conducted in a temperate and a tropical region, predation decreased sessile invertebrate abundance, richness and diversity on both natural and standardized artificial seagrass at tropical but not temperate sites. Further, predation reduced invertebrate richness at both local and regional scales in the tropics. Additional experiments demonstrated that predation reduced invertebrate recruitment in the tropics but not the temperate zone. Finally, direct observations of predators showed higher but variable consumption rates on invertebrates at tropical relative to temperate latitudes. Together, these results demonstrate that strong predation in the tropics can have consequential impacts on prey communities through discrete effects on early life stages as well as longer‐term cumulative effects on community structure and diversity. Our detailed experiments also provide some of the first data linking large‐scale biogeographic patterns, community‐scale interaction outcomes and direct observation of predators in the temperate zone and tropics. Therefore, our results support the hypothesis that predation is stronger in the tropics, but also elucidate some of the causes and consequences of this variation in shaping contemporary patterns of diversity.
Enzymes and metabolites associated with mitigation of paraquat toxicity were compared in two paraquat-tolerant mutants and a sensitive wild-type strain of the fern Ceratopteris richardii Brongn. In 21-day-old gametophytes, the specific activities of superoxide dismutase, catalase, peroxidase, glutathione reductase, dehydroascorbate reductase, and ascorbate peroxidase showed no differences that would explain mutant tolerance. Constitutive levels of ascorbate and glutathione also did not differ significantly in the three strains. An experiment testing the inducibility of paraquat tolerance revealed no change in the dose response of mutant or wild type gametophytes after exposure to sublethal concentrations of the herbicide. Uptake of paraquat by whole gametophytes was also equivalent in mutants and wild type. These data suggest that the physiological basis for tolerance in these mutants, unlike several other tolerant biotypes reported, does not lie in the oxygen radical scavenging system, in an inducible stress response, or in a block to whole-plant uptake.Paraquat-tolerant mutants of the fern Ceratopteris richardii Brongn. have been selected by means of an in vitro, whole-plant screening system (14,15). Genetic analyses oftwo mutant strains, HaPQ2 and HaPQ45, indicate that a 10-to 20-fold increase in tolerance is conferred in both by different recessive mutations in the same locus (14). We are conducting a series of biochemical, structural, and physiological studies of these mutants to determine the mechanism of tolerance.Investigations of paraquat tolerance and resistance in other species suggest several possible explanations for the trait in Ceratopteris. Because paraquat kills green tissue via increased production of superoxide and its peroxide products (11, 27), tolerance could be due to improved catabolism of active oxygen through a series of reactions located in the chloroplast (7, 8, 10, 12, A mutation increasing the activity of one of these enzymes or of the level of an intermediary electron carrier (glutathione or ascorbate) essential to this detoxification scheme could explain tolerance. Although they are extrachloroplastic, catalase and peroxidase could be also involved in the removal of H202, and enhanced activities of superoxide dismutase, catalase, and peroxidase have been reported for polygenic mutants of Lolium perenne (13). Mutant enhancement of an inducible (rather than constitutive) defense system is also possible; for example, in Spirodela oligorrhiza, paraquat tolerance has been induced by adaptation to low levels ofbenzyl viologen, a nontoxic structural analog of paraquat (18).While oxygen detoxification mutations may alter the organism's response to paraquat-mediated superoxide formation, other mutations could prevent paraquat's reduction to the monovalent radical either by changing the ability of PSI to reduce paraquat or by limiting the herbicide's access to its site of reduction in the chloroplast. Some seedling-lethal mutations of maize reported by Miles (21) show paraquat re...
Abstract. A new procedure is described for purifying proteins that specifically bind to DNA. DNA is entrapped in polyacrylamide gel particles which can then be used in standard column chromatographic procedures. The method was developed using Escherichia coli DNA polymerase as the test material. The crude enzyme was applied at low ionic strength and eluted at high ionic strength with a 200-fold increase in specific activity on a single passage through the column. The method is versatile and simple and is not restricted to DNAprotein systems. Any macromolecule can be entrapped in the gel particles; these can interact with other large or small molecules in the liquid phase. The gel is stable at elevated temperatures and can therefore be used in hybridization experiments.The binding of DNA-specific proteins to DNA provides the basis for a highly efficient and relatively simple procedure for isolating and purifying such proteins. Several methods have been described1-4 for immobilizing DNA on solid matrices which are then employed in standard column chromatographic procedures. We present here a new method in which the immobile matrix is composed of polyacrylamide gel particles. Aside from being versatile and simple, the method has the main advantages that no chemical steps are needed to fix the DNA in the matrix and the same column can be used repeatedly. The gel is made by dissolving DNA in the monomer solution before polymerization. The pore size of the gel particle is such that the DNA remains trapped, unless it is attacked enzymatically. So far, we have used only native DNA in the gel, but there is no reason why denatured DNA, RNA, or in fact any other macromolecule cannot be used since the pore size may be varied at will; therefore, even small molecules can be entrapped in the particles. The gel is stable at elevated temperatures, so that it is also possible to carry out hybridization experiments using this method. If the molecules that one seeks to purify are too large to enter the gel particle, this procedure can still be used, for there appears to be enough immobilized DNA protruding from the surface to be able to interact efficiently with the molecules in the liquid phase.We report here the details of this new procedure using as a test material a crude fraction of DNA polymerase previously described.5 One passage through the DNA-gel column increased the specific activity about 200 times. The physical characterization of this polymerase will be described in detail elsewhere.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.