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Kurt B. Petersen Martin Burd 《Biological reviews of the Cambridge Philosophical Society》2017,92(3):1739-1754
The primitive land plant life cycle featured the production of spores of unimodal size, a condition called homospory. The evolution of bimodal size distributions with small male spores and large female spores, known as heterospory, was an innovation that occurred repeatedly in the history of land plants. The importance of desiccation‐resistant spores for colonization of the land is well known, but the adaptive value of heterospory has never been well established. It was an addition to a sexual life cycle that already involved male and female gametes. Its role as a precursor to the evolution of seeds has received much attention, but this is an evolutionary consequence of heterospory that cannot explain the transition from homospory to heterospory (and the lack of evolutionary reversal from heterospory to homospory). Enforced outcrossing of gametophytes has often been mentioned in connection to heterospory, but we review the shortcomings of this argument as an explanation of the selective advantage of heterospory. Few alternative arguments concerning the selective forces favouring heterospory have been proposed, a paucity of attention that is surprising given the importance of this innovation in land plant evolution. In this review we highlight two ideas that may lead us to a better understanding of why heterospory evolved. First, models of optimal resource allocation – an approach that has been used for decades in evolutionary ecology to help understand parental investment and other life‐history patterns – suggest that an evolutionary increase in spore size could reach a threshold at which small spores yielding small, sperm‐producing gametophytes would return greater fitness per unit of resource investment than would large spores and bisexual gametophytes. With the advent of such microspores, megaspores would evolve under frequency‐dependent selection. This argument can account for the appearance of heterospory in the Devonian, when increasingly tall and complex vegetative communities presented competitive conditions that made large spore size advantageous. Second, heterospory is analogous in many ways to anisogamy. Indeed, heterospory is a kind of re‐invention of anisogamy within the context of a sporophyte‐dominant land plant life cycle. The evolution of anisogamy has been the subject of important theoretical and empirical investigation. Recent work in this area suggests that mate‐encounter dynamics set up selective forces that can drive the evolution of anisogamy. We suggest that similar dispersal and mating dynamics could have underlain spore size differentiation. The two approaches offer predictions that are consistent with currently available data but could be tested far more thoroughly. We hope to re‐establish attention on this neglected aspect of plant evolutionary biology and suggest some paths for empirical investigation. 相似文献
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O W Petersen P E H?yer J Hilgers P Briand B van Deurs 《Virchows Archiv. B, Cell pathology including molecular pathology》1985,50(1):27-42
Epithelial cell islets in primary monolayer cultures of human breast biopsies were characterized by combined immuno-, enzyme- and DNA cytochemistry as well as by analysis of attachment-, spread- and growth patterns. For cultivation we used explants from reduction mammoplasties, benign lesions, primary carcinomas and metastases. Milk fat globule membrane antigen (MFGM-A) was detected with a monoclonal antibody, and the tetrazolium reaction for glucose 6-phosphate dehydrogenase (G6PDH) as well as DNA content of the cultured cells were quantified. Spreading and growth of individual islets were studied by image analysis. Fibroblast-like cells did not express MFGM-A, and whereas epithelial (MFGM-A positive) cell islets of normal and benign origin showed cells with no or low G6PDH reaction, respectively, the majority of epithelial cell islets from 11 out of 21 carcinomas showed strong reaction. Cell islets with strong G6PDH reaction were sometimes hyperdiploid. Moreover, whereas cell islets with no or low reaction from both benign lesions and carcinomas readily attached and spread in a serum-free medium and showed population doubling times of 30 to 110 h, cell islets with strong reaction from carcinomas and metastatic lesions required serum for attachment and their growth rate was too low to be determined. 相似文献
6.
Matthew Westover Jared Baxter Rick Baxter Casey Day Ryan Jensen Steve Petersen Randy Larsen 《PloS one》2016,11(5)
Greater sage-grouse populations have decreased steadily since European settlement in western North America. Reduced availability of brood-rearing habitat has been identified as a limiting factor for many populations. We used radio-telemetry to acquire locations of sage-grouse broods from 1998 to 2012 in Strawberry Valley, Utah. Using these locations and remotely-sensed NAIP (National Agricultural Imagery Program) imagery, we 1) determined which characteristics of brood-rearing habitat could be used in widely available, high resolution imagery 2) assessed the spatial extent at which sage-grouse selected brood-rearing habitat, and 3) created a predictive habitat model to identify areas of preferred brood-rearing habitat. We used AIC model selection to evaluate support for a list of variables derived from remotely-sensed imagery. We examined the relationship of these explanatory variables at three spatial extents (45, 200, and 795 meter radii). Our top model included 10 variables (percent shrub, percent grass, percent tree, percent paved road, percent riparian, meters of sage/tree edge, meters of riparian/tree edge, distance to tree, distance to transmission lines, and distance to permanent structures). Variables from each spatial extent were represented in our top model with the majority being associated with the larger (795 meter) spatial extent. When applied to our study area, our top model predicted 75% of naïve brood locations suggesting reasonable success using this method and widely available NAIP imagery. We encourage application of our methodology to other sage-grouse populations and species of conservation concern. 相似文献
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O. G. Petersen 《Plant biology (Stuttgart, Germany)》1899,17(11):168-171
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Type II callus cultures were initiated from immature tassels of a maize genotype with an A188/B73 genetic background using N6 medium containing 1.0 mg/liter 2,4-D, 100 mg/liter casamino acids, 25 mM proline, and 0.2% phytagel™. Inclusion of 10 μM AgNO3 in this medium significantly increased the frequency and vigor of the type II callus response. Friable calli emerged from these explants after two consecutive 2-week subculture intervals. Tassels from 10 to 30 mm long were capable of producing type II cultures. The plants regenerated from these cultures were green and indistinguishable from plants regenerated from immature embryo-derived calli. 相似文献
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The suggestion that the electron acceptor A1 in plant photosystem I (PSI) is a quinone molecule is tested by comparisons with the bacterial photosystem. The electron spin polarized (ESP) EPR signal due to the oxidized donor and reduced quinone acceptor (P
870
+
Q-) in iron-depleted bacterial reaction centers has similar spectral characteristics as the ESP EPR signal in PSI which is believed to be due to P
700
+
A
1
-
, the oxidized PSI donor and reduced A1. This is also true for better resolved spectra obtained at K-band (24 GHz). These same spectral characteristics can be simulated using a powder spectrum based on the known g-anisotropy of reduced quinones and with the same parameter set for Q- and A1
-. The best resolution of the ESP EPR signal has been obtained for deuterated PSI particles at K-band. Simulation of the A1
- contribution based on g-anisotropy yields the same parameters as for bacterial Q- (except for an overall shift in the anisotropic g-factors, which have previously been determined for Q-). These results provide evidence that A1 is a quinone molecule. The electron spin polarized signal of P700
+ is part of the better resolved spectrum from the deuterated PSI particles. The nature of the P700
+ ESP is not clear; however, it appears that it does not exhibit the polarization pattern required by mechanisms which have been used so far to explain the ESP in PSI.Abbreviations hf
hyperfine
- A0
A0 acceptor of photosystem I
- A1
A1 acceptor of photosystem I
- Brij-58
polyoxyethylene 20 cetyl ether
- CP1
photosystem I particles which lack ferridoxin acceptors
- ESP
electron spin polarized
- EPR
electron paramagnetic resonance
- I
intermediary electron acceptor, bacteriopheophytin
- LDAO
lauryldimethylamine
- N-oxide, P700
primary electron donor of photosystem I
- PSI
photosystem I
- P700
T
triplet state of primary donor of photosystem I
- P870
primary donor in R. sphaeroides reaction center
- Q
quinore-acceptor in photosynthetic bacteria
- RC
reaction center 相似文献