Dual Pattern of Potassium Transport in Plant Cells: A Physical Artifact of a Single Uptake Mechanism

Analysis of potassium transport in plant root cells shows tworate-influencing regions: an unstirred boundary layer adjacentto the cell wall acts as a rate-limiting region and the negativelycharged cell wall acts as a rate-enhancing region. The rate-enhancingregion gives rise to a pseudo ‘dual mechanism’.These two regions act in concert to influence significantlythe characteristics of the concentration-dependent potassiumuptake process. The anomalous ion uptake behaviour found inthe literature is explained on the basis of a single activeuptake mechanism operating under the influence of these tworegions. The most critical property in support of the conceptof a ‘dual mechanism’ for cation uptake in plantroots is explained on this basis. It is unnecessary to invokeseparate groups of enzymes, each one of which is active overdifferent concentration ranges. One mechanism operating overthe entire concentration range is sufficient. Key words: Potassium transport, Rate-limiting region, Rate-enhancing region     

Differences in Cell Cycle Duration of Sister Cells in Secondary Root Meristems of Cocos nucifera L.

Cell lengths of Gl/Gl pairs of sister cells and in mitotic packetsof cells were measured in secondary roots of Cocos nuciferaL. Due to symplastic growth cell length ratios of sister cells,over a cell cycle, remained constant for the dwarf, hybrid andtall varieties of C. nucifera; the mean cell length ratio, betweenthe larger and smaller cell, was between 116:1 and 1 –20:1.From the cell length ratios, mean differences in cell cycleduration for sister cells were calculated to lie between 0–22and 0–27 of the average cell cycle duration. Cumulative distributions of the cell length ratios of sistercells, when converted to differences in cell cycle durationand plotted on semi-log graph paper deviated from an exponentialdistribution. In 86 per cent of the sister cells studied, thelarger cell of a sister pair divided first, however in the remaining14 per cent, half had the smaller cell of a sister pair dividingfirst while in the other half of the sister pairs, the cellswere of equal length but one had entered mitosis ahead of itssister. These results support neither cell cycle models basedon a cell sizer control per se nor on a random transition frominactive to active parts of the cell cycle.     

The separation of Pterodroma madeira (Zino's Petrel) from Pterodroma feae (Fea's Petrel) (Aves: Procellariidae)

The taxonomic status of petrels from the North East Atlantic has long been a matter of debate. Breeding colonies of petrels occurring on the islands of Madeira, Bugio and Cape Verde were originally thought to be outlying populations of the polytypic species Pterodroma mollis . Subsequent taxonomic treatments have varied considerably in their classification of birds from these islands. The petrel populations on Madeira and Bugio represent some of Europe's rarest breeding birds and their exact species designation, and hence relation to conservation mandates, is a question of considerable importance. In this study we use molecular techniques alongside more traditional taxonomic characters to confirm the existence of two species of the genus Pterodroma in the Archipelago of Madeira. We also discuss identification of these species in the field and the implications for their conservation management.     

Sex‐specific foraging behaviour in tropical boobies: does size matter?

Sex differences in the foraging behaviour of adults have been observed in a number of sexually size-dimorphic birds, and the usual inference has been that these sex-specific differences are driven primarily by differences in body size. An alternative explanation is that foraging differences result from sex differences unrelated to size, such as sex-specific nutritional requirements. To examine these alternative hypotheses, the foraging behaviour of parents was compared between two sympatric and congeneric species of seabird, the Brown Booby Sula leucogaster , which is highly sexually size-dimorphic (females 38% larger) and the Red-footed Booby S. sula , in which sex differences in body size are less marked (females 15% larger). Using temperature and depth loggers, we found that there were highly significant differences in the foraging trip durations and diving behaviour of male and female Brown Boobies. These sex differences were less marked in Red-footed Boobies. Thus, our interspecies comparison revealed that the magnitude of the difference between the sexes matched the sexual size dimorphism of the species, providing support for the size hypothesis.     

Massasauga Home Range Patterns in the Midwest

Abstract: The massasauga (Sistrurus catenatus) has drastically declined throughout its range mainly due to habitat loss and human persecution. Populations of the massasauga that occur north and east of the Missouri River, USA, are currently candidates for listing under the United States Endangered Species Act. In areas where land managers wish to improve habitat for existing populations or create habitat for repatriation efforts, an understanding of massasauga spatial ecology is necessary to ensure that adequate sized blocks of habitat are created and properly managed. We studied spatial ecology of massasaugas at 2 sites in Wisconsin and 3 sites in Missouri over an 11-year period. Our results indicated that male massasaugas had larger spatial requirements than all other cohorts. Our study sites supporting viable populations indicated that managers interested in restoring or enhancing massasauga habitat should use 100 ha as a minimum restoration or management target. (JOURNAL OF WILDLIFE MANAGEMENT 72(3):754–759; 2008)     

In Vivo Analysis of Heterogeneous Brain Deformation Computations for Model-Updated Image Guidance

Abstract

Neurosurgical image-guidance has historically relied on the registration of the patient and preoperative imaging series with surgical instruments in the operating room (OR) coordinate space. Recent studies measuring intraoperative tissue motion have suggested that deformation-induced misregistration from surgical loading is a serious concern with such systems. In an effort to improve registration fidelity during surgery, we are pursuing an approach which uses a predictive computational model in conjunction with data available in the OR to update the high resolution preoperative image series. In previous work. we have developed an in vivo experimental system in the porcine brain which has been used to investigate a homogeneous finite element rendering of consolidation theory as a tissue deformation model. In this paper, our computational approach has been extended to include heterogeneous tissue property distributions determined from an image-to-grid segmentation scheme. Results produced under two different loading conditions show that heterogeneity in the stiffness properties and interstitial pressure gradients varied over a range of physiologically reasonable values account for 1-3% and 5-8% of the predicted tissue motion, respectively, while homogeneous linear elasticity is responsible for 60-70% of the surgically-induced motion that has been recoverable with our model-based @approach.     

Cortical Cell Breakdown and Lateral Root Primordium Development in Vicia faba L

The effect of the formation of a cavity in the cortex of theprimary root of Vicia faba adjacent to lateral root primordiaon root development has been investigated. Premature exposureof such primordia to the external medium by removing the overlyingtissues of the primary root has no effect on primordium developmentif that primordium was within 48 h of emerging as a lateralroot. Similar exposure of primordia which were at an earlierstage of development and consisted of between 3400 and 7000cells resulted in the generation of a stationary phase, withmost of the nuclei arrested in G1 (presynthetic interphase),48–72 h after exposure began, followed by nuclear degenerationby 96 h. Since no mature vascular tissue was found in theseprimordia until after they emerged as secondary roots, all ofthe nutrients necessary for the maintenance of cell proliferationin these meristems must reach them by simple diffusion fromthe surrounding medium. A preliminary analysis of the liquidcontents of the cavity next to developing primordia demonstratesit to be rich in carbohydrates and it is clear, from the resultsreported in this paper, that cell proliferation in primordia,consisting of a mean number of 5400 cells, is largely dependenton the substances present in the cavity fluid, although somematerials reach the primordium by diffusion from the cells ofthe primary root to which the primordium remains attached.     

Changes in the cryptogam flora of the Wealden sandrocks, 1688–1984

The cryptogam flora of 15 sandrock sites in the central Weald, U.K. was assessed and compared with previous records beginning in 1688. A total of 264 species was recorded (29 algae, 90 lichens, 165 bryophytes and eight ferns) of which 18 lichens, 21 bryophytes and one fern were not relocated. Air pollution, changes in the microclimate brought about by invasion of trees and shrubs and trampling appear to be the main cause for the decline in the flora, although over-collection of rarities was also a factor.