Seasonal changes in the activation of crossbridge motions of isolated thick filament from Limulus striated muscle

Summary In dynamic light scattering, measurements of the intensity-intensity time correlation function from a suspension of rod-like particles of length L could reveal dynamical information related to translational and internal motions of those particles. For a suspension of thick filaments isolated from the myosin-regulated, striated muscles of Limulus at KL>1 (where K is the scattering vector), the average characteristic linewidth ( ) increased with the addition of Ca²⁺ or with the depletion of ATP. The increase in the with the addition of Ca²⁺ could be due to the presence of energy-requiring, high-frequency motions of the crossbridges activated by Ca²⁺. The increase in which occurred with the depletion of ATP was assumed to be mainly due to the thermal motions of the crossbridges after they had moved radially away from the filament backbone. The percentage increase in following the addition of Ca²⁺ was found to be seasonal, i.e., values of obtained from thick filaments isolated between the middle of June and the middle of September were smaller than those obtained during the rest of the year. The effect of temperature on the percentage increase in was also different. The increase showed a maximum at about 35°C during the summer and at about 25°C at other times. However, the percentage increase in developed under ATP-depleted conditions showed no temperature-related maximum. The number of bound Ca²⁺ per myosin molecule was 1 during the summer and 2 at other times.Abbreviations DLS dynamic light scattering - L length - K scattering vector - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis - average characteristic line width Deceased     

Seasonal nutrient variation in trembling aspen

Summary Variation in concentrations of N, K, Mg, and Ca in vegetative-buds, leaves, twigs, and male catkins of trembling aspen (Populus tremuloides Michx.), determined throughout a growing season in central Minnesota, reflected the different physiological roles of the nutrients. Practical implications are discussed.     

The seasonal cycle of the phytoplankton in the coastal waters of Ghana

Seasonal changes in the phytoplankton at four depths off Tema, Ghana were investigated between September 1973 and November 1974. The physico-chemical factors show that there are two marine seasons, the season of major upwelling (July–October), characterized by low water temperatures (< 25°C), high salinity (> 35) and high nutrient levels, and a non-upwelling period (November–June) when water temperatures are higher and salinity and nutrients are lower. The latter marine season is broken by a small, unpredictable upwelling (December-January). Phytoplankton cell counts are high (> 1000 × 103 cells/1) during the major upwelling period and can be very low (< 2 × 10³ cells/1) during the non-upwelling period. Dinoflagellates form the main components of the phytoplankton population during the nonupwelling period and diatoms form the dominant components at other times. There is a close relationship between the physicochemical factors and the phytoplankton population especially during the major upwelling period. For example there is a good correspondence between the peaks in phytoplankton numbers and low levels of nutrients such as silicate, nitrate and phosphate with the reverse taking place at other times.     

The hypothalamo-hypophysial system in the ground squirrel,Citellus erythrogenys Brandt

Summary Monthly observations of the Gomori-positive hypothalamo-hypophysial neurosecretory system (HHNS) of the ground squirrel, Citellus erythrogenys Brandt, were carried out light microscopically using several quantitative methods. From the beginning of hibernation, formation of neurosecretory material (NSM) in the neurosecretory cells (NSC) progressively decreases and release of neurohormones from the HHNS is almost fully inhibited. A maximal accumulation of NSM in the perikarya of the NSC and in the posterior pituitary (PP) is found in December. By this time the volume of the cell nuclei and nucleoli is at a minimum. Signs of activation of the HHNS appear and become more conspicuous as the time of arousal from torpor approaches. The amount of NSM in the NSC and the PP decreases simultaneously with the increase in volume of the NSC. Hyperemia and activation of glial elements is visible throughout the HHNS. The morphological signs of activation reach their peak in March. After reproduction is completed (April to beginning of May), the NSC and the PP are almost devoid of NSM. Beginning with June and during the summer and autumn months a progressive accumulation of NSM in the NSC and the PP parallels gradual diminution in the volume of the NSC structures and the glial cells. Mechanisms and effector pathways by which the HHNS influences seasonal adaptation of the organism and reproduction are discussed.     

Studies on a Morphologically Distinct Colchicine-Resistant Variant of Entamoeba sp.*

Colchicine has a temperature-dependent cytotoxic effect on Entamoeba sp. (Laredo isolate) that is most apparent when the drug is applied during the initiation of cultures at a concentration of 7.5 mM or higher. Continued transfer of cultures in medium containing progressively increasing concentrations of colchicine has resulted in a variant that grows prolifically in the presence of colchicine (7.5 mM) with a generation time comparable to that of the parent stock. Comparison of a number of parameters of the 2 variants revealed that colchicine resistance was accompanied by a change in cell shape, a reduced membrane permeability, which could partially be overcome by the addition of dimethyl sulfoxide (DMSO), and a reduced tolerance to osmotic stress. However, the parent strain and resistant variant were equally susceptible to cycloheximide and puromycin suggesting that the acquired colchicine resistance may not be explained on the basis of an entirely unspecific generalized reduced ability for drug uptake. Colchicine resistance and altered structure were found to be stable over a long period of time. The possible interdependence of these 2 parameters and their relation to cell motility in Entamoeba sp. are discussed.     

Seasonal reproductive cycle in the mussel,Lamellidens corrianus

Seasonal reproductive cycle of the freshwater mussel, Lamellidens corrianus has been studied. These mussels are functional or simultaneous hermaphrodites. The spawning was at its peak during the months of September to December. The gonads were in growing stages with reduced gonadal activity during January to April, whereas the maturation of gonads was found to be intense during May to August.     

Seasonal fluctuation of zooplankton populations in lower Delaware Bay

Quantitative zooplankton samples were obtained monthly or bi-monthly 15 times from June 1974 to May 1975 at three stations in lower Delaware Bay. Two 12-hour cruises were also conducted at one of the stations.Arthropods dominated the samples in terms of number of species and number of individuals. The number of zooplankton from surface samples ranged from 58/m³ in August to 21,092/ m³ in June, while bottom samples varied from 259/m³ in August to 30,395/ m³ in October. In general, larger concentrations of individuals were found in bottom samples.Only on three occasions did meroplankton exceed the holoplankton, and these occurred at the shallow water stations. Meroplankton comprised a larger percentage of the bottom samples than surface samples. Zoeae of Neopanope sayi and Uca sp. contributed mainly to the large proportion of meroplankton in July 1974, veligers of Mytilus edulis in January 1975, and nauplii of Balanus sp. in May 1975.Copepods were the largest component of the population throughout most of the year. At all stations and depths, Arctica tonsa dominated most of the summer samples. In the spring of 1975, A. tonsa was replaced by Centropages hamatus, Temora longicornis, and Pseudocalanus minutus.During the 12-hour cruises there were higher numbers of individuals in the bottom waters in the day with migration to surface waters in the afternoon and evening. Based on cluster analysis, five time-related assemblages were discerned: June, July–August, September–November, December, January–May. Comparison of Delaware Bay zooplankton with other estuarine systems indicated that the densities obtained locally were most similar to those reported in the York River, Virginia.     

Ecological studies of spores of aquatic hyphomycetes in the cringle brook,lincs

The aquatic Hyphomycete spora of the Cringle Brook, Lincs, was examined by foam sampling and by the use of cellophane impaction traps between August, 1968 and January, 1970.The species most frequently found (Tetracladium marchalianum, Alatospora acuminata and Flagellospora curvula) were generally in agreement with those found by other workers in temperate areas. Impaction trap samples generally contained fewer species than foam samples but filiform spore types such as Flagellospora were more frequently found on traps than in foam suggesting that impaction is more selective towards the filiform spore type than is foam. Many species increased in frequency in autumn accompanying and following leaf fall, and the winter spora was dominated by Alatospora acuminata, Clavariopsis aquatica, Clavatospora stellata, Flagellospora curvula and Lemonniera aquatica. During the summer the spora was dominated by Tetracladium marchalianum.The role of foam and impaction in the balance of aquatic spore populations is discussed in relation to techniques available for their study.