Stability of pre- and post-fire spatial structure of pine trees in Aleppo pine forest

The study reported here describes for the first time the similarity between pre- and post-fire spatial patterns of the trees in a Mediterranean pine forest demonstrating that the pre-fire ancestor microsite is occupied also by the next generation. Although Aleppo pine Pinus halepensis Mill, is an obligatory post-fire seeder, it is adapted to regenerate in its pre-fire growing microsite. thus keeping suitable growing sites from generation to generation. We studied the effect of the dead burned adult pines on the density and size of their recruited saplings 2, 5, 11 and 20 yr after fire. A comparison of pine sapling density and size was made between the "near" zone (under the former effect of the burned canopy) and the'far'zone (beyond the former effect of the burned canopy).
In the site 2 yr after fire, seedling density was 56% higher in the "far" zone than in the'near'zone, but seedling .size was similar. However in the site 20 yr after fire, densities were similar in both zones, but the size was bigger by 89% in the "near" zone. Thus, population recruitment after fire seems to peak near the burned pine trees rather than at u distance from them, in contrast to Janzen's original'distance hypothesis' model suggested for undisturbed rainforest. Mere we present a new hypothetical model for the spatial pattern of post-fire regeneration of obligate seeder tree species forming open forests. It is proposed that in such trees the microsites which were kept by the burned adult trees, which are killed by the fire, are also the favorable regeneration microsite for the post-fire generation.     

Microtubule distribution in gravitropic protonemata of the mossCeratodon

Summary Tip cells of dark-grown protonemata of the mossCeratodon purpureus are negatively gravitropic (grow upward). They possess a unique longitudinal zonation: (1) a tip group of amylochloroplasts in the apical dome, (2) a plastid-free zone, (3) a zone of significant plastid sedimentation, and (4) a zone of mostly non-sedimenting plastids. Immunofluorescence of vertical cells showed microtubules distributed throughout the cytoplasm in a mostly axial orientation extending through all zones. Optical sectioning revealed a close spatial association between microtubules and plastids. A majority (two thirds) of protonemata gravistimulated for >20 min had a higher density of microtubules near the lower flank compared to the upper flank in the plastid-free zone. This apparent enrichment of microtubules occurred just proximal to sedimented plastids and near the part of the tip that presumably elongates more to produce curvature. Fewer than 5% of gravistimulated protonemata had an enrichment in microtubules near the upper flank, whereas 14% of vertical protonemata were enriched near one of the side walls. Oryzalin and amiprophos-methyl (APM) disrupted microtubules, gravitropism, and normal tip growth and zonation, but did not prevent plastid sedimentation. We hypothesize that a microtubule redistribution plays a role in gravitropism in this protonema. This appears to be the first report of an effect of gravity on microtubule distribution in plants.Abbreviations APM amiprophos-methyl - DIC differential interference contrast - DMSO dimethyl sulfoxide - EGTA ethylene glycolbis-(-amino-ethylether) N,N,N',N'-tetraacetic acid - FITC fluorescein isothiocyanate - GS gravitropic stimulus - MT microtubule - PIPES piperazine-N,N'-bis-2-ethanesulfonic acid     

The "near zone" effect in dynamic chaos

The dynamics of the system with a determined chaotic behavior (Lorentz system) was studied by comparing the histograms. It was shown that the dynamics of the system exhibits phenomena similar to those observed in studies of fluctuations in physical systems. In particular, upon comparison of histograms constructed from different time intervals, the "near zone" effect makes itself evident. It was shown that a very slight modulation of only one parameter of the system leads to a change in behavior.     

Spatial distribution of growth rates and of epidermal cell lengths in the elongation zone during leaf development in Lolium perenne L.

Relative elemental growth rates (REGR) and lengths of epidermal cells along the elongation zone of Lolium perenne L. leaves were determined at four developmental stages ranging from shortly after emergence of the leaf tip to shortly before cessation of leaf growth. Plants were grown at constant light and temperature. At all developmental stages the length of epidermal cells in the elongation zone of both the blade and sheath increased from 12 m at the leaf base to about 550 m at the distal end of the elongation zone, whereas the length of epidermal cells within the joint region only increased from 12 to 40 m. Throughout the developmental stages elongation was confined to the basal 20 to 30 mm of the leaf with maximum REGR occurring near the center of the elongation zone. Leaf elongation rate (LER) and the spatial distributions of REGR and epidermal cell lengths were steady to a first approximation between emergence of the leaf tip and transition from blade to sheath growth. Elongation of epidermal cells in the sheath started immediately after the onset of elongation of the most proximal blade epidermal cells. During transition from blade to sheath growth the length of the blade and sheath portion of the elongation zone decreased and increased, respectively, with the total length of the elongation zone and the spatial distribution of REGR staying near constant, with exception of the joint region which elongated little during displacement through the elongation zone. Leaf elongation rate decreased rapidly during the phase when only the sheath was growing. This was associated with decreasing REGR and only a small decrease in the length of the elongation zone. Data on the spatial distributions of growth rates and of epidermal cell lengths during blade elongation were used to derive the temporal pattern of epidermal cell elongation. These data demonstrate that the elongation rate of an epidermal cell increased for days and that cessation of epidermal cell elongation was an abrupt event with cell elongation rate declining from maximum to zero within less than 10 h.Abbreviations LER leaf elongation rate - REGR relative elemental growth rates     

Non-uniform distribution and seasonal variation of endogenous indol-3yl-acetic acid in the cambial region of Pinus contorta Dougl.

Endogenous, free indol-3yl-acetic acid (IAA) levels were measured in the main stem in the 10-year-old cambial zone, in the adjoining differentiating xylem, and in the adjoining mature xylem of 15–20-year-old Pinus contorta Dougl. by single-ion-current monitoring, combined gas chromatography — mass spectrometry, on several dates from early spring to early winter. Microscopy was used to determine the state of cambial activity on each harvest date. The IAA levels were found to be nearly constant at 1 g g^-1 DW in the cambial zone from March to July, then to increase to near 2 g g^-1 DW during the remainder of the growth season. No clear correlation was evident between number of fusiform cells per radial file and IAA content in the cambial zone. By contrast, the IAA content in differentiating xylem was higher than that in the adjoining meristematic zone on all harvest dates and also exhibited marked seasonal variation, peaking near 16 g g^-1 DW in mid summer, and declining to 1 g g^-1 DW in autumn. In mature xylem, IAA levels were very low and showed negligible variation. The fresh weight to dry weight ratio of differentiating xylem was greater than that of the cambial zone, and greater in the cambial zone than in mature xylem.     

Effect of a hypertonic mannitol solution on the peri-infarct area of an isolated frog heart

The influence of the hypertonic (3%) solution of mannitol on the process of the excitability recovery (in the near necrotic zone) appeared as a result of the necroses tissue effect on the ventricle has been investigated in the experiments on the isolated frog's heart. The analogous perfusion was conducted by Ringer solution in the control experiments. The process of isopotential phase S-T recovery was practically the same at heart perfusion with Ringer solution or with mannitol. Simultaneous registration of ventricular mechanogram showed the pronounced negative inotropic effect of mannitol. It is suggested that the positive effect of mannitol which has been noted under clinic conditions during the treatment of ischemic disease, doesn't connect with the effect of hypertonic solution on the cells excitability of periinfarcted (near necrotic) zone.     

Inbreeding and road effect zone in a Ranidae: the case of Agile frog, Rana dalmatina Bonaparte, 1840

Inbreeding has often been invoked in the extinction of local populations. In eleven western France populations of Agile frog studied, observed heterozygosity was significantly lower than expected in all cases, giving new evidence of such a depression in small populations. It especially occurred in ponds located near an highway rather than in undisturbed populations (FIS = 0.544 and 0.315, respectively). Thus, our results argue for a "road effect zone". Discussing about road distance and conservation policies, we propose that roads are directly involved in inbreeding and in local extinction. Thus, road construction ought to consider conservation management.     

Testaceans (Protozoa: Testacea) in Quaternary Permafrost Sediments of Bykovsky Peninsula, Arctic Yakutia

The results of the first protozoological study in terms of paleoecology of long-term sediments and buried soils formed in the cryolite zone of northeastern Siberia are discussed. The data on testaceans (Protozoa: Testacea) inhabiting various sites of Bykovsky Peninsula, Laptev Sea coast near estuary of Lena, within the last 53000 years (Late Pleistocene and Holocene) are presented.     

Ischemia-Related Subcellular Redistribution of Sodium Channels Enhances the Proarrhythmic Effect of Class I Antiarrhythmic Drugs: A Simulation Study

Background

Cardiomyocytes located at the ischemic border zone of infarcted ventricle are accompanied by redistribution of gap junctions, which mediate electrical transmission between cardiomyocytes. This ischemic border zone provides an arrhythmogenic substrate. It was also shown that sodium (Na⁺) channels are redistributed within myocytes located in the ischemic border zone. However, the roles of the subcellular redistribution of Na⁺ channels in the arrhythmogenicity under ischemia remain unclear.

Methods

Computer simulations of excitation conduction were performed in a myofiber model incorporating both subcellular Na⁺ channel redistribution and the electric field mechanism, taking into account the intercellular cleft potentials.

Results

We found in the myofiber model that the subcellular redistribution of the Na⁺ channels under myocardial ischemia, decreasing in Na⁺ channel expression of the lateral cell membrane of each myocyte, decreased the tissue excitability, resulting in conduction slowing even without any ischemia-related electrophysiological change. The conventional model (i.e., without the electric field mechanism) did not reproduce the conduction slowing caused by the subcellular Na⁺ channel redistribution. Furthermore, Na⁺ channel blockade with the coexistence of a non-ischemic zone with an ischemic border zone expanded the vulnerable period for reentrant tachyarrhythmias compared to the model without the ischemic border zone. Na⁺ channel blockade tended to cause unidirectional conduction block at sites near the ischemic border zone. Thus, such a unidirectional conduction block induced by a premature stimulus at sites near the ischemic border zone is associated with the initiation of reentrant tachyarrhythmias.

Conclusions

Proarrhythmia of Na⁺ channel blockade in patients with old myocardial infarction might be partly attributable to the ischemia-related subcellular Na⁺ channel redistribution.     

A new species of Comarostaphylis (Ericaceae,Arbuteae) from Tamaulipas,Mexico

Comarostaphylis sharpii is described from the vicinity of Rancho del Cielo near Gómez Farías in the Sierra de Guatemala of southwestern Tamaulipas, Mexico. It occurs in a narrow zone of Humid Pine-Oak Forest at elevations between 1200 and 2100 m.     

Dependence of 'macroscopic fluctuations" on geographic coordinates (from materials of Arctic (2000) and Antarctic (2001) expeditions

The detailed structure of histograms constructed from the results of synchronous measurements of the alpha-activity of 239Pu microsamples, conducted in Pushchino (Moscow Region, Russia) and on board the ship "Academician Fedorov" during the Arctic and Antarctic expeditions (2000 and 2001) was analyzed. It was shown that, if the histograms were constructed over a total period of 15 min and more, the "local zone effect" and the circadian periodicity in the similarity of histogram structure, observed during measurements in Pushchino, are not found in measurements on board the ship near the North Pole (latitude 82 degrees). If the histograms were constructed over a total time of 1 min, a strict periodicity ("stellar day" 23 h 56 min) in the appearance of similar histograms in Pushchino and the Arctic and a strict synchronicity of the appearance of similar histograms of measurements in Pushchino and on board the ship at the same local geographical time were observed. During the Antarctic expedition, the effect of synchronicity of the appearance of similar histograms in Pushchino and on board the ship decreased as the ship moved towards the South Pole and the difference in latitude between the points of measurements increased.     

THE ULTRASTRUCTURE OF THE VITELLINE BODY IN THE OOCYTE OF THE SPIDER TEGENARIA PARIETINA

The vitelline body in the mature oocyte of the spider Tegenaria parietina is composed of 4 different zones. 1. The central zone contains granular areas, vesicles, and a few lamellae. 2. The lamellar zone consists of numerous concentric lamellae. These sheets, 45 A in thickness, are stacked in groups. The fine structure and the regular arrangement recall those of myelin sheets, retinal rods, and chloroplasts. Between the stacks of lamellae, finely granular masses and various vesicles are to be found. 3. The "zone of transition" consists of a finely granular substance accumulated in abundant masses. This substance is composed of very closely packed granules about 50 to 60 A in diameter. Very often, near the lamellae, the granules show alignment giving a gradual transition from grains to lamellae. 4. The vesicular zone contains ergastoplasm, dense particles, mitochondria, and Golgi material. It is suggested that the peculiar ultrastructure of these cytoplasmic components may be related to an intense metabolic activity.     

Histologial Studies on the Root-Knot Nematodes Nonresistant and Resistant Root Apex of Humulus lupulus L.

The nematodes (Meloidogy incognita Chitwood.) invade near the root apex of the hop (Humulus lupulus L.), and usually lie near the meristematic zone. Fallowing their entrance, there are the formation of the giant cells and the consequent continuous divisions and activities of the flat meristematic cells, which result in formation of the nematode galls. Their sizes are also related to the number of nematodes. String beads nematode galls are often formed at the nematode-non resistant root part of the "Comet". The process of nematodes entering and later changing of the cells and tissue is almost the same as the formation of the nematode gall in other plants. Fewer nematodes can also enter the root tip of the highly resistant "Qingdao Dahua", but the subsequent special differentiation of the cells and tissues in the root have greatly restrained the activities of nematodes and ultimately to their death.     

森林草地转换对景观视觉效果的影响

基于景观保护的视点,定量研究了森林草地转换对景观视觉效果的影响．结果表明,中景域的可视区域比近景域和远景域大,草地建设对中景域景观视觉效果的影响也最大,因此,中景域是重要的景观保护对象．对草地内林地的可视量分析可知,各景域的可视林地多分布在400～600m高海拔上。25°以上的坡度范围内分布偏少．并探讨了草地建成后应采取的景观管理和保护对策,以增加草地景观的视觉效果．     

Further evidence that zinc is required throughout the root zone for optimal plant growth and development

The effect of variable Zn supply with depth in a soil profile was examined in two wheat genotypes differing in their Zn efficiency. Gatcher (Zn-inefficient) and Excalibur (Zn-efficient) were grown in a low Zn soil in pots with two treatment zones. The upper zone (10 cm) was supplied with Zn while Zn was either supplied or withheld from the lower zone (25 cm). In both genotypes, withholding Zn from the lower zone had no effect on root growth in either the upper or lower zones; neither did it affect plant appearance prior to booting. However, withholding Zn from the lower zone delayed head emergence in Gatcher by some 10 d and depressed grain yield by 20%. In Excalibur, Zn treatment had no effect on head emergence or grain yield. In Gatcher, withholding Zn from the lower zone depressed water usage by 12% during a 60 d period preceding maturity. No effect of Zn treatment on water usage was seen in Excalibur. Tissue Zn concentrations closely reflected the lower zone Zn treatments in both genotypes. Irrespective of the Zn treatment, Excalibur had higher Zn concentrations in flag leaves but lower concentrations in grain than Gatcher. In whole shoots, genotypic differences in Zn concentration only occurred when Zn was added to the lower zone; Excalibur having almost twice that of Gatcher. Clearly, if Zn is not supplied to the entire root system there is the potential for impaired root function and plant development, and for reduced grain yield. Approaches to managing this problem are discussed.     

Observations on the marginal ruffles of an established fibroblast-like cell line

Summary LW13K2 cells, a clone of a spontaneously in vitro transformed derivative of embryonic Lewis rat fibroblastic cells, were studied by phase contrast cine-light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The ruffles found at the advancing edge of cells grown on glass substrates in vitro form and recede in a period of less than one min if they do not make an attachment of the substrate. If they fail to make an attachment they may form pinocytotic channels near the leading edge as described by Price (1972) and/or collapse, generally backwards, towards the cell body. The spines which appear to reinforce the membranous ruffles are the last structures to disappear, and accumulate in an irregular array behind the ruffling edge; this area is behind that in which pinocytosis occurs. In comparison with the sparse numbers of ribosomes found in the trailing edge, they are present in notable concentrations near the leading, ruffling edge of the cell. No membrane vesicles have been found in or near the ruffling edges at the ruffle-spine concentration zone.     

On species composition and distribution of lanternfish larvae (Myctophidae) in the eastern South Pacific

The results of the study of species composition and distribution of lanternfish larvae (Myctophidae) in July through September of 1980 in open waters of the eastern South Pacific in areas situated beyond the 200-mile zones of Ecuador, Peru, and Chile are provided. In collections of ichthyoplankton from this region, larvae of 19 taxonomic forms of myctophids were found, of which the eastern Pacific endemic Diogenichthys laternatus ranked first by numbers and frequency of occurrence. Specific features of distribution of larvae of the most abundant species were considered, and the map of the total distribution density of larvae of all species of myctophids in the study area was compiled. It was found that their highest concentrations were recorded in the zone of the equatorial front in the north of the region near the boundary with the 200-mile zone near the Galapagos Islands, and that these aggregations consisted mainly of larval D. laternatus. Large concentrations of larval myctophids were attributed to strong convergent zones. Based on collected materials, the tentative value of total numbers of larval myctophids during the survey was calculated.     

Halimeda growth and diversity on the deep fore-reef of Enewetak Atoll

The deep fore-reef at Enewetak has been examined from the submersible Makali'i. Green algae grow to about-150 m at photon flux densities of approximately 1 Em^-2s^-1. Halimeda cover is 50% at many sites down to-90 m. Halimeda populations are important within the zone of scleractinian corals down to about-65 m, while a Halimeda zone with low coral cover or lacking corals between-65 m and-150 m probably is an important source of reef carbonate. Halimedas of the deep fore-reef, like those of the lagoon, constitute an important structural component in reef building. Other calcareous green algae such as Tydemania are less important on the deep fore-reef, but growth of coralline red algae continues to over-200m. Halimeda diversity is high down to near the base of the euphotic zone.     

Reasons for the limitation of mangrove along the west coast of northern Peru

Along the west coast of South America mangroves are found only outside the area influenced by the cold Peruvian Current. At 6° S (near ‘Cerro Illescas’) the current turns west to the open sea in the direction of the Galapagos Islands. Dense mangrove vegetation with a tree height up to 15 m occurs only north of 3° 35′ S from the delta of the river Tumbes (Peru). At 3° 44′ S some small individuals of Rhizophora and at 5° 30′ S a small stand of Avicennia can be found. In the transition zone between 3° 35′ and 6° S no mangrove forest occurs. The reasons for the lack of mangal in the transition zone are:

1. Evapotranspiration and atmospheric humidity show significant differences between the mangrove region and the transition zone. In this zone soil conditions like salinity, water and organic matter content and the geological structure can also be considered as inhibiting mangrove growth.
2. Topographic conditions in this zone are not suitable for mangal and the lack of a regular annual flow from rivers provides a sharp limit for the existence of mangal in the delta of the river Tumbes. Nevertheless, cultivation of mangrove species south of the mangrove region is possible and seems promising.

     

The blood circulation inside the spleen. I. The arterial blood vessels general distribution in the rat spleen

As an attempt to investigate the different pathways followed by the blood into the spleen and to analyse their functional significance, a technique was used mainly based on the intraarterial perfusion of a Prussian blue "solution" added of some chemical mediators and vasoactive substances. Such technique provides results which may be analysed taking into account the effect of the anaesthetic used, that may influence the findings. From the anaesthetic used, the sulfuric ether and the barbital sodium produce vasoconstriction of the white pulp blood vessels, whereas the chlorpromazine-promethazine doesn't have this effect, and so the Prussian blue appears inside these vessels. The vasodilator drugs, such as succinonitrile and papaverine hydrochloride, show a general vasodilator effect on the splenic arterial system. Teh arterial vessels of the white and the red pulp, including those placed at the subcapsular areas, become enlarged; into the white pulp, either the central or the peripheral blood vessel plexus of the lymphatic follicle becomes evident. The latter readily constitutes the perifollicular and the pericolumnar plexus. The blood vessels of this plexus become permeable to the Prussian blue "solution" by the heparin sodium effect, and so the dye particles enter the marginal zone and the splenic sinuses. In addition, from the white pulp arteries arise 2 types of anastomotic arterioles which appear enlarged after succinonitrile treatment: The short anastomotic arterioles that crosses the marginal zone entering the red pulp near the white pulp; the long anastomotic arterioles which enter the red pulp and after a long course end up into or around a collector sinus. The addition of histamine dihydrochloride to the perfusion solutions shows a slight vasodilator effect mainly on the subcapsular penicillar arterioles, including the helicine arterioles. The adrenergic stimulation of the splenic blood vessels induces a generalized arterial constriction, except of the anastomotic arterioles, that becomes open; in such way, the blood pathway follows the course of the anastomotic arterioles and the collector arterioles also become constricted. The adrenergic vasoconstrictor effect is inhibited by the phenoxy-benzamine hydrochloride. The addition of acetylcholine chloride, in the dosage, used, induces a generalized arterial vessel constriction, mainly of the perifollicular plexus. This effect is inhibited by atropine sulfate which, on the other hand, produces evident enlargement of the perifollicular and pericolumnar arterial plexus.