Flexion-relaxation response to gravity

The objective of this report was to study the influence of the orientation of gravitational loading on the behavior of anterior and posterior trunk muscles during anterior trunk flexion-extension. Participants (N=13) performed five (5) cycles of trunk flexion-extension while standing with gravity parallel to the body axis and five (5) cycles while in the supine condition (e.g. sit-ups) with gravity perpendicular to the body axis. Surface electromyographic (EMG) patterns from lumbar paraspinal, rectus abdominis, external oblique, rectus femoris, semimembranosis, and biceps femoris muscles were analyzed during each condition. EMG signals were synchronized with lumbar flexion and trunk inclination angles. Flexion-extension from the standing position resulted in a myoelectric silent period of the lumbar posterior muscles (e.g. flexion-relaxation phenomena (FRP)) as well as the hamstring muscles through deep angles during which activity was observed in abdominal muscles. Flexion-extension during sit-ups, however, resulted in a myoelectric silent period of the abdominal muscles and the quadriceps through deep angles during which the lumbar posterior muscles were active. In this condition, the FRP was not observed in posterior muscles. The new findings demonstrate the profound impact of the orientation of the gravity vector on the FRP, the abdominal muscles reaction to gravitational loads during sit-ups and its relationships with lumbar antagonists and thigh musculature. The new findings suggest that gravitational moments requirements dominate the FRP through the prevailing kinematics, load sharing and reflex activation-inhibition of muscles in various conditions. Lumbar kinematics or fixed sensory motor programs by themselves, however, are not the major contributor to the FRP. The new findings improve our insights into spinal biomechanics as well as understanding and evaluating low back disorders.     

The response to gravity is correlated with the number of statoliths in Chara rhizoids.

In contrast to higher plants, Chara rhizoids have single membrane-bound compartments that appear to function as statoliths. Rhizoids were generated by germinating zygotes of Chara in either soil water (SW) medium or artificial pond water (APW) medium. Differential-interference-contrast microscopy demonstrated that rhizoids form SW-grown plants typically contain 50 to 60 statoliths per cell, whereas rhizoids from APW-grown plants contain 5 to 10 statoliths per cell. Rhizoids from SW are more responsive to gravity than rhizoids from APW because (a) SW rhizoids were oriented to gravity during vertical growth, whereas APW rhizoids were relatively disoriented, and (b) curvature of SW rhizoids was 3 to 4 times greater throughout the time course of curvature. The growth rate of APW rhizoids was significantly greater than that of SW-grown rhizoids. This latter result suggests that APW rhizoids are not limited in their ability for gravitropic curvature by growth and that these rhizoids are impaired in the early stages of gravitropism (i.e. gravity perception). Plants grown in APW appeared to be healthy because of their growth rate and the vigorous cytoplasmic streaming observed in the rhizoids. This study is comparable to earlier studies of gravitropism in starch-deficient mutants of higher plants and provides support for the role of statoliths in gravity perception.     

The response of digging ants to gravity

Summary Workers ofFormica lemani, confined in a cavity surrounded above and below by sand, showed a significant tendency to dig upwards. This orientation persisted in darkness and disappeared if the dishes were rotated about a horizontal axis.When workers ofFormica lemani andMyrmica ruginodis were placed on a sand surface in apparatus which was rocked slowly –30° to each side of vertical in the dark, their tunnels showed changes in hourly alinement which regressed significantly on the angle of the apparatus to the vertical. The regression appeared to be more important inF. lemani than inM. ruginodis. Workers ofLasius niger failed to show a significant regression.The variance of the hourly inclination of tunnels in rocked experiments was significantly greater than that in control experiments (not rocked) inF. lemani andM. ruginodis, but not inL. niger. These differences dissappeared when the variance due to regression on rocking was eliminated.The total variance in hourly inclination was significantly greater inLasius niger than in the other two species and the within-ants variance was also significantly greater inF. lemani than inM. ruginodis.

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Zusammenfassung Arbeiterinnen vonFormica lemani Bondroit, in einer Hohle oben und unten von Sand beschrankt, graben vorzuglich aufwarts. Diese Steurung kommt im Dunkel noch vor; wenn man die Sandteller langsam um eine waagerechte Achse drehe, die Steurung verschwindet.Arbeiterinnen vonF. lemani undMyrmica longinodis Nylander auf Sandoberflache in einem langsam durch 60° hin und her schwingenden Apparat graben in wechselnden Richtungen, die vom Winkel zwischen Apparat und Senkrecht abhangen. Diese Regression scheint wichtiger beiF. lemani als beiM. ruginodis zu sein. Also besetzen grabende Arbeiterinnen dieser beiden Arten eine Schwerkraftorientierung. BeiLasius niger gibt es keine Regression und deswegen auch keine Schwerkraftorientierung.Die Varianz der Neigungen der Tunnels in Schwingversuchen ist grösser als die in ungeschwungenen Controlversuchen beiF. lemani undM. ruginodis; beiL. niger dementgegen, nicht. Diese Unterschiednissen verschwinden wenn man die Regressionvarianz ausnehme.Die Gesamtvarianz ist grösser beiL. niger als bei die anderen Arten.

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Résumé Les ouvrières de la fourmiFormica lemani Bondroit, confinées dans du sable placé aussi bien au-dessus qu'au-dessous, creusent toujours dans un sens ascensionnel. Cette orientation persiste en pleine obscurité, mais disparaît lorsqu'on fait tourner les boîtes de sable autour de leur axe horizontal.Des ouvrières deF. lemani et deMyrmica ruginodis Nylander, placées sur une surface de sable qui oscille de 60° à gauche et à droite, montrent des changements d'alignement des tunnels qui dépendent de l'angle entre l'appareil et la verticale. Cette régression est plus importante chezF. lemani queM. ruginodis. Les ouvrières qui creusent possèdent alors une orientation à la pesanteur. ChezLasius niger (L.), par contre, la régression (et par conséquent l'orientation) manque.La variance de l'inclinaison des tunnesl est réduite dans des expériences de contrôle non oscillées, par comparaison aux expériences oscillées, chezF. lemani etM. ruginodis. Ces différences disparaissent quand on élimine la variance due à la régression. ChezL. niger, les deux expéreinces ne diffèrent pas.La variance totale de l'inclinaison est plus grande chezL. niger que chez les deux autres espèces. Ceci confirme ce qui a été constaté dans les travaux précédents.

     

Root-hair response to vector-free gravity: role of Ca2+ ions

In plants, apical growth is demonstrated by a variety of cells, including root hairs (RH) which are tubular outgrowths of root epidermal cells. They are likely to be involved in uptake of nutrients and water, anchorage of plants, maintenance of contact between roots and soil, and root exudation. Over the last years, it has become clear that calcium is involved in various processes which result in tip growth. Previous studies from our laboratory have demonstrated an increase in calcium level in root cells of pea seedlings grown under conditions of space flight and clinorotation. On the basis of these data, we have suggested that such effects of microgravity and clinorotation might be due to the enhancement of Ca2+ influx into hyaloplasm evidently through Ca2+ channels. In this regard, it was interesting to examine the effects of clinorotation and Ca2+ channel blockers (verapamil and nifedipine) on orientation and structure of growing RH that might be an appropriate model system being sensitive to calcium for studying the gravitational effects at cellular level.     

ECG voltage modifications as response to gravity changes

The aim of the study was to analyze ECG (QRS) voltage responses to body fluid shift due to gravity chances. Acute changes in gravity were created by two ways: 1) changes in gravity value during parabolic flights (within 27 subjects 45 ECG have been analyzed); 2) changes in gravity direction due to rotation of the body during postural tests (within 11 subjects 14 ECG have been analyzed). Results and conclusions. Gravity change leads to body fluid shift and changes of intrathoracic organs and tissues electroconduction. It influences on ECG voltage. During parabolic flights in up-right position: R amplitude in Z axis increases in hypergravity (+0.19 mV) and decreases in microgravity (-0.24 mV). During postural tests, R amplitude in Z axis increases in orthostatic position (+0.09 mV) and decreases in antiorthostatic position (-0.025 mV). Changes in QRS voltage during parabolic flights are more important than during postural tests. This could be due to more effective blood redistribution during parabolic flights.     

Auxin-mediated response of cucumber seedlings to gravity]

Gravity regulates peg formation because cucumber seedlings grown in a horizontal position develop a peg on the lower side of the transition zone (TR zone) but not on the upper side. Studies on peg formation have suggested the regulation of peg formation by gravity as follows. Cucumber seedlings potentially develop a peg on both the lower and upper sides of the TR zone. The development of the peg on upper side of the TR zone is suppressed in response to gravity. A phytohormone, auxin, induces peg formation. Upon gravistimulation the auxin concentration on the upper side of the TR zone is reduced to a level below the threshold value necessary for peg formation. The unequally distributed auxin across TR zone is caused by a change in accumulation of auxin influx carrier (CsAUX1) protein and auxin efflux carrier (CsPIN1) protein in response to gravity. In addition, TR zone before peg initiation expresses both CsARF2 (putative activator of auxin response factor) and CsIAA1 (putative repressor of auxin-inducible gene expression), by which TR zone could respond the auxin gradient regulated by gravity.     

Plants respond to gravity with gravity related waves

Gravity related waves in plants control plant shapes by their velocity, vertical to horizontal velocity ratios, and the stepwise change in velocity from horizontal to vertical. Velocities are measured directly while velocity ratios can be derived from internodal spacings or measurements of velocities. Plant wave frequencies are the same in every direction. The wave proofs are overwhelming with plant communication and ac field interaction as added proof.     

The response of single human cells to zero gravity

Summary The 59-day Skylab III earth-orbital mission carried an experiment designed to observe the effects of zero-gravity on a strain of diploid human embryonic lung cells, WI-38. The experiment (NASA Exp. No. S015) was performed in a miniaturized, fully automated tissue-culture laboratory package called the Woodlawn Wanderer Nine. The package, which weighed less than 10 kg, photographed two perfused cultures for 28 days using phase-contrast microscopes and 16-mm time-lapse cameras; fixed 10 perfused cultures in gluteraldehyde one at a time over a 12-day period; and returned to earth eight perfused cultures in a viable state for subsequent subculture and study. Two ground control experiments using specimens from the same clone were run simultaneously with the flight experiment in identical packages. The controls were subjected to simulated flight vibration profile within an hour after spacecraft liftoff. All packages were sealed at 1-atmosphere pressure. Analysis of the flight and control films showed no differences in mitotic index, cell cycle or migration rates. Growth curve, DNA microspectrophotometry, phase microscopy and ultrastructural studies on the fixed cultures revealed no effects of zero-gravity. Karyotyping and chromosome-banding studies were performed on subcultures of the returned viable cells and these showed no significant differences from the controls. Minor unexplained differences were found in the biochemical constituents of the spent media of the flight and control experiments. Within the limits of this, experimental design it was found that the zerogravity environment produced no detectable effects on WI-38.     

Malaria: living with drug resistance

The epidemiological factors associated with the development and spread of drug-resistant malaria have been recently explored by Wemsdorfer in a paper in which he looked at parasite-drug-human-vector interactions that affect the occurrence and dynamics of drug resistance. The question that decision-makers must be asking themselves, as we face the 21st century, is: how will we live with drug resistance? Allan Schapira, Peter Beales and M. Elizabeth Halloran are ideally placed to consider this question. Extracting lessons from the past, they focus on drug-resistant Plasmodium falciparum in Africa. They propose a mathematical model, which will improve the conceptual basis for policy decisions and which has implications for drug development as well as for malaria-control programmes.     

Abscisic acid and the response of the roots of Zea mays L. seedlings to gravity

Summary Exogeneous application of abscisic acid (ABA) to intact roots of LG 11 maize seedlings inhibits root elongation and induces bending of the root in response to gravity in darkness, even though the roots of these seedlings are not normally positively geotropic in the dark. ABA cannot, however, induce geotropic curvature in dark-exposed decapped roots, thus confirming that the root cap is the site of graviperception in the intact root.Abbreviation ABA abscissic acid     

Denmark: the elderly living in style.

In the next 20 years every country in Western Europe will see a rise in its total numbers of people aged over 60, and since old people are now living longer the proportion aged over 75 will also rise. Both physical and mental disorders become much more common between 60 and 75, so that if these old people are to be provided with accommodation and medical services at contemporary standards many more places will be needed in sheltered flats, nursing homes, and geriatric hospitals. Yet in the current economic recession most European countries are trying to cut back on public expenditure. How do politicians and administrators reconcile the conflict between the demands created by demographic change and the freeze on public spending? How will the care of the elderly change in response to this conflict? Tony Smith is examining the ways in which old people are looked after in several European countries and their plans for the future. This first article deals with Denmark.     

Cytoplasmic free Ca2+ in Arabidopsis roots changes in response to touch but not gravity.

Changes in cytoplasmic Ca2+ concentration ([Ca2+]i) have been proposed to be involved in signal transduction pathways in response to a number of stimuli, including gravity and touch. The current hypothesis proposes that the development of gravitropic bending is correlated with a redistribution of [Ca2+]i in gravistimulated roots. However, no study has demonstrated clearly the development of an asymmetry of this ion during root curvature. We tested this hypothesis by quantifying the temporal and spatial changes in [Ca2+]i in roots of living Arabidopsis seedlings using ultraviolet-confocal Ca(2+)-ratio imaging and vertical stage fluorescence microscopy to visualize root [Ca2+]i. We observed no changes in [Ca2+]i associated with the graviresponse whether monitored at the whole organ level or in individual cells in different regions of the root for up to 12 h after gravistimulation. However, touch stimulation led to transient increases in [Ca2+]i in all cell types monitored. The increases induced in the cap cells were larger and longer-lived than in cells in the meristematic or elongation zone. One millimolar La3+ and 100 microM verapamil did not prevent these responses, whereas 5 mM EGTA or 50 microM ruthenium red inhibited the transients, indicating an intracellular origin of the Ca2+ increase. These results suggest that although touch responses of roots may be mediated through a Ca(2+)-dependent pathway, the gravitropic response is not associated with detectable changes in [Ca2+]i.