Influence of the g-force on the circumnutations of sunflower hypocotyls

Circumnutations of hypocotyls of sunflower ( Helianthus annuus L. cv. Californicus) were studied under 1 g and 3 g conditions. Root mean square values of the hypocotyl deviation from the plumbline and period of the movements were determined from Calculations of the autocorrelation functions of the movements. The amplitude and the period of the circumnutations increased under 3 g as compared to 1 g . A transition from 3 to 1 g or vice versa also caused changes in period and amplitude of the movoments. The results are interpreted as a support for the idea that gravity influences the circumnutation parameters in this sunflower variety. A comparison is made with published results on the dwarf sunflower ev. Teddy Bear where the force influence is very small or negligible. Simulations of a model for circumnutations show movements which are in qualitative agreement with the experimental results, provided adaptation to g -levels is included in the model. Finally, the results are discussed with the recent Spacelab-experiment (SLI) as a background.     

Physical model of water in a split-root system

Summary A physical model, based on Darcy's law and an Ohm's-law analogy, was developed to show that water can move from a wetter side of a root system to a drier side or vice versa. In the model, a wick in the form of an inverted Y was used, with the two ends of the Y in separate beakers and the third end (stem) of the Y extending into the air. The left root, right root, and stem were about 6,5, and 4 cm long, respectively. The difference in total head (potential) between the left root and the right root was varied for different potentials applied to the stem. Experiments were done either in a darkened laboratory or with a sunlamp shining on the stem. The stem was thus exposed to low-evaporation (in the dark) or high-evaporation (with the sunlamp) conditions. Total heads (sum of head due to gravity and head due to pressure-other heads were negligible) and flows of water were calculated or measured for each part of the split-root system (left root, right root, crown, stem). The results showed that the direction and quantity of water flowing in each part of the system depended upon the total head for the stem, crown, and each half of the root (the flow could be up, down, left, or right), and that the gravity component of the total head was important in moving water down the plant when light intensity was low.     

Gravitational gradients and blood flow patterns in specialized arboreal (Ahaetulla nasuta) and terrestrial (Crotalus adamanteus) snakes

Blood pressure and blood flow patterns were recorded from the carotid artery and aortae of a thick-bodied terrestrial snake (Crotalus adamanteus) and a thin-bodied arboreal species (Ahaetulla nasuta) anesthetized with ketamine hydrochloride. Hemodynamic stress induced by rotation resulted in pronounced changes in the blood flow patterns and pressure in C. adamanteus: rotation of A. nasuta produced changes of a similar type, but of a much lower magnitude. The markedly different responses of these two species, the baroreceptor reflexes of which were disrupted, suggest that morphological factors – such as differential gross cardiac displacement, or variation in the interaortic foramen – in addition to physiological factors, are important in determining a snake's ability to withstand hemodynamic stress. Accepted: 8 April 1997     

Limited period of graviresponsiveness in germinating spores of Ceratopteris richardii

Rhizoids of the fern Ceratopteris richardii Brogn. usually emerge 40 h after germination is initiated by light, and more than 90% of them emerge growing in a downward direction. However, when the spores are germinated on a clinostat, the emerging rhizoids show no preferential orientation. This indicates that under normal 1 · g conditions the initial growth direction of rhizoids can be oriented by gravity. If the orientation of the spores is changed 3 h or less after the start of germination, the growth direction of most emerging rhizoids becomes downward relative to the new orientation. However, if the orientation of the spores is changed by 180° 8 h or more after germination is initiated by light, most rhizoids emerge growing upward; i.e., the same direction as if there had been no orientation change. Emerged rhizoids also do not change their direction of growth if their orientation is changed. These results indicate that the growth direction of emerging rhizoids is set by gravity prior to actual emergence, and that the time of full orientation responsiveness is limited to a period ranging from the initiation of germination to about 3–4 h after the start of germination. There is a gravity-oriented nuclear movement beginning at about 13 h after germination, and this movement appears to predict the initial growth direction of rhizoids.These studies were made possible by grant NAGW 1519 to S.J.R. and grant NGT-51065 to E.S.E., both from the National Aeronautics and Space Administration.     

Evaluating spread of invaders from gravity scores - A way of using gravity models in ecology

This study is a theoretical excursion into gravity models and their usability in evaluating importance of spatial structure and population development for the spread of colonizing organisms. A so called “gravity score” for sites is deduced, and such a score could be used for predicting risk of colonization once one site in an area has been subject to introduction of a new species. The analysis further suggests that factors deciding spread between sites differs from those that govern expected population sizes. Gravity models of the kind presented here includes both population dynamics and spatial structure and could be a complement to other models describing organism spread.     

Sediment dynamics during the Cenomanian-Turonian (cretaceous) oceanic anoxic event in Northwestern Germany

Summary The epicontinental pelagic to hemipelagic Upper Cenomanian and Lower Turonian successons of the Lower Saxony Basin (northwestern Germany) are represented by the Rotpl?ner facies on swells (multicolored marls and marly limestones) and the basinal Black Shales facies (marly limestones (Turbidites), black shales) in the local basins. Facies units are described with their lateral and vertical variation from both depositional environments and their correlation is discussed. The distinct Cenomanian-Turonian boundary facies is due to dilution of pelagic carbonate by siliciclastic material, volcanic ashfall, and substantial changes in carbonate, sedimentation rates by about an order of magnitude. The observed sediment geometries origin from preservation of sediments in areas where normal faults occur and erosion of the formerly deposited units in unfaulted areas (preservation of relicts). Erosion and redeposition on swells occurs in thin (<50 cm thick) debris flow and mud flow channels (1–100 m wide), sheet flows, and by turbidity currents. During the Upper Cenomanian the sediment transport is governed by gravity flow which is increasingly superimposed by storm deposition during the Lower Turonian. Lense-shaped tempestites (probably below average storm wave base) occur at the base of the Turonian (entry ofMytiloides hattini) in morphologically highest swell positions and migrate across the entire basin until the late Lower Turonian. The basinal facies is characterised by laminated and biotrubated black shales and mud turbidites that vary over short distances. Laminae show graded bedding and erosive contacts and were deposited by turbidity currents. Intercalated marly limestones are mud turbidities (some mudflows) that are coarsening upwards until the early Lower Turonian. Larger slides occurred predominantly in the late Upper Cenomanian. The sediment distribution is closely related to sea level changes and reflects short- and long-term fluctuations generating comparable stratigraphic trend in the sections, although basin and swell facies are always clearly distinguished. Lokal basin margins (e.g. primary fordeeps of sal domes) were probably limited by larger normal faults that prevented facies gradation between both depositional environments.     

Secondary sensory cells in the gravity receptor system of the statocyst of Octopus vulgaris

Summary The presence of secondary sensory cells in the Octopus gravity receptor system has been demonstrated. In serial thin sections of the receptor cells (hair cells) no axons were found leaving the cells. Instead, synapses were observed with synaptic vesicles lying inside the receptor cells. Both data clearly indicate that the receptor hair cells represent secondary sensory cells. In addition, efferent contacts to the receptor cells could be confirmed.This work was supported in part by grant Wo 160/5 of the Deutsche Forschungsgemeinschaft to Prof. Dr. H.G. WolffThe experimental work was done in part at the Zoological Station in Naples and at the Sechenov Institute of Evolutionary Physiology and Biochemistry of the USSR Academy of Sciences (Laboratory of Prof. Dr. Ya.A. Vinnikov), Leningrad, USSR. The authors thank Prof. Vinnikov and Dr. Tsirulis for stimulating discussions     

Apoplast as the site of response to environmental signals

When the life cycle of plants is influenced by various environmental signals, the mechanical properties of the cell wall are greatly changed. These signals also modify the levels and structure of the cell wall constituents and such modifications are supposed to be the cause of the changes in the wall mechanical properties. These changes in the cell wall, the major component of the apoplast, can be recognized as the response of plants to environmental signals. The analysis of the mechanism leading to the response suggests that the apoplast is involved not only in the response but also in the perception and transduction of environmental signals in concert with the receptors of signals located on the plasma membrane. Thus, the apoplast plays a principal role in the communication of plants with the outer world and enables the plants to adapt themselves and survive in the environment full of stresses.