Regulation of spiral growth in planorbid gastropods

Extensive experimentation has been performed on the planorbid Planorbarius metidjensis in order to determine which mechanism allows the snail to coil its shell regularly. Individuals of this species, like all Planorbidae, are permanently active and secrete their shells while crawling on the substrate. Experiments consisted of attaching weights to either side of the shell (which is carried almost vertically) in an umbilical position; these weights cause the shell to fall towards the substrate on the loaded side. It can be demonstrated, qualitatively and quantitatively, that during further growth the shell tube deviated initially (i.e. within the first half whorl after loading) towards the loaded side. In a later stage, when the animal is able to re-balance the shell-load complex by muscular activity, the shell tube gradually deviates away from the loaded side. This behaviour is to be expected if, after loading, secretion of the shell continued with the aperture parallel to the substrate and forming a constant angle with the direction of growth. The main implication is that in normal conditions the living posture largely controls the correct coiling of the shell. Minor experiments made with another planorbid species, Gyraulus laevis , confirm these conclusions. The growth pattern of planorbids requires that the snail has constant information on the orientation of the shell with respect to the substrate. This is permitted by the particular physiological ecology of this group, members of which, unlike terrestrial gastropods, are permanently active.     

The problem of handedness reversal during the spiral growth of Phycomyces

One may easily conclude that the mechanism of cell wall growth of the sporangiophore of Phycomyces is an extremely complex one since the sporangiophore not only grows vertically (stretches) but also rotates (twists) about its longitudinal axis during growth. The result is spiral growth. The spiraling changes direction during the sporangiophore's development going from an initial left-handed spiral to a right-handed one and finally returning to the left-handed form. We believe that these observations can be explained in the following way. The cell's turgor pressure causes both longitudinal and radial deformation in the soft, thin, plastic region of the growing cell wall thus causing the wall to stretch. The cell wall microfibrils, which are initially oriented in a near transverse direction in the upper region of the growing zone, are displaced toward the longitudinal axis as a result of vertical stretch. This fibril displacement, from a transverse to a longitudinal direction, causes a horizontal displacement of the cell wall. This horizontal displacement is coupled with the vertical stretch to generate a spiral effect, i.e. spiral growth. We are further proposing that interfibril slippage occurs as the cell wall softens between stages IVa and IVb and it is this slippage that accounts for the change in the direction of spiraling when the sporangiophore goes from the left-handed form to the right-handed one.     

Electrostatically induced growth of spiral lipid domains in the presence of cholesterol

The formation of crystalline domains of the phospholipid l--dimyristoyl-phosphatidic acid containing 1 mol% cholesterol, was studied as a function of head group charge by fluorescence microscopy with monolayers at the air/water interface. It is shown that the usual dendritic growth occurs at low pH (8), whereas spiral domains are formed at high pH (11), where the head group contains two negative charges. The findings are ascribed to an electrostatically induced chain tilt that, in conjunction with an in-plane dipole moment, causes a ferroelectric state. This allows for domain aggregation and orientation originating in elongated domains that, additionally, are bent because of the chirality of the molecules. The structure is stabilized and further elongated due to the anisotropic edge activity of cholesterol.     

Overcoming the constraints of spiral growth: the case of shell remodelling

As animals grow in size, their relationship to the physical environment necessarily changes, but molluscs and brachiopods whose accretionary skeletons expand at one end of a hollow cone conform to logarithmic-spiral growth and retain a constant shape. Dissolution and remodelling of previously formed parts of the skeleton can alleviate the constraints of strict logarithmic-spiral growth. How, when, where and in which clades mineral skeletal resorption has evolved are important questions because they relate to the conditions and history of skeletal formation and to the way in which ocean acidification in the past influenced that history. A synthesis of data on mineral dissolution in shells shows that resorption from the inner surface of bivalve shells occurs under temporarily anaerobic conditions within the closed shell, but functional remodelling is unknown in bivalves. Resorption and functional remodelling occur in brachiopods, gastropods and terrestrial hermit crabs, and to a lesser extent in scaphopods and cephalopods. Internal whorl resorption leading to a more compact visceral mass has evolved at least ten times in gastropods. Contrary to expectations stemming from patterns in the availability of calcium, gastropod remodelling is a phenomenon of warm, calcium-rich environments and not of cold acidified conditions. There is therefore no evidence that internal whorl resorption increases calcium-use efficiency. Resorption is one of several mechanisms that have enabled animal skeletons to become more dynamic and adaptable during ontogeny.     

The analysis of spiral growth in phycomyces using a novel optical method

A conical mirror was designed and used to measure simultaneously the elongational and rotational displacement of a number of markers on the growing zone of the sporangiophore of Phycomyces. The results obtained by this new optical method demonstrate that the rotational rate is roughly proportional to the elongational rate, except in the lower region of the growing zone where a significant amount of rotation occurs without measurable elongation. From the data presented in this report, we have constructed a model that appears to explain the mechanism responsible for the left-handed spiral growth of the developing sporangiophore.     

Enhanced growth and ethylene increases spiral grain formation in Picea abies and Abies balsamea trees

Spiral grain angle in Norway spruce (Picea abies) trees and balsam fir (Abies balsamea) seedlings was investigated in relation to growth rate, endogenous and applied ethylene. Trees from stands of Norway spruce, which were irrigated and fertilised in order to enhance growth, and trees having different growth rates in non-treated stands were studied. Stem growth rate at the stand level (m³ ha^-1 year^-1) was measured annually, or by means of microscopy on stem sections as the number and size of tracheids produced. Enhanced growth increased ethylene evolution and maintained a high level of left-handed spiral grain angle in comparison to slower-growing trees. An increased number of earlywood tracheids in fast growing trees was correlated to a more left-handed spiral grain angle. Ethrel, applied to stems of balsam fir seedlings, increased the internal ethylene levels in parallel with increased left-handed spiral grain angle. The results indicate that ethylene regulates the extent of spiral grain angle.     

Gravitropic moss cells default to spiral growth on the clinostat and in microgravity during spaceflight

In addition to shoots and roots, the gravity (g)-vector orients the growth of specialized cells such as the apical cell of dark-grown moss protonemata. Each apical cell of the moss Ceratodon purpureus senses the g-vector and adjusts polar growth accordingly producing entire cultures of upright protonemata (negative gravitropism). The effect of withdrawing a constant gravity stimulus on moss growth was studied on two NASA Space Shuttle (STS) missions as well as during clinostat rotation on earth. Cultures grown in microgravity (spaceflight) on the STS-87 mission exhibited two successive phases of non-random growth and patterning, a radial outgrowth followed by the formation of net clockwise spiral growth. Also, cultures pre-aligned by unilateral light developed clockwise hooks during the subsequent dark period. The second spaceflight experiment flew on STS-107 which disintegrated during its descent on 1 February 2003. However, most of the moss experimental hardware was recovered on the ground, and most cultures, which had been chemically fixed during spaceflight, were retrieved. Almost all intact STS-107 cultures displayed strong spiral growth. Non-random culture growth including clockwise spiral growth was also observed after clinostat rotation. Together these data demonstrate the existence of default non-random growth patterns that develop at a population level in microgravity, a response that must normally be overridden and masked by a constant g-vector on earth.     

Overexpression of Bcl-2 or Bcl-xL prevents spiral ganglion neuron death and inhibits neurite growth

Spiral ganglion neurons (SGNs) provide afferent innervation to the cochlea and rely on contact with hair cells (HCs) for their survival. Following deafferentation due to hair cell loss, SGNs gradually die. In a rat culture model, we explored the ability of prosurvival members of the Bcl-2 family of proteins to support the survival and neurite outgrowth of SGNs. We found that overexpression of either Bcl-2 or Bcl-xL significantly increases SGN survival in the absence of neurotrophic factors, establishing that the Bcl-2 pathway is sufficient for SGN cell survival and that SGN deprived of trophic support die by an apoptotic mechanism. However, in contrast to observations in central neurons and PC12 cells where Bcl-2 appears to promote neurite growth, both Bcl-2 and Bcl-xL overexpression dramatically inhibit neurite outgrowth in SGNs. This inhibition of neurite growth by Bcl-2 occurs in nearly all SGNs even in the presence of multiple neurotrophic factors implying that Bcl-2 directly inhibits neurite growth rather than simply rescuing a subpopulation of neurons incapable of extending neurites without additional stimuli. Thus, although overexpression of prosurvival members of the Bcl-2 family prevents SGN loss following trophic factor deprivation, the inhibition of neurite growth by these molecules may limit their efficacy for support of auditory nerve maintenance or regeneration following hair cell loss.     

Focal delivery of fibroblast growth factor-1 by transfected cells induces spiral ganglion neurite targeting in vitro

Sensory cells in the cochlea of the rat transiently express acidic fibroblast growth factor (FGF-1) during the developmental period of terminal innervation in the sensory epithelium. To explore the potential role of FGF-1 in terminal innervation events, the response of cochlear ganglion neurons to FGF-1 was evaluated in culture. Explants from the spiral ganglion of postnatal day 5 rats were cultured in the presence of exogenous FGF-1, with or without heparin. FGF-1 in the culture medium produced a dose-dependent increase in the number and length of neurites produced by spiral ganglion neurons, a response that was enhanced by heparin. To assess the effects of FGF-1 produced by a focal, cellular source, additional explants were cocultured with 3T3 cell transfectants that secrete FGF-1. Neurites that came into contact with FGF-1 secreting cells branched, formed bouton-like terminal swellings on the surface of the transfectants, and stopped extending. The results suggest that FGF-1 may stimulate neurite extension into the sensory epithelium of the cochlea and that focal production of FGF-1 may contribute to the formation of contacts on sensory cells by developing neurites. J. Cell. Physiol. 177:123–129, 1998. © 1998 Wiley-Liss, Inc.     

Patterns of spiral phyllotaxy

The author investigates theoretical variants of spiral phyllotaxy using structural coefficient--the distance between consequent members in genetic spiral, expressed in parts of circle. The meanings of structural coefficient in which parastichies change their isomerism are determined as critical points. The author describes the overlapping of parastichies of lower lane by higher lane parastichies and presents the methods of overlapping determination. Parastichies with minimal distance between members in lane are clearly determined on shoots. Methods and formulas for calculation of structural coefficient using the number of members in parastichy circle are presented. Orthostichy is considered as a special case of parastichy location. Orthostichies are equal to parastichies in maximum critical points.     

旋割法制备气管螺旋条评价

目的通过改进螺旋剪法建立制备气管螺旋条的旋割法。方法 40只豚鼠,用旋割法和螺旋剪法制备离体豚鼠气管螺旋条,在Kreb＇s液中平衡孵育2 h后,以组胺histamine（浴槽浓度2.0×10-3g/L）和乙酰胆碱acetylcholine（浴槽浓度2.0×10-4g/L）引发气管螺旋条收缩,用BL420生物信号采集系统与张力传感器测定标本张力变化值。数据采用SPSS11.5软件在α=0.05的信度下进行t检验。结果 2 g负荷下,旋割法标本histamine引发收缩幅度是螺旋剪法制备标本的1.31倍,乙酰胆碱引发收缩幅度旋割法是螺旋剪法制备标本的1.208倍,经t检验,P〈0.05,差异均具有显著性;旋割法标本,histamine引发2 g负荷标本收缩幅度是1 g负荷的1.48倍,乙酰胆碱引发2 g负荷标本的收缩幅度是1 g负荷的1.38倍,经t检验,P〈0.05,差异均具有显著性;旋割法标本经hista-mine或acetylcholine激发收缩,洗净药物重复激发6次收缩幅度的RSD值分别为19.8%和19.1%,螺旋剪法标本经histamine或acetylcholine 6次重复引发诱发收缩幅度的RSD值分别35.3%和33.7%。结论与螺旋剪法制备气管螺旋条标本比较,旋割法制备螺旋条标本对收缩诱导剂histamine与acetylcholine的敏感性高,标本负荷以2 g较好,旋割法标本重复利用收缩幅度变化值较螺旋剪法标本小。     

Subclassification of spiral monocentric whorls

Despite all the papers on the classification of dermatoglyphic features, there is no definitive in sight yet. With this work we intend to contribute to adapt the subclassification of spiral monocentric whorls to their biologic nature. The results in this work show that clockwise whorls on the right hand match counter-clockwise ones on the left, and counter-clockwise spirals on the right are joined together with clockwise on the left. We propose the building of two new subclasses of spiral monocentric whorls to replace the traditional ones in order to conserve the bilateral identification of these pattern types.     

The spiral glands of Nereis

Summary The spiral organs of Nereis have been shown to be compound glands and not photoreceptors. The ducts of two or three types of secretory cells attach themselves in a serial manner to a spirally wound axial columella which lies just below the cuticle. The large intra-cellular ducts terminate in a number of fine ducts which penetrate the columella and open through it into the lumen of the gland. This communicates to the outside through a pore in the cuticle. The secretions are muco-polysaccharides which are probably mixed in the lumen before discharge.We should like to acknowledge the support of this work by the Science Research Council.     

Function of spiral grain in trees

Summary Through spiral grain, conduits for sap lead from each root to all branches. This uniform distribution of sap is indicated by the paths of vessels and tracheids, and has been proven experimentally by means of dyed sap injected into the base of stems or taken up by roots. Trees receiving water only from roots at one side of the root collar nevertheless stay green and continue growing. Spiral grain in bark distributes food from each branch to other flanks of the stem and to most roots. Experimental interruptions of the sap and food conduits caused the cambial zone to reorient new conduit cells in new directions, bypassing the interruption. In particular, spiral grooves cut into the stem surface caused spiral grain. The new cells reorient through division and growth. Although spiral grain is largely under genetic control, trees appear to have a spiral grain especially where needed for distribution of water when root spheres are dry at one side. Compared with straight-grained trees, spiral-grained stems and branches bend and twist more when exposed to strong wind, in this way offering less wind resistance and being less likely to break. Through the bending and twisting, snow slides down from branches rather than breaking them, but the main function of spiral grain is the uniform distribution of supplies from each root to all branches, and from each branch to many roots.