Mobilities of the cercal wind-receptor hairs of the cricket, Gryllus bimaculatus

The deflection sensitivities of cercal filiform hairs of the cricket, Gryllus bimaculatus, were determined by direct measurement. The tangential velocity of deflecting hair shafts in response to stimulus air motion was measured in situ by a laser-Doppler velocimeter with surface scattering of the shaft. The velocity of the stimulus air motion in a small wind tunnel was calibrated by the same velocimeter with smoke from a joss-stick. The mobility of the hair was obtained from former measurements with reference to the latter calibration of the single apparatus. A Gaussian white noise signal was employed as a stimulus waveform, and the stimulus-response transfer function was calculated through a cross-correlation method, which provides greater precision and wider frequency for a longer period of measurement. The mobility of hair was expressed in deflection amplitudes and phase shifts in reference to the velocity sinusoid of a stimulus at various frequencies. The measurements established the following conclusions. The wind receptor hairs comprise an array of mechanical band-pass filters whose best frequencies are inversely proportional to the length. The motion dynamics of the wind-receptor hairs have strong damping. Accepted: 24 February 1998     

Cortical microtubules and microfibril deposition in the cell wall of root hairs ofEquisetum hyemale

Summary The cell wall of root hairs ofEquisetum hyemale is shown to be composed of three different cell wall textures. The growing cell wall at the tip of the hair is composed of a dispersed texture of microfibrils, which continues along the outside of the whole hair. With increasing distance from the tip an increasing number of helicoidally arranged lamellae is deposited. These findings correspond with the observed isotropism of young hairs in polarized light.Hairs of approximately 4 days old become positive birefringent, indicating that longitudinally oriented layers prevail over layers with a transverse direction. This phenomenon starts at the base of the hair. Full-grown hairs are positive birefringent up to the tip and concordantly show a thick additional inner cell wall layer which forms a helical pattern the length of the hair, with a mean microfibril angle of 25 with the cell axis.Cortical microtubules, subjacent to the dispersed, the helicoidal and the helical wall texture are axially aligned and, thus, not in coalignment with the last deposited microfibrils.Coated and smooth vesicles are present in the cortical cytoplasm of both growing and full-grown hairs. Electron-dense profiles (20 nm in diameter), surrounded by a halo (of 50 nm) were observed on the wall-plasmalemma interface in full-grown hairs only. A relation of these structures with microfibril deposition could not be demonstrated. They might represent channels transporting material to the wall, which, in full-grown hairs, is heavily impregnated with a tawny brown substance.The general hypothesis that cortical microtubule orientation directs microfibril deposition is disputed.     

Morphological synergism in root hair length,density, initiation and geometry for phosphorus acquisition in Arabidopsis thaliana: A modeling approach

Low phosphorus availability regulates root hair growth in Arabidopsis by (1) increasing root hair length, (2) increasing root hair density, (3) decreasing the distance between the root tip and the point at which root hairs begin to emerge, and (4) increasing the number of epidermal cell files that bear hairs (trichoblasts). The coordinated regulation of these traits by phosphorus availability prompted us to speculate that they are synergistic, that is, that they have greater adaptive value in combination than they do in isolation. In this study, we explored this concept using a geometric model to evaluate the effect of varying root hair length (short, medium, and long), density (0, 24, 48, 72, 96, and 120 root hairs per mm of root length), tip to first root hair distance (0.5, 1, 2, and 4 mm), and number of trichoblast files (8 vs. 12) on phosphorus acquisition efficiency (PAE) in Arabidopsis. SimRoot, a dynamic three-dimensional geometric model of root growth and architecture, was used to simulate the growth of Arabidopsis roots with contrasting root hair parameters at three values of phosphorus diffusion coefficient (D _e=1×10^–7, 1×10^–8, and 1×10^–9 cm² s^–1) over time (20, 40, and 60 h). Depzone, a program that dynamically models nutrient diffusion to roots, was employed to estimate PAE and competition among root hairs. As D _e decreased from 1×10^–7 to 1×10^–9 cm² s^–1, roots with longer root hairs and higher root hair densities had greater PAE than those with shorter and less dense root hairs. At D _e=1×10^–9 cm² s^–1, the PAE of root hairs at any given density was in the order of long hairs > medium length hairs > short hairs, and the maximum PAE occurred at density = 96 hairs mm^–1 for both long and medium length hairs. This was due to greater competition among root hairs when they were short and dense. Competition over time decreased differences in PAE due to density, but the effect of length was maintained, as there was less competition among long hairs than short hairs. At high D _e(1×10^–7 cm² s^–1), competition among root hairs was greatest among long hairs and lowest among short hairs, and competition increased with increasing root hair densities. This led to a decrease in PAE as root hair length and density increased. PAE was also affected by the tip to first root hair distance. At low D _e values, decreasing tip to first root hair distance increased PAE of long hairs more than that of short hairs, whereas at high D _e values, decreasing tip to first root hair distance increased PAE of root hairs at low density but decreased PAE of long hairs at very high density. Our models confirmed the benefits of increasing root hair density by increasing the number of trichoblast files rather than decreasing the trichoblast length. The combined effects of all four root hair traits on phosphorus acquisition was 371% greater than their additive effects, demonstrating substantial morphological synergy. In conclusion, our data support the hypothesis that the responses of root hairs to low phosphorus availability are synergistic, which may account for their coordinated regulation.     

通河林区黄鼬(Mustela sibirica)冬季被毛形态结构的功能适应性

被毛在哺乳动物适应性进化过程中执行保温和保护两个重要功能,其形态结构上存在的功能适应性特征因所处的部位不同而表现出适应性分化现象,由动物体躯干至四肢末端呈显著的梯度变化。以黑龙江省通河林区黄鼬东北亚种(Mustela sibirica manchurica)冬季雌雄成体各10只完整毛皮对象,研究了背中部、腹中部和后肢下部3个部位的直针毛、披针毛、绒针毛、绒毛,以及后趾部硬毛的被毛性状因子,统计分析表明:通河林区黄鼬相同身体部位4种类型毛的长度和细度指标均为直针毛披针毛绒针毛绒毛,相同部位4种类型毛长度的相关性极显著,直针毛细度与披针毛细度相关性极显著(P0.01),绒针毛细度与绒毛细度相关性极显著(P0.01),这种特征使得被毛在整体结构上为实施保温和保护功能奠定基础;同时,黄鼬被毛各性状的保温功能从背部向后趾部呈递减趋势,而保护功能则呈现递增趋势,被毛形态结构性状上的分化与动物机体异温性充分结合,对于黄鼬适应寒冷的森林生态环境具有重要意义。     

Direction sensitivity of the filiform hair population of the cricket cereal system

Each cercus on the adult cricket Acheta domesticus bears 1000–2000 filiform hair mechanoreceptors. In order to determine the extent of identifiability of individual hair receptors, the structural characteristics of ten putative identified hairs were measured in 21–25 different animals. For these ten hairs, the sets of preferred directions and circumferential locations had standard deviations of 6.8° and 5.9°, respectively. There was no significant inter-animal covariance between a hair's preferred direction and its circumferential location. The preferred directions of 246 different identified hairs were then measured from 16 animals in order to characterize the distribution of preferred directions of hairs on a single typical cercus. These data were transformed from the frame of reference of the cercus into that of the cricket, generating an estimate of the representation of air-current stimulus direction provided by the entire ensemble of filiform hairs on both cerci. The distribution of hair directional sensitivities was continuous but extremely non-uniform, and more complex than previous studies had suggested.Abbreviations MT medial-transverse - LT lateral-transverse - AL anterior-longitudinal - PL posterior-longitudinal - MAO medial-anterior-oblique - MPO medial-posterior-oblique - LAO lateral-anterior-oblique - LPO lateral-posterior-oblique - T transverse - L longitudinal - O oblique - CNS central nervous system     

FLAGELLAR HAIRS IN PRASINOPHYTES (CHLOROPHYTA): ULTRASTRUCTURE AND DISTRIBUTION ON THE FLAGELLAR SURFACE1

The flagellar hair ultrastructure of 16 strains of species of the prasinophycean genera Mantoniella, Mamiella, Pseudoscourfieldia, Nephroselmis, Tetraselmis, Scherffelia, Pterosperma, and Pyraminonas was examined in detail by whole-mount electron microscopy. The flagellar hairs of all genera displayed a high degree of ultrastructural complexity that was completely conserved within each strain. In all strains, flagellar hairs occurred on the sides of the flagella (lateral hairs); in several strains, special flagellar hairs also were found on the flagellar tips (tip hairs; absent in the Chlorodendrales and in Nephroselmis). Two groups of lateral hairs were distinguished: 1) T-hairs (“Tetraselmis-type” flagellar hairs), characterized by a smooth, tubular shaft of ca. 15 nm diameter and an overall length of 0.5–1.3 μm, and 2) P_t-hairs (“Pterosperma-type lateral flagellar hairs”), which were considerably longer (ca. 1.5–5.4 μm), characterized by a thick shaft of ca. 30 nm diameter, which was covered with a layer of regularly spaced small particles of ca. 10 nm diameter. In both groups of flagellar hairs, a strain-specific number of subunits (1–101) in linear arrangement was attached to the distal end of the shaft. Tip hairs were either structurally related to T-hairs (Mamiellales, Pseudoscourfieldia) or represented a separate group, P_t-hairs (“Pterosperma-type flagellar tip hairs”; Pterosperma, Pyramimonas). In four genera (Mantoniella, Mamiella, Pseudoscourfieldia, Nephroselmis), both groups of lateral hairs occurred together on the same cell. Interestingly in these taxa the P_t-hairs were exclusively attached to the shorter immature flagella (no. 2), but, in contrast, in Mantoniella and Pseudoscourfieldia the tip hairs were restricted to the longer mature flagellum (no. 1). Thus, flagella of different developmental status differ in their hair-scale complement. The occurrence, distribution, and ultrastructure of flagellar hairs can be used to identify and classify prasinophytes at all taxonomic levels.     

Evolution of the cercal sensory system in a tropical cricket clade (Orthoptera: Grylloidea: Eneopterinae): a phylogenetic approach

The diversity of sensory systems in animals has poorly been explored on a phylogenetic basis at the species level. We addressed this issue using cricket cerci, comprising abdominal appendages covered with touch‐ and air‐sensitive hairs. Scanning electron microscopy measurements and spatial analyses of hair positioning were used to quantify the structural diversity of cercal structures. Eighteen Eneopterinae and two Gryllidae (outgroups) were studied from a phylogenetic perspective. Cerci were revealed to be complex, diverse, and variable between cricket species. Based on maximum likelihood estimations, the ancestral Eneopterinae cercus had a small size, and its hair equipment allowed the use of both air and touch mechanoreception. The evolution of Eneopterinae cerci was mainly unconstrained by the phylogeny; it was rather a punctuated process, involving apical transformations, and was mostly unrelated to environmental patterns. All studied species have enhanced their overall perceptive capacities compared to the ancestor. Most have longer cerci with more and/or longer hairs. Sensory abilities have improved either in the direction of touch or air movement detection, or both, without discarding the potential for any sensory capacity that was already present ancestrally. This pattern is consistent with the hypothesis of an evolutionary trade‐off for sensory performances. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 614–631.     

Hypaphorine, an indole-3-acetic acid antagonist delivered by the ectomycorrhizal fungus Pisolithus tinctorius, induces reorganisation of actin and the microtubule cytoskeleton in Eucalyptus globulus ssp bicostata root hairs

Hypaphorine, an indole alkaloid from the ectomycorrhizal fungus Pisolithus tinctorius Coker & Couch., counteracts indole-3-acetic acid (IAA) activity and controls the rate of root hair elongation in Eucalyptus globulus ssp. bicostata. The present investigation shows that hypaphorine changes cytoskeletal organisation in elongating root hairs of the host. The actin cytoskeleton was investigated by two different fixation and labelling procedures, which gave similar results. In control root hairs, actin organisation was characterised by (i) an actin cap at the very tip region, (ii) a subapical region with reduced labelling and containing fine actin filaments, and (iii) axial bundles of actin filaments running from the subapical part to the base of the root hair. In the hypaphorine-treated root hairs no actin cap was distinguished. The fine actin filaments occurring in the subapical region were replaced by a few thick actin filament bundles that extended from the subapical region toward the root hair tip. In the hypaphorine-treated hairs the total number of actin filament bundles along most of the root hair length was significantly reduced, presumably due to aggregation of pre-existing actin filaments. The first signs of alteration to the cytoskeleton could be detected as soon as 15 min after hypaphorine treatment. In hypaphorine-treated, but not in control root hairs, a patch of aggregated microtubules regularly occurred at a distance of approximately 10 m from the tip, possibly as a consequence of changes induced by hypaphorine in the actin cytoskeleton. The hypaphorine-induced aggregations in the actin and microtubule cytoskeletons could stabilise the structure of cytoskeletal elements, which in turn could hinder the vesicle delivery at the tip necessary for elongation. Such cytoskeletal alterations may be a consequence of the antagonism between IAA and hypaphorine. The latter view was supported by restoration of the actin cytoskeleton in hypaphorine-treated root hairs by IAA application.     

Structural scaling and functional design of the cercal wind-receptor hairs of cricket

We have estimated the intrinsic mechanical parameters of cricket cercal wind-receptor hairs. The hairs were modeled as an inverted pendulum, and mechanical parameters of the equation of motion were determined from data given by a systematic measurement of mobility by the least-square error method. The theoretical torque which turns the hair shaft is given by the drag force due to the moving air. The drag force is given by the method of Stokes' mechanical impedance of an oscillating cylinder in viscous fluid. The effect of the boundary layer in which air is stagnating on the substrate surface is also taken into account. The moment of inertia of a hair shaft shows a clear length dependency to the power of 4.32 of the hair length. The torsional resistance within the hair base and the stiffness of hair-supporting spring also show clear length dependencies to the power of 2.77 and 1.67, respectively. The torsional resistance within the hair base is so large that the hair is a strongly damped non-oscillatory second-order system. The large resistance within the hair base represents an efficient energy absorption by the sensory cell. The resistance seems to match with the source impedance, i.e., the frictional resistance at the site of air-hair contact. The impedance matching provides the condition of maximum power transmission from the moving air to the sensory cell. Structural scaling is discussed in relation to the functional scaling of the frequency-range fractionation of the mechanical filter array with a common biological design. Accepted: 24 February 1998     

Taxonomic and functional implications of stigma morphology in species ofCassia,Chamaecrista, andSenna (Leguminosae:Caesalpinioideae)

Two stigma forms occur inChamaecrista andSenna, but only one inCassia. In the common chambered form, a stigma pore is positioned on the reflexed style tip and is the entrance to a tapering chamber. The pore rim is fringed by hairs which vary in number, size, distribution and shape. In the alternative form the stigma is situated at the apex of the curved style and is crateriform. The crater rim is fringed by hairs of variable number and shape. The stigmatic hairs are predominantly unicellular and cutinized. Stigma and hair differences aid in the taxonomy of the genera. Their functions in pollination biology are discussed.     

Reconstruction and morphometry of silkmoth olfactory hairs: A comparative study of sensilla trichodea on the antennae of male Antheraea polyphemus and Antheraea pernyi (Insecta,Lepidoptera)

Summary Olfactory trichoid hairs on the antennae of male Antheraea silkmoths were reconstructed with respect to the following parameters: number, shape, course, and dimensions of outer dendritic segments as well as the numbers of their microtubules; inner and outer dimensions of the cuticular hair shafts; and number and distribution of pores and pore tubules in the hair walls. The smallest distances between dendritic membranes and inner hair surfaces were determined with respect to the possibility of pore tubule contacts. It was shown that most hairs contain one thick and one, or frequently two, thin dendrites. The number of microtubules in the dendrites is correlated with dendrite diameter, which decreases towards the hair tip. The dendrites form numerous swellings and constrictions: this beading occurs especially along the thin dendrites. The dendrites do not run straight, but rather follow a sinuous course in the hairs. The density of wall pores is lowest in the basal region of the hairs. Only in relatively few places do the dendritic membranes get near enough the hair walls to come into the probable range of the pore tubules. In the sensilla trichodea of A. polyphemus, the hairs as well as the dendrites have markedly smaller diameters than in A. pernyi.     

Spatial and temporal localization of SPIRRIG and WAVE/SCAR reveal roles for these proteins in actin-mediated root hair development

Root hairs are single-cell protrusions that enable roots to optimize nutrient and water acquisition. These structures attain their tubular shapes by confining growth to the cell apex, a process called tip growth. The actin cytoskeleton and endomembrane systems are essential for tip growth; however, little is known about how these cellular components coordinate their activities during this process. Here, we show that SPIRRIG (SPI), a beige and Chediak Higashi domain-containing protein involved in membrane trafficking, and BRK1 and SCAR2, subunits of the WAVE/SCAR (W/SC) actin nucleating promoting complex, display polarized localizations in Arabidopsis thaliana root hairs during distinct developmental stages. SPI accumulates at the root hair apex via post-Golgi compartments and positively regulates tip growth by maintaining tip-focused vesicle secretion and filamentous-actin integrity. BRK1 and SCAR2 on the other hand, mark the root hair initiation domain to specify the position of root hair emergence. Consistent with the localization data, tip growth was reduced in spi and the position of root hair emergence was disrupted in brk1 and scar1234. BRK1 depletion coincided with SPI accumulation as root hairs transitioned from initiation to tip growth. Taken together, our work uncovers a role for SPI in facilitating actin-dependent root hair development in Arabidopsis through pathways that might intersect with W/SC.     

Root hair elongation is inhibited by hypaphorine, the indole alkaloid from the ectomycorrhizal fungus Pisolithus tinctorius, and restored by indole-3-acetic acid

Hypaphorine, the major indolic compound isolated from the ectomycorrhizal fungus Pisolithus tinctorius, controls the elongation rate of root hairs. At inhibitory concentrations (100 μM), hypaphorine induced a transitory swelling of root hair tips of Eucalyptus globulus Labill. ssp. bicostata. When the polar tip growth resumed, a characteristic deformation was still visible on elongating hairs. At higher hypaphorine concentrations (500 μM and greater), root hair elongation stopped, only 15 min after application. However, root hair initiation from trichoblasts was not affected by hypaphorine. Hypaphorine activity could not be mimicked by related molecules such as indole-3-acetic acid (IAA) or tryptophan. While IAA had no activity on root hair elongation, IAA was able to restore the tip growth of root hairs following inhibition by hypaphorine. These results suggest that hypaphorine and endogenous IAA counteract in controlling root hair elongation. During ectomycorrhiza development, the absence of root hairs might be due in part to fungal release of molecules, such as hypaphorine, that inhibit the elongation of root hairs. Received: 27 October 1999 / Accepted: 14 March 2000     

The role of actin in root hair morphogenesis: studies with lipochito-oligosaccharide as a growth stimulator and cytochalasin as an actin perturbing drug

Root hairs develop from bulges on root epidermal cells and elongate by tip growth, in which Golgi vesicles are targeted, released and inserted into the plasma membrane on one side of the cell. We studied the role of actin in vesicle delivery and retention by comparing the actin filament configuration during bulge formation, root hair initiation, sustained tip growth, growth termination, and in full-grown hairs. Lipochito-oligosaccharides (LCOs) were used to interfere with growth ( De Ruijter et al . 1998 , Plant J. 13, 341–350), and cytochalasin D (CD) was used to interfere with actin function. Actin filament bundles lie net-axially in cytoplasmic strands in the root hair tube. In the subapex of growing hairs, these bundles flare out into fine bundles. The apex is devoid of actin filament bundles. This subapical actin filament configuration is not present in full-grown hairs; instead, actin filament bundles loop through the tip. After LCO application, the tips of hairs that are terminating growth swell, and a new outgrowth appears from a site in the swelling. At the start of this outgrowth, net-axial fine bundles of actin filaments reappear, and the tip region of the outgrowth is devoid of actin filament bundles. CD at 1.0 μ m , which does not affect cytoplasmic streaming, does not inhibit bulge formation and LCO-induced swelling, but inhibits initiation of polar growth from bulges, elongation of root hairs and LCO-induced outgrowth from swellings. We conclude that elongating net-axial fine bundles of actin filaments, which we call FB-actin, function in polar growth by targeting and releasing Golgi vesicles to the vesicle-rich region, while actin filament bundles looping through the tip impede vesicle retention.     

Age-associated thin hair displays molecular,structural and mechanical characteristic changes

Hair thinning occurs during normal chronological aging in women and in men leading to an increased level of thinner hair shafts alongside original thicker shafts. However, the characteristics of age-associated thin hairs remain largely unknown. Here we analyzed these characteristics by comparing at multiscale thin and thick hairs originated from Caucasian women older than 50 years. We observed that the cortex of thick hair contains many K35(+)/K38(?) keratinocytes that decrease in number with decreasing hair diameter. Accordingly, X-ray diffraction revealed differences supporting that thin and thick hairs are different with regards to the nature of the intermediate filaments making up their cortices. In addition, we observed a direct correlation between hair ellipticity and diameter with thin hairs having an unexpected round shape compared to the elliptic shape of thick hairs. We also observed fewer cuticle layers and a reduced frequency of a medullae in thin hairs. Regarding mechanical properties, thin hairs exhibited a surprising increased rigidity, a decrease of the viscosity and a decrease of the water diffusion coefficient. Hence, aged-associated thin hairs exhibit numerous modifications likely due to changes of hair differentiation program as evidenced by the modulations in the expression of hair keratins and keratin-associated proteins and by the X-ray diffraction specters. Hence, hair thinning with age does not consist simply of the production of a smaller hair. It is rather a more profound process likely relying on the implementation of an “aged hair program” that takes place within the hair follicle.     

Root hair-specific disruption of cellulose and xyloglucan in <Emphasis Type="Italic">AtCSLD3</Emphasis> mutants,and factors affecting the post-rupture resumption of mutant root hair growth

The glycosyl transferase encoded by the cellulose synthase-like gene CSLD3/KJK/RHD7 (At3g03050) is required for cell wall integrity during root hair formation in Arabidopsis thaliana but it remains unclear whether it contributes to the synthesis of cellulose or hemicellulose. We identified two new alleles, root hair-defective (rhd) 7-1 and rhd7-4, which affect the C-terminal end of the encoded protein. Like root hairs in the previously characterized kjk-2 putative null mutant, rhd7-1 and rhd7-4 hairs rupture before tip growth but, depending on the growth medium and temperature, hairs are able to survive rupture and initiate tip growth, indicating that these alleles retain some function. At 21°C, the rhd7 tip-growing root hairs continued to rupture but at 5oC, rupture was inhibited, resulting in long, wild type-like root hairs. At both temperatures, the expression of another root hair-specific CSLD gene, CSLD2, was increased in the rhd7-4 mutant but reduced in the kjk-2 mutant, suggesting that CSLD2 expression is CSLD3-dependent, and that CSLD2 could partially compensate for CSLD3 defects to prevent rupture at 5°C. Using a fluorescent brightener (FB 28) to detect cell wall (1 → 4)-β-glucans (primarily cellulose) and CCRC-M1 antibody to detect fucosylated xyloglucans revealed a patchy distribution of both in the mutant root hair cell walls. Cell wall thickness varied, and immunogold electron microscopy indicated that xyloglucan distribution was altered throughout the root hair cell walls. These cell wall defects indicate that CSLD3 is required for the normal organization of both cellulose and xyloglucan in root hair cell walls.     

Development of cricket sensory hairs: changes of dynamic mechanical properties

Summary Mechanical oscillation properties of cricket (Acheta domesticus) filiform hair sensilla were measured at different larval stages, as an indication of larval sensory capacities and for comparison with data in the literature on central nervous changes during development. The hairs were stimulated by airborne vibration over a frequency range of 10 to 220 Hz. Best frequency, angular displacement at best frequency, slope of angular-displacement tuning curve and phase of hair deflection relative to air particle velocity were tested for correlation with hair length, which is proportional to the age of a sensillum. The ranges found for the various oscillation parameters in early larval stages were similar to or larger than those in adults. Oscillation properties changed with both the developmental stage of the hair sensilla and that of the whole animal. Four individually identifiable hair sensilla were analysed separately; the sensory neurons of two of them are known to change synaptic properties during maturation. Angular displacement at a given stimulus intensity was maximal for all hairs after differentiation, and decreased during further development. The hairs did not show clear common changes for any of the other oscillation parameters. Yet particular changes were found for individual hairs.     

Multiple cyclic nucleotide‐gated channels coordinate calcium oscillations and polar growth of root hairs

Calcium gradients underlie polarization in eukaryotic cells. In plants, a tip‐focused Ca²⁺‐gradient is fundamental for rapid and unidirectional cell expansion during epidermal root hair development. Here we report that three members of the cyclic nucleotide‐gated channel family are required to maintain cytosolic Ca²⁺ oscillations and the normal growth of root hairs. CNGC6, CNGC9 and CNGC14 were expressed in root hairs, with CNGC9 displaying the highest root hair specificity. In individual channel mutants, morphological defects including root hair swelling and branching, as well as bursting, were observed. The developmental phenotypes were amplified in the three cngc double mutant combinations. Finally, cngc6/9/14 triple mutants only developed bulging trichoblasts and could not form normal root hair protrusions because they burst after the transition to the rapid growth phase. Prior to developmental defects, single and double mutants showed increasingly disturbed patterns of Ca²⁺ oscillations. We conclude that CNGC6, CNGC9 and CNGC14 fulfill partially but not fully redundant functions in generating and maintaining tip‐focused Ca²⁺ oscillations, which are fundamental for proper root hair growth and polarity. Furthermore, the results suggest that these calmodulin‐binding and Ca²⁺‐permeable channels organize a robust tip‐focused oscillatory calcium gradient, which is not essential for root hair initiation but is required to control the integrity of the root hair after the transition to the rapid growth phase. Our findings also show that root hairs possess a large ability to compensate calcium‐signaling defects, and add new players to the regulatory network, which coordinates cell wall properties and cell expansion during polar root hair growth.     

Endoplasmic microtubules configure the subapical cytoplasm and are required for fast growth of Medicago truncatula root hairs

To investigate the configuration and function of microtubules (MTs) in tip-growing Medicago truncatula root hairs, we used immunocytochemistry or in vivo decoration by a GFP linked to a MT-binding domain. The two approaches gave similar results and allowed the study of MTs during hair development. Cortical MTs (CMTs) are present in all developmental stages. During the transition from bulge to a tip-growing root hair, endoplasmic MTs (EMTs) appear at the tip of the young hair and remain there until growth arrest. EMTs are a specific feature of tip-growing hairs, forming a three-dimensional array throughout the subapical cytoplasmic dense region. During growth arrest, EMTs, together with the subapical cytoplasmic dense region, progressively disappear, whereas CMTs extend further toward the tip. In full-grown root hairs, CMTs, the only remaining population of MTs, converge at the tip and their density decreases over time. Upon treatment of growing hairs with 1 microM oryzalin, EMTs disappear, but CMTs remain present. The subapical cytoplasmic dense region becomes very short, the distance nucleus tip increases, growth slows down, and the nucleus still follows the advancing tip, though at a much larger distance. Taxol has no effect on the cytoarchitecture of growing hairs; the subapical cytoplasmic dense region remains intact, the nucleus keeps its distance from the tip, but growth rate drops to the same extent as in hairs treated with 1 microM oryzalin. The role of EMTs in growing root hairs is discussed.     

Urotensin I-like immunoreactivity in the midgut endocrine cells of the insects Gryllus bimaculatus and Periplaneta americana

Summary The occurrence of urotensin I (UI)-like immunoreactivity is demonstrated in the midgut of the cricket Gryllus bimaculatus and the cockroach Periplaneta americana. The immunoreactivity is restricted to endocrine cells dispersed in the epithelium of the midgut. The UI-positive endocrine cells are numerous in the cricket, but much fewer in the cockroach. These UI-positive cells are different from bovine pancreatic polypeptide (BPP)-immunoreactive cells which represent a dominant cell type in the midgut of both insects. This study suggests the possibility that the neuropeptide UI or a closely related substance may also occur in animals other than fishes.