Statocyte Cell Research Articles

Ophrys mammosa subsp. mammosa Desf.’nın stolon anatomisi

As a result of the detailed literature reviews, it has been determined that there are a limited number of studies on the stolon anatomy of orchids. In this study, Ophrys mammosa subsp. mammosa taxon by examining the stolon anatomy of the, it is aimed to contribute to the explanation of the tuber ontogeny of the genus. As material, microtome sections were taken from the embedding preparations with historesin kit in Ophrys mammosa subsp. mammosa stolons and stained with toluidin blue. From anatomical sections; It was determined that the vascular bundles in the middle part of the stolon are spaced and meristele distributed asymmetrically and the presence of statocyte cells in the lower part, the presence of a velamen in the outermost and several rows of exodermis under it, and an inner parenchymatic wide cortex. As a result; It has been emphasized that the anatomy of the orchid stolon is partially similar to the tuber that will develop in the future, and the importance of the findings in terms of tuber biology is discussed.

Root system architecture and gravity perception of a mangrove plant,Sonneratia alba J. Smith

We describe the features of the root system and the gravitropism of roots produced bySonneratia alba. The root system consists of four root types with different growth directions: (a) Pneumatophores, which are negatively orthogravitropic and their statocytes are very large (922 μm2) and the statolith is located near the proximal wall, (b) Cable roots and (c) Feeding roots which are both diagravitropic and their statoliths are settled along the longitudinal wall, and (d) Anchor roots which are positively orthogravitropic. The statocyte cells are the smallest (420 μm2) and statoliths settled at the distal wall. We found that all roots with marked gravitropism have statoliths that settle along different walls of the statocyte. This implies that the statoliths sensing of gravity is done by gravity on mass, and that they are denser than surrounding cytoplasm and this position is related to root growth direction. This finding matches the statoliths sediment under the effect of gravity. Irrespective of statolith, position and direction of growth may be stable.

Root cytoskeleton: its role in perception of and response to gravity.

We have critically evaluated the possible functions of the plant cytoskeleton in root gravisensing and graviresponse and discussed the evidence that microtubules (MTs) and actin microfilaments (MFs) do not control differential cell growth during bending of roots. On the other hand, MF and MT networks are envisaged to participate in gravisensing because of the mechanical properties of the cytoskeletal structures that interconnect plant cell organelles with the plasma membrane. In restrained gravisensing, forces are suggested to be transmitted to membranes because large-scale gravity-dependent repositioning of organelles is effectively prevented due to the cytoskeleton-mediated anchorage of their envelopes at the plasma membrane. From the cytoskeletal point of view, we can also envisage an unrestrained gravity sensing when cytoskeletal tethers are not strong enough to preserve the tight control over distribution of organelles and the latter, if heavy enough, are allowed to sediment towards the physical bottom of cells. This situation obviously occurs in root cap statocytes because these uniquely organized cells are depleted of prominent actin MF bundles, endoplasmic MT arrays, and ER elements in their internal cytoplasm. Nevertheless, indirect evidence clearly indicates that sedimented root cap statoliths are enmeshed within fine but dynamic MF networks and that their behaviour is obviously under, at least partial, cytoskeletal control. The actomyosin-enriched domain among and around amyloplasts is proposed to increase the perception of gravity due to the grouping effect of sedimenting statoliths. Cytoskeletal links between myosin-rich statoliths, and cell peripheries well equipped with dense cortical MTs, membrane-associated cytoskeleton, as well as with ER elements, would allow efficient restrained gravisensing only at the statocyte cell cortex. As a consequence of cytoskeletal depletion in the internal statocyte cytoplasm and bulk sedimentation of large amyloplasts, restrained gravisensing is spatially restricted to the bottom of the statocyte irrespective of whether roots are vertical or horizontal. This spatial aspect allows for efficient gravisensing via amplification of gravity-induced impacts on the cellular architecture, a phenomenon which is unique to root cap statocytes.

The behaviour of normal and agravitropic transgenic roots of rapeseed ( Brassica napus L.) under microgravity conditions

In the TRANSFORM experiment for IML-2 on the Space Shuttle Columbia, normal (wild type = WT) and genetically transformed agravitropic rapeseed roots were tested under microgravity conditions. The aim of the experiment was to determine if the wild-type roots behaved differently (growth, morphology, gravitropical sensitivity) from the transgenic roots. The appearance of the organelles and distribution of statoliths (i.e. amyloplasts with starch grains) in the gravitropic reactive cells (statocytes) under weightlessness was compared for the two types of roots. Attempts have also been made to regenerate new plants from the root material tested in space. Both the WT and the transgenic root types showed the expected increase in length during 36 h of photorecording. Contrary to the results of the ground controls, no significant difference in elongation rates was found between the WT and transgenic roots grown in orbit. However, there are indications that the total growth both in the WT and the transgenic roots was higher in the ground control than for roots in orbit. After a 60 min 1 × g stimulation of the roots on board the Shuttle, no detectable curvatures were obtained in either the transgenic or the WT roots. However, it cannot be excluded that a minute curvature development occurs in the root tips but was not detected due to technical reasons. The ultrastructure was well preserved in both the WT and the transgenic roots, despite the fact that the tissue was kept in the prefixative for over 3 weeks. No marked differences in ultrastructure were observed between the transformed root statocyte cells and the equivalent cells in the wild type. There were no obvious differences in root morphology during the orbital period. Light micrographs and morphometrical analysis indicate that the amyloplasts of both the wild type and transformed root statocytes are randomly distributed over the cells kept under micro- g conditions for 37 h after a 14 h stimulation on the 1 × g centrifuge. The main scientific conclusion from the TRANSFORM experiment is that the difference in growth found in the ground control between the WT and the transgenic root types seems to be eliminated under weightlessness. Explanations for this behaviour cannot be found in the root ultrastructure or in root morphology.

The role of extracellular free-calcium gradients in gravitropic signalling in maize roots

Gravitropism in roots has been proposed to depend on a downward redistribution of calcium across the root cap. However, because of the many calcium-binding sites in the apoplast, redistribution might not result in a physiologically effective change in the apoplasmic calcium activity. To test whether there is such a change, we measured the effect of gravistimulation on the calcium activity of statocyte cell walls with calcium-specific microelectrodes. Such a measurement must be made on a tissue with gravity sensing cells at the surface. To obtain such a tissue, decapped maize roots (Zea mays L. cv. Golden Cross Bantam) were grown for 31 h to regenerate gravitropic sensitivity, but not root caps. The calcium activity in the apoplasm surrounding the gravity-sensing cells could then be measured. The initial pCa was 2.60 +/- 0.28 (approx 2.5 mM). The calcium activity on the upper side of the root tip remained constant for 10 min after gravistimulation, then decreased 1.7-fold. On the lower side, after a similar lag the calcium activity increased 1.6-fold. Control roots, which were decapped but measured before recovering gravisensitivity (19 h), showed no change in calcium activity. To test whether this gradient is necessary for gravitropic curvature, we eliminated the calcium activity gradient during gravitropism by applying a mobile calcium-binding site (dinitro-BAPTA; 1,2-bis(2-amino-5-nitro-phenoxy)ethane-N,N,N',N'-tetraacetic acid) to the root cap; this treatment eliminated gravicurvature. A calcium gradient may be formed by proton-induced calcium desorption if there is a proton gradient. Preventing the formation of apoplastic pH gradients, using 10 and 50 mM 2-(N-morpholino)ethanesulfonic acid (Mes) buffer or 10 mM fusicoccin to stimulate proton excretion maximally, did not inhibit curvature; therefore the calcium gradient is not a secondary effect of a proton gradient. We have found a distinct and rapid differential in the apoplasmic calcium activity between the upper and lower sides of gravistimulated maize root tips which is necessary for gravitropism.

Amyloplast Sedimentation in Shoot Statocytes having a Large, Central Vacuole: Further Interpretation from Electron Microscopy

The claim (Lawton, Juniper, and Hawes, 1986) that amyloplasts sediment through the central vacuole of geostimulated shoot statocytes has been critically examined. As the result of our TEM study of Taraxacum statocytes and from theoretical considerations of amyloplast sedimentation, we conclude that it is possible for individual amyloplasts surrounded by a layer of tonoplast-bounded cytoplasm to travel occasionally through the vacuole, but unlikely that the majority of the amyloplasts in a statocyte sediment in this manner. We put forward a scheme for amyloplast movement in shoot statocytes which emphasizes the fluidity of the tonoplast membrane. In this scheme, it is expected that most amyloplasts sediment in peripheral cytoplasm down the statocyte cell wall, but amyloplasts may also, as they sediment, create or break transvacuolar strands, or move through already existing transvacuolar strands, or fall through the vacuole while enclosed by some cytoplasm and tonoplast membrane. Finally, it is suggested that the tonoplast membrane may have been neglected as a membrane site for detection of the gravity stimulus through interaction with sedimenting amyloplasts.

Sensory endings of the ascidian static organ (Chordata, Ascidiacea)

The ultrastructure of the static organ is examined in larvae of Diplosoma macdonaldi, a colonial ascidian, and Styela plicata, a solitary ascidian; the results are similar. As previous workers found, the cell body of a unicellular statocyte lies in the lumen of the sensory vesicle and contains the statolith. A narrow neck connects the cell body to an anchoring foot in the floor of the sensory vesicle. Two previously undescribed sensory endings project into the lumen just to the left of the statocyte, one anterior and one posterior to the neck. A network of fine processes from each ending contacts the statocyte body. It is proposed that movements of the statocyte cell body are detected by these endings. They arise from neurons in the ventral wall of the sensory vesicle that project axons to the visceral ganglion. The placement of the sensory endings may allow discrimination of the directon of statocyte deflection.

The Polarity of Movement of Endogenously Produced IAA in Relation to a Gravity Perception Mechanism

The polarity of radioactive IAA transport in segments of the leaf sheath base of Avena fatua L. is reversed upon their inversion through 180° transport towards the apex being greater than towards the base. Changes in rates of transport leading to this reversal can be detected within 10–20 min, correlating with the timing of statolith movements from the base to the apex of statocyte cells and conforming to a proposed model for the gravity control of auxin transport. Transport of H3-trytophan-derived H3-IAA was found to undergo similar changes in polarity upon re-orientation as did exogenously applied H3 or C14 IAA. It is concluded that the proposed model also relates to the movement of endogenously produced IAA.

Amyloplast Movement and the Geotropic Response

When nodal segments cut from flowering plants of Lolium multiflorumLam. were held horizontally for 20 min and then vertically for 20 min, and the process repeated continuously, a total time of geostimulation of 110 min was needed to obtain 5° bending of the false-pulvinus. Alternate treatments of 5 min horizontal and 20 min vertical repeated continuously halved the total time of geostimulation for 5° bending. Although some amyloplasts of statocyte cells have moved to the new lowermost wall within 5 min of geostimulation it is suggested that movement of amyloplasts rather than their position in statocyte cells determines the geotropic response.

Morphology and ultrastructure of the gravity-sensitive leaf sheath base of the grass Echinochloa colonum L

When a flowering stalk of Echinochloa colonum is held horizontally, growth is initiated in the lower side of each leaf sheath base, restoring the inflorescence to an upright position. Changes in the gravity vector are perceived by specialised statolithcontaining tissue which is associated with each of the symmetrically-arranged vascular bundles within the leaf sheath bases. The morphological and ultrastructural features of these gravity-sensitive regions have been examined by light and electron microscopy. Each statocyte cell contains a large central vacuole with a thin lining of cytoplasm. Up to 50 spherical starch statoliths lie along the lowermost side of the cells and these sediment readily following geotropic stimulation. Statoliths are found in contact with the plasmalemma, or may be prevented from touching it by bands of microtubules. Dictyosomes and mitochondria are numerous, but endoplasmic reticulum is sparse. The nuclei tend to remain at the original apex of each cell. Statocytes of the leaf sheath base are compared and contrasted with those of the root tip.

Movement of Cell Organelles and the Geotropic Curvature in Roots of Norway Spruce (Picea abies)

AbstractThe geotropic development in roots of Norway spruce [(Picea abies (L.)] H. Karst, has been followed by light and electron microscopy and compared with the movement of cell organelles (statoliths) in the root cap cells. The geotropic curvature develops in two phases: (a) an initial curvature in the root cap region, which results in an asymmetry in the extreme root tip and which appears after about 3 h stimulation in the horizontal position; and (b) the geotropic curvature in the basal parts of the root tip, which after 8 h is distributed over the entire elongation zone. A graphic extrapolation, based on measurements of the root curvatures after various stimulation periods, indicates a presentation time in the range of 8 to 10 min.The root anatomy and ultrastructure have been examined in detail in order to obtain information as to which organelles may act as gravity receptors. The root cap consists of a central core (columella) distinct from the peripheral part. The core contains three to four rows of parenchymatic cells each consisting of 15 to 18 storeys of statocyte cells with possibly mobile cell organelles. Amyloplasts and nuclei have been found to be mobile in the root cap cells, and the movement of both types of organelles has been followed after inversion of the seedlings and stimulation in the horizontal position for various periods of time at 4°C and 21°C. Three‐dimensional reconstructions of spruce root cap cells based on serial sectioning and electron microscopy have been performed. These demonstrate that the endoplasmic reticulum (ER)‐system and the vacuoles occupy a considerable part of the statocyte cell. For this reason the space available for free movement of single statolith particles is highly restricted.

Gravity-regulation of Cell Elongation in Nodes of the Grass Echinochloa colonum

Summary A bending response to a gravitational stimulus in the nodes of the grass Echinochloa colonum is evoked within 35—45 min of their being placed horizontal. The bending is attributable to cell elongation which is initiated in the leaf sheath base when it is displaced from the vertical. If the nodes alone are excised, some elongation occurs in the normal vertical position, but when placed horizontally, elongation on the lower side is enhanced and on the upper side is reduced. The extent of cell elongation is thus regulated by the orientation of the node with respect to gravity, and can be related to the position of statoliths within the statocyte cells. Two models are proposed: the first is based on a positional sensitivity within the statocyte cells, the second depends on a positional association of the statocyte cells with adjacent bundle sheath cells.