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At least 109 records · Page 6Linked to original sources
PubMed2002

SCHIZORIZA controls an asymmetric cell division and restricts epidermal identity in the Arabidopsis root.

The primary root of Arabidopsis has a simple cellular organisation. The fixed radial cell pattern results from stereotypical cell divisions that occur in the meristem. Here we describe the characterisation of schizoriza (scz), a mutant with defective radial patterning. In scz mutants, the subepidermal layer (ground tissue) develops root hairs. Root hairs normally only form on epidermal cells of wild-type plants. Moreover, extra periclinal divisions (new wall parallel to surface of the root) occur in the scz root resulting in the formation of supernumerary layers in the ground tissue. Both scarecrow (scr) and short root (shr) suppress the extra periclinal divisions characteristic of scz mutant roots. This results in the formation of a single layered ground tissue in the double mutants. Cells of this layer develop root hairs, indicating that mis-specification of the ground tissue in scz mutants is uncoupled to the cell division defect. This suggests that during the development of the ground tissue SCZ has two distinct roles: (1) it acts as a suppressor of epidermal fate in the ground tissue, and (2) it is required to repress periclinal divisions in the meristem. It may act in the same pathway as SCR and SHR.

Arabidopsis↗
PubMed1996

Amyloplast distribution in hairy roots induced by infection with Agrobacterium rhizogenes.

To elucidate the rapid and plagiotropic growth of hairy root induced by A. rhizogenes, a root apex was investigated with respect to it's amyloplast deposition, activity of alpha-amylase and glucose content. The amyloplasts distributed in the hairy roots were fewer than those of the adventitious root. Since auxin availability is enhanced in hairy roots, it could affect the statolith degradation by elevating alpha-amylase activity so that the energy requirement for rapid growth could be fulfilled as represented of glucose content. Consequently, it is suggested the overall decrease of starch grains could result in the lack of gravi-response in hairy roots.

Daucus carota↗
PubMed1991

Measurement of circumnutation in maize roots.

The movement of growing primary roots of maize was measured using a computer driven video-digitizer system. Real time measurements with two perpendicularly mounted video cameras permit measurements of growth movements in three dimensions and allow precise control of growth experiments. The spatial reconstruction and the angular orientation of the oscillating tips revealed that roots fluctuate in growth rate, straight growth and tip orientation. The movements of roots were less uniform than circumnutational activity of shoots and occurred in roots growing in the dark or light, submersed in buffer or suspended in air. The movements led to tip orientation deviating more than 30 degrees from the vertical without causing gravi-reaction. Large angular fluctuations occurred in cycles lasting on average 80 min. and could be observed even in decapped roots. The data suggest that endogenous movements are the result of internal growth regulation, possibly derived from differential sensitivity or adaptation of the elongating tissue. The ability of roots to respond to reorientation seems to depend upon the extent and direction of previous movements. Endogenous movements are likely to contribute to the gravitropic response and to irregular growth under conditions of microgravity.

Gravitation↗
PubMed1996

Space stress and genome shock in developing plant cells.

In the present paper I review symptoms of stress at the level of the nucleus in cells of plants grown in space under nonoptimized conditions. It remains to be disclosed to what extent gravity "unloading" in the space environment directly contributes to the low mitotic index and the chromosomal anomalies and damage that is frequently, but not invariably, demonstrable in space-grown plants. Evaluation of the available facts indicates that indirect effects play a major role and that there is a significant biological component to the susceptibility to stress damage equation as well. Much remains to be learned on how to provide strictly controlled, optimal environments for plant growth in space. Only after optimized controls become possible will one be able to attribute any observed space effects to lowered gravity or to other significant but more indirect effects of the space environment.

Cell Cycle↗
PubMed1993

Inhibitory effects of KN-93, an inhibitor of Ca2+ calmodulin-dependent protein kinase II, on light-regulated root gravitropism in maize.

Light is essential for root gravitropism in Zea mays L., cultivar Merit. It is hypothesized that calcium mediates this light-regulated response. KN-93, an inhibitor of calcium/calmodulin kinase II (CaMK II), inhibits light-regulated root gravitropism but does not affect light perception. We hypothesize that CaMK II, or a homologue, operates late in the light/gravity signal transduction chain. Here we provide evidence suggesting a possible physiological involvement of CaMK II in root gravitropism in plants.

Benzylamines↗
PubMed1985

Movement of calcium across tips of primary and lateral roots of Phaseolus vulgaris.

Calcium (Ca) movement across tips of primary and lateral roots of Phaseolus vulgaris was determined by applying 45Ca2+ to one side of the root and collecting radioactivity in an agar receiver block on the opposite side of the root. The ratios of cpm in receiver blocks on the bottom of primary roots : cpm in receiver blocks on the top of the primary roots were 1.87 and 2.47 after 1 and 2 hr, respectively. This polar transport of Ca across tips of primary roots correlated positively with a graviculture of 43 degrees after 2 hr. The ratio of cpm in receiver blocks on the bottom of lateral roots : cpm in receiver blocks on the top of lateral roots was 1.20 after 2 hr. The decreased polar movement of Ca across tips of lateral roots correlated positively with lateral roots being nongraviresponsive. These data 1) support the suggestion that gravistimulation induces polar movement Ca toward the lower side of tips of primary roots, and 2) suggest that the reduced polar movement of Ca across tips of lateral roots may be involved in uncoupling gravistimulation from gravicurvature in lateral roots.

Biological Transport↗
PubMed1985

Amyloplast sedimentation kinetics in gravistimulated maize roots.

Amyloplast sedimentation in gravistimulated maize (Zea mays L.) roots was measured using the change in angle from the center of the cell to each amyloplast as an index of sedimentation. Using tissue fixed after gravistimulation, the relationship between mean amyloplast angle and the duration of gravistimulation was found to be linear when plotted on a logarithmic time scale. Extrapolated values for the onset of angular change are 5.9 s after the start of gravistimulation for the entire population of amyloplasts and 11.8 s for lead amyloplasts. By multiplying the instantaneous angular velocity (in radians) by the cell center to amyloplast radius, it is possible to calculate the initial sedimentation velocity to be 19.1 micrometers min-1 at 5.9 s. During sedimentation, the mean amyloplast angles surpass the calculated cell corner angle of 123 at 2.2 min for all amyloplasts and at 19 s for lead amyloplasts near the new lower wall. Thus, substantial sedimentation occurs within the presentation time, calculated to be 4.1 min. These kinetics are consistent with several hypotheses of graviperception.

Gravitation↗
PubMed1984

Graviresponsiveness and columella cell structure in primary and secondary roots of Ricinus communis.

In order to determine what structural changes are associated with the onset of graviresponsiveness by plant roots, we have monitored the quantitative ultrastructures of columella (i.e., graviperceptive) cells in primary and secondary roots of Ricinus communis. The relative volumes of cellular components in lateral (i.e., minimally graviresponsive) roots were not significantly different from those of primary roots. The relative volumes of cellular components in secondary roots growing laterally were not significantly different from those of graviresponsive secondary roots. Therefore, the onset of graviresponsiveness by secondary roots of R. communis is not correlated with changes in organellar concentrations in columella cells. These results are discussed relative to a model for the differential graviresponsiveness of plant roots.

Ricinus communis↗
PubMed1997

Cytochalasin D does not inhibit gravitropism in roots.

It is generally thought that sedimenting plastids are responsible for gravity sensing in higher plants. We directly tested the model generated by the current statolith hypothesis that the gravity sensing that leads to gravitropism results from an interaction between the plastids and actin microfilaments. We find that the primary roots of rice, corn, and cress undergo normal gravitropism and growth even when exposed to cytochalasin D, a disruptor of actin microfilaments. These results indicate that an interaction between amyloplasts and the actin cytoskeleton is not critical for gravity sensing in higher plants and weaken the current statolith hypothesis.

Actin Cytoskeleton↗
PubMed1999

Gravitropic response of adventitious roots cultivated in light and darkness on sucrose-free medium.

Elongation of adventitious roots of Dracaena fragrans was investigated under photoautotrophic conditions. Root elongation decreased and stopped when cultures were transferred to darkness. Upon return to light roots renewed growth after a 5 day lag period. During the first two days of intensive new growth roots were agravitropic elongating in random directions. Investigation showed that transient absence of geotropic response was connected with disappearance of starch grains in root tip which occurred due to sucrose starvation of cultures in continuous darkness.

Culture Media↗
PubMed1975

The development of seedling shoots under space flight conditions.

The assumption that gravity is the major factor in the process of formation of plant polar axis was used as a working basis for the experiment. It was hypothesized by Merkys in 1973 that the effect of gravity related to axial polarity is similar to the process which determines the lateral polarity of shoots under the influence of gravity. There are two possibilities: (i) the development and morphogenesis of shoots takes place directly under the influence of gravity, or (ii) this process, at least during the first growth phases, is determined in the course of the germ development in the seed. In accordance with that assumption, the experiment was carried out in 1973. A special system was used for germinating and cultivating "Pioneer" and "Grybovsky rannyj" peas. The duration of the experiment under flight conditions was 48 hours in darkness, at 20 degrees C. The experimental conditions were the following: 1, the experiment in flight; 2, imitation of flight conditions using the horizontal clinostat; 3, vertical clinostat; 4, control (vertical plants). When the system was brought down to earth, the material was fixed and subjected to morphological and biochemical analysis. On the basis of the analysis, the following conclusion was drawn: during the first growth phases, the morphogenesis of shoots and roots apparently does not change under flight conditions. This conclusion was confirmed by planting those seedlings under earth conditions; normal plants were obtained whose growth and development were similar to the control seedlings. The problem of the influence of changed gravity, or the lack of it, on the growth and development of plants is discussed. The possible role of gravity on the formation of the polarity axes is also discussed from the point of view of generative development and the determination of some peculiarities of morphogenesis.

Cell Polarity↗
PubMed2001

Orientation of root hair growth is influenced by simulated microgravity.

We have tried to investigate the mechanisms supporting the plagiotropic growth (growth in parallel to the Earth) of root hairs in simulated microgravity. Our strategy to understand the regulation of such type of growth depends upon the study of cytoskeleton topography and calcium ions distribution in root hairs both in control and simulated microgravity.

Actins↗
PubMed2003

Novel hydrotropism mutants of Arabidopsis thaliana and their altered waving response and phototropism.

Roots display positive hydrotropism in response to a moisture gradient, which is important for plants to escape from water stress and regulate the directional growth by interacting with other growth movements such as gravitropism, phototropism and waving response. On Earth, hydrotropism is interfered by gravitropism in particular, so that microgravity conditions or agravitropic mutants have been used for the study of hydrotropism. However, we have recently established an experimental system for the study of hydrotropism in Arabidopsis roots that easily develop hydrotropism in response to moisture gradient by overcoming gravitropism. Using the Arabidopsis system, we isolated hydrotropism mutants named root hydrotropism (rhy). In the present study, we examined the hydrotropism, gravitropism, phototropism, waving response and elongation growth of rhy4 and rhy5 roots that were defective in positive hydrotropism. Interestingly, rhy4 roots curved away from the water source and showed a reduced waving response. Both rhy4 and rhy5 showed normal gravitropism and a slight reduction in phototropism. These results suggest that there is a mutual molecular mechanism underlying hydrotropism, waving response and/or phototropism. Thus, we have obtained novel hydrotropic mutants that will be used for revealing molecular mechanism of root hydrotropism and its interaction with waving response and/or phototropism.

Arabidopsis↗
PubMed1977

Ultrastructure of gravity-perceiving cells in plant roots.

The root cap is the gravity-perceiving organ of plant roots. The central statenchyma consists of polarly organized statocytes which are characterized by sedimentable amyloplasts and by a striking distal endoplasmic reticulum (e.r. complex). During the normal downwards orientated growth of the root, the amyloplasts are sedimented onto the e.r. complex. Some observations indicate that the amyloplasts stress the e.r. complex by their sedimentation. The stress possibly influences the structural and functional state of the e.r. membranes. Therefore, graviperception is probably a function of differential stress on the e.r. complexes. The amyloplasts are partly or totally separated from the e.r. complex under experimental conditions such as deviations of the roots from the perpendicular between 30 and 180 degrees, rotation of the roots on the horizontal klinostat at 2 rev/min and at 55-120 rev/min, and placing the roots into an electric field at 2000-3000 V/cm. These are important facts for an understanding of the nature of graviperception. Spacelab experiments may help to verify the interpretation of results obtained in the experiments in simulated weightlessness.

Brassicaceae↗