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PubMed1986

Bilateral receptive fields and callosal connectivity of the body midline representation in the first somatosensory area of primates.

Experiments were performed in order to study the receptive field (RF) organization and the callosal connectivity of the trunk representation zone in areas 3b and 1 of the postcentral cortex of macaque monkeys. Multiunit microelectrode recordings showed that neurons responding to tactile stimulation of bilateral RFs across the midline of the body were contained in three topographically distinct zones of the trunk map. In one zone, at the junction between cytoarchitectonic areas 3b and 1, RFs straddled the dorsal midline of the trunk. In the other two zones, one located caudally in area 1 in front of the postcentral dimple, and the other rostrally in area 3b in the depth of the posterior bank of the central sulcus, RFs straddled the ventral midline of the trunk. The first one and the other two zones are referred to here as the dorsal and the ventral midline representation zones, respectively. Elsewhere in the trunk map, neurons responded only to stimulation of contralateral RFs. The callosal connectivity of the trunk map was studied by means of the transport of horseradish peroxidase (HRP). Multiple injections of HRP in electrophysiologically identified sites of the trunk representation in one hemisphere labeled both callosal fiber terminals and callosally projecting neurons in the contralateral homotopic cortex. Dense patches of callosal neurons intensely labeled with HRP were present in the cortical regions representing the body midlines and were distributed for the most part in layer III. Some neurons lightly labeled with HRP were scattered in other zones of the trunk map. Callosal terminations were densest within the midline zones and very sparse or absent in the lateral trunk zones. Correlation of physiological and anatomical data obtained either separately or from the same animal demonstrated that cortical regions containing bilateral-field neurons also contained the highest density of labeled callosal terminations and neurons. This correlation suggests a role for the corpus callosum in the perception of the body midline, either by generating the bilateral RFs of these neurons or by coordinating the activity of the regions containing neurons with thalamically generated bilateral RFs.

Abdomen↗
PubMed2002

Genetic contributions to altered callosal morphology in schizophrenia.

Patients with schizophrenia exhibit abnormalities in midsagittal corpus callosum area, shape, and/or displacement. Our goal was to confirm these findings and to establish the genetic and nongenetic contributions to altered callosal morphology in schizophrenia. Relationships between ventricular enlargements potentially contributing to callosal displacements were assessed as a secondary goal. High-resolution magnetic resonance images were obtained from co-twins of monozygotic and dizygotic pairs discordant for schizophrenia and healthy control twins (N = 40 pairs). Investigators blind to group status segmented the corpus callosum and ventricles in native brain volumes aligned using a rigid-body transformation with no scaling. Total and parcellated midsagittal callosal areas and measures indexing vertical displacements of the corpus callosum were used in statistical tests to identify schizophrenia and sex effects and to dissociate genetic and nongenetic influences on morphology. Anatomical mesh modeling methods provided group average and surface variability maps of the callosum. Callosal areas did not differ between groups defined by sex or biological risk. Vertical displacements of the callosum, pronounced in male patients, were confirmed in schizophrenia and observed between dizygotic, but not monozygotic co-twins discordant for schizophrenia. Like their affected twins, however, unaffected monozygotic co-twins of the schizophrenia probands exhibited significant callosal displacements. Lateral and third ventricle enlargements were related to callosal displacements. Results clearly support that genetic rather than disease-specific or shared environmental influences contribute to altered callosal morphology in schizophrenia. An upward bowing of the callosum may thus provide an easily identifiable neuroanatomic marker to screen individuals possessing a biological vulnerability for schizophrenia.

Brain Mapping↗
PubMed1991

Segregation of callosal and association pathways during development in the visual cortex of the primate.

The segregation of callosal and association pathways in the developing visual cortex of the monkey was studied using the retrograde tracers fast blue and diamidino yellow. Quantitative analysis of the laminar distribution of labeled callosal and association neurons made it possible to reveal the shifting pattern of connections that characterizes the development of these two pathways. In the adult, callosal neurons are restricted to supragranular layers, where they are concentrated at the bottom of layer 3. Association neurons are located both in infra- and supragranular layers. Supragranular layer association neurons are concentrated in layer 2, with limited spread into layer 3 so that there is little overlap with callosal neurons. In the immature brain, callosal neurons are characterized by a tangential distribution that is more widespread than in the adult, while their laminar distribution undergoes little developmental change. Association neurons show two types of changes in their laminar distribution: (1) in the early fetus, there is a large excess of association neurons in supragranular layers, the adult distribution being achieved some time after birth; and (2) during maturation there is a selective elimination of at least 50% of the projections originating from the lower part of layers 2/3. Hence, the adult radial segregation of association and callosal pathways is achieved in part by regressive phenomena. The developmental reduction of bihemispheric projections is largely independent of changes in the organization of association neurons. Quantitative analysis of the morphology and spatial location of neurons sending axon collaterals to both hemispheres suggests that they constitute a subset of callosal neurons and that their frequency is determined by factors that regulate directly this population. These results are discussed with respect to the specification of visual cortical pathways during ontogenesis.

Amidines↗
PubMed1990

[The morphological characteristics of the callosal neurons of the first auditory area of the cortex (AI) in the cat].

Cortical stratification of callosal neurons in the primary auditory cortex (AI) of cat was studied by means of horseradish peroxidase (HRP). Two main groups of callosal neurons were revealed. The first group comprising 60% of all AI callosal neurons consisted predominantly of layer III large pyramidal neurons. Average area of these pyramidal neuron perikaryon profiles was 261.8 +/- 8.8 microns2. The number of HRP-labelled callosal neurons in layer III was 22% of all cells in this layer. The second group comprising 27% of all AI callosal neurons consisted mainly of large cells of layers V and VI which could not be classified as pyramidal neurons. Average area of these nonpyramidal neuron perikaryon profiles was 250.3 +/- 8.4 microns 2. In layer I callosal neurons were not revealed, in layers II and IV accordingly 6% and 7% of AI callosal neurons were located.

Animals↗
PubMed1985

Maturation of visual callosal connections in visually deprived kittens: a challenging critical period.

The number of callosally projecting neurons (callosal neurons) which can be labeled in cortical areas 17 and 18 by horseradish peroxidase (HRP), injected in the contralateral visual cortex, is reduced to about 50% of normal in cats reared with their eyelids bilaterally sutured. In the same animals the density of HRP anterogradely transported to areas 17 and 18 is also decreased. The apparent loss of callosal neurons is limited to layers III and IV (subzone a), whereas layer VI (subzone c) is unaffected. The effect is obtained after 3 months or more but not after 1 month of deprivation. Two months of visual experience following deprivation do not restitute a normal number of callosal neurons. However, 10 days of normal visual experience preceding the deprivation are sufficient to prevent the effects of the latter. Animals deprived of vision after a short period of normal visual experience and animals allowed normal vision after 1 month of visual deprivation have a more widespread distribution of callosal neurons than do normal animals; in this way they are similar to previously described cats reared with convergent or divergent strabismus, monocular enucleation, or monocular eyelid suture. The results suggest that: vision is actively responsible for both the maintenance and the elimination of fractions of the juvenile callosal connections; the elimination which normally takes place during the second postnatal month requires normal binocular vision; and activity-dependent competition between callosal and other axons can explain the role of vision.

Animals↗
PubMed1996

Distribution of visual callosal neurons in normal and strabismic cats.

It has been suggested that synchronous activation of cortical loci in the two cerebral hemispheres during development leads to the stabilization of juvenile callosal connections in some areas of the visual cortex. One way in which loci in opposite hemispheres can be synchronously activated is if they receive signals generated by the same stimulus viewed through different eyes. These ideas lead to the prediction that shifts in the cortical representation of the visual field caused by misalignment of the visual axes (strabismus) should change the width of the callosal zone in the striate cortex. We tested this prediction by using quantitative techniques to compare the tangential distribution of callosal neurons in the striate cortex of strabismic cats to that in normally reared cats. Animals were rendered strabismic surgically at 8-10 days of age and were allowed to survive a minimum of 18 weeks, at which time multiple intracortical injections of the tracer horseradish peroxidase (HRP) were used to reveal the distribution of callosally projecting cells in the contralateral striate cortex. HRP-labeled cells were counted in coronal sections, and data from four animals with divergent strabismus (exotropia) and four with convergent strabismus (esotropia) were compared to those from four normally reared animals. Although our data from strabismic cats do not differ markedly from those reported previously, we find that the distribution of callosal cells in the striate cortex of these cats does not differ significantly from that in our normally reared control cats. These results do not bear out the prediction that surgically shifting the visual axes leads to stabilization of juvenile callosal axons in anomalous places within the striate cortex.

Animals↗
PubMed1998

Timing and origin of the first cortical axons to project through the corpus callosum and the subsequent emergence of callosal projection cells in mouse.

A precise knowledge of the timing and origin of the first cortical axons to project through the corpus callosum (CC) and of the subsequent emergence of callosal projection cells is essential for understanding the early ontogeny of this commissure. By using a series of mouse embryos and fetuses of the hybrid cross B6D2F2/J weighing from 0.36 g to 1.0 g (embryonic day E15.75-E17.25), we examined the spatial and temporal distribution of callosal projection cells by inserting crystals of the lipophilic dye (DiI: 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) into the contralateral white matter just lateral to the midsagittal plane. Around 0.4 g or E15.8, retrogradely labeled cells were found restricted to a discrete cluster continuously distributed from the most ventral part of presumptive cingulate cortex to the hippocampus. During subsequent development, however, the tangential distribution of these labeled cells in ventromedial cortex did not extend further dorsally, and in fetuses where the CC became distinct from the hippocampal commissure (HC), labeled axons of cells in the ventral cingulate cortex were observed to intersect the callosal pathway and merge with labeled axons of the HC derived from cells in the hippocampus. The first cortical axons through the CC crossed the midline at about 0.64 g or E16.4, and these axons originated from a scattered neuronal population in the dorsal to lateral part of the presumptive frontal cortex. The earliest callosal cells were consistently located in the cortical plate and showed an immature bipolar appearance, displaying an ovoid- or pearl-shaped perikaryon with an apical dendrite coursing in a zig-zagging manner toward the pial surface and a slender axon directed toward the underlying white matter. Callosal projection cells spread progressively with development across the tangential extent of the cerebral cortex in both lateral-to-medial and rostral-to-caudal directions. In any cortical region, the first labeled cells appeared in the cortical plate and their number in the subplate was insignificant compared to that in the cortical plate. Thus, these results clarify that the CC is pioneered by frontal cortical plate cells, and the subsequent ontogeny of callosal projection cells proceeds according to the gradient of cortical maturation.

Animals↗
PubMed1991

Prenatal specification of callosal connections in rhesus monkey.

Anatomical tracing and quantitative techniques were used to examine the tempo and pattern of maturation for callosal projection neurons in the monkey prefrontal cortex (PFC) during fetal and postnatal development. Nineteen monkeys were injected with retrograde tracers (fluorescent dyes, horseradish peroxidase conjugated to wheat germ agglutinin [WGA-HRP] or HRP crystals) at various ages between embryonic day 82 (E82) and adulthood. The size of injection sites was varied in fetal, newborn, and adult cases. In adults, labeled neurons were found in greatest density in the homotopic cortex of the opposite hemisphere and considerable numbers were also observed in a constellation of heterotopic areas including the medial and lateral orbital cortex, the dorsomedial convexity, and the pregenual cortex. The majority of labeled neurons were consistently concentrated in the lower half of layer III in all areas. In cases with large injection sites, callosal neurons of layer III formed a continuous and uninterrupted band that extended over the entire lateral surface of the prefrontal cortex spanning both homotopic and heterotopic areas. In contrast, in cases with small injection sites, the labeling of layer III neurons exhibited discontinuities. Between embryonic ages E82 and E89, injections limited to the cortical layers labeled only a small number of neurons in the opposite hemisphere, indicating that few callosal axons have invaded the cortex by this age. However, by E111 comparable injections labeled a large number of callosal neurons and many features of their distribution were adult-like. The number and constellation of cytoarchitectonic areas that were labeled in the frontal cortex of the opposite hemisphere were the same as in adults and the majority of callosal neurons were found in supragranular layer III. Finally, in fetal animals beyond E111, labeled neurons extended as a nearly unbroken band over a wide expanse of the dorsolateral PFC, resembling the pattern seen in adult monkeys with large injections. The conclusion we draw from these results, together with our earlier findings (Schwartz and Goldman-Rakic: Nature 299:154, 1982), is that callosal neurons whose axons enter the cortical layers of the primate prefrontal cortex achieve their mature laminar and areal distribution prior to birth and do so largely by cumulative processes.

Aging↗
PubMed1993

Laminar termination patterns of thalamic, callosal, and association afferents in the primary auditory area of the rhesus monkey.

Thalamic, callosal, and association afferents to the primary auditory konicortex, area KA, were investigated in rhesus monkeys with the aid of anterograde tract tracing techniques (radioactively labeled amino acids, wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), and the Fink-Heimer silver impregnation method). Different patterns of anterograde label in KA were produced by radioactively labeled amino acid injections in the contralateral primary auditory area, the ipsilateral medial geniculate body (MGB), or auditory association cortex of the superior temporal gyrus (STG). Thalamic afferents from the MGB were found throughout KA in layers IV and III where the density waxed and waned, forming regular patches of higher density label separated by areas of less dense label. Callosal afferents from the contralateral auditory cortices were found in layers IV, III, and II in larger, more spatially separated, and irregular patches. In contrast, association afferents from the auditory association cortex of the STG were found in a continuous band in layer I. To determine the extent to which the patches of callosal afferents overlap with or interdigitate between the high-density thalamic clusters, two types of double anterograde labeling experiments were undertaken. In one set of experiments isotope injections of the MGB were made in conjunction with transection of the corpus callosum in the same animal. In another set of experiments isotope injections of the MGB were made in one hemisphere and an injection of WGA-HRP was made in the opposite supratemporal plane, including KA, in the same animal. Both approaches demonstrate that the patches of callosal afferents in KA mainly occur between the high-density patches of thalamic afferents, although there is a variable degree of overlap at their periphery. Thus it seems that thalamic and callosal inputs to KA are organized in a largely complementary fashion while input from the lateral association cortex is continuous and overlaps both. When considered in light of pertinent anatomical and physiological studies in a variety of species, it appears that the areas mainly occupied by callosal or thalamic inputs may be differentially involved in frequency analysis and sound localization, respectively.

Animals↗
PubMed1995

Comparison of the patterns of callosal connections in lateral parietal cortex of the rat, mouse and hamster.

In a recent study of the second somatosensory area (SmII) in the rat it was reported that the somatotopic map in the cortex lateral to the primary somatosensory area (SmI) is closely related to local features of the callosal pattern. The existence of this relationship suggests that knowledge of the overall pattern of callosal connections in the cortex lateral to SmI may facilitate the description of the somatotopic organization of lateral parietal cortex in other rodents. We tested this suggestion by comparing the callosal patterns in lateral parietal cortex in the rat, mouse and hamster. Our finding that the callosal pattern in the mouse closely resembles that in the rat supports the idea that the callosal pattern reflects the underlying somatotopy because the maps of SmII described previously in the mouse and rat are very similar to each other. In addition, on the basis of our observation that the callosal pattern in the hamster is very similar to that in the rat and mouse, we predict that these three rodent species share a common somatotopic plan in lateral parietal cortex.

Animals↗
PubMed1992

Emergence of callosally projecting neurons with stellate morphology in the visual cortex of the kitten.

Callosally projecting neurons in areas 17 and 18 of the adult cat can be classified into two types on the basis of their dendritic morphology: pyramidal and stellate cells. The latter are nearly exclusively of the spinous type and are predominantly located in upper layer IV. Retrograde transport of the carbocyanine dye DiI, applied to the corpus callosum, showed that, up to P6, all callosally projecting neurons resemble pyramids in the possession of an apical dendrite reaching layer I. At P10, however, callosally projecting neurons with stellate morphology were found. A study was designed to distinguish whether these neurons are late in extending their axons to the corpus callosum or, alternatively, have transient apical dendrites. To this end, callosally projecting neurons were retrogradely labeled by fluorescent beads injected in areas 17 and 18 at P1-P3 and then either relabeled with DiI applied to the corpus callosum at P10 or intracellularly injected with Lucifer Yellow at P57. Double-labeled stellate and pyramidal cells were found in similar proportions to those found for the total, single-labeled population of callosally projecting neurons. It is therefore concluded that callosally projecting spiny stellate cells initially possess an apical dendrite and a pyramidal morphology. At P6, i.e. close to the time when stellate cells appear, layer IV neurons with an atrophic apical dendrite were found, suggestive of an apical dendrite in the process of being eliminated.

Animals↗
PubMed1980

Postnatal shaping of callosal connections from sensory areas.

Horseradish peroxidase (HRP) was injected unilaterally into the first and second visual areas (V1 and V2; areas 17 and 18) of 20 kittens aged between 2 and 90 days and into the second somatosensory area (S2) of 16 kittens aged between 1 and 52 days. The radial and tangential (normal and parallel to the pial surface, respectively) distributions of neurones giving origin to callosal axons (callosal neurones) were studied. In adult cats, callosal efferent zones (CZs) are defined by the distribution of callosal neurones. CZs occupy in the visual cortices, tangentially and radially restricted parts of areas 17, 18, 19 of the lateral suprasylvian gyrus and in the somatosensory cortices, parts of S1 and S2. At birth, callosal neurones are distributed throughout the tangential extent of visual and somatosensory areas; they are also more widespread in depth than in the adult. During the first postnatal month, as a result of the gradual disappearance of callosal neurones from parts of the visual and somatosensory areas, the adult CZs emerge. The CZ in areas 17 and 18 undergoes a further tangential reduction during the second and third postnatal months.

Aging↗
PubMed1984

Callose deposition during gravitropism of Zea mays and Pisum sativum and its inhibition by 2-deoxy-D-glucose.

In etiolated corn (Zea mays L.) and etiolated pea (Pisum sativum L.) seedlings, a gravitropic stimulation induces the deposition of callose. In the corn coleoptiles this occurs within 5 min of gravity stimulation, and prior to the beginning of curvature. Both gravitropic curvature and callose deposition reach their maxima by 12 h. Within the first 2 h more callose is deposited on the upper (concave) side, but after 2-3 h, this deposition pattern is reversed. An inhibitor of protein glycosylation, 2-deoxy-D-glucose (DDG), inhibits callose production and considerably retards gravitropic bending in both species of plants. Mannose can relieve the inhibition of gravitropic bending by DDG. The pea mutant "Ageotropum", which does not respond to gravity when etiolated, also fails to produce callose in response to a gravitic stimulus. These correlations indicate that callose deposition may be a biochemical component of gravitropism in plant shoots.

Deoxyglucose↗
PubMed1988

The pattern of callosal connections in posterior neocortex of congenitally anophthalmic rats.

In an effort to assess the innate capacity of the central visual system to specify corticocortical connectivity in the absence of retinal afferents, we examined the tangential distribution of callosal cells and terminations in posterior neocortex of congenitally anophthalmic rats. Although our results indicate that the callosal pattern is clearly anomalous in these rats, all features of the normal visual callosal pattern are recognizable in mutant rats, indicating that central visual pathways can generate many aspects of normal interhemispheric connectivity in the absence of input from the periphery. On the other hand, the presence of anomalies in the pattern indicates that the eyes are necessary to fine-tune the distribution of callosal connections at some developmental stage. Moreover, the fact that abnormalities in the callosal pattern of mutant rats are the same as those previously described in rats enucleated at birth suggests that the eyes begin to exert their influence on callosal development after birth.

Agenesis of Corpus Callosum↗
PubMed1981

The distribution of the callosal projection to the occipital visual cortex in rats and mice.

The principal finding in this study is that the callosal projection to the occipital cortex in rats and mice follows a complex and highly reproducible pattern which has not previously been described in detail. In some regions, the callosal projection is associated with well defined cytoarchitectonic boundaries such as the border between areas 17 and 18a. However, extrastriate cortex lateral to area 17 receives callosal inputs which are not related to previously defined cytoarchitectonic boundaries. Following intraocular injections of [3H]fucose, transneuronal label occupies area 17 and mainly the posterior part of area 18a. A region in posterolateral area 18a which is 'subdivided' into callosal and sparsely callosal regions appears to receive an input from the lateral geniculate nucleus, based on transneuronal autoradiography. Comparison of the distribution of callosal axons and transneuronal label suggests that regions of murid cortex similar to areas 18, 19 and lateral suprasylvian cortex in cats may be located posteriorly in area 18a.

Animals↗
PubMed1985

The callosal connexions of the primary somatic sensory cortex in the monkey.

The callosal connexions of the primary somatic sensory cortex, SI, of the monkey have been studied with axonal degeneration methods after the placement of lesions of varying size in the cortex of one hemisphere and after section of the corpus callosum. For the correlation of the distribution of the degeneration with the cytoarchitectonic subdivisions of SI and with their boundaries, planar reconstructions of the extents of the subdivisions and of area 5 were made. The extent of area 5 is surprisingly large, being about the same as SI, and area 3a can be recognized as a distinct subdivision along the entire medio-lateral extent of SI. The callosal fibres end in narrow, irregular bands aligned in the medio-lateral dimension and there are accentuations at the boundaries of the cytoarchitectural subdivisions. In the representations of the trunk and face, the bands of degeneration are present across the entire antero-posterior extent of SI and with increases at the boundaries, while in the limb regions the degeneration becomes restricted to the boundaries. It is suggested that the callosal connexions of the somatic sensory cortex, like those in the visual and auditory areas, are connecting those parts of the cortex in the two hemispheres that are concurrently activated by a peripheral stimulus. The parts of SI that are devoid of callosal connexions are related to the distal limbs. The callosal connexions are homo- and heterotopical; an architectonic subdivision within the callosally connected regions projects to the same and other architectonic subdivisions at the same medio-lateral level in the opposite hemisphere; the cortex containing the representation of the caudal trunk near the post-central dimple is connected with the same region in the other hemisphere and with that of the separate representation of the caudal trunk in the posterior part of the cingulate sulcus, while the representation of the occipital region at the post-central dimple is connected both with the homotopical site in the other hemisphere and with the other representation of this part of the periphery at the level of the lower end of the intraparietal sulcus.

Animals↗
PubMed1998

Prenatal protein restriction alters synaptic mechanisms of callosal connections in the rat visual cortex.

Mild prenatal protein malnutrition, induced by reduction of the casein content of the maternal diet from 25 to 8%, calorically compensated by the addition of excess carbohydrates, leads to so-called "hidden" malnutrition in the rat. This form of malnutrition results in normal body and brain weights of pups at birth, but in significant alterations of their central nervous system neurochemical profiles. Since severe forms of prenatal malnutrition induce morpho-functional deficits on callosal interhemispheric communication together with brain neurochemical disturbances, we evaluated, in rats born from mothers submitted to an 8% casein diet, the potassium-induced release of [3H]-noradrenaline in visual cortex slices, as well as functional properties of callosal-cortical synapses by determining cerebral cortical excitability to callosal inputs and fatigability and temporal summation of transcallosal evoked responses. Rats born from mothers submitted to a 25% casein diet served as controls. At birth prenatally malnourished pups had significantly higher cortical percent net noradrenaline release (14.79 +/- 1.11) than controls (9.14 +/- 1.26). At 45-50 days of age, rehabilitated previously malnourished rats showed, when compared to controls; (i) significantly reduced percent net noradrenaline release in the visual cortex (4.50 +/- 0.52 vs 11.31 +/- 1.14); (ii) decreased cortical excitability to callosal inputs as revealed by significantly increased chronaxie (607.2 +/- 82.8 microseconds vs 351.3 +/- 47.7 microseconds); (iii) enhanced fatigability of transcallosal evoked responses as revealed by significantly decreased stimulus frequency required to fatigate the responses (4.9 +/- 0.8 Hz vs 9.2 +/- 1.3 Hz); and (iv) decreased ability of callosal-cortical synapses to perform temporal summation, as revealed by significantly reduced percent response increment to double-shock (54.2 +/- 6.2 vs 83.0 +/- 11.0, for a 3.2-ms interstimulus time interval). These changes, resulting from mild prenatal protein restriction, are discussed in relationship to developmental processes leading to the formation of synaptic contacts between callosal axons and their appropriate cortical target during perinatal age.

Animals↗
PubMed2002

An Arabidopsis callose synthase.

Beta-1,3-glucan polymers are major structural components of fungal cell walls, while cellulosic beta-1,4-glucan is the predominant polysaccharide in plant cell walls. Plant beta-1,3-glucan, called callose, is produced in pollen and in response to pathogen attack and wounding, but it has been unclear whether callose synthases can also produce cellulose and whether plant cellulose synthases may also produce beta-1,3-glucans. We describe here an Arabidopsis gene, AtGsl5, encoding a plasma membrane-localized protein homologous to yeast beta-1,3-glucan synthase whose expression partially complements a yeast beta-1,3-glucan synthase mutant. AtGsl5 is developmentally expressed at highest levels in flowers, consistent with flowers having high beta-1,3-glucan synthase activities for deposition of callose in pollen. A role for AtGsl5 in callose synthesis is also indicated by AtGsl5 expression in the Arabidopsis mpk4 mutant which exhibits systemic acquired resistance (SAR), elevated beta-1,3-glucan synthase activity, and increased callose levels. In addition, AtGsl5 is a likely target of salicylic acid (SA)-dependent SAR, since AtGsl5 mRNA accumulation is induced by SA in wild-type plants, while expression of the nahG salicylate hydroxylase reduces AtGsl5 mRNA levels in the mpk4 mutant. These results indicate that AtGsl5 is likely involved in callose synthesis in flowering tissues and in the mpk4 mutant.

Arabidopsis↗