Biomedical subjects

D F Mandoli

Publications and source records attributed to D F Mandoli.

10 recordsLinked to original sources

PubMed2001

Relationships between growth, morphology and wall stress in the stalk of Acetabularia acetabulum.

With carbon particles we analyzed patterns of growth in Acetabularia acetabulum (Lam.) P.C. Silva, a giant unicell famous for classic development studies. We focused on the stalk apex, which generates the stalk, whorls of hairs, and whorls of gametophores. To gain visual and physical accessibility, we amputated the youngest whorls of hair and the original apex and performed experiments on the apex that regenerated. Video analysis indicated that most growth occurred near the tip of the new apex. Less growth occured throughout the cut-interwhorl. We also analyzed cell wall thickness along stalks cleared of cytoplasm. Correlating growth data to wall morphology suggests growth near the apex may be proportional to stress on the cell wall. We propose that turgor-pressure wall stress modulates local apical cell wall growth rates. A supplementary model, relating cell wall curvature and growth rate in the cut-interwhorl, characterizes how the stalk's final dimensions and nearly cylindrical shap may arise. See http://faculty.washington.edu/mandoli/vondassow for supplementary data, analysis, and mathematical appendices. We believe this is the first quantiative description of apex morphogenesis of A. acetabulum.

Acetabularia↗

PubMed2001

Asymmetric subcellular mRNA distribution correlates with carbonic anhydrase activity in Acetabularia acetabulum.

The unicellular green macroalga Acetabularia acetabulum L. Silva is an excellent system for studying regional differentiation within a single cell. In late adults, physiologically mediated extracellular alkalinity varies along the long axis of the alga with extracellular pH more alkaline along the apical and middle regions of the stalk than at and near the rhizoid. Respiration also varies with greater respiration at and near the rhizoid than along the stalk. We hypothesized that the apical and middle regions of the stalk require greater carbonic anhydrase (CA) activity to facilitate inorganic carbon uptake for photosynthesis. Treatment of algae with the CA inhibitors acetazolamide and ethoxyzolamide decreased photosynthetic oxygen evolution along the stalk but not at the rhizoid, indicating that CA facilitates inorganic carbon uptake in the apical portions of the alga. To examine the distribution of enzymatic activity within the alga, individuals were dissected into apical, middle, and basal tissue pools and assayed for both total and external CA activity. CA activity was greatest in the apical portions. We cloned two CA genes (AaCA1 and AaCA2). Northern analysis demonstrated that both genes are expressed throughout much of the life cycle of A. acetabulum. AaCA1 mRNA first appears in early adults. AaCA2 mRNA appears in juveniles. The AaCA1 and AaCA2 mRNAs are distributed asymmetrically in late adults with highest levels of each in the apical portion of the alga. mRNA localization and enzyme activity patterns correlate for AaCA1 and AaCA2, indicating that mRNA localization is one mechanism underlying regional differentiation in A. acetabulum.

Acetabularia↗

PubMed2000

Calcification and measurements of net proton and oxygen flux reveal subcellular domains in Acetabularia acetabulum.

Vegetative adults of Acetabularia acetabulum (L.) Silva were studied as a model system for subcellular patterning in plants, and a description of several phenotypic and physiological characteristics that reveal patterns of subcellular differentiation in this unicellular macroalga was undertaken. Initially, calcification patterns were studied. Under favorable conditions, the rhizoid and most of the stalk calcified. Only the apical 10-20% of the stalk and a small region adjacent to the rhizoid remained uncalcified. Calcification in algae has been reported to result from a biologically mediated local increase in alkalinity. To test this model extracellular pH and extracellular hydrogen ion gradients were examined with ion-selective, self-referencing, electrodes. In the light, A. acetabulum displayed a general pattern of extracellular alkalinity around the entire alga, although in some individuals the region near the rhizoid and the rhizoid itself displayed extracellular acidity. Acetabularia acetabulum also displayed net hydrogen ion influx at the rhizoid and the apical half of the stalk, variable flux in the lower part of the stalk, and net hydrogen ion efflux at the base of the stalk next to the rhizoid. The lack of complete correlation between external pH patterns and calcification suggests that other factors contribute to the control of calcification in this alga. To examine whether net hydrogen ion flux patterns correlated with photosynthetic or respiration patterns, oxygen flux was measured along the stalk using self-referencing O2 electrodes. Photosynthetic oxygen evolution occurred at comparable levels throughout the stalk, with less evolution in the rhizoid. Respiration mainly occurred near and in the rhizoid, with less O2 consumption occurring more apically along the stalk. Our studies of calcification patterns, net hydrogen ion flux and O2 flux revealed several overlapping patterns of subcellular differentiation in A. acetabulum.

Calcification, Physiologic↗

PubMed1999

The roles of light and the nucleus in the regulation of reproductive onset in Acetabularia acetabulum.

At reproductive onset the marine green alga Acetabularia acetabulum (L.) P.C. Silva redirects growth from vertical elongation of the axis of the plant to lateral expansion of a disk-shaped reproductive structure, the "cap." We used amputation to synchronize cap initiation and to facilitate investigation of the light requirements during amputation-induced cap initiation. Following amputation of a nascent cap, most plants initiate one whorl of vegetative hairs and then a cap. Both hair and cap initiation required photosynthesis, as indicated by studies with 3-(3',4'-dichlorophenyl)-1, 1-dimethylurea, but did not require the nucleus. Amputation-induced hair initiation occurred in red light, but 10 min of blue light given in a background of red light significantly increased hair initiation, supporting previous studies that hair initiation is a blue-light-triggered photomorphogenic event. Amputation-induced cap initiation also occurred in red light, but daily 10-min flashes of blue light given in a background of red light did not significantly enhance cap initiation. We also examined the light requirements of intact plants at each phase of development. In the absence of blue light, juveniles and adults with </=13.7 +/- 4.3 whorls of hairs arrested in development and failed to initiate caps. In contrast, very late adults with >/=13.7 +/- 4.3 whorls of hairs initiated caps in the absence of blue light, suggesting that there is a point in late adult development beyond which cap initiation does not require blue light. Several plausible interpretations of the role of light and the nucleus in the regulation of reproductive onset are discussed to try to reconcile these data with those in the literature.

Acetabularia↗

PubMed1999

Aaknox1, a kn1-like homeobox gene in Acetabularia acetabulum, undergoes developmentally regulated subcellular localization.

Homeobox-containing genes play developmentally important roles in a wide variety of plants, animals and fungi. As a way of studying how development is controlled in the unicellular green macroalga Acetabularia acetabulum, we used degenerate PCR to clone a knotted1-like (kn1-like) homeobox gene, Aaknox1 (Acetabularia acetabulum kn1-like homeobox 1). Aaknorx1 is the first knotted1-like homeobox gene to be cloned from a non-vascular plant and shows strong conservation with kn1-like genes from the vascular plants (ca. 56% amino acid identity within the homeodomain). Sequencing of cDNA clones indicates that Aaknor1 possesses at least two distinct polyadenylation sites spaced ca. 600 bp apart. Southern analysis suggests that several other kn1-like homeobox genes exist in the Acetabularia genome. Northern analyses demonstrate that expression of Aaknox1 is developmentally regulated, with peak levels of expression during early reproductive phase. Northern analyses further demonstrate that Aaknox1 mRNA undergoes a change in its subcellular localization pattern during the progression from late vegetative to early reproductive phase. In late adult phase, Aaknox1 is distributed uniformly throughout the alga; in early reproductive phase, Aaknox1 is present in a gradient with the highest concentration of the mRNA at the base of the stalk, near the single nucleus. These data suggest that Aaknox1 may have a role during early reproductive development and that mRNA localization may be one mechanism by which A. acetabulum regulates gene expression posttranscriptionally.

Acetabularia↗

PubMed1996

Coordination of cellular events that precede reproductive onset in Acetabularia acetabulum: evidence for a 'loop' in development.

Amputated apices from vegetative wildtype cells of the uninucleate green alga Acetabularia acetabulum can differentiate a reproductive structure of 'cap' in the absence of the nucleus (Hämmerling, J. (1932) Biologisches Zentralblatt 52, 42-61). To define the limits of the ability of wildtype cells to control reproductive differentiation, we determined when during development apices from wildtype cells first acquired the ability to make a cap in the absence of the nucleus and, conversely, when cells with a nucleus lost the ability to recover from the loss of their apices. To see when the apex acquired the ability to make a cap without the nucleus, we removed apices from cells varying either the developmental age of the cells or the cellular volume left with the apex. Cells must have attained the adult phase of development before the enucleate apex could survive amputation and make a cap. Apices removed from cells early in adult growth required more cell volume to make a cap without the nucleus than did apices removed from cells late in adult growth. To define the limits of the cell to recapitulate development when reproduction falters, we analyzed development in cells whose caps either had been amputated or had spontaneously aborted. After loss of the first cap, cells repeated part of vegetative growth and then made a second cap. The ability to make a second cap after amputation of the first one was lost 15-20 days after cap initiation. Our data suggest that internal cues, cell age and size, are used to regulate reproductive onset in Acetabularia acetabulum and add to our understanding of how reproduction is coordinated in this giant cell.

Acetabularia↗

PubMed1984

Photobiology of diagravitropic maize roots.

Light-induced modification of gravitropism in etiolated roots of Zea mays cv Bear x W38 is a low fluence response mediated by phytochrome. This cultivar has a threshold of 10(-6) mol m(-2) and becomes saturated with 10(-2) mol m(-2) of red light. The maximum light-mediated response of 32 degrees downward from horizontal occurs in roots 10 to 30 millimeters in length, 120 to 165 minutes after irradiation. Reciprocity is valid from 2 to at least 9,000 seconds and the response can be about 90% reversed by far red light. Photoreversibility is lost (;escape' occurs) about 20 minutes after red irradiation but appears to be regained 60 to 80 minutes later. A red light-induced (or synchronized) nutation in the apparent curvature rather than unusual escape characteristics may explain these results.

Journal Article↗

PubMed1983

Phytochrome-mediated cellular photomorphogenesis.

Red light-induced cell elongation and division in intact, etiolated oat (Avena sativa cv Lodi) seedlings have been assessed. The middle of coleoptile was especially responsive in the very low fluence range whereas the region immediately below the coleoptile tip and the two regions just above the coleoptilar node were more responsive than the entire organ in the low fluence range. These responses in the coleoptile are both the result of an increase in cell elongation. Coleoptile cell division is slightly inhibited in the very low and slightly stimulated by red light in the low fluence range.The one-sixth of the mesocotyl closest to the node is more suppressed in its growth than is any other region in the very low fluence range. However, the low fluence response involved the entire mesocotyl equally. In the apical one-sixth of the mesocotyl, a strong suppression of cell division and a weak suppression of cell elongation occurs. In the lower five regions of the mesocotyl, red light in both fluence ranges suppresses only cell elongation. Apparently, the difference between red light-induced oat growth stimulation and suppression primarily involves differences in the response of the cell elongation process.

Journal Article↗

PubMed1982

Optical properties of etiolated plant tissues.

Etiolated tissues of several plants are multiple bundles of fiber optics capable of coherent transfer of light over at least 20 mm. The acceptance angles (the angles at which light can be intercepted and then internally reflected longitudinally) for mung beans, oats, and corn are 47 degrees , 59 degrees , and 52 degrees -54 degrees , respectively. The shapes of the curves that describe the acceptance angles are the same for various tissues of the same plant but differ between species. The pattern of light transmitted longitudinally through a tissue is dependent on the angle at which the light intercepts the side of the tissue and is strongly influenced by the tissue geometry. When 0.5 mm of the tip is irradiated, the amount of light traveling down the "shaded" side of the coleoptile is equal to or 2- to 3-fold greater than the amount traveling down the "lighted" side.

Journal Article↗

PubMed1981

Phytochrome control of two low-irradiance responses in etiolated oat seedlings.

Light-induced coleoptile stimulation and mesocotyl suppression in etiolated Avena sativa (cv. Lodi) has been quantitated. Etiolated seedlings showed the greatest response to light when they were illuminated 48 to 56 hours after imbibition. Two low-irradiance photoresponses for each tissue have been described. Red light was 10 times more effective than green and 1,000 times more effective than far red light in evoking these responses. The first response, which resulted in a 45% mesocotyl suppression and 30% coleoptile stimulation, had a threshold at 10(-14) einsteins per square centimeter and was saturated at 3.0 x 10(-12) einsteins per square centimeter of red light. This very low-irradiance response could be induced by red, green, or far red light and was not photoreversible. Reciprocity failed if the duration of the red illumination exceeded 10 minutes. The low-irradiance response which resulted in 80% mesocotyl suppression and 60% coleoptile stimulation, had a threshold at 10(-10) einsteins per square centimeter and was saturated at 3.0 x 10(-8) einsteins per square centimeter of red light. A complete low-irradiance response could be induced by either red or green light but not by far red light. This response could be reversed by a far red dose 30 times greater than that of the initial red dose for both coleoptiles and mesocotyls. Reciprocity failed if the duration of the red illumination exceeded 170 minutes. Both of these responses can be explained by the action of phytochrome.

Journal Article↗