Effect of Lead and Colchicine on Morphogenesis in Protonemata of the Moss Funaria hygrometrica

Protonemata of Funaria hygrometrica grown in artificial mediacontaining different lead concentrations grow more slowly thancontrols and show a disturbance of polar growth, changed arrangementof chloroplasts, alterations of nucleus and septa position.Morphological effects are dose-dependent. At the lowest leadconcentration (10^-6 M), only a delay in development was observed,but no cellular alterations, At 10^-5 M Pb nuclear migration,cellular shape, size and position of plastids, were alteredand a variety of aberrant forms were present. At 10^-4 M, besidesthese alterations, a drastic reduction of the protonemal system,high vacuolation and the growth of protonemal filaments fromleaves were evident. The highest concentration, (10^-3 M), causeddeath. Patterns of protonemal development and cellular arrangementin lead-treated samples showed similarities as well as differences,if compared to alterations induced by colchicine. Indirect immunofluorescencedemonstrated a correlation between lead concentration and alterationof cytoskeletal organization (alterations similar to those inducedby colchicine). Hypotheses are raised to account for effects of lead on microtubulestructure, arrangement and cytoplasm organization.Copyright1995, 1999 Academic Press Funaria hygrometrica, lead, protonemal development, cytomorphogenesis, microtubules     

Apical Growth of Protonemata in Adiantum capillus-veneris IV. Phytochrome-Mediated Induction in Non-Growing Cells

In non-growing two-celled protonemata of Adiantum capillus-veneris,apical growth was induced most effectively by red light irradiation;half of the samples were induced to grow by 660 nm light ofca. 1.5 J m^–2 and the maximum number by ca. 70 J m^–2.The reciprocity law was valid in this photoinduction. The growthresumption became detectable 6 hr after the light irradiationand reached a plateau within 24 hr irrespective of given fluences.When non-growing samples were irradiated with red light of 4.6W m^–2 for 4 sec or shorter, the effect was fully reversedby a subsequent irradiation with far-red light to the far-redlight control level. But, when the red light was given for 16sec or longer, photoreversibility became partial. An interveningdark period of 2 min between red and far-red light did not significantlyinfluence the photoreversibility so that the escape reactionin the dark may not be attributed to the above-mentioned lossof photoreversibility. By means of a local irradiation with a narrow red light beam(10 µm in width), the apical cell was found to be photosensitivefor the growth induction, but basal cell was not. Photoreceptivesite was not localized in any particular region of the apicalcell, but was rather dispersed in the entire apical cell. (Received January 26, 1981; Accepted March 10, 1981)     

Effects of Colchicine, Vinblastine, Cytochalasin B and Phalloidin on the Seismonastic Movement of Mimosa pudica Leaf and on Motor Cell Ultrastructure

Fleurat-Lessard, P., Roblin, G., Bonmort, J. and Besse, C. 1988.Effects of colchicine, vinblastine, cytochalasin B and phalloidinon the seismonastic movement of Mimosa pudica leaf and on motorcell ultrastructure.—J. exp. Bot. 39: 209–221. Colchicine at 1 x 10^–3 mol dm^–3 does not affectthe seismonastic movement of Mimosa pudica leaves but disruptsmicrotubules in motor cells. Vinblastine at 5 x 10^–3 moldm^–3 does not affect this movement and partly disruptsmicrotubules. Vinblastine at 1 x 10^–4 mol dm^–3 alwaysdisrupts microtubules, even after a 12 h reversibility whenthe movement is restored. These drugs, applied at the same respectiveconcentrations, do not alter cytoplasmic and vacuolar fibrils.Cytochalasin B and phalloidin alter the seismonastic movementof Mimosa leaves when applied at concentrations of 1.25 x 10^–3and 2.4 x 10^–4 mol dm^–3 respectively. These drugs,used at the same respective concentrations, also affect themotor cell structure and, in particular, modify the arrangementand the structure of the fibrils but they do not destroy themicrotubules. These data suggest that microtubules are not directly involvedin the seismonastic reaction whereas fibrils, formed by thin(3.0 nm wide) filaments, may be implicated in this reaction. Key words: Colchicine, cytochalasin B, phalloidin, Mimosa pudica, motor cells, vinblastine     

Analysis of Shoot Apical Growth of Picea sitchensis Seedlings

During the first 100 days after sowing (March-June) the followingchanges took place at the terminal shoot apices of Picea sitchensisseedlings: plastochrones (T) decreased from over 24 h to 4 h;apical domes enlarged from less than 0·20 mm to 0·45mm diameter (D); the ‘projected’ area of tissuesproduced by the apical domes (i.e. viewed from above) increasedin amount from less than 0·012 to 0·024 mm² day^-1;about 15 per cent of this tissue was re-invested in the apicaldomes, the rest was used to produce primordia; and the volume-doublingtimes of the apical dome tissues decreased from over 150 h to50 h. After 100 days there was no further re-investment in theapical domes, but the domes did not decrease abruptly in size.Less tissue was produced per day, but the primordia were smallerso that the rate of primordia formation did not fall precipitously.Plastochrone ratios were inversely related to D, but the relationshipbetween T and D depended on whether T was decreasing or increasing.Progenies which were known to be fast growing tended to build-uptheir apical domes rapidly (i.e. have large ‘re-investmentratios’) and to be capable of producing small primordia.These attributes can evidently be evaluated on seedlings andcould help to lessen the cost of tree breeding progeny-testprogrammes. meristem, Picea sitchensis, Sitka spruce, growth, shoot apex     

Size of the Chrysanthemum Shoot Apex in Relation to Inflorescence Initiation and Development

The size of the apical dome of Chrysanthemum morifolium Ramat.at the transition to inflorescence initiation in continuouslight (long days) was not systematically influenced by eitherthe temperature or the irradiance under which the plants weregrown. It was generally 0.26 mm in diameter and c. 3.6 x 10^–3mm³ in volume when the first bract was initiated. The dimensionsof the apical dome of plants in short days were only slightlysmaller at this stage. Similarly, each step in the further developmentof the chrysanthemum inflorescence was associated with a narrowrange of apex sizes, indicating that inflorescence initiationand development are closely related to apex size. Chrysanthemum morifolium Ramat, shoot apex, inflorescence initiation     

Apoptotic Cell Death and Cellular Surface Negative Charge Increase in Maize Roots Exposed to Cytotoxic Stresses

Maize root meristematic tissues were exposed to cytotoxic reagents,the RNA-synthesis inhibitor Actinomycin D (ActD), the protein-synthesisinhibitor cycloheximide (CHX) and the mitosis inhibitor colchicine(COL). Morphological and biochemical evidence of specific apoptoticnuclei and chromosomes in individual treated cells was identifiedusing a simple and highly efficient chromosome spreading-basedTUNEL assay, DNA laddering and DNA gel blotting. All of thesedrugs induced DNA cleavage, dose-dependent oligomeric ladders,and characteristic nuclear and chromosomal condensations. Resultsfrom DNA gel blotting showed that DNA ladders could be inducedby exposure to 0.1 mg l^-1ActD, 100 mg l^-1CHX and 500 mg l^-1COLfor 6 h, 6 h and 12 h respectively. The sequence of changesin single cells was studied in detail. DNA cleavage was foundto occur before condensation and disorganization of the nucleus,followed by deformation and condensation of metaphase chromosomes,and marginalization of chromatin. Finally, nucleoli disappearedand fragmentation of the nucleus occurred. Meanwhile, changesin the outer surface charge of apoptotic cells were assessedby electrophoresis. Results indicated quantitatively that thesurface negative charge increased during these apoptotic processes.Our results also showed that the apoptotic pathway induced byeach of these drugs could be reversed before serious cleavageof DNA into oligonucleosomal fragments and universal chromatincondensation. Copyright 2001 Annals of Botany Company Cytotoxin, chromosome spreading, apoptosis, cell electrophoresis     

Modification in Cell Shape Unrelated to Cellulose Microfibril Orientation in Growing Thallus Cells of Chaetomorpha moniligera

Cellulose microfibril orientation patterns in thallus cellsof Chaetomorpha moniligera were studied, and the relationshipbetween the microfibril and the peripheral microtubule arrangementsduring cell-shape modification by colchicine was examined. Inthe cuttings from growing thalli, linearly arranged cylindricalcells developed into cask-shaped cells during 4–6 daysof culture at 27?C. In the cylindrical cells, microfibrils formingthe innermost portion of the wall were arranged alternatelyin longitudinal and transverse directions, but peripheral microtubuleswere always arranged only in a longitudinal direction. Thesefeatures were also noted in the cask-shaped cells. Colchicineat 10^–3M and 3?10^–3M accelerated both cell expansionand wall thickening with matrix deposition, but the directionsin which both microfibrils and microtubules were arranged werethe same as those of the cylindrical cells. These results indicatethat (1) the microfibril and microtubule arrangements of Chaetomorphaare not necessarily correlated, (2) changes in cell shape ofChaetomorpha are not necessarily accompanied by changes in thearrangement of cell-wall microfibrils, and (3) colchicine playsa role in the loosening and thickening of cell walls by enhancingmatrix deposition. (Received June 2, 1986; Accepted February 13, 1987)     

Alterations in ultrastructure and subcellular localization of Ca2+ in poplar apical bud cells during the induction of dormancy

In poplar (Populus deltoides Bartr. ex Marsh), bud dormancyand freezing tolerance were concomitantly induced by short-day(SD) photoperiods. Ultrastructural changes and the alterationin subcellular localization of calcium in apical bud cells associatedwith dormancy development were investigated. During the developmentof dormancy, the thickness of cell walls increased significantly,the number of starch granules increased, and there was a significantaccumulation of storage proteins in the vacuoles of the apicalbud cells. The most striking change was the constriction andblockage of the plasmodesmata. It was demonstrated that antimonate precipitation is a reliabletechnique for studying subcellular localization of calcium inpoplar apical bud cells. Under the long day (LD) photoperiod,electron-dense calcium antimonate precipitates were mainly localizedin vacuoles, intercellular spaces and plastids. Some antimonateprecipitates were also found in the cell walls and at the entranceof the plasmodesmata. However, there were few Ca²⁺ depositsfound in the cytosol and nucleus. After 20 d of SD exposure,when development of bud dormancy was initiated, calcium depositsin intercellular spaces were decreased, whereas some depositswere found in the cytosol and nuclei. From 28–49 d ofSD exposure, while dormancy was developing, a large number ofCa²⁺ precipitates were found in the cytosol and nuclei. Whendeep dormancy was reached after 77 d of SD exposure, Ca²⁺ depositsbecame fewer in both cytosol and nuclei, whereas numerous depositswere again observed in the cell walls and in the intercellularspaces. These results suggest that under the influence of SDphotoperiods, there are alterations in subcellular Ca²⁺ localization,and changes in ultrastructure of apical bud cells during thedevelopment of dormancy. The constriction and blockage of plasmodesmatamay cause the cessation of symplastic transport, limit cellularcommunication and signal transduction between adjacent cells,which in turn may lead to events associated with growth cessationand dormancy development in buds. Key words: Poplar, apical bud cells, Ca²⁺ subcellular localization, dormancy     

PENETRATION OF SUGARS FROM THE CHEMOSENSORY HAIR TIP IN THE FLESHFLY

(1) The penetrations of ¹⁴C-D-glucose and 3-O-methyl-¹⁴C-D-glucoseinto the isolated head of the fleshfly, Boettcherisca peregrina,from the tip of the longest chemosensory hair on the labrumwere investigated. (2) Both ¹⁴C-D-glucose and 3-O-methyl-¹⁴C-D-glucosepenetrated into the hair almost linearly with time and movedrapidly into the labrum. The isotopic activity was finally detectedin the head. (3) The isotopic activity of the hair dipped into¹⁴C-D-glucose solution increased in the preparation which hadbeen pretreated with 7.5 x 10^–2M colchicine for 30 min,whereas in the case of 3-O-methyl-¹⁴C-D-glucose no effect by7.5 x 10^–2M colchicine was found. (4) Both ¹⁴C-D-glucoseand 3-O-methyl-l4C-D-glucose which penetrated from the poreof the hair tip were detected in the dendritefree lumen andin the dendrite-containing lumen of the chemosensory hair. (5)These results suggest that D-glucose not only moves in the dendrite-freelumen and the dendrite-containing lumen but also in the dendrite(s).The suggestive results that 3-O-methyl-D-glucose moves in thedendrite(s) could not be obtained. ^*Present address: Department of Physiology, Medical Collegeof Miyazaki, Miyazaki, Japan.     

Axillary Bud Formation in Two Isogenic Lines of Tomato Showing Different Degrees of Apical Dominance

Grafting experiments have been carried out in which rootstocksof the cultivar Craigella were paired with scions of an isogenicline Craigella Lateral Suppressor (ls ls) and vice versa, andthe levels of hormones in the roots and shoots of the graftedplants examined. The roots of Craigella plants differed from those of LateralSuppressor in that they contained a higher proportion of a cytokininthat co-chromatographed with N⁶ - (²—isopentenyl) adenosine.Reciprocal grafts did not lead to any qualitative or quantitativechanges in the cytokinins in the roots of either line. GraftingLateral Suppressor scions on Craigella rootstocks led to anincrease in the IAA content of the apical region and the ABAcontent of the stem tissue immediately below it, but when Craigellascions were grafted on Lateral Suppressor rootstocks there wereno changes in the level of either hormone. Cytokinins applied to the leaf axils of Lateral Suppressor plantsresulted in lateral bud initiation in the axils above the pointof treatment but not if the plants were also given a short periodof far-red light at the end of the photoperiod. Cytokinins wereineffective in initiating lateral buds in grafted Lateral Suppressorscions. It is suggested that root-produced cytokinins influence lateralbud outgrowth indirectly by way of their effect on the levelsof IAA and ABA in the shoot. Lycopersicon esculentum Mill., tomato, apical dominance, growth regulation, indol-3yl acetic acid, abscisic acid, cytokinins     

Effects of Intermittent Desiccation on Nutrient Economy and Growth of Two Ecologically Contrasted Mosses

The mossesBrachythecium rutabulum (Hedw.) B., S. & G. andPseudoscleropodiumpurum (Hedw.) Fleisch. were cultivated for more than 50 d ina growth cabinet with or without weekly drying interludes of24 h. Some plants also received applications of a dilute NPKnutrient solution at weekly intervals. The continuously hydratedplants showed appreciably more biomass production than thosereceiving intermittent desiccation. Desiccation led to somebleaching of the green tissues inB. rutabulum but not inP. purumwhich appeared more desiccation-tolerant. NPK addition causeda further significant growth stimulation in continuously hydratedplants, but not in intermittently desiccatedB. rutabulum. Pseudoscleropodiumpurum showed NPK-induced growth stimulation even when intermittentlydesiccated. Net uptake of N was similar in desiccated and hydratedplants in both species. Considerable net uptake of P and K⁺occurredin continuously wetB. rutabulum , but uptake was much reducedin intermittently desiccated plants. Net uptake of P and K⁺byP.purum was similar in desiccated and hydrated samples. IntracellularK⁺, leaked from the cells during the desiccation treatment,was retained by cation exchange on the negatively charged cellwalls in both species. Levels of intracellular K⁺and Mg²⁺inthe new growth were maintained at the expense of the pool ofexchangeable cations. The growth stimulation and the net uptakeof nutrients under intermittent desiccation was greatest whenthe NPK application was made at the start of rehydration, possiblybecause of accentuated uptake in the early stages of recovery.The results support the hypothesis thatP. purum has a lowernutrient requirement thanB. rutabulum and highlight the importanceof continuous hydration for the latter's more productive plantlife strategy. The data also show that considerable new growthof bryophyte tissues is possible without additional nutrientabsorption. Brachythecium rutabulum ; Pseudoscleropodium purum ; mineral nutrition; desiccation; solute leakage; plant life strategies     

Correlative Inhibition of Lateral Bud Growth in Phaseolus vulgaris L. Ethylene and the Physical Restriction of Apical Growth

Restriction of apical growth in Phaseolus by enclosing the upperpart of the shoot in sealed or ventilated tubes induced developmentof axillary buds beneath the enclosure. Enclosed parts of shootsshowed a reduction of leaf growth and, in experiments wherethe tubes were sealed, of internode extension. Enclosure ofthe shoots in large vessels that did not restrict leaf expansion,but which contained 0?5 vols 10^–6 ethylene, similarlyinduced axillary bud growth. Analysis of the gaseous extractof physically restricted shoots showed a 2?5-fold increase inethylene concentration. The results suggest involvement of ethylenein the release of correlative inhibition brought about by physicalrestriction of apical growth.     

Comparison of the Disruption of Mitosis and Cell Plate Formation in Oat Roots by DCPA, Colchicine and Propham

Holmsen, J. D. and Hess, F. D. 1985. Comparison of the disruptionof mitosis and cell plate formation in oat roots by DCPA, colchicineand propham.—J. exp. Bot. 36: 1504–1513. Concentrationsof DCPA, propham and colchicine were selected to cause from0% to greater than 60% inhibition of oat (Avena sativa L. ‘Victory’)root growth after 24 h exposure. Root growth progressively declinedas concentrations were raised from 1·0 to 5·6mmol m^–3 DCPA, 1·0–5·0 mmol m^–3propham, and 50–500 mmol m^–3 colchicine. In additionto inhibiting root growth each mitotic disrupter caused theroot tips to swell to an extent dependent upon concentration.All three compounds effectively disrupted mitosis at concentrationsthat caused less than maximal root growth inhibition. Mitoticdisruption was manifest as a reduction in the number of normalmitotic figures and an increase in the number of condensed prophase,multipolar and anaphase bridge division figures. The frequencyof each type of division figure was different for each of thethree compounds. DCPA disrupted mitosis more effectively whencompared with propham and colchicine at concentrations whichcaused the same amount of root growth inhibition. Each mitoticdisrupter also induced the formation of aberrant cell walls.DCPA was the most effective at disrupting cell plate formation,whereas colchicine was least effective. These data suggest thatthe mechanism of action of DCPA is distinct from the mechanismof colchicine or propham Key words: Avena sativa L., mitotic disruption, DCPA, colchicine, propham     

Cell Cycle Duration in the Root Meristem of Sonoran Desert Cactaceae as Estimated by Cell-flow and Rate-of-cell-production Methods

Slow rates of cactus growth in the Sonoran Desert and high productivityof some Cactaceae under cultivation suggest that relativelylow growth rates are not the consequence of a long cell divisioncycle but of short optimal periods for growth and adverse environmentalfactors. To verify this hypothesis, the duration of the celldivision cycle (T)in the root apical meristem of seedlings ofthree sympatric species from the Sonoran Desert [Ferocactuspeninsulae(F. A. C. Weber) Britton & Rose ‘Townsendianus’(Britton & Rose) N. P. Taylor, stat. nov.,Stenocereus gummosus(Engelm.)Gibson & Horak andPachycereus pringlei(S. Watson) Britton& Rose] was estimated with the rate-of-cell-production (RCP)and the cell-flow (colchicine) methods. Both methods were appliedduring the steady-state growth phase, which was relatively shortin the first two species because of the determinate patternof root growth. The RCP method permitted estimation ofTin eachroot individually. Durations of the cell division cycle wereinversely proportional to the rate of root growth (r²rangedfrom 0.42 to 0.88,P<0.05).T,determined by the cell-flow method,ranged from 14.4 to 19.3 h in these species and was within thesame range asTdetermined by the RCP method. The averageTdeterminedby the RCP method was 67 to 75% of that determined by the cell-flowmethod. Results obtained with both methods are compared andanalysed. The proposed hypothesis appears to be correct, indicatingthat these species can be more productive under cultivationthan in the wild due to the relatively short duration of thecell division cycle. Adaptive features of these findings arealso considered.Copyright 1998 Annals of Botany Company Cactaceae, cell division cycle, root growth, root meristem, Sonoran Desert     

Regulation of Tubulin Degradation in Isolated Zinnia Mesophyll Cells in Culture

Tubulin degradation in isolated Zinnia mesophyll cells in culturewas investigated by pulse-chase labeling with [³⁵S]-methionineand two-dimensional electrophoresis. Tubulin degradation changesdynamically during culture. Almost no tubulin degradation occursin the cells on the first day in culture. Treatment of thesecells with colchicine activates the degradation of tubulin,but not of proteins other than tubulin. In the presence of colchicine,the and ß-subunits of tubulin are degraded togetherand the half life of each subunit is approximately 6 h. After2 d in culture, there is active degradation of tubulin evenin the absence of colchicine. Colchicine did not inhibit new synthesis of tubulin in Zinniacells. This is very different from the results reported in culturedmammalian cells, whereby unpolymerized tubulin elevated by colchicine-treatmentdepresses its own synthesis. These and previous results dealing with changes in the leveland synthesis of tubulin in cultured Zinnia cells (Fukuda 1987),are discussed in relation to the regulation of tubulin metabolismin cultured Zinnia cells. ¹Present address: Biological Institute, Faculty of Science,Tohoku University, Aoba-yama, Sendai, 980 Japan. (Received September 5, 1988; Accepted December 20, 1988)     

Actin filament disruption inhibits L-type Ca(2+) channel current in cultured vascular smooth muscle cells

To clarifyinteractions between the cytoskeleton and activity of L-typeCa²⁺ (Ca_L) channels in vascular smooth muscle(VSM) cells, we investigated the effect of disruption of actinfilaments and microtubules on the L-type Ca²⁺ current[I_Ba(L)] of cultured VSM cells (A7r5 cellline) using whole cell voltage clamp. The cells were exposed to eachdisrupter for 1 h and then examined electrophysiologically andmorphologically. Results of immunostaining using anti--actin andanti--tubulin antibodies showed that colchicine disrupted both actinfilaments and microtubules, cytochalasin D disrupted only actinfilaments, and nocodazole disrupted only microtubules.I_Ba(L) was greatly reduced in cells that wereexposed to colchicine or cytochalasin D but not to nocodazole.Colchicine even inhibited I_Ba(L) by about 40%when the actin filaments were stabilized by phalloidin or when thecells were treated with phalloidin plus taxol to stabilize bothcytoskeletal components. These results suggest that colchicine mustalso cause some inhibition of I_Ba(L) due toanother unknown mechanism, e.g., a direct block of Ca_Lchannels. In summary, actin filament disruption of VSM cells inhibitsCa_L channel activity, whereas disrupting the microtubulesdoes not.

     

Chilling injury in cotton (Gossypium hirsutum L.) : Effects of antimicrotubular drugs

When exposed to 4°C for more than three days, intact cotton(Gossypium hirsutum L.) seedlings and isolated cotyledonarydiscs suffered chilling injury as shown by the leakage of electrolytesfrom the tissue and the development of necrotic areas. Applicationof antimicrotubular drugs such as colchicine, demecolcine orpodophyllotoxin during chilling significantly accelerated andenhanced tissue damage. Lumicolchicine, the stereoisomer ofcolchicine, was ineffective. Non-chilled tissues showed hardlyany damage when treated with the same levels of antimicrotubulardrugs. Prior treatment with 10^–5 M abscisic acid (ABA)prevented the appearance of symptoms of damage caused by chillingand the antimicrotubular drugs during the first 2 to 3 daysand greatly reduced it at later stages. Our present resultssuggest that chilling damage may be due at least in part, tothe cold-induced disassembly of microtubules. Furthermore, themode of action of ABA might be related to factors which influencethe physiological stability of the microtubule network. ¹Preliminary report of this work was presented at the 10th InternationalConference on Plant Growth Substances, Madison, Wisconsin, 1979. ³Incumbent of the Seagram Chair in Plant Sciences. (Received April 15, 1980; )     

Apical electrolyte concentration modulates barrier function and tight junction protein localization in bovine mammary epithelium

In vitro mammary epithelial cell models typically fail to form a consistently tight barrier that can effectively separate blood from milk. Our hypothesis was that mammary epithelial barrier function would be affected by changes in luminal ion concentration and inflammatory cytokines. Bovine mammary epithelial (BME-UV cell line) cells were grown to confluence on permeable supports with a standard basolateral medium and either high-electrolyte (H-elec) or low-electrolyte (L-elec) apical medium for 14 days. Apical media were changed to/from H-elec medium at predetermined times prior to assay. Transepithelial electrical resistance (R_te) was highest in monolayers continuously exposed to apical L-elec. A time-dependent decline in R_te began within 24 h of H-elec medium exposure. Change from H-elec medium to L-elec medium time-dependently increased R_te. Permeation by FITC-conjugated dextran was elevated across monolayers exposed to H-elec, suggesting compromise of a paracellular pathway. Significant alteration in occludin distribution was evident, concomitant with the changes in R_te, although total occludin was unchanged. Neither substitution of Na⁺ with N-methyl-D-glucosamine (NMDG⁺) nor pharmacological inhibition of transcellular Na⁺ transport pathways abrogated the effects of apical H-elec medium on R_te. Tumor necrosis factor alpha, but not interleukin-1 nor interleukin-6, in the apical compartment caused a significant decrease in R_te within 8 h. These results indicate that mammary epithelium is a dynamic barrier whose cell-cell contacts are acutely modulated by cytokines and luminal electrolyte environment. Results not only demonstrate that BME-UV cells are a model system representative of mammary epithelium but also provide critical information that can be applied to other mammary model systems to improve their physiological relevance. transepithelial electrical resistance; apical cation concentration; paracellular permeability; mastitis; inflammatory cytokines; occludin     

Intracellular Localization of 3H-IAA in the Apical Bud of Lycopersicon esculentum

Driss-Ecole, D. and Perbal, G. 1987. Intracellular localizationof ³H-IAA in the apical bud of Lycopersicon esculentum.—J.exp. Bot. 38: 1362–1372. High resolution autoradiography of ³H-IAA was performed on ultra-thinsections of the apical bud of Lycopersicon esculentum treatedby DCC or glutaraldehyde. A quantitative study of the localizationof the labelling in the compartments (cell wall, cytoplasm,vacuoles and nucleus) of four types of cells (cells of the lateralzone of the apex, cells of the pith meristem, proximal and distalcells of the upper part of the pith) was made. The statisticalanalysis of the results has proved that the variability of thelabelling of the cell compartments in the four cell types wassimilar after treatment by DCC or glutaraldehyde. The densityof labelling is higher in each compartment of the meristematiccells compared with those of the differentiating cells. Thecells of the pith meristem can be distinguished from the meristematiccells of the lateral zone of the apex by a greater density oflabelling in the cytoplasm and the nucleus. These two cellulartypes contain a high density of radioactivity in vacuoles. Byconsidering the percentage of labelling of each compartmentrelative to the total labelling in the cell, it can be shownthat the meristematic cells are characterized by a high percentagein the nucleus whereas the vacuoles of the differentiating cellscontain the highest percentage of radioactivity. Key words: ³H-IAA, tomato shoot     

The spontaneous growth response of maize coleoptile segments and the change in tissue 8

Decapitated segments from maize (Zea mays L.) coleoptiles orientedvertically in an upright position show a strong spontaneousgrowth response (SGR) 3 h after decapitation. The latent periodof the SGR is markedly reduced when these segments are orientedin an inverted position. Coleoptile segments with intact tipsexhibit a weak and transient SGR in the vertical upright orientation.However, in the inverted orientation, these segments show atypical SGR. The data are inconsistent with the current hypothesisthat the SGR is caused by a time-dependent increase in tissuesensitivity to auxin. The parallel increase in membrane potentialdifference and growth rate during the time-course of the SGRindicates a possible role for PM H⁺-ATPase in the establishmentof the SGR in maize coleoptile segments. Key words: Auxin, spontaneous growth response, membrane potential, plasma membrane H⁺-ATPase, Zea mays L.