Differences in the timing of cell death,differentiation and function among three different types of ray parenchyma cells in the hardwood <Emphasis Type="Italic">Populus sieboldii</Emphasis> × <Emphasis Type="Italic">P</Emphasis>. <Emphasis Type="Italic">grandidentata</Emphasis>

Differences in the timing of cell death, differentiation and function among three different types of ray parenchyma cells in the hardwood Populus sieboldii × P. grandidentata which form uniseriate and homocellular rays were examined and clarified. Ray parenchyma cells died within 5 years, and the disappearance of nuclei from ray parenchyma cells did not occur successively from the pith side, even within individual radial cell lines of a given ray. Cell death occurred earliest in contact cells, which were connected to adjacent vessel elements through pits, in the fourth annual ring from the cambium. Cell death occurred next in intermediate cells, which were located within the same cell lines as contact cells but were not adjacent to vessel elements, in the fourth annual ring from the cambium. Finally, isolation cells, which were located within the other cell lines of a given ray, died in the fifth annual ring from the cambium. Secondary wall thickenings in contact cells and intermediate cells were initiated before those in isolation cells in the current year’s xylem. Most starch grains were localized in intermediate cells, and there were more lipid droplets in contact cells and intermediate cells than in isolation cells. In addition, the largest quantities of protein were found in contact cells. Our results indicate that the position within a ray and neighboring short-lived vessel elements might affect the timing of cell death and differentiation and, thus, the function of long-lived ray parenchyma cells in Populus sieboldii × P. grandidentata.     

The Possible Role of Potassium in the Activation of Axillary Buds of Bidens pilosus L. after Decapitation of the Apex: AN EXAMINATION BY X-RAY MICROANALYSIS

Growth of axillary buds in Bidens pilosus L. can be inducedby decapitation of the shoot apex. By means of X-ray microanalysisit is demonstrated that immediately after decapitation K⁺ isapparently accumulated in the stem tissue around the node. Conventionalelectron microscopy on sections of this part of the tissue revealedthat xylem parenchyma cells of those bundles that lead intothe cotyledons are differentiated as transfer cells. The possiblerole of K⁺ transport processes in growth initiation and regulationis discussed.     

Autoradiographic detection of uptake of bacterial3H-DNA label by barley seeds and isolated barley embryos

Barley seeds and extirpated embryos were cultivated in³H-DNA fromBacillus subtilis. Control group of embryos was cultivated in³H-thymidine. Uptake of the label from³H-DNA was observed after both methods of application, to halves of seeds and to embryos, and the label was localized almost exclusively in some of the nuclei of meristematic cells.     

Ontogenesis of Tannin Coenocytes in Sambucus racemosa L. I. Development of the Coenocytes from Mononucleate Tannin Cells

Tannin coenocytes in shoots of Sambucus racemosa L. developfrom mono-nucleate tannin cells which can be distinguished amongthe cells of the first internode, and which keep on growing.After karyokinesis without cytokinesis bi-nucleate tannin cellsoccur which yield a synchronous karyokinesis leading to 4 nucleiin the tube. The number of nuclei in the coenocyte is 2ⁿ wheren equals the number of karyokineses that have occurred. Sometimesthe number of nuclei is different and one nucleus is bigeerthan the rest indicating that a previous fusion of nuclei hasoccurred. The distribution of nuclei in the coenocyte supportsthe possibility of fusion of chromosome sets at the moment ofnuclear envelope dispersion. Sambucus racemosa L., coenocytes, synchronous karyokinesis, development     

Total Uptake and Incorporation into DNA of 3H-Thymidine, 3H-Deoxyuridine, and 3H-Thymine in the Primary Root of Vicia faba L.: II. EXCISED ROOTS

Total uptake of ³H-thymidine, ³H-thymine, and ³H-deoxyuridineand incorporation of these substances into DNA have been investigatedin excised roots in Vicia faba. Total uptake was found to behigher in excised roots than in intact ones. This was a consequenceof exogenous ³H-DNA precursors entering the excised roots throughthe cut surface. Where the cut surface was not immersed in the³H-thymidine solution ³H uptake was also higher than in intactroots. In this case ³H uptake scemed to be correlated with water-lossfrom the cut surface. Incorporation of ³H-thymidine, ³H-thymine,and ³H-deoxyuridine into DNA was found to be higher in excisedroots than in intact ones, probably as a result of a decreasein the size of the relevant endogenous precursor pools. It issuggested that this decrease resulted from the cessation ofthe supply of DNA precursors to these roots from the cotyledons.     

Graft Formation in Sitka Spruce: A Scanning Electron Microscope Study

Low-temperature and conventional scanning electron microscopyhave been used to examine the callus formed at the graft interfacein Picea sitchensis (Bong.) Carr. Callus cells are producedby both cambium and ray parenchyma dedifferentiation and redifferentiationin scion and stock. Adhesion between the cells derived fromscion and rootstock is thought to be my means of pectinaceousbeads at the surface of the callus cells, preceding a more generalfusion of cell walls. The cambia of the two graft componentsare prevented from growing towards each other by the presenceof callus. Instead, the differentiation of new cambium withinthe callus, in the vicinity of the cambia exposed at the preparedsurfaces of the scion and rootstock, links them to form a continuouscambial layer around the combined stem. Callus, cambium, differentiation, grafting, Picea sitchensis     

Leaf-like Structure in the Photosynthetic, Succulent Stems of Cacti

This research examined the hypothesis that as cacti evolve tothe leafless condition, the stem epidermis and cortex becomemore leaflike and more compatible with a photosynthetic role.All cacti in the relict genus Pereskia have non-succulent stemsand broad, thin leaves. All members of the derived subfamilyCactoideae are ‘leafless’, having an expanded cortexthat is the plant's only photosynthetic tissue. In Pereskia,leaves have a high stomatal density (mean: 50.7 stomata mm^–2in the lower epidermis, 38.1 mm^–2 in the upper epidermis),but stems have low stomatal densities (mean: 11.3 mm ₂, threeof the species have none). Stems of Cactoideae have a high stomataldensity (mean: 31.1 mm^–2, all species have stomata). Theouter cortex cells of stems of Cactoideae occur in columns,forming a palisade cortex similar to a leaf palisade parenchyma.In this palisade cortex, the fraction of tissue volume availablefor gas diffusion has a mean volume of 12.9%, which is identicalto that of Pereskia leaf palisade parenchyma. Pereskia stemcortex is much less aerenchymatous (mean: 5.3% of cortex volume).Cactoideae palisade cortex has a high internal surface density(0.0207 cm₂ cm^–2 which is higher than in Pereskia stemcortex (0.0150 cm₂ cm^–3) but not as high as Pereskia leafpalisade parenchyma (0.0396 cm₂ cm^–3). Pereskia stem cortexhas no cortical bundles, but Cactoideae cortexes have extensivenetworks of collateral vascular bundles that resemble leaf veins. Cactaceae, cactus, intercellular space, stomatal density, internal surface/volume, evolution     

Mast cell activation is not required for induction of airway hyperresponsiveness by ozone in mice

Exposure to ambient ozone(O₃) is associated withincreased exacerbations of asthma. We sought to determine whether mastcell degranulation is induced by in vivo exposure toO₃ in mice and whether mast cellsplay an essential role in the development of pulmonarypathophysiological alterations induced byO₃. For this we exposed mastcell-deficientWBB6F₁-kit^W/kit^W-v(kit^W/kit^W-v)mice and the congenic normalWBB6F₁ (+/+) mice to air or to 1 or 3 parts/million O₃ for 4 h andstudied them at different intervals from 4 to 72 h later. We foundevidence of O₃-induced cutaneous,as well as bronchial, mast cell degranulation. Polymorphonuclear cellinflux into the pulmonary parenchyma was observed after exposure to 1 part/milllion O₃ only in mice thatpossessed mast cells. Airway hyperresponsiveness to intravenousmethacholine measured in vivo under pentobarbital anesthesia wasobserved in bothkit^W/kit^W-vand +/+ mice after exposure to O₃.Thus, although mast cells are activated in vivo byO₃ and participate inO₃-induced polymorphonuclear cellinfiltration into the pulmonary parenchyma, they do not participate detectably in the development ofO₃-induced airwayhyperresponsiveness in mice.

     

Pathway of Photosynthate Transfer in the Developing Seed of Vicia faba L. Transfer in Relation to Seed Anatomy

The seed coat vascular system of the developing seed of Viciafaba consists of a chalazal and two lateral veins. The veinsare embedded in parenchymatous tissue which lies beneath thehypodermis and is divided into chlorenchyma, ground parenchymaand thin-walled parenchyma. The thin-walled parenchyma cellsand, in old seed coats, the vascular parenchyma of the veinsundergo additional secondary wall development to form transfercells. Thus, transfer cells line the entire inner surface ofthe seed coat. Initial distribution of ¹⁴C-photosynthates andsodium fluorescein within the seed coat was in the vascularsystem. Subsequent transfer towards the embryo was either radiallythrough vascular parenchyma and thin-walled parenchyma to thin-walledparenchyma/transfer cells, or by lateral spread within the groundand thin-walled parenchyma/transfer cells of the non-vascularregion of the seed coat prior to radial transfer. One-thirdof the ¹⁴C-photosynthate delivered to the enclosed embryo wasestimated to be transferred via the non-vascular region of theseed coat. The cotyledons consist of a single-layered epidermisenclosing storage parenchyma in which a differentiating reticulatevascular system is embedded. Epidermal cells juxtaposed to theseed coat develop wall ingrowths characteristic of transfercells. Initial distribution of ¹⁴C-photosynthate within thecotyledons reflected the unequal delivery to the seed apoplastfrom the vascular and non-vascular regions of the seed coat.Subsequent even distribution of photosynthate within the cotyledonspossibly occurred by transfer within their vascular system. Key words: Cellular pathway, photosynthate transfer, seed anatomy, transfer cell     

Nuclear and Cell Sizes in Different Regions of Root Meristems of Zea mays L.

Nuclear volumes and cell areas were determined for seven regionsof the meristem of roots of Zea mays. Roots were fixed in 10per cent neutral buffered formalin, in 3 per cent glutaraldehydeor in acetic acid/alcohol; they were prepared as sections oralls were teased apart. Mean volumes of interphase nuclei weresimilar in all regions of the root except the vascular tissueof the stele. Mean nuclear volumes and the overall range ofvolumes were similar in sub-populations of cells with differentproportions of G¹, S and G² cells, e.g. in row I of root capinitials, whose cells lack a G¹ phase, and in quiescent centrecells, which are mainly in G¹. Nuclear volume does not appearto be closely correlated with DNA content. Nuclear volumes covereda 6 to 12-fold range within a meristem and even within specificregions, in which cells are part of the same cell lineages,there was a 4- to 9-fold range. Nuclear volumes were comparedin sister cells in rows I and II of the root cap initials. In10 per cent of the pairs, sister nuclei had identical volumes;the other pain had different volumes and mean difference was68 µm³. Mechanisms by which this variability could begenerated are discussed, particularly asymmetry, at mitoses,of factors that regulate nuclear growth. Zea mays L., nuclear volume, cell size, root mcristem, DNA content, mitosis     

In Vitro Culture of Hermaphrodite Floral Buds of Cucumis melo L.: Microsporogenesis and Ovary Formation

A method has been described by which floral buds of hermaphroditemelons isolated at various stages from archesporium to preleptotenein the pollen mother cells (PMC) can be grown through to pollen-grainformation in culture. Floral buds cultured for this period ina medium with thymidine-methyl-³H (³H-T) showed incorporationof label into the nuclei of tapetal cells and PMCs. The labelincorporated into the PMC was probably due to pre-meiotic DNAsyn-thesis. In other tissues of the floral buds, ³H-T incorporationproceeded through meiosis. Metabolic and environmental factorsinvolved in normal differentiation of the microsporogenous tissueof floral buds cultured in vitro are discussed.     

Tritiated-thymidine Labelled Nuclei in Primordia and Newly-emerged Lateral Roots of Vicia faba L.

The utilization of ³H-TdR in DNA synthesis and the distributionof labelled nuclei have been determined in large primordia (LP)and newly emerged lateral roots (JE) of Vicia faba followingdifferent exposure periods. This nucleoside appears to reachLP and the more basal, unemerged parts of JE by way of the vasculartissue of the primary root, while those parts of JE which projectout from the epidermis of the primary obtain ³H-TdR directlyfrom the surrounding medium. The utilization of ³H-TdR in thesynthesis of DNA in basal segments of JE is also complicatedby the temporary quiescence of nuclei in this part of thesemeristems as LP elongate to form lateral roots.     

Cellular pathway of photosynthate transport in coats of developing seed of Vicia faba L. and Phaseolus vulgaris L. I. Extent of transport through the coat symplast

The extent of post-phloem solute transport through the coatsymplasts of developing seeds of Vicia faba L. and Phaseolusvulgaris L. was evaluated. For Vicia seed coats, the membrane-impermeantfluorochrome, CF, moved radially from the chalazal vein to reachthe chlorenchyma and thin-walled parenchyma transfer cell layers.Thereafter, the fluorochrome moved laterally in these two celllayers around the entire circumference of the seed coat. Transferof CF from the chalazal vein was inhibited by plasmolysis ofattached ‘empty’ seed coats. In contrast, the spreadof phloem imported CF was restricted to the ground parenchymaof Phaseolus seed coats. Fluorochrome loaded into the outermostground parenchyma cell layer was rendered immobile followingplasmolysis of excised seed-coat halves. Phloem-imported [¹⁴C]sucroseand the slowly membrane permeable sugar, L-[¹⁴C]glucose, werepartitioned identically between the vascular and non-vascularregions of intact Vicia seed coats. For ¹⁴C-photosynthates,these partitioning patterns in attached ‘empty’Vicia seed coats were unaffected by PCMBS, but inhibited byplasmolysis. Tissue autoradiographs of intact Phaseolus seedcoats demonstrated that a pulse of ¹⁴C-photosynthate moved fromthe veins to the grounds tissues. In excised Vicia seed coats,preloaded with ¹⁴C-photosynthates, the cellular distributionof residual ¹⁴C-label was unaffected by PCMBS. In contrast,PCMBS caused the ¹⁴C-photosynthate levels to be elevated inthe veins and ground parenchyma relative to the branch parenchymaof Phaseolusseed coat halves. Based on the above findings, itis concluded that the phloem of Vicia seed coats is interconnectedto two major symplastic domains; one comprises the chlorenchyma,the other the thin-walled parenchyma plus thin-walled parenchymatransfer cells. For Phaseolusseed coats, the phloem forms amajor symplastic domain with the ground parenchyma. Key words: Phaseolus vulgaris L, phloem unloading, photosynthate transport, seed coat, symplast, Vicia faba L     

Effects of colchicine on the mitosis of Physarum polycephalum

Colchicine treatment delayed mitosis in the plasmodium of Physarumpolycephalum. This effect was observed when colchicine-pulsetreatments were performed at the late G2 phase. ³H-colchicine-bindingactivity was mainly localized in the nuclei and increased inthe late G2 phase. ¹ Present address: Department of Biochemistry, The Public HealthResearch Institute of The City of New York, Inc., New York,U.S.A. (Received September 22, 1977; )     

Calcium Movement, Graviresponsiveness and the Structure of Columella Cells and Columella Tissues in Roots of Allium cepa L.

Roots of Allium cepa L. cv. Yellow are differentially responsiveto gravity. Long (e.g. 40 mm) roots are strongly graviresponsive,while short (e.g. 4 mm) roots are minimally responsive to gravity.Although columella cells of graviresponsive roots are largerthan those of nongraviresponsive roots, they partition theirvolumes to cellular organelles similarly. The movement of amyloplastsand nuclei in columella cells of horizontally-oriented rootscorrelates positively with the onset of gravicurvature. Furthermore,there is no significant difference in the rates of organellarredistribution when graviresponsive and nongraviresponsive rootsare oriented horizontally. The more pronounced graviresponsivenessof longer roots correlates positively with (1) their caps being9.6 times more voluminous, (2) their columella tissues being42 times more voluminous, (3) their caps having 15 times morecolumella cells, and (4) their columella tissues having relativevolumes 4·4 times larger than those of shorter, nongraviresponsiveroots. Graviresponsive roots that are oriented horizontallyare characterized by a strongly polar movement of ⁴⁵Ca²⁺ acrossthe root tip from the upper to the lower side, while similarlyoriented nongraviresponsive roots exhibit only a minimal polartransport of ⁴⁵Ca²⁺. These results indicate that the differentialgraviresponsiveness of roots of A. cepa is probably not dueto either (1) ultrastructural differences in their columellacells, or (2) differences in the rates of organellar redistributionwhen roots are oriented horizontally. Rather, these resultsindicate that graviresponsiveness may require an extensive columellatissue, which, in turn, may be necessary for polar movementof ⁴⁵Ca²⁺ across the root tip. Allium cepa, onion, root, columella tissue, columella cell, gravitropism, calcium, ultrastructure     

Autoradiographic detection of the uptake of the label from bacterial3H-DNA in relation to the kinetics of the mitotic cycle in barley embryos

Extirped barley embryos were pre-cultivated in aerated liquid nutrient solution for 24 h and then cultivated for 6 h in nutrient solution containing either³H-DNA fromBacillus subtilis or³H-thymidine. After this treatment the embryos were thoroughly washed and transferred to the fresh nutrient medium. Samples were fixed at different intervals up to 24 h. Feulgen squashes were made and covered with autoradiographic emulsion. Microautodiagrams of different parts of the embryos (root meristem, shoot apex plus meristem of the third leaf, second leaf meristem, coleoptile, scutelum) were observed. Labelling of the nuclei after the application of both³H-DNA and³H-thymidine was found in the proliferating parts of the embryos but no label was found in the scutelum. The labelling index values were almost similar in different embryo organs after the treatment with³H-DNA and³H-thymidine. Labelling index and the fraction of labelled mitoses at different intervals after the application of the labelled substances were almost similar after treatment with³H-DNA and³H-thymidine, except some variations due to irrelevant differences in the kinetics of the mitotic cycle. No disappearance of the activity of³H-DNA was observed at different intervals after removal from the labelled solutions during cultivation for other 24 h in non-labelled nutrient medium either containing DNA fromBacillus subtilis or without it. The embryos which were immersed into 0.2% NaCl solution with either one of the labelled compounds did not show any initiation of the S phase nor uptake of³H-DNA. All these results demonstrate that the label from³H-DNA is localized in those cell nuclei which were in the S phase during treatment but they do not yet distinguish unambiguously between the adsorbtion of polymerous DNA or its degradation and reutilization of low-molecular weight products.     

Organelle DNA Synthesis in the Quiescent centre of Arabidopsis thaliana (Col.)

The behaviour of cell nuclei and organelle nucleoids (organellenuclei) was studied in the root apical meristem of 3-d-old seedlingsof Arabidopsis thaliana (Col.). Samples were embedded in Technovit7100 resin, cut into thin sections and stained with 4'-6-diamidino-2-phenylindole(DAPI) for observation of DNA. DNA synthesis in cell nucleiand organelle nucleoids was investigated using the incorporationof [³H] thymidine or 5-bromo-2'-deoxyuridine (BrdU). Incorporated[³H] thymidine and BrdU were detected by microautoradiographyor immunofiuorescence microscopy, respectively. Central cellsand cells just above the central cells of the quiescent centre(QC) showed an extremely low activity of DNA synthesis. However,DNA synthesis occurred in at least one organelle nucleoid ofall cells in the QC within 24 h. This suggests the cells inthe QC are quiescent with regard to nuclear DNA synthesis, butnot with regard to the organelle nucleoids. Key words: Arabidopsis thaliana, quiescent centre, root apical meristem, mitochondrial nucleoid (nuclei), plastid nucleoid (nuclei)     

Mechanisms of solute efflux from seed coats: whole-cell K+ currents in transfer cell protoplasts derived from coats of developing seeds of Vicia faba L.

In developing seed ofVicia faba L., solutes imported throughthe phloem of the coats move symplastically from the sieve elementsto a specialized set of cells (the thin-walled parenchyma transfercells) for release to the seed apoplast. Potassium (K⁺) is thepredominant cation released from the seed coats. To elucidatethe mechanisms of K⁺ efflux from seed coat to seed apoplast,whole-cell currents across the plasma membranes of protoplastsof thin-walled parenchyma transfer cells were measured usingthe whole-cell patch-clamp technique. Membrane depolarizationelicited a time-dependent and an instantaneous outward current.The reversal potential (E_R of the time-dependent outward currentwas close to the potassium equilibrium potential (E_K and itshifted in the same direction as E_K upon changing the externalK⁺ concentration, indicating that this current was largely carriedby an efflux of K⁺. The activation of the time-dependent outwardK⁺ current could be well fitted by two exponential componentsplus a constant. The instantaneous outward current could alsobe carried by K⁺ efflux as suggested by ion substitution experiments.These K⁺ outward rectifier currents elicited by membrane depolarizationare probably too small to represent the mechanism for the normalK⁺ efflux from seed coat cells. Membrane hyperpolarization morenegative than –80 mV activated a time-dependent inwardcurrent. K⁺ influx was responsible for the inward current asthe current reversed at membrane voltage close to E_K and shiftedin the same direction as E_K when external [K⁺] was varied. Activationof this K⁺inward rectifier current was well fitted with twoexponential components plus a constant. A regulating functionfor this current is suggested. Key words: Potassium outward rectifier, potassium inward rectifier, transfer cell protoplast, seed coat, Vicia faba L     

Effects of Growth Hormone Application on the Secondary Growth of Roots and Stems in Picea sitchensis (Bong.) Carr

Indol-3-ylacetic acid (IAA), gibberellin A3 (GA) and 6 benzylaminopurine(BAP) were applied factorially each at 3x10^–2 M in lanolinto the roots and stems of Sitka spruce seedlings and the activityof the two secondary meristems, the vascular cambium and phellogen,and of the parenchymatous tissues between them, was examined.All the treatments, with the exception of GA produced a localizedstimulation of radial growth at the point of application andthere was a similarity in the response of the various tissuesin both the root and stem. Radial growth of the xylem was notsignificantly affected in the roots whereas in the stems BAPand IAA stimulated growth. In the phloem BAP produced significantstimulation in both roots and stems and IAA stimulated growthin the roots. Growth of the parenchyma and periderm externalto the phloem was also strongly stimulated by both BAP, andIAA in roots and stems. In roots and stems the application of BAP altered the derivativesproduced by the vascular cambium, resulting in the productionof large multiseriate rays in the xylem, and giving rise toan overall increase in the proportion of ray tissue. Picea sitchensis (Bong.) Carr, Sitka spruce, secondary growth, xylem, phloem, periderm, wood rays, Indol-3-ylacetic acid, gibberellin A3, 6 benzylaminopurine, growth hormones     

Inhibitory effect of lycorine on cell division and cell elongation

Lycorine, an alkaloid isolated from bulbs of Amarillidaceae,was found to be a powerful inhibitor of cell division and elongation.Adding different concentrations of lycorine from 10^–6M to 10^–4 M in an appropriate growth-medium strongly inhibitedcell division in explants of lettuce pith parenchyma. The sameresult was obtained with liquid yeast cultures growing exponentially. Lycorine-treated meristematic cells of the primary roots ofVicia faba also showed rapid inhibition of the mitotic indexwhile interphase cells increased proportionately. Lycorine alsoinhibited endogenous and auxin-induced cell elongation in Avenacoleoptiles and pea segments. Since both cell division and cell elongation require proteinsynthesis and RNA synthesis, the assumption is that lycorineprobably inhibits one of the two syntheses. ¹This study was supported by a contract between the NationalResearch Council of Italy and University of Bari, Instituteof Botany. (Received November 27, 1972; )