EFFECT OF GROWTH RATE,MORPHOGENIC ACTIVITY,AND PHYLOGENY ON SHOOT APICAL ULTRASTRUCTURE IN OPUNTIA POLYACANTHA (CACTACEAE)

Dormant short shoot apices of Opuntia polyacantha were cultured under three conditions: cytokinin and high sucrose to stimulate the formation and rapid growth of a leafy long shoot; cytokinin and no sucrose (slow growth of a leafy long shoot); gibberellic acid and high sucrose (rapid growth of a spiny short shoot). These meristems, and also dormant (uncultured) ones, were analyzed by stereological, ultrastructural techniques. By comparing meristems growing with cytokinin but with or without sucrose, correlations between metabolic rate and apical ultrastructure were studied; comparison of leaf-producing and spine-producing meristems permitted examination of correlations with morphogenic role; comparison with published data for four other species permitted study of phylogenetic effects, and comparison with dormant apices revealed information about meristem activation. Ultrastructure varied according to each condition: metabolic rate, morphogenic activity and species can be distinguished by quantitative methods. Apical ultrastructure is most strongly correlated with rate of growth such that apices of differing species resemble each other if growing at similar rates, whereas apices of a single species differ markedly if growing at differing rates or if performing different morphogenic activities. Hyaloplasm is an excellent indicator of metabolic rate; mitochondria, nuclei, and vacuoles are not.     

Human T lymphocyte activation in the presence of acute myelogenous leukaemia blasts: studies of allostimulated interferon-γ secretion

 Normal peripheral blood mononuclear cells (PBMC responders) were cultured together with non-irradiated allogeneic PBMC (more than 95% leukaemia blasts) derived from patients with acute leukaemia (referred to as leukaemic PBMC stimulators). Cytokine secretion was determined as cytokine concentrations in supernatants. Both normal PBMC and enriched CD4⁺ and CD8⁺ T cells responded to allostimulation with interferon (IFNγ) secretion. Interleukin-1 (IL-1) receptor antagonist and IL-2-neutralizing antibodies decreased IFNγ secretion. Exogenous IL-1β, IL-2 and IL-7 increased allostimulated IFNγ secretion, whereas decreased levels were seen in the presence of IL-6, IL-10 and granulocyte-colony-stimulating factor (G-CSF). During allorecognition IFNγ -neutralizing antibodies decreased acute myelogenous leukaemia (AML) blast secretion of G-CSF. We conclude that (i) both CD4⁺ and CD8⁺ T cells show allostimulated cytokine secretion in response to allogeneic stimulator cells containing a dominating population of native, cytokine-secreting leukaemia blasts, and (ii) IFNγ released during this response can modulate the function of allogeneic AML blasts. Received: 4 June 1996 / Accepted: 15 October 1996     

A MORPHOMETRIC STUDY OF THE ULTRASTRUCTURE OF ECHINOCEREUS ENGELMANNII (CACTACEAE). I. SHOOT APICAL MERISTEMS AT GERMINATION

At germination the shoot apical meristems of Echinocereus engelmannii were discs with a volume of 666,000 μm³ and were composed of a unistratose tunica (volume: 260,000 μm³) and a corpus which was two cell-layers thick (volume: 406,000 μm³). Four days after germination the nucleus constituted 28.9% of the volume of the cell, and the vacuole constituted 24.5%. The mitochondria were 13.3% of the volume of the tunica cytoplasm, the chloroplasts 9.4%, and the dictyosomes only 1.2%. The endoplasmic reticulum was too sparse to be accurately measured. The organelles of the corpus were identical in size and shape to those of the tunica, but there were statistically significant differences in their cellular and cytoplasmic densities: the more distal corpus layer (C1) was less vacuolate (16.6% of the cell volume), and both corpus layers contained more chloroplasts, 12.0% of the cytoplasmic volume in C1 and 14.3% in the more proximal corpus layer (C2). During the first four days after germination there was a dramatic increase in the size of the central vacuole (e.g., from 15.4% to 24.5% in the tunica), and the mitochondria increased in density from 10.2% of the cytoplasmic volume to 13.3%. Chloroplast density also increased in all meristem layers, but the dictyosome density decreased, as much as a 30% loss in C2. There was also a highly significant reduction in the number of cisternae per dictyosome, from 5.47 to 4.77. Surprisingly, there was no change in heterochromatin: ca. 27% of the volume of the nuclei of all layers was heterochromatic at all stages studied. Thus, the organellar structure of corpus cells is distinctly different from that of tunica cells, and as the apical meristem becomes active after germination, the changes which occur are not uniform in the meristem but rather are zone-specific.     

A MORPHOMETRIC STUDY OF THE ULTRASTRUCTURE OF ECHINOCEREUS ENGELMANNII (CACTACEAE). IV. LEAF AND SPINE PRIMORDIA

A stereological morphometric study of leaf primordia (P1 and P2) of Echinocereus engelmannii indicated that primordia are significantly different ultrastructurally from the shoot apical meristem tissues (tunica and peripheral zone) that produce the primordia. Leaf initiation involves readjustments of rates of synthesis and growth of cytoplasm, vacuoles, mitochondria, chloroplasts, and dictyosomes, such that leaf initiation must be a complex process in which different cell components are affected individually. Furthermore, leaf primordia are ultrastructurally distinct from spine primordia. Leaf and spine primordia as young as these are not yet irrevocably determined, thus different types of primordia, from the time of their inception and before their determination, have distinctly unique metabolisms; primordia are not merely generalized, uncommitted outgrowths whose developmental fate is set at some time later than inception.     

Anatomical Adaptations to Xeric Conditions in Maihuenia (Cactaceae), a Relictual, Leaf-Bearing Cactus

Maihuenia and Pereskia, constitute Pereskioideae, the subfamily of Cactaceae with the greatest number of relictual features, but the two genera differ strongly in habit and ecological adaptations. Plants of Maihuenia occur in extremely xeric regions of Patagonia and are small cushion plants with reduced, terete leaves and soft, slightly succulent trunks. Plants of Pereskia occur only in mesic or slightly arid regions and are leafy trees with hard, woody trunks and thin, broad leaves. Maihuenias have many more anatomical adaptations to arid conditions than do pereskias: maihuenias lack sclerenchyma in their phloem and cortex (M. poeppigii also lacks xylem sclerenchyma and can contract during drought); their wood consists of vessels, axial parenchyma, and wide-band tracheids and can store water as well as minimize embolism damage; one species channelizes water flow by producing intraxylary bark; and at least some stem-based photosynthesis occurs because maihuenias have small patches of persistent stem epidermis that bears stomata and overlies a small amount of aerenchymatous chlorenchyma. Pereskias lack all these features. Although closely related, maihuenias have fewer relictual features than do pereskias, and plants of Pereskia probably are more similar to the ancestral cacti. Received 8 March 1999/ Accepted in revised form 29 May 1999     

Theoretical aspects of surface-to-volume ratios and water-storage capacities of succulent shoots

Surface-to-volume (S/V) ratios of drought-adapted plants affect transpiration, photosynthesis, and water-storage capacity. The S/V ratio of cladodes and flat leaves is S/V = 2/T, where T is thickness: even slight thickening greatly reduces S/V. During rain/drought cycles succulent stems swell and shrink without tearing by having flexible ribs, but ribs increase S/V above that of a smooth cylindrical stem with equal volume: the increased surface area is S(ribbed)/S(cylindrical) = N[x + (π/N)]/π(1 + x), where N is number of ribs and x is rib height relative to the radius of the inner stem. Numerous low ribs provide moderate expandability (storage volume) with little increase in S/V and are adaptive where droughts are short. Tall ribs provide greater expandability but greatly increase S/V and probably are adaptive only in mesic habitats. Having ～8-15 ribs, each about as tall as the inner stem radius, provides large storage capacity and intermediate increase in S/V. By increasing absolute size, S/V is reduced so greatly that even large ribs can have an S/V smaller than that of a narrow cylindrical or spherical stem with less volume.     

Water-storing and Cavitation-preventing Adaptations in Wood of Cacti

Ancestral cacti presumably had abundant, fibrous, heavily lignifiedwood, similar to that present in the relictual, leaf-bearinggenus Pereskia. During the evolutionary radiation of the subfamilyCactoideae, diverse types of bodies and woods arose. Severalevolutionary lines have retained an abundant, fibrous wood:all wood cells, even ray cells, have thick lignified walls,and axial parenchyma is only scanty paratracheal. Aside froma diversity of vessel diameters, there seems to be little protectionagainst cavitation during water-stress, and little water-storagecapacity. This strong wood permits the plants to be tall andto compete for light in their tree-shaded semi-arid habitats.In other evolutionary lines, the wood lacks fibres, and almostall cells have thin, unlignified walls. Vessels occur in anextensive matrix of water-storing parenchyma, and tracheidsare also abundant, constituting over half the axial tissue insome species. There is excellent protection against cavitation,but little mechanical support for the plant body; however, theseplants are short and occur in extremely arid, unshaded sites.Scandent, vinelike plants of two genera produce a dimorphicwood—while their shoots are extending without externalsupport, they produce fibrous, lignified wood, but after leaningagainst a host branch, they produce a parenchymatous, unlignifiedwood.Copyright 1993, 1999 Academic Press Cactaceae, cactus, water-stress, wood, evolution, xylem     

A High-Affinity Binding Protein for the Regulatory Subunit of cAMP-Dependent Protein Kinase II in the Centrosome of Human Cells

In the human lymphoblastic cell line KE 37, Northern blot analysis with cDNA probes for human regulatory subunits RIIα and RIIβ of the cAMP-dependent protein kinase (A-kinase) type II and immunoblotting or immunoprecipitation studies with several antibodies directed against RIIα and RIIβ show that these two isoforms are expressed. The major isoform α is mostly cytosolic, whereas the β isoform appears concentrated in the Golgi-centrosomal area, as judged by immunofluorescence and cell fractionation. Using a ³²P-labeled RII overlay on Western blots, a 350-kDa RII-binding protein (AKAP 350) was specifically identified in centrosomes isolated from this cell line, whereas a Golgi fraction has previously been demonstrated to contain an 85-kDa RII-binding protein (AKAP 85). AKAP 350 is highly insoluble and can partially be extracted from centrosomes as a complex of AKAP 350 and RII subunit. AKAP 350 was identified as a specific centrosomal protein previously demonstrated in the pericentriolar material. The potential significance of a specific subcellular distribution for different RII-binding proteins in nonneuronal cells is discussed.     

CYTOKININ- AND GIBBERELLIC ACID-INDUCED EFFECTS ON THE STRUCTURE AND METABOLISM OF SHOOT APICAL MERISTEMS IN OPUNTIA POLYACANTHA (CACTACEAE)

The dormant axillary buds of Opuntia polyacantha can be activated by either cytokinins or gibberellic acid. Under the influence of benzylaminopurine (BAP), the axillary bud meristem increases greatly in size and becomes mitotically active. The primordia produced by the meristem develop as normal photosynthetic leaves. Gibberellic acid (GA) also causes the meristem to become mitotically active, but the meristem does not increase in size. The primordia produced under the influence of GA develop as normal cactus spines. Leaf-producing meristems and spine-producing meristems have the same zonation, despite the differences in size. The meristems are composed of a uniseriate tunica, a central mother cell zone, peripheral zone, and a pith rib meristem. The mitotic activity of each of the zones in the leaf-producing meristem differs significantly from the mitotic activity of the corresponding zones in the spine-producing meristem.