REJUVENATION OF SENESCENT CELLS OF SPONGIOCHLORIS TYPICA2

Thick-walled, oil-filled akinetes of the green alga Spongiochloris typica, long in the stationary phase of growth, were transferred to fresh media. Ultra-structural changes were observed during a 51-hr period after transfer. Akinetes, when transferred to fresh media, may follow 1 of 3 pathways:

• 1 Remain unchanged; these cells appear to be moribund perhaps due to an over-accumulation of lipid.
• 2 Undergo immediate zoosporogenesis; seems to occur in cells with 4, 8, or more nuclei.
• 3 Return to the vegetative state; this was common in smaller cells with less than 4 nuclei; however, zoosporogenesis eventually did occur when 4, 8, or more nuclei were present.

     

ULTRASTRUCTURE OF MYXOMYCETE PLASMODIA OF VARIOUS TYPES

Myxomycete plasmodia of 4 types (other than Physarum polycephalum), namely, Didymium clavus, Hemitrichia vesparium, Stemonitis fusca, and Clastoderma debaryanum, were sectioned and studied by electron microscopy. Organelles of all species have been described. In general, they are similar in the various species studied and resemble those found in animal cells and the cells of some lower plants. Mitotic figures and centrioles were not observed. Fibrils of 3 types were found; they were most prominent in Clastoderma debaryanum.     

ELECTRON MICROPROBE ANALYSIS OF SILICA IN EPIDERMAL CELLS OF EQUISETUM

Patterns of silica deposition on the outer epidermal cell walls of Equisclum arvense and E. hycmalc var. affine were examined by means of electron microprobe analysis. Silica is deposited primarily in discrete knobs and rosettes on the epidermal surface in E. arvense and essentially in a uniform pattern on and in the entire outer epidermal cell walls of E. hyemale var. affine. This markedly contrasts with patterns of silica deposition in internodal epidermal cells of Avena saliva (Gramineae) where silica is deposited primarily in cell walls and cell lumina, and to a much lesser extent, on the outer epidermal surface. Semi-quantitative analysis with the electron microprobe shows that in intercalary meristematic cells of E. aruense, silicon is not present in any cells, but that in mature epidermal cells above the intercalary meristem it is present in significant quantities. The study thus suggests that silica deposition must be a very rapid process in Equisclum and Avena.     

DNA CONTENT OF SEVEN SPECIES OF ASTEREAE AND ITS SIGNIFICANCE TO THEORIES OF CHROMOSOME EVOLUTION IN THE TRIBE

Relative amounts of nuclear DNA were determined in root tip cells of seven species of Astereae: Aster hydrophilus Greene, A. oblongifolius Nutt., A. riparius H.B.K., Machaeranthera boltoniae (Greene) Turner and Home, M. brevilingulata (Sch-Bip.) Turner and Home, M. parviflora Gray, and M. tenuis (S. Wats.) Turner and Home. The results show that A. hydrophilus and M. brevilingulata, with a chromosome number of n = 9, have less nuclear DNA than other closely related species which are either n = 4 or n = 5. Cytological analyses of meiosis in the intergeneric hybrid M. parviflora X A. hydrophilus showed cells with two or more small chromosomes of the latter species pairing with single large chromosomes of the former. Pachytene cells of the hybrids M. parviflora X A. hydrophilus, M. parviflora X A. riparius, and M. boltoniae X M. tenuis showed some unpaired chromosome segments. The significance of these results to chromosome evolution in the tribe Astereae is discussed.     

MOLYBDENUM DEPENDENCE,NITRATE UPTAKE AND PHOTOSYNTHESIS OF FRESHWATER PLANKTON ALGAE1,2

The effects of molybdenum on photosynthesis and nitrate uptake by two species of freshwater algae, Navicula pelliculosa (Bréd.) Hilse and Chlamydomonas reinhardtii Dang. Were examined. Photosynthetic rates in cells of N. Pelliculosa deprived of Mo for 48 h were significantly lower than in nondeprived cells; the rates were 2.6 and 4.5 μg C/10⁶ cells/h, respectively. There was no significant reduction in photosynthetic rates of C. reinhardtii under the 2 treatments, the rates were both ca. 6.0 μg C/10⁶ cells/h. These observed rates in the 2 species were not altered by added Mo concentrations as high as 1.0 ppm. The chlorophyll a values in 48 h Mo-deprived cells were 1.15 μg/10⁶ cells compared to 1.57 μg/10⁶ cells provided with this metal. Molybdenum deficiency did not affect the chlorophyll a concentration in Chlamydomonas; the chlorophyll levels were 2.44μg/10⁶ cells. Nitrate uptake by Mo-deprived cells of N. Pelliculosa was significantly lower than in cells cultured in Mo; the rates were 0.087 and 0.238 μM NO_a⁻/10⁶ cells/h, respectively. Uptake rates by C. reinhardtii were similar with or deprived of Mo. The K_m values for No₃⁻ uptake were 14.9 and 148.0 μM for N. Pelliculosa and C. reinhardtii, respectively.     

THE FEMALE GAMETOPHYTE OF THREE SPECIES OF GRINDELIA AND OF PRIONOPSIS CILIATA (COMPOSITAE)

In the four species studied, Grindelia stricta ssp. blakei, G. arizonica, G. lanceolata, and Prionopsis ciliata (Haplopappus ciliatus), the female gametophyte develops according to the Polygonum (normal) type from the chalazal megaspore of a row of four. In most cases only two antipodal cells are formed, the micropylar one originally containing two nuclei. The number of nuclei increases in both cells; one or both antipodal cells typically grow laterally into the integument, often extending to near the surface of the ovule. This resembles the condition previously reported in Grindelia squarrosa. Since the four species of Grindelia have similar antipodal outgrowths, such outgrowths may be considered typical for this genus. The fact that Prionopsis resembles Grindelia in regard to outgrowths from the antipodal cells and differs in this respect from typical Haplopappus helps to justify its separation from Haplopappus, and perhaps its suggested merger with Grindelia.     

ENHANCEMENT OF INTRACELLULAR PROLINE LEVEL IN CELLS OF ANACYSTIS NIDULANS (CYANOBACTERIA) EXPOSED TO DELETERIOUS CONCENTRATIONS OF COPPER1

The intracellular proline level in Anacystis nidulans cells was enhanced when the cells were exposed to sublethal concentrations of Cu²⁺; the degree of enhancement was positively related to the concentration of Cu²⁺. Analysis by high-performance liquid chromatography confirmed that the enhancement of proline levels was the most pronounced change in the composition of the free amino acid pool during copper treatment. A direct supply of exogenous proline to the cultures lowered the inhibitory influence of Cu²⁺on the growth of cells. Further experiments showed that the supply of exogenous proline lowered the leakage of potassium ions from cells exposed to deleterious concentrations of Cu²⁺. The inhibition of potassium leakage was particularly pronounced when proline was supplied prior to Cu²⁺treatment. The present study suggests that enhanced proline protects cell membranes from being affected by deleterious concentrations of Cu²⁺.     

FINE STRUCTURE OF NUCLEAR CRYSTALS IN LEAVES OF TWO DIANTHUS SPECIES

Examination of leaf cells of Dianthus barbatus with the election microscope revealed the presence of crystals in the nuclei, but not in the cytoplasm or in other organelles. They were at first thought to be viral crystalline inclusions, but no evidence could be adduced to support this possibility. The crystals were found in the nuclei of cells from all parts of the leaf, including parenchyma cells of the vascular elements. They were usually 0.5–2 μ long, and occasionally up to 5 μ. In longitudinal section they appeared as electron-dense striations, about 10–15 mμ wide, alternating with electron-transparent bands, 6–8 mμ wide. In cross section they had a honeycomb appearance, resulting from closely packed hexagonal elements, with electron-transparent centers. Similar crystals were found in nuclei of D. chinensis leaf cells, but not in other members of the Caryophyllaceae, including two varieties of D. caryophyllus, D. deltoides, D. arenarius, Silene acaulis, Lychnis chalcedonica, Saponaria calibrica, and Stellaria media. This appears be the first fine structural report of a lattice inclusion in nuclei of cells of healthy higher plants.     

CRYOPRESERVATION OF THE GAMETOPHYTIC CELLS OF LAMINARIALES (PHAEOPHYTA) IN LIQUID NITROGEN1

The gametophytic cells of six species of Laminariales, Laminaria japonica Areschoug, L. longissima Miyabe, Kjellmaniella crassifolia Miyabe, Ecklonia stolonifera Okamura, E. kurome Okamura, and Undaria pinnatifida (Harvey) Suringar, were subjected to cryopreservation in liquid nitrogen. The cells were suspended in various cryoprotective solutions and slowly cooled to –40°C over a period of 4 h. After this slow cooling step, the suspensions were immediately immersed in liquid nitrogen. All the species of Laminariaceae used in the present study survived maximally in a mixture of ethylene glycol and proline. On the other hand, the gametophytic cells of Undaria pinnatifida, a member of the Alariaceae, survived maximally in the mixture of glycerol and proline. The viability of the thawed gametophytic cells decreased during postthawing incubation. The decrease in viability continued for 4–6 days, and the minimum levels ranged from 36.2% to 67.2%. After 4–6 days of incubation, the percentage viability of all strains began to increase due to the renewal of cell division.     

EFFECTS OF CO2 CONCENTRATION DURING GROWTH ON THE INTRACELLULAR STRUCTURE OF CHLORELLA AND SCENEDESMUS (CHLOROPHYTA)1

Effects of CO₂ concentration during growth on intracellular structure were studied with ftve species of Chlorella and Scenedesmus obliquus. Cells grown under ordinary air conditions (low-CO₂ cells) had a well developed pyrenoid surrounded by starch, while those grown under high CO₂ conditions (high-CO₂ cells) had a less developed pyrenoid or no detectable pyrenoid. Two mitochondria, one at each side of the neck of the projection of the chloroplast close to the pyrenoid, were found in low CO₂ cells of C. vulgaris 11h. Usually, lamellar stacks extended in parallel in the chloroplast of low-CO₂ cells of C. vulgaris 11h, while a grana-like structure was found in high-CO₂ cells. However, in C. pyrenoidosa, grana like structures were found more commonly in low-CO₂ cells than in high-CO₂ cells. These results suggest that development of pyrenoid starch is generally correlated with growth under low CO₂ conditions, whereas CO₂-effects on lamellar stacking are species dependent.     

CHANGES IN PLASTID AND MITOCHONDRION CONTENT DURING MATURATION OF GENERATIVE CELLS OF SOLANUM (SOLANACEAE)

A study was made of the number of plastids and mitochondria present in generative cells of Solanum immediately after microspore mitosis, and the fate of these organelles during development of the pollen was determined. Changes were followed via electron microscopy of anthers of S. chacoense and S. tuberosum Group Phureja × S. chacoense. In earliest stages the generative cells were oval and had one surface along the intine and other surfaces in contact with the vegetative cell. As the pollen matured the generative cells elongated, became spindle-shaped, and were completely engulfed in the vegetative cells. At the earliest stages studied, both mitochondria and plastids were present in the generative cell. Plastids of the generative cell were, in contrast to those of the vegetative cells, fewer, smaller, and lacking in starch. Through the maturation stages the content of these organelles in the vegetative cells remained unchanged. While the generative cells retained mitochondria until anthesis, their plastids disappeared completely during maturation. This selective loss during generative cell maturation could lead to transmission of those characteristics encoded in plastid DNA through the pistillate parent only. The mechanism could explain earlier genetic evidence that plastid characters of Solanum were transmitted uniparentally.     

PHASE-MICROSCOPIC OBSERVATIONS OF FUSIONS OF NUCLEI IN SOMATIC CELLS OF A HETEROKARYON OF SCHIZOPHYLLUM COMMUNE

Pairs of nuclei in apical cells of a common-B heterokaryon (A41 B41 + A2 B41) of Schizophyllum commune fused prior to the nuclear division. It is assumed that each fusion was followed by a reduction division. Five consecutive fusions and divisions in a single hypha were photographed in situ with a phase microscope. These fusions and reduction divisions are possibly related to the genetically determined phenomenon of somatic recombination as a part of the parasexual cycle in fungi.     

A REINTERPRETATION OF THE ONTOGENY OF THE ASCOCARP OF SPECIES OF THE ERYSIPHACEAE

A study of four species of Erysiphaceae (Uncinula salicis, Podosphaera leucotricha, Erysiphe cichoracearum, and Microsphaera diffusa) revealed that the binucleate stages of the ascocarp are initiated in a similar manner to those of Diporotheca rhizophila Gordon & Shaw. The “appendages” developing on immature ascocarps are considered to be receptive hyphae. Appendages characteristic of mature ascocarps are produced much later. Lysis of certain centrum cells occurs, and asci are initiated from some of the remaining binucleate centrum cells. Resorption of centrum cells by the asci is supported by this investigation, corroborating Björling's earlier studies on Erysiphe graminis.     

EXPRESSION AND EFFECTS OF MUTANT Bombyx mori ACETYLCHOLINESTRASE1 IN BmN CELLS

The main mechanism of toxicity of organophosphate (OP) and carbamate (CB) insecticides is their irreversible binding and inhibition of acetylcholinestrase (AChE), encoded by ace1 (acetylcholinestrase gene 1), leading to eventual death of insects. Mutations in AChE may significantly reduce insects susceptibility to these pesticides. Bombyx mori is an important beneficial insect, and no OP‐ or CB‐resistant strains have been generated. In this study, wild‐type ace1 (wace1) and mutant ace1 (mace1) were introduced into BmN cells, confirmed by screening and identification. The expression of wace1 and mace1 in the cells was confirmed by Western blot and their expression levels were about 21‐fold higher than the endogenous ace1 level. The activities of AChE in wace1 and mace1 transgenic cells were 10.6 and 20.2% higher compared to control cells, respectively. mace1 transgenic cells had higher remaining activity than wace1 transgenic cells under the treatment of physostigmine (a reversible cholinesterase inhibitor) and phoxim (an OP acaricide). The results showed that ace1 transgene can significantly improve ace1 expression, and ace1 mutation at a specific site can reduce the sensitivity to AChE inhibitors. Our study provides a new direction for the exploration of the relationship between AChE mutations and drug resistance.     

ACCUMULATION OF 203HG BY THE MARINE DIATOM CHAETOCEROS COSTATUM

Dividing and nondividing cell populations of Chaetoceros costatum Pavillard were placed in light; nondividing populations were also placed in the dark, and one population was killed by formalin. No difference in²⁰³Hg uptake was seen in nondividing cells in the light and dark, while cells accumulated about 2 times as much²⁰³Hg as living cells, presumably by surface adsorption. Dividing cells in light accumulated²⁰³Hg longer than did nondividing cells, indicating the possibility of some active uptake of Hg.     

RESPONSES OF FRESHWATER ALGAE TO INHIBITORY VANADIUM CONCENTRATIONS: THE ROLE OF PHOSPHORUS1

We found that species-specific differences exist among a variety of freshwater algae and cyanobacteria in the extent to which growth and photosynthesis are inhibited by vanadium. A major factor controlling the degree of inhibition by vanadium was the phosphorus state (P-sufficient vs. P-deficient) of the organisms. In P-sufficient cultures, vanadium was inhibitory when the vanadium concentration exceeded the phosphate concentration. In P-deficient cultures, the depression of photosynthesis by vanadium increased with increasing phosphorus deficiency. Our conclusion that vanadium competed with phosphate for uptake sites was supported by the following three observations: 1) the decreased influx of ³²P-PO ₄ into P-deficient cells in the presence of vanadium, 2) the amelioration of vanadium inhibition of photosynthesis by the addition of phosphate, and 3) the accumulation of vanadium by cells. At vanadium concentrations that severely inhibited growth, the cells of Scenedesmus obliquus (Turp.) Kruger were larger than normal and contained more vacuoles, lipid, and starch bodies than normal cells. Four-celled coenobia were replaced by unicells. Scenedesmus acutusf: alternans Hortobagyi cells from vanadium-inhibited cultures had 7.5 times more vanadium per cell than control cultures and contained numerous granules that did not stain for polyphosphate and may be composed of condensed vanadate molecules. The cellular P quota and turnover time of PO₄in the medium are important regulators of the extent of inhibition by vanadium.     

THE ACCLIMATIVE CHANGES IN PHOTOCHEMISTRY AFTER COLONY FORMATION OF THE CYANOBACTERIA MICROCYSTIS AERUGINOSA1

Microcystis aeruginosa (Kütz.) Kütz. commonly occurs as single cells at early recruitment but forms large colonies in summer. Colony formation will induce many acclimative changes. In this study, we demonstrated the photochemical changes before and after colony formation. In the laboratory, light curves showed that colonies were more responsive to high light than single cells. The values of the maximal slope of electron transport rate (ETR)—light curve (α), relative maximal electron transport rate (rETR_max), and onset of light saturation (I_k) of colonies were significantly higher than those of single cells (P < 0.05), indicating that colonies have higher photosynthetic capability than single cells, especially in high light, where values of rETR_max and I_k of colonies were 2.32 and 2.41 times those of single cells. Moreover, the dark‐light experiments showed that colonial cells can more effectively resist darkness damage. In addition, pigments of colonial cells were higher than those of single cells (P < 0.05). The higher pigment contents probably contribute to higher photosynthetic capability. In the field, the inhibition rate of F_v/F_m in single cells increased significantly faster than that of colonies as light increased (P < 0.05), but nonphotochemical quenching (NPQ) value of colonies was higher (32.4%) than that of single cells at noon, which indicated colonial cells can more effectively resist high‐light inhibition than single cells (P < 0.05). Polysaccharides of colonies were significantly higher compared to those in unicellular cells (P < 0.05) based on their contents and ultrastructural characteristics. This finding implies that colonies could not effectively decrease photoinhibition by negative buoyancy regulation. In fact, NPQ may be an important mechanism for avoiding photodamage. All of these phenomena can help explain the ecological success of colonial M. aeruginosa in eutrophic water.     

PHYSIOLOGICAL IMPLICATIONS OF VICIA FABA AND NICOTIANA TABACUM GUARD-CELL ULTRASTRUCTURE

The guard cells of Vicia faba and Nicotiana tabacum contain numerous mitochondria, elements of endoplasmic reticulum, spherosomes, and peroxisome-like microbodies. A full ribosomal complement appears in young but not in fully mature guard cells. Numerous small lipid droplets external to the plasmalemma were noted in mature Vicia guard cells. Chloroplasts were found in both epidermal and guard cells of both species. Full photosynthetic capacity was indicated by the grana fretwork of guard-cell chloroplasts. A specialized peripheral reticulum was observed in the guard-cell chloroplasts of Vicia. Plasmodesmata were observed in both walls between sister guard cells and between guard and epidermal cells. In the latter case plasmodesmata were found primarily in pit fields of transverse walls. It is postulated that the small volume of guard cells allows them an osmotic advantage over larger neighboring cells in generating turgor.     

EVALUATION OF THE SPECIFICITY OF A LYMPHOID CHALONE

An extract from calf spleens, injected into mice, was found to inhibit their lymphocyte proliferative response to PHA-M and PWM in vitro. Despite the ability of the spleen extract to inhibit the response of lymphocytes to stimuli in vitro, no effect was observed on the repopulation of lymphocytes in the peripheral blood of sublethally irradiated mice. The data suggest that the spleen extract acts as a specific inhibitor of the immune competent cells since neither the precursors of lymphocytes nor other haematopoietic cells were affected.