Kit W. Lee

Infection of a chlorella-like alga with the virus, PBCV-1: Ultrastructural studies☆

Ultrastructural studies revealed that the virus, PBCV-1, adsorbs to the surface of the Chlorella-like green alga NC64A and enzymatically digests a portion of the host cell wall. The viral DNA is then released into the interior of the cell leaving an empty capsid on the surface. Thus uncoating of the viral genome occurs at the surface of its host. PBCV-1 also adsorbs to and digests the host wall of either heat-killed, methanol-extracted, or purified cell wall fragments.

C3-C4 intermediate species in the genus Flaveria: leaf anatomy, ultrastructure, and the effect of O2 on the CO2 compensation concentration

Leaf anatomical, ultrastructural, and CO2-exchange analyses of three closely related species of Flaveria indicate that they are C3−C4 intermediate plants. The leaf mesophyll of F. floridana J.R. Johnston, F. linearis Lag., and F. chloraefolia A. Gray is typical of that in dicotyledonous C3 plants, but the bundle sheath cells contain granal, starch-containing chloroplasts. In F. floridana and F. chloraefolia, the chloroplasts and numerous associated mitochondria are arranged largely centripetally, as in the closely related C4 species, F. brownii A.M. Powell. In F. linearis, fewer mitochondria are present and the chloroplasts are more evenly distributed throughout the bundle sheath cytosol. There is no correlation between the bundle sheath ultrastructure and CO2 compensation concentration. (Γ) values of these C3−C4 intermediate Flaveria species. At 21% O2 and 25°C, Γ for F. chloraefolia, F. linearis, and F. floridana is 23–26, 14–19, and 8–10 μl CO2 l-1, respectively. The O2 dependence of Γ is the greatest for F. chloraefolia and F. linearis (similar to that for C3−C4 intermediate Panicum and Moricandia species) and the least for F. floridana, whose O2 response is identical to that for F. brownii from 1.5 to 21% O2, but greater at higher pO2. The variation in leaf anatomy, bundle sheath ultrastructure, and O2 dependence of Γ among these Flaveria species may indicate an active evolution in the pathway of photosynthetic carbon metabolism within this genus.

Assembly site of the virus PBCV-1 in a Chlorella-like green alga: ultrastructural studies

Abstract Ultrastructural studies revealed that PBCV-1 capsid assembly and DNA packaging occur in distinct regions in the cytoplasm of the host Chlorella -like green alga.

Anatomical, ultrastructural and enzymic studies of leaves of Moricandia arvensis, a C3-C4 intermediate species

Abstract The possibility that reduced photorespiration in the crucifer Moricandia arvensis is due to a limited C4-photosynthesis system similar to that in the C3-C4 intermediate Panicum milioides (Rathnam, C.K.M. and Chollet, R. (1979) Biochim. Biophys. Acta 548, 500−519) was investigated. The anatomical, physiological and biochemical features of this crucifer which are similar to those of P. milioides are: (a) the presence of prominent leaf vascular bundle sheaths which contain numerous, centripetally arranged chloroplasts and mitochondria; (b) a CO2 compensation concentration of 16 ± 3 μl/l at 21% O2 and 25°C; (c) a C3-type phosphoenolpyruvate carboxylase exhibiting a maximal velocity which is 2–3-times that of the enzyme from C3 plants; and (d) aspartate and alanine aminotransferase activities which are 2–3-fold higher than in a representative C3 species. However, M. arvensis differs from the C3-C4 intermediate Panicum species in that the activities of the three known C4 acid decarboxylating enzymes present in leaves of C4 plants (NAD- and NADP-malic enzymes and phosphoenolpyruvate carboxykinase) and pyruvate, orthophosphate dikinase (a key C4-related enzyme) are low or undetectable. From these comparative results we conclude that the mechanism by which photorespiration is reduced in M. arvensis is qualitatively different from the limited C4-like CO2-concentrating system operating in P. milioides.

Viral infection of the symbiotic chlorella-like alga present in Hydra viridis☆

Attempts to culture the Chlorella-like green alga found in a symbiotic association with the Florida strain of a green hydra, Hydra viridis, have been unsuccessful. Ultrastructural studies of the algae isolated from the host revealed that large (185 nm in diameter) viral particles appeared in the nuclear region of the algae 2 to 6 hr after their isolation from the hydra. By 12-20 hr, the entire population of algae was lysed. The source of the virus is unknown since it has not been detected in thin sections of intact hydra or in algal cells immediately after their isolation. The virus attached to the algal cell wall in a manner reminiscent of many bacteriophage infections. Attempts to infect three other culture-grown Chlorella strains with crude lysates or purified viral particles have been unsuccessful.

Structure and function of the photoreceptor stentorins in Stentor coeruleus. I. Partial characterization of the photoreceptor organelle and stentorins

The unicellular ciliary protozoan, Stentor coeruleus, exhibits photophobic and phototactic responses to visible light stimuli. The pigment granule contains the photoreceptor chromoproteins (stentorins). Stentorin localized in the pigment granules of the cell serves as the primary photoreceptor for the photophobic and phototactic responses in this organism. An initial characterization of the pigment granules has been described in terms of size, absorbance spectra and ATPase activity. Two forms of the stentorin pigments have been isolated from the pigment granules. Stentorin I has an apparent molecular weight of 68,600 and 52,000 by SDS-PAGE (at 10 and 13% gel, respectively) or 102,000 by steric exclusion HPLC, whereas stentorin II is a larger molecular assembly probably composed of several proteins (mol. wt. greater than 500,000). Stentorin I is composed of at least two heterologous subunits corresponding to apparent mol. wts. of 46,000 (fluorescent, Coomassie blue negative) and 52,000 (fluorescent, Coomassie blue positive) on SDS-PAGE (13% gel). However, these values were found to be strongly dependent on the degree of crosslinking in the acrylamide gel. Stentorin II appears to be the primary photoreceptor whose absorption and fluorescence properties are consistent with the action spectra for the photoresponses of the ciliate to visible light.

CHANGES IN THE ULTRASTRUCTURE OF SYMBIOTIC ZOOXANTHELLAE (SYMBIODINIUM SP., DINOPHYCEAE) IN FED AND STARVED SEA ANEMONES MAINTAINED UNDER HIGH AND LOW LIGHT1

The ultrastructure of symbiotic dinoflagellates (Symbiodinium sp., zooxanthellae) in the sea anemone Aiptasia pallida Verrill was examined in well‐fed or starved (up to 120 days) anemones maintained under two light levels (5 and 50 μmol · m−2· s−1). Cell size of zooxanthellae was not affected by feeding history; however, both light and feeding history affected the relative cell volume of chloroplasts, lipids, and vacuoles. Stereological analysis of transmission electron micrographs showed that algae in low‐light starved anemones had 10 times as much lipid (17.4% of cell volume) as those in well‐fed anemones under the same light conditions (1.8%). The lipid content of algae from anemones in high light increased from 15.4% in well‐fed anemones to 30.1% in starved anemones. The starch content of zooxanthellae in low‐light anemones was law (4.1%) and not affected by feeding history, while the starch content of zooxanthellae in high‐light anemones was greater (10.7%), with some differences among groups. Algal photoacclimation to low light included an increase in chloroplast relative volume from 17% (in well‐fed high‐light anemones) to 33% in well‐fed low‐light anemones. Starvation of the host resulted in a significant decrease in chloroplast volume in zooxanthellae in anemones at both light levels. Morphometry provides quantitative confirmation of biochemical and physiological data on zooxanthellae, because the changes in zooxanthellae with starvation of the host are consistent with other indicators of nutrient limitation of zooxanthellae of A. pallida held without food for long periods of time.

Soybean root nodule ultrastructure during dark-induced stress and recovery

SummaryRoot-nodules of soybean plants dark-stressed for 8 days and then allowed to recover for up to 17 days were examined by transmission electron microscopy. Control nodules possessed all the ultrastructural features characteristic of infected and uninfected nodule cells. Minimal changes in the appearance of host cells and bacteroids occurred during the first four days of dark stress. After 8 days of dark stress, damage was observed in the cellular and organelle membranes; however, very few changes were observed in the bacteroids. Nodule structure continued to degrade during the first two days of recovery after which time nodules either recovered or completely degraded. In the former case, structural integrity returned to all nodule cells. In the latter case all structural integrity of the host cell disappeared; however, bacteroids appeared intact suggesting that they remained viable.

CRYPTOGLENA PIGRA: A EUGLENOID WITH ONE CHLOROPLAST12

The taxonomic status of Cryptoglena pigra Ehrb., interpreted from observations based on bright‐field microscopy, has been uncertain. Examination with the electron microscope of a clone of C pigra isolated by E. G. Pringsheim reveals certain features which, collectively, are distinctly euglenoid: periplast associated with muciferous bodies and subpellicular microtubules; canal and reservoir with microtubules; one flagellum with a swelling and emergent through a canal, and a second flagellum without a swelling and nonremergent; stigma (eyetpot) closely apprrssed to but not part of the chloroplast; nucleus with permanently condensed chromosomes attached to the inner nuclrar membrane; mitochondria with disc‐shaped cristae constricted at the base; chloroplast with thylakoids often in triplets; and paramylon grains in the cytoplasm. Unlike most euglenoids, C. pigra possesses a single chloroplast that in transverse thin sections is U‐shaped.

Influence of cereal leaf epicuticular wax on Diuraphis noxia probing behavior and nymphoposition

The effect of cereal leaf surface wax on Diuraphis noxia (Mordvilko), the Russian wheat aphid, probing behavior and nymphoposition was evaluated. Ultrastructure of leaf epicuticular wax from wheat (Triticum aestivum L.) c.v. ‘Arapahoe’ and ‘Halt’ was different from barley (Hordeum vulgare L.) c.v. ‘Morex’, and oat (Avena sativa L.) c.v. ‘Border’. Both wheat cultivars had similar rod‐shaped epicuticular wax, while barley and oat plants had flakes. The chemical composition comparison of gas chromatograms also indicated that the extract of the two wheat cultivars had similar pattern of peaks, while the barley and oat leaves had similar peaks. Cereal variety significantly affected aphid probing behavior (P < 0.05), but wax removal using ethyl ether swab did not (P > 0.05). Aphids initiated significantly more probes on Border oat leaves than on Morex barley irrespective of wax removal, although total probing duration per aphid was not significantly different among the four cereals examined. Accumulative salivation duration per aphid on oat leaves with wax was significantly longer than other cereal leaves with wax, while accumulative ingestion duration per aphid on Arapahoe wheat and Morex barley was significantly longer than on oat. Nymphoposition of D. noxia on cereal leaves maintained on the benzimidazole‐agar medium showed that aphids produced a greater number of nymphs on Morex barley and less on Border oat leaves, although wax removal did not affect aphid nymphoposition. Removal of leaf epicuticular waxes from the 4 cereal genotypes using ethyl ether swab indicated that the influence of wax on plant resistance to D. noxia probing and reproduction was limited. Morex barley was the most favorable, while Border oat was the least favorable cereal host of D. noxia.