Nitrogen delivery to maize via mycorrhizal hyphae depends on the form of N supplied

Arbuscular mycorrhizal fungi can enhance nutrient acquisition by a plant via their extraradical hyphae. This is particularly true for phosphorus, but the case for nitrogen (N) has been less clear. In our growth systems there was a small air-gap between root and hyphal compartments, which eliminated diffusion of nutrients between compartments. Moreover, our methods allowed us to distinguish between nitrate and ammonium. We found that N transfer to Zea maize L. depends on the sources fed to the hyphae of Glomus aggregatum Schenck & Smith. In experiment 1, despite the fact that plant demand for N was already met, plants received 10 times as much ¹⁵N from ammonium than from nitrate. In experiment 2, 74% of shoot-N was derived from the slow-release urea added to the hyphal compartment while only 2.9% was derived from the nitrate-N. Intraradical hyphae isolated from roots contained a considerable amount of ¹⁵N in the cell wall even when ¹⁵N-nitrate was the source. We conclude that the mycorrhizal fungus can rapidly deliver ammonium-N to the plants, and that while the fungus can absorb nitrate, it apparently lacks the capacity to transfer it to the plant.     

Ultrastructural Changes of the "Truncated Cone" during the Acrosome Reaction in Japanese Abalone Spermatozoa

An electron-dense structure termed the "truncated cone" covers the apical surface of the acrosomal contents except for the trigger region in Haliotis discus spermatozoa. The truncated cone, having a slant height of 0.3 μm and diameters of circular top and base of 0.3 and 0.6 μm, shows striations with a periodicity of 6.6 to 8.0 nm. During the acrosome reaction, the truncated cone elongates simultaneously with the protrusion of the acrosomal process through the truncated cone. As the growth of the acrosomal process further proceeds, the truncated cone transforms into a cylindrical shape and eventually reaches 1 μm in length and 0.2 μm in diameter. The elongated truncated cone is characterized by regularlly helical striations with a periodicity of 19 to 21 nm with an inclination of 40° to 46°. These results may suggest that the truncated cone is composed of coiled filaments, which coil up further during the acrosome reaction causing the truncated cone to slenderize and elongate. The elongation is also achieved by stretching of the coil. In H. discus hannai Ino, structural changes in the truncated cone show close homology to those in H. discus. No such morphologically unique organelle has been found in other species thus far.     

STUDIES ON CHLOROPHYLLASE OF CHLORELLA PROTOTHECOIDESI. ENZYMATIC PHYTYLATION OF METHYL CHLOROPHYLLIDE

1. The relation between chlorophyll content and the hydrolyticactivity of chlorophyllase in Chlorella protothecoides was examined.An increase in the activity was parallel to that in chlorophyllcontent during the development of green colouration, or greeningcourse, in the bleached cells. The activity sharply declinedand a parallel disappearance of chlorophyll was also found duringbleaching of the green cells.
2. A partially purified water-solublepreparation of chlorophyllasewas obtained by n-butanol treatmentand fractionation with coldacetone. It showed high activityand hydrolyzed 2 mg chlorophylla per hr per mg protein.
3. Forseparation and identification of the pigments concernedin thechlorophyllase reaction, a new solvent system of paperchromatographywas introduced.
4. When methyl chlorophyllide a and phytol wereincubated withthe enzyme, two products were formed. By comparisonwith theRf values of isolated pure substances, one was identifiedaschorophyll a and the other as chlorophyllide a. This enzymedid not catalyze the phytylation of free chlorophyllide a, butit had the ability to attach phytol to methyl chlorophyllidea. The final step in the biosynthesis of chlorophyll a is brieflydiscussed.

¹ Contribution No. 158 from the Department of Biology, Facultyof Science, Kyushu University. Supported in part by a grant-in-aidfor Fundamental Scientific Research from the Ministry of Education.     

Effects of an experimental drought and recovery on soil emissions of carbon dioxide,methane, nitrous oxide,and nitric oxide in a moist tropical forest

Changes in precipitation in the Amazon Basin resulting from regional deforestation, global warming, and El Niño events may affect emissions of carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and nitric oxide (NO) from soils. Changes in soil emissions of radiatively important gases could have feedback implications for regional and global climate. Here, we report the final results of a 5‐year, large‐scale (1 ha) throughfall exclusion experiment, followed by 1 year of recovery with natural throughfall, conducted in a mature evergreen forest near Santarém, Brazil. The exclusion manipulation lowered annual N₂O emissions in four out of five treatment years (a natural drought year being the exception), and then recovered during the first year after the drought treatment stopped. Similarly, consumption of atmospheric CH₄ increased under drought treatment, except during a natural drought year, and it also recovered to pretreatment values during the first year that natural throughfall was permitted back on the plot. No treatment effect was detected for NO emissions during the first 3 treatment years, but NO emissions increased in the fourth year under the extremely dry conditions of the exclusion plot during a natural drought. Surprisingly, there was no treatment effect on soil CO₂ efflux in any year. The drought treatment provoked significant tree mortality and reduced the allocation of C to stems, but allocation of C to foliage and roots were less affected. Taken together, these results suggest that the dominant effect of throughfall exclusion on soil processes during this 6‐year period was on soil aeration conditions that transiently affected CH₄, N₂O, and NO production and consumption.     

Clinical,Pathological, and Etiologic Aspects of Acquired Dermal Melanocytosis

To study the pathogenesis of acquired dermal melanocytosis (ADM), we reviewed the clinical, immunohistochemical, and ultrastructual features of 34 cases (female, 33, and male, 1) of ADM. The patients’ ages at onset ranged from 8 to 51 years and averaged 26.8+12.7 years. There was a positive family history. Gray-brown macules were mostly recognized on the face. Not only active dermal melanocytes but also non-pigmented c-KIT-and TRP-2-positive immature melanocytes were detected in the dermis. Taken together those clinical and histological findings, activation of pre-existing immature melanocytes by sunlight, estrogen, and/or progesterone, and some other factors, may be the most likely mode of the development of ADM. Moreover, using cultured murine neural crest cells as a model of c-KIT-positive immature melanocytes, we confirmed that endothelin-1, which is produced and secreted by keratinocytes after UV-irradiation, affects melanocytes and accelerated melanogenesis.     

Ultrastructural Study of Schizogony of Eimeria bovis in Cell Cultures*

SYNOPSIS. First-generation schizogony of Eimeria bovis in bovine cell culture was studied by electron microscopy. The intracellular sporozoite retained its structure for at least 6 days at which time it rounded up and lost its apical complex. Although the refractile body underwent certain morphologic changes, it was retained throughout the parasite's growth. The beginning of mitosis was marked by the formation of a cytoplasmic funnel which traversed the nucleus opening on each side toward a pair of centrioles. Subsequently, there developed an intranuclear spindle. Separation of the daughter nuclei was preceded by the formation of typical centrocones. Differentiation of merozoites was accomplished by exogenesis during the last mitotic division. A dense fiber, interpreted as a link connecting the merozoite anlage with its nucleus, extended from the developing apical complex to the nearest division pole. In the anlage, the inner membrane complex was at first composed of patches associated with pairs of subpellicular microtubules. Rhoptries appeared early in merogenesis, whereas micronemes formed at the time the merozoites detached from the residuum. The level of amylopectin, low in schizonts, rose at the beginning of merozoite formation.     

Permanent bleaching of Euglena by chloramphenicol

Chloramphenicol produced permanently bleached cells in darkgrown, but not in light grown cultures of Euglena gracilis.The bleaching was presumably based not on alteration of thegenetic information site of chloroplasts, but on interferencewith the replication of proplastids where protein synthesiswas restricted. (Received September 14, 1968; )     

Insertion and withdrawal of extremely elongated genitalia: a simple mechanism with a highly modified morphology in the leaf beetle,Lema coronata

Complicated genital structures are widely known in many animals. It is assumed that an increasing morphological complexity of genital structures would also increase the difficulty of inserting and withdrawing the structures. We examined the insertion and withdrawal mechanisms of extremely elongated genitalia in the Japanese leaf beetle, Lema (Lema) coronata. Insertion and withdrawal processes are completed quickly. Investigation of genital morphology showed that there are no protractor or retractor muscles attached to the elongated part. Instead, the elongated part is tightly enveloped by a membrane. Because of the close fit between the elongated part and its surrounding membrane, eversion of the membrane allows for insertion of the elongated part, and retraction of the membrane induces withdrawal of the elongated part. This surrounding membrane makes it possible to store the median ejaculatory guide (MEG) in a small genital cavity, with the basal portion of the elongated part extending internally against the entrance. This unusual character state is observed only in members of the subgenus Lema, which also have the elongated part. This condition can be considered to be a preadaptation for extreme elongation of genitalia. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 512–520.