ELECTRON MICROSCOPIC OBSERVATIONS ON THE EXTRA-GRANULAR ZONE OF THE EMBRYO OF THE SEA URCHIN,HEMICENTROTUS PULCHERRIMUS*

“Extra-granular zone” proposed by Dan and Dan (3) was studied with the electron microscope. Two stages are noticed during the process of its formation; at first, a relatively yolk granule-free zone constitutes the egg periphery which should correspond to that observed by Dan and Dan , and later, this zone is occupied by a layer of the vacuoles (about 1.3 μm in mean diameter) with highly electron-transparent inclusions which migrated to the egg surface from the inner cytoplasm after fertilization. These vacuoles are scarcely found in the micromeres of 16-cell stage embryo.     

MARKED DECREASE IN THE RIGIDITY OF STARFISH OOCYTES INDUCED BY 1-METHYLADENINE1

Extreme rigidity of immature starfish oocytes as measured by compression method was found to decline during the early phase of their maturation when induced by 1-methyladenine (1-MeAde). The onset of this decrease in stiffness occurred within 5 to 9 min of 1-MeAde treatment, well before the breakdown of the germinal vesicle, progressively declining to reach a minimum stiffness after 20 min. Dithiothreitol, known as an artificial maturation-inducing agent, caused a similar change. The stiffness is thus expected to serve as a quantitative indicator of the early process of cytoplasmic events, which would induce the breakdown of the germinal vesicle. Cytochalasin B (3 μg/ml) also reduced the stiffness, but unlike the former two agents, the effect was reversible, and did not interfere with the process of maturation. Due to the effect of cytochalasin B, it became possible to enucleate immature oocytes by centrifugal force. Non-nucleate fragments thus obtained still maintained their marked stiffness, which was decreased by the action of 1-MeAde, with a time-course similar to that of intact oocytes.     

EFFECT OF MANGANESE IONS ON THE IAA-INDUCED ELONGATION OF AVENA COLEOPTILE SECTIONS INHIBITED BY SOME ORGANIC ACIDS

1.Organic acids, such as citric, -ketoglutaric, succinic, fumaricand L-malic acids, inhibit the IAA-induced growth of Avena coleoptilesections. But pyruvic acid has no effect on the growth. 2.High concentrations of MnCl₂ (for example 10^–3 m) alleviatethe inhibition due to L-malic, -ketoglutaric, succinic and fumaricacids, but not that due to D-malic, tartaric and malonic acids. 3.A mechanism of the alleviating effect of Mn⁺⁺ on the inhibitiondue to the organic acids is discussed with the reference tothe activating effect of Mn⁺⁺ on "malic" enzyme. ¹Contribution No. 6 from the Botanical Gardens. Faculty of Science,University of Tokyo, Koishikawa, Tokyo.     

铅锌矿区土壤和植物重金属污染调查分析

对有色金属矿区土壤和植物重金属污染状况调查结果表明,由于遭受尾矿砂及矿毒水污染,矿区土壤极端贫瘠,土壤中Pb、Cd、Zn和Cu含量分别达764.74、4.10、372.75和95.57 mg.kg-1,重金属污染较为严重。在矿区周边有9种优势植物能够在污染土壤上定居,对Cu、Cd、Pb和Zn 4种重金属元素均有不同程度的积累,积累量均未达到超累积植物所规定的临界含量。其中的野菊花〔Dendranthema indicum(L.)Des Mou l.〕、旋鳞莎草〔Cyperusm ichelianus(L.)L ink〕、五节芒〔M iscanthus floridulus(Lab ill.)W arb.ex Schum.et Laut.〕3种植物地上部生物量较大且对某些重金属向地上部转运能力较强,对重金属污染土壤有一定的修复潜力。     

MORPHOLOGICAL OBSERVATIONS ON THE SPERMATOZOA OF ECHINOTHURID SEA URCHINS*

The morphology of the spermatozoa of three species of echinothurid sea urchins, Asthenosoma ijimai, Araeosoma owstoni, Hapalosoma gemmiferum, was investigated by means of transmission and scanning electron microscopy. The spermatozoa of these three species of echinothurid sea urchins have similar fine structure, but they differ in several features from the more familiar regular sea urchins. 1) The external anatomy of the head region of the echinothurid spermatozoon is diagnostic in that it has a highly elongated head. 2) The spermatozoon of echinothurid sea urchins has a very long slender nucleus, protruding on its proximal end, so that the shape of the nucleus resembles a sperhead. 3) The acrosomal granule in the acrosomal vesicle of the echinothurid spermatozoon is not a mass of homogenous particulate material but an electron opaque rod condensed in the central part of the acrosomal vesicle. Scanning electron microscopic examination revealed that echinothurid spermatozoa form acrosomal processes similar to those of other regular sea urchins. 4) The basal body is situated just beneath the middle of the posterior protrusion of the nucleus. The distal centriole is located beside the basal body almost in contact with it. The axis of the distal centriole is almost but not quite parallel to that of the basal body. A satellite complex can be recognized around the posterior part of the proximal centriole.     

Increases in Nuclear DNA Content without Mitosis in Benzyladenine-treated Primary Leaves of Intact and Decapitated Bean Plants

Primary leaves of intact bean plants (Phaseolus vulgaris L.cv. Yamashiro-kurosando-saito) were treated with benzyladenine(BA) beginning on the seventh day after sowing when cell proliferationin the leaves had finished. Nuclear DNA contents were measuredby cytofluorometry combined with 4',6-diamidino-2-phenylindole(DAPI) staining. In the untreated controls, most mesophyll andabaxial epidermal cells contained a nucleus whose DNA contentwas 2C; whereas most adaxial epidermal cells contained a 4Cnucleus. Benzyladenine treatment induced 4C nuclec in mesophylland abaxial epidermal cells; but BA induced 8C nuclei in adaxialepidermal cells. To compare the effects of endogenous cytokininaccumulation, bean plants were decapitated above the primaryleaves on day 7 and continually disbudded thereafter. Changesin the nuclear DNA content in primary leaves attached to thedecapitated plants was similar to that for BA-treated primaryleaves. No multinucleate cells were formed and no mitotic figureswere present in the BA-treated leaves or in the primary leavesof decapitated plants. Our results indicate that both BA treatmentand decapitation induced one round of nuclear DNA synthesiswithout mitosis in a large number of mesophyll and epidermalcells.