Ultrastructural Changes During Encystment of Schizopyrenus russelli*

Ultrastructural changes associated with the encystment of Schizopyrenus russelli have been studied by electron microscopy. Before encystment small “black bodies” appear in the cytoplasm and later migrate toward the periphery. The outer cyst wall is secreted at this stage as a thin discontinuous layer which thickens and subsequently becomes continuous. Concomitant with this, the endoplasmic reticulum surrounds the mitochondria. The inner cyst wall later appears as a multilayered structure which presumably is cast off from the plasma membrane. Between the inner and outer layers of the cyst wall, there is a middle, less electron-dense layer wherein extruded cytoplasmic material is found embedded at certain places.     

Role of Riboflavin and Certain Amino Acids in the Excystment of Schizopyrenus russelli*

SYNOPSIS. A simple medium, consisting of riboflavin and a mixture of L-glutamic acid, L-tryptophan, L-isoleucine, L-serine, and L-proline has been shown to induce rapid and mass scale excystment in Schizopyrenus russelli. Whereas percentage excystment was found to depend on the concentration of riboflavin and amino acids, more than 80% of cysts were found to excyst within 4 hr, when adequate amounts of these were supplied. Several individual amino acids, particularly L-glutamic acid, L-tryptophan, and L-proline, also supported considerable excystment, but riboflavin was always indispensable.     

Correlation of encystment and division in Schizopyrenus russelli.

Schizopyrenus russelli, a free-living soil ameba, grows and encysts in the presence of bacteria. The encystment occurs with decline in the division rate. This is accompanied by incorporation of [U-14C] glucose into cyst cellulose. The degree of multiplication (but not of encystment) is a function of bacterial concentration. Berenil, a trypanocidal drug, while allowing excystment, completely inhibited multiplication of emerged amebae and their encystment. Addition of this drug after 24 hr, when amebae had gone into a phase of active division failed to check encystment, although it still inhibited further multiplication of the amebae. The findings suggest that a phase of cell division may be a prerequisite for encystment.     

Isolation,Structure and Composition of Cyst Wall of Schizopyrenus russelli*

SYNOPSIS. A procedure is described for the isolation of cyst wall of Schizopyrenus russelli free of cytoplasmic material. It has 27.3% protein, 37.5% carbohydrate (of which 13.1% is cellulose), and 15.1% lipids. Sialic acid is absent. It has a relatively electrondense inner thick layer and a less electron-dense outer thin layer. The space between the 2 layers is 25 nm in younger cysts and 2.5 μ in fully mature cysts. This space is filled with a fibrillar spongy material likely to be cellulose.     

Action of Ultraviolet Radiation on Excystment and Concomitant Macromolecular Syntheses in Schizopyrenus russelli*

SYNOPSIS. Excystment of Schizopyrenus russelli was associated with increase in DNA, RNA, and protein. Both excystment and these macromolecular increases were sensitive to ultraviolet radiation. The effect of UV was partly reversed by incubation in the dark at 28 C, but not at 4 C. Excystment from cysts preincubated in the excystment medium (before UV treatment) was relatively resistant to radiation.     

花生叶片衰老过程中某些酶活性的变化

人们对花生叶片衰老的现象早就有所认识 ,认为叶片变黄脱落、叶斑病加重是花生叶片衰老的主要特征 ,但真正对花生叶片衰老的研究较少且意见不一。Ｋｖｉｅｎ和Ｏｚｉａｓ Ａｋｉｎｓ( 1 991 )认为花生播后1 46ｄ(饱果期 )叶片仍未表现衰老迹象 ,叶中Ｎ含量仍保持 2 8ｍｇ/ｇ的较高水平 ;Ｓａｈｒａｗａｔ等 ( 1 987)研究发现 ,随着花生叶片的衰老 ,叶片中Ｎ、Ｐ、Ｋ、Ｃｕ、Ｍｎ、Ｚｎ的含量逐渐降低 ,而叶片中Ｍｇ的含量有增加趋势 ,Ｃａ的含量随衰老明显升高。Ｎａｒａｙａｎａｎ和Ｃｈａｎｄ( 1 986)研究指出 ,花生主茎上、下叶片叶比重 …     

Changes in Some Enzyme Activities during Growth and Organogenesis in Dark-Grown Tobacco Callus Cultures

Enzymes involved in malate metabolism, viz., glutamic-oxalacetictransaminase, malate dehydrogenase, malic enzyme and phosphoenolpyruvatecarboxylase, had severalfold higher specific activities in organ-formingcallus cultures of tobacco compared to non-organ-forming cultures.These activities increased considerably during the days precedingshoot and root differentiation. While malate accumulated untilday 15 in non-organ-forming callus, it accumulated up to day6 in shoot-and root-forming callus. Total and reducing sugarsaccumulated until day 3 and declined thereafter in all the cultures.Thus, tobacco callus may utilize this pathway for deriving reducingpower which is required for organogenetic processes. (Received April 30, 1987; Accepted December 1, 1987)     

Changes of Some Mitochondrial Enzyme Activities of Cucumber Leaves during Ammonium Toxicity

The following enzyme activities were determined in the mitochondria of cucumber leaves (Cucumis sativus L. cv. Suisei No. 2) during ammonium toxicity: malate dehydrogenase, succinate dehydrogenase, glutamate dehydrogenase, cytochrome c oxidase, NADH diaphorase, NADH oxidase, succinate: cytochrome c oxidoreductase, NADH: cytochrome c oxidoreductase and adenosine triphosphatase. The activities of all enzymes except ATPase increased more or less during ammonium toxicity. Generally speaking the marked increase was found at 7 days treatment with 200 mg/1 NH₃-N. The adenosine triphosphatase activity of injured plants was lower than that of normal plants through treatment. The addition of various organic acids (15 mM) to the culture solution contaning 200 mg/1 NH₃-N (14.3 mM NH₄Cl) suppressed the ammonium toxicity. The accumulation of free ammonia in the leaves was also repressed by the addition of organic acids. The results of present and previous reports suggest that the increase of respiratory metabolism due to ammonium toxicity is required for the supply of organic acids, specially δ-ketoglutaric acid, to counteract ammonia. Uncoupling in mitochondria resulting in the increase of respiration does not seem to occur during ammonium toxicity.     

Changes in Some Enzyme Activities and Respiration in the Early Stage of Callus Formation in a Carrot-root Tissue Culture

The respiratory rate increased in two phases during early stages of callus formation in carrot (Daucus carota)-root phloem slices cultured in vitro, showing separate peaks at about 24 and 96 h of culture. In the first phase (within 24 h of culture), the activities of phosphoglucose isomerase, phosphofructokinase and succinate dehydrogenase did not increase, but active syntheses of RNA and protein, indicated by experiments with incorporation of [¹⁴C]-uracil and -leucine, resulted in an active turnover of ATP, to which the first increase in the respiratory rate may be attributable. On the other hand, the activity of phosphoribosylpyrophosphate synthetase, an enzyme related to nucleic acid synthesis, increased in the first 24 h of culture. In the second phase (24–96 h of culture), the activities of the respiratory enzymes investigated increased. This increase was repressed by cycloheximide, indicating de novo syntheses of the respiratory enzymes during this time, which may result in an enlargement of the respiratory capacity, to which the second increase in respiration may be mainly attributable. In the first phase, exogenous supplied 2,4-dichlorophenoxyacetic acid had little or no effect on the respiratory rate and the activities of the respiratory enzymes, but it enhanced synthesis of RNA and the activity of phosphoribosylpyrophosphate synthetase. In the second phase, it increased all the activities of enzymes investigated as well as the respiratory rate and RNA synthesis.     

Some Enzyme Activities in the Testate Amoeba Netzelia tuberculata1

ABSTRACT. Testate amoebae occur in diverse environments including well aerated streams and anoxic bottom sediments. They consume a wide variety of food including algal prey, bacteria, and detritus. Since little is known about the physiological ecology of many of these widespread organisms, some respiratory and digestive enzyme activities were assessed using Netzelia tuberculata, which is readily cultivated in the laboratory. Activities, expressed as units/μg protein are as follows: acid aryl phosphatase, 19.0 × 10^?1; acid protease, 26 × 10^?3; cytochrome oxidase, 2.3 × 10^?4; and lactate dehydrogenase, 3.6 × 10^?4. No amylase was detected in these specimens, which may help to explain why starch grains, apparently consumed from algal prey, are expelled from the cytoplasm and used as wall-construction particles.