Toshiyuki Miura

Lipofuscin and lipofuscin-like substances

Lipofuscin is defined as being a yellowish brown, lipid-rich, heterogeneous, cytoplasmic granular pigment emitting an intense yellow autofluorescence when excited with ultraviolet light, which accumulates in various tissues of animals during their aging. It is believed that the pigments are derived from the reaction of some of reactive secondary products including malonaldehyde, formed during membranous lipid peroxidation, with amino groups of phospholipids and proteins, etc., and that these formations are accompanied by alteration of the membrane structure and inactivation of the enzymes. The fluorescence measurement of the pigments is widely used as a parameter of lipid peroxidation in vivo as well as in vitro. However, their origin, chemical structure, biological significance or fate has not as yet been fully elucidated. This article introduces and discusses the recent studies on these problems.

Elevation of thiobarbituric acid values in the rat liver intoxicated by T-2 toxin

In the present study we first demonstrated that T-2 toxin markedly stimulated lipid peroxidation specifically in the liver of rats. The amount of lipid peroxides in the liver, estimated by the thiobarbituric acid (TBA) method, increased dose dependently, being proportional to the extent of its acute toxicity measured by various parameters in rats fed a commercial diet. Further, to elucidate the mechanism of lipid peroxidation and its role in hepatic injury caused by T-2 toxin, time-course studies on the correlation between lipid peroxide content and some biological and histopathological data were undertaken in rats given 4 mg of the toxin/kg perorally. The TBA reactive substances in the liver began to increase after 6 hr. However, much earlier than this there were some other alterations, which included decreases in the amount of cytochrome P-450 in the liver, of GPT (thereafter an increase) and phospholipids in the plasma, and of basophilic masses in the hepatocytes (arrayed as a rough endoplasmic reticulum in the electron micrograph). The vitamin E-deficient study showed that vitamin E markedly inhibited the stimulative effect of T-2 toxin on lipid peroxidation, but not diminish any other measured parameters of the injury. The toxin-induced stimulation of lipid peroxidation does not appear to be caused by activation of microsomal NADPH-cytochrome c reductase nor by a decrease in the level of cytosolic glutathione peroxidase. These results suggest that T-2 toxin might induce some alteration of the membrane structure and consequently might stimulate lipid peroxidation in situ.

On the Foliar Application and the Distribution of Sr-90 in Sugar Beet Plants

In connection with fission products, it is nescessary to pay an attention for the radioactive contamination of crop plants and soils and is also a very important problem from the standpoint of the public health and of vegetation to prevent the absorption of such dangerous elements. In last year, we presented the report on absorption and distribution of Sr90g by roots of lowland rice and wheat plants, and ITO and TAKENAGA reported also that physiological responses of Sra90-ion in beet plants might differ completely from Ca45-ion, namely Ca45 was always transported into interveinal tissues and Sr90 in the leaf margin portion throughout veins. On the other hand, the growth of plants cultivated in the nutrient solution containing Ca45 was greater than in case of Sr90. Accumulation in leaf, of Ca45 being absorbed by roots have been also investigated prevlously by SAYRE, BIDDULPHl, LANGSTON using other plans. In the present paper, the investigations on foliar application of Ca45 or Sr90 to beet leaves are reported as follows: 1). On July 25th, foliar application of Sr90 to a certain portion of the lower surface of decided leaf was carried out when sugar beet seedlings (Honiku No.192) grown uniformly were transferred to the aerated nutrient solutions shown in Table 1. 2) Foliar applied Sr90 was unable to be translocated to other leaves and roots when seedling was growing in nutrient solution containing Ca equivalent to 100, 60 or 20% of the standard concentration of Ca of Hoaglands nutrient system, but, in case of 0% Ca, being replaced completely with Sr, this labeled element was transported to roots and to the upper leaves related to phyllotaxes as shown in Fig. 4 and 5 and excreted gradually into the external nutrient solution through the roots since the eighth day of this experiment. At last, it became to unable to recognize existence of Sr90 in whole plant at the 12th day. 3) After foliar application of Ca45 and Sr90, the former was pervaded in interveinal tissues, and the latter was translocated along veins as shown in Fig. 1. By the abbve results, it became clear that necessity of Ca for the growth of plants is more dominated than Sr, though Ca and Sr are thought to be similar regarding various physiological reactions in past.

On Absorption and Distribution of Sr-90 by Lowland Rice and Wheat Plants

1). Lowland rice plants grown on the soil applied with labeled Sr absorbed until their middle stage of spike differentiation 92.2 percent of the element of the total amount absorbed till the harvest time the quantities being denoted in counts per minute. The absorbed Sr-90 was distributed in the ratio of 38.4 % in the roots, 41.8 % in the culm and 19.8 % in the spike. Sr-90 adsorbed by soil colloid micelle which was extracted with 1 N-KCl solution amounted from 10 to 20 times of that free in the soil being extracted with pure water. 2). Absorptin of Sr-90 by wheat plants was also studied Sr-90 being administered into the nutrient solution was mostly absorbed by the wheat plant until its middle stage of spike dfferentiation. The absorbed ratios for root, culm and spike were similar respectively to the above mentioned absorbing ratios in lowland rice, as shown in the diagram. With a higher concentration of Sr-90 in the nutrient solution in exchange of that of calcium, an increase in the absorption of the former was observed. Frow those results, the present authors consider that Sr-90 is absorbed distinctively in the edible fraction of those crops, without regards to comparatively increased supply of calcium in the nutrient solution, and recognize that labeled strontium woulld become one of the most important contaminating isotope in soil