PHOTOOXIDATIVE CONSUMPTION AND PHOTOREDUCTIVE FORMATION OF ASCORBIC ACID IN GREEN LEAVES

1. From leaves of barley and spinach, cellular components wereisolated and brought together under various conditions to investigatethe fate of ascorbic acid as affected by the components in thelight and dark. 2. A new colorimetric method for assaying ascorbic acid andsome other reducing substances was devised, measuring the colorof molybdenum-blue developed by the substances in the presenceof excess amounts of phosphomolybdate and inorganic acid. 3. The photooxidation of ascorbic acid by green and yellow filtrates,prepared from green and etiolated leaves of barley, was studiedby the ordinary as well as the new colorimetric method. In thepresence of oxygen, the oxidation of ascorbic acid was foundto be accelerated by light in the green filtrate, but not inthe yellow filtrate. 4. The oxidation of the endogenous reducing substance containedin the supernatant fraction of spinach leaf extracts was studiedin the presence of washed chloroplasts (spinach). In the presenceof oxygen, the rate of oxidation in the light was markedly higherthan in the dark. From the changes in absorption spectrum accompanyingthe reaction, the endogenous reducing substance in questionwas identified as ascorbic acid. 5. The occurrence of an endogenous precursor of ascorbic acidin spinach leaf extracts was disclosed. The photoreduction ofthis precursor into ascorbic acid was studied in the precenceof spinach chloroplasts. A specific inhibition of this reactionby phosphoglycerate and glycerophosphate was discovered. 6. The experimental results obtained were discussed in connectionwith the role of ascorbic acid in photosynthesis. (Received September 13, 1960; )     

Light intensity regulates growth and reproduction of a snail grazer (Gyraulus chinensis) through changes in the quality and biomass of stream periphyton

1. The light : nutrient hypothesis (LNH) proposes that herbivore growth rates are maximised at intermediate light‐to‐nutrient ratios. A reduction to light intensity (i.e. decreased light‐to‐nutrient ratio) should lead to reduced food availability for herbivores while excessive light intensity in oligotrophic environments (i.e. increased light‐to‐nutrient ratios) should increase the C : N and C : P ratios of producers. However, this hypothesis has not yet been supported by studies on stream ecosystems. 2. We tested the LNH by experimental application of controlled natural gradients in light intensity to oligotrophic laboratory channels that included periphyton and the freshwater snail Gyraulus chinensis. 3. The results in this oligotrophic environment indicate that light regulated the flow of matter between trophic levels and grazer reproduction by controlling C : P ratios of the producers.     

日本三宅岛火山土壤中硫代硫酸盐氧化菌的分离、生物学特性及鉴定

【目的】利用培养法从日本三宅岛火山土壤(堆积年限131年)中分离到一株能氧化分解硫代硫酸盐的细菌MU2A-22T。【方法】用培养法对该菌株MU2A-22T进行了生理生化性质以及分类学位置上的确定。【结果】菌株MU2A-22T为革兰氏阴性,短杆状或球状。理化性质表明该菌株能利用葡萄糖、L-阿拉伯糖、葡萄糖酸盐、己二酸酯、dL-苹果酸钠、硫代硫酸钠(最适浓度为2.5 mmol/L)为唯一碳源进行自养生长。最适生长温度为25°C 30°C,最适pH为6.0 8.0。菌株MU2A-22T的16S rRNA序列与菌株Paracoccus solventivorans 6637T亲缘关系最近,序列相似性为97%,编码核酮糖-1,5-二磷酸羧化酶/加氧酶(Rubisco)的基因也被确定。对Paracoccus属内几种近缘菌的脂肪酸分析,证明菌株MU2A-22T中含有Paracoccus属的特征氨基酸,其中含量大于10%的分别为C18:1(74.7%)和C18:0(12.1%)。DNA-DNA杂交实验表明,菌株MU2A-22T与Paracoccus solventivorans 6637TDNA的相似度为49.3%。MU2A-22T菌株G+C含量为66.5%66.7%。【结论】菌株MU2A-22T为Paracoccus属内的一新种菌(登录号GQ452286),命名为Paracoccus scorialis sp.nov.。     

Contribution of hyperglycemia on diabetic complications in obese type 2 diabetic SDT fatty rats: effects of SGLT inhibitor phlorizin

The spontaneously diabetic torii (SDT) fatty rat is a new model of type 2 diabetes showing overt obesity, hyperglycemia and hyperlipidemia. With early onset of diabetes mellitus, diabetic microvascular complications, including nephropathy, peripheral neuropathy and retinopathy, are observed at young ages. In the present study, blood glucose levels of female SDT fatty rats were controlled with phlorizin, a non-selective SGLT inhibitor, to examine whether and how these complications are caused by hyperglycemia. Phlorizin treatment adequately controlled plasma glucose levels during the experiment. At 29 weeks of age, urinary albumin excretion considerably increased in SDT fatty rats. Glomerulosclerosis and tubular pathological findings also indicate diabetic nephropathy. These renal parameters tended to decrease with phlorizin; however, effects were partial. Sciatic nerve conduction velocities were significantly delayed in SDT fatty rats compared with Sprague-Dawley (SD) rats. Intraepidermal nerve fiber density, an indicator of subclinical small nerve fiber neuropathy, significantly decreased in SDT fatty rats. Retinal dysfunction (prolongation of peak latency for oscillatory potential in electroretinograms) and histopathological eye abnormalities, including retinal folding and mature cataracts were also observed. Both nerve and eye disorders were prevented with phlorizin. These findings indicate that severe hyperglycemia mainly causes diabetic complications in SDT fatty rats. However, other factors, such as hyperlipidemia and hypertension, may affect diabetic nephropathy. These characteristics of diabetic complications will become helpful in evaluating new drugs for diabetic complications using SDT fatty rats.     

Cyst distribution and excystment conditions for the dinoflagellate Peridinium penardii (Lemm.) Lemm. in a reservoir

SUMMARY. 1. Cyst distribution and a possible excystment site of the dinoflagellate Peridinium penardii (Lemm.) Lemm. in a reservoir were surveyed.
2. The presence of vegetative cells of P. penardii from all lake bottom mud samples, taken from several sites throughout the reservoir and cultured in vitro , showed that viable cysts of P. penardii were ubiquitous on the bottom of the reservoir.
3. Culture bottles containing bottom mud with cysts of P. penardii were suspended at several depths at four stations in the reservoir. Vegetative cells of P. penardii were found in all bottles suspended at 0.5 m and almost none deeper than 20.0 m. Water depth was a critical environmental factor in preventing excystment.
4. The place where P. penardii first excysts annually was predicted to be at the head of the reservoir using the data of cyst distribution, excystment conditions and morphology of the lake basin.     

Nutrient utilization and requirement under photoheterotrophic growth of Marchantia polymorpha: Improvement of the culture medium

Previously we reported on a suspension culture of chlorophyllous cells of a liverwort, Marchantia polymorpha L., under photoheterotrophic conditions. The chemically defined medium was a modified Murashige and Skoog's medium, which contained, besides glucose, inorganic salts, a growth regulator (2,4-D), and twenty-four organic compounds as micro constituents. Because of this complexity, we undertook a simplification of the medium. Having examined the utilization of the major nutrients and the requirements for the micro constituents, we have succeeded in improving the medium. The new medium contains phosphate at 3.13 mM and only eight out of the twenty-four original micro organic constituents. In this new medium, the cells grow under a well-balanced nutritional condition, with richer chlorophyll and at a higher rate during the exponential phase than in the original medium.     

Growth allocation between height and stem diameter in nonsuppressed reproducing Abies mariesii trees

To understand the growth patterns with respect to competition and leaf‐mass increase in reproducing trees, growth allocation between height and stem diameter was examined for nonsuppressed reproducing Abies mariesii trees in a subalpine forest in northern Honshu, Japan. The growth allocation was analyzed by dividing the relative growth rate of the stem volume into the relative contributions of height and stem‐diameter growth. During a 9‐yr period, height growth and seed‐cone production showed obvious annual variation, while stem‐diameter growth recorded moderate variation. For two of three years of seed‐cone production during the 9‐yr period, trees with larger seed‐cone production were associated with less height growth in the following year of seed‐cone production; however, there was no trend of height growth in the year of seed‐cone production. In the following year of mast seeding, trees with larger stem‐volume growth were associated with less height growth. This trend was also shown for the relationship between the cumulative stem‐volume growth during the 9‐yr period and growth allocation to height, suggesting that trees with a larger biomass increase depress the allocation of photosynthate to competition with a large expenditure for reproduction. In contrast to this, trees with a smaller biomass increase might allocate photosynthate to competition with surrounding trees. The results of this study suggest that an increase in reproductive organs during life history and annual variation in reproduction are closely associated with the growth patterns of the stem in A. mariesii trees.