Nutrient requirements and stress response of Populus simonii and Paulownia tomentosa

The aim of this investigation was to estimate the optimum nutrient requirements and responses to low relative nutrient addition rates of seedlings of two important broadleaf tree species in China, Populus simonii Carr. and Paulownia tomentosa (Thunb.) Steud. In preliminary experiments the optimum nutrient proportions were estimated under high concentration conditions. The nutrients consumed were replaced by means of daily additions determined by pH and conductivity titrations without changing the nutrient solutions. A relatively high K level was needed in relation to nitrogen; higher than in birch or grey alder seedlings. To obtain a high relative growth rate, suitable proportions by weight were 100 N:70 K:14 P:7 Ca:7 Mg for the Populus seedlings and 100 N:75 K:20 P:8 Ca:9 Mg for the Paulownia seedlings.
In studies of nutrient stress responses the relative nutrient addition rate was used as the treatment variable under low conductivity conditions. The responses and relationships were similar to those described for birch, grey alder and Salix . The relative addition rate, and there was also a strong linear regression between relative growth rate and nitrogen status. Relative growth rates were high and the maximum weight increase was about 19% day⁻¹ in Populus and over 25% day⁻¹ in Paulownia . The nitrogen productivity of Paulownia was very high, 0.26 g dry weight (g N)⁻¹ h⁻¹, and for Populus it was 0.16 g dry weight (g N)⁻¹ h⁻¹.     

Possible evidence for novel metabolism of nitrogen gas by a green alga

We report the isolation of a cukaryotic green alga ( Chlorella , strain WPI-2) which accumulates large stores of nitrogen (N) during growth in N-free medium and seems to incorporate¹⁴N₂, yet does not reduce acetylene to ethylene. Total N accumulation during growth on N-free medium and in gases free of combined N was measured by three methods: Kjeldahl, oxidative pyrolysis via chemiluminescence (Antek N analyzer), and Dumas (Coleman N analyzer). Increases in N ranging from 22–64%± 1% were observed. Isotope dilution studies using cells labelled with ¹⁵NO ₃- and then shifted to ¹⁴N₂ in N-free medium showed dilution of the ¹⁵N isotope by ¹⁴N from 5.67 to 5.32%± 0.05%. Using a variety of conditions, we were unable to demonstrate the reduction of acctylene to ethylene by WPI-2, although diazotrophic cyanobacteria gave positive results. Although the data on WPI-2 are not conclusive in establishing this alga as a diazotroph, the data do suggest that within the Chlorophyceae there may exist a novel form of nitrogen gas metabolism.     

Effect of Folate Deficiency on Local Cerebral Glucose Utilization in the Rat

There is considerable debate on the role of folate in CNS function. Recent work indicates that folate deficiency may affect CNS serotonin metabolism, and clinical studies describe many consequences of such a deficiency. On the other hand some workers maintain that folate deficiency alone causes CNS abnormalities. We maintained rats, through dietary deprivation, at folate levels below 4 ng/ml for more than 6 weeks and showed that at that time both their liver and brain folate levels were significantly reduced. We then studied their local cerebral glucose utilization (LCGU) using the [14C]deoxyglucose technique. This method assesses cerebral function by measuring regional metabolic activity. We also determined LCGU in rats given the same diet but replenished with folate (folate control) and in others given free access to commercially available food (normal controls). Our results show that this degree of folate deficiency has no effect on cerebral function. This contrasts with the focal suppression of LCGU we previously reported in a model of vitamin B12 deficiency.     

The effect of oxygen on nitrate and nitrite assimilation in leaves of Zea mays L. under dark conditions

The assimilation of nitrate under dark-N₂ and dark-O₂ conditions in Zea mays leaf tissue was investigated using colourimetric and ¹⁵N techniques for the determination of organic and inorganic nitrogen. Studies using ¹⁵N indicated that nitrate was assimilated under dark conditions. However, the rate of nitrate assimilation in the dark was only 28% of the rate under non-saturating light conditions. No nitrite accumulated under dark aerobiosis, even though nitrate reduction occurred under these conditions. The pattern of nitrite accumulation in leaf tissue in response to dark-N₂ conditions consisted of three phases: an initial lag phase, followed by a period of rapid nitrite accumulation and finally a phase during which the rate of nitrite accumulation declined. After a 1-h period of dark-anaerobiosis, both nitrate reduction and nitrite accumulation declined considerably. However, when O₂ was supplied, nitrate reduction was stimulated and the accumulated nitrite was rapidly reduced. Anaerobic conditions stimulated nitrate reduction in leaf tissue after a period of dark-aerobic pretreatment.     

Cerebral Blood Flow and Oxidative Metabolism in Conscious Fischer-344 Rats of Different Ages

Abstract: The cerebral metabolic rates for O₂ and for glucose were measured in conscious, fasted male Fischer-344 rats at the ages of 3, 12, and 24 months, and cerebral blood flow was determined with ¹⁴C-iodoantipyrine. The metabolic rates for oxygen and glucose were obtained by multiplying blood flow by the O₂ and glucose concentration differences, respectively, between blood in the femoral artery and in the superior sagittal sinus. Mean cerebral blood flow and the metabolic rates for oxygen and glucose did not differ significantly (p > 0.05) between 3 and 12 or between 12 and 24 months. Nor did the arteriovenous differences for O₂ and for glucose change significantly with age. Because the superior sagittal sinus drains blood mainly from the cerebral cortex, the results indicate that average cerebral cortical oxidative metabolism, and the coupling ratios between the cerebral metabolic rate for oxygen and cerebral blood flow and between the cerebral metabolic rate for glucose and cerebral blood flow, do not change significantly with age in the Fischer-344 rat.     

Seasonal variation of nitrogenous compounds in the xylem sap of Citrus

Samples of tracheal sap of Citrus sinensis (L.) Osbeck cv. Washington Navel were taken from field trees throughout the year and the nitrogen composition of the sap was determined. The nitrogenous fraction of the sap was composed mainly of free amino acids (92–97% of total nitrogen) and nitrates throughout the year. Proline was the most abundant amino acid during almost the entire cycle, and its concentration was especially high during the autumn and winter period. Nevertheless, a significant part (40–60%) of the total organic nitrogen was transported as arginine. Total nitrogen as well as amino acids and nitrates were maximal at spring flush. At spring flush and summer flush there was also a diversification of α-amino nitrogen among different amino acids. During the spring flush, nitrates, asparagine and γ-aminobutyric acid in the xylem sap seemed to have a radicular origin, whereas glutamic acid and arginine were released from the surrounding parenchyma. The results suggest a metabolic transformation in the wood parenchyma of nitrogenous compounds coming from the roots (including reduction of nitrates) and a turnover of different nitrogen metabolites between the xylem and surrounding cells.     

Nutrition of winter wheat during the life cycle. I. Yield and accumulation of dry matter and minerals

Mineral uptake by winter wheat (Trilicum aestivum L. cv. Martonvasari 8) was studied throughout the life cycle. Accumulation of macronutrients (i.e. total nitrogen, phosphorus, potassium, sodium, magnesium and calcium) and the water content of roots and shoots of plants grown in complete nutrient solution were higher than those of plants grown in two types of soils. The supply of macronutrients was in some cases limiting for soil-grown plants as revealed by a comparison of available and accumulated amounts of these nutrients. Their supply was abundant, however, for solution-grown plants. This led to a doubling of grain yield for the latter plants with a three fold increase in accumulation of dry matter and a five-fold increase in fresh weight. The efficiency ratios of solution-grown plants to soil-grown plants were approximately 1 for N and Na, 0.5 for Mg and Ca, and 0.3 for P and K.     

The influence of a deep-storage reservoir on the physicochemical limnology of a Central Texas River

A study was conducted to determine a physicochemical profile of a new deep-storage reservoir and to determine the influence of impoundment and thermal stratification in the reservoir on the physicochemical limnology of the parent river. The presence of thermal stratification from May through November caused the most significant change in water conditions. Of 23 parameters studied, 12 remained unchanged, 10 improved, and 2 deteriorated (Table VI).The greatest downstream changes in water conditions from those upstream from the reservoir were a decrease in temperature, an increase of ammonia, and the presence of hydrogen sulfide during the period of thermal stratification. Ammonia did not increase to a level considered to be toxic to aquatic species. It could, however, serve as a nutrient for certain species of plants and result in a change in community structure.Water tempeature downstream from the reservoir was always within the annual temperature range of the river upstream from the reservoir; however, the summer maximum in the tailrace was decreased to a temperature that could interfere wih the normal life cycle of many species.     

Electron paramagnetic resonance of single crystal deoxycobaltohemoglobin

Single crystals of horse ^CoHb were obtained by reduction of ^CoHb⁺ crystals with dithionite. Epr measurements showed that the g? and ^Coà tensors are both axial and share the same principal axis systems. Of the four subunits, the “heme” normals of C? and d? subunits ãb?plane 29 ± 1° from b?; they have the same orientation as the hemes in methemoglobin. The normals of “hemes” à and B? are 47 above the ãb? plane as compared to 16° in methemoglobin.     

The Effect of Light and Exogenously Supplied Ammonium Ions on Glutamate Dehydrogenase Activity and Isoforms in Young Mustard (Sinapis alba L.) Seedlings

Glutamate dehydrogenase (GDH, E.C. 1.4.1.3) of mustard cotyledons was investigated during the first 4 days of seedling development. The enzyme was found to be composed of seven catalytically active isoforms (each with a molecular mass of 270 kDa) which exhibited a charge heterogeneity when investigated by isoelectric focusing. Antibodies against the purified isoform 7, raised in rabbits, cross-reacted with each of the isoforms in Western blotting experiments. In addition, each of the isoforms was composed of four immunopositive reacting polypeptides with 19, 21, 23 and 25 kDa. During development of the seedlings, a shift in the isoform pattern towards the more acidic forms was found which was more pronounced when the seedlings were supplied with 15 mM NH₄Cl. The time course of changes in total GDH level can be correlated with the time course of disappearance of storage proteins. Both parameters are negatively regulated by light possibly via the photoreceptor, phytochrome. There are some indications that GDH in young mustard cotyledons mainly acts in the deaminating direction.