Normalizing the thermal effects of radiofrequency radiation: body mass versus total body surface area

The current guideline for exposure to radiofrequency radiation (RFR) was developed through assessment of the biological effects data collected primarily from the rat. The consensus that a lack of hazardous biological effects occurred below a whole-body-averaged specific absorption rate (SAR) of 4.0 W/kg led to the proposition of a 0.4 W/kg guideline with a built-in safety factor of 10. This paper demonstrates that if the RFR absorption rate in the rat had been normalized with respect to total body surface area rather than body mass, the exposure guideline would be 2.3 W/m2, which translates to an SAR of approximately 0.06 W/kg for an adult human. It is further shown that a given RFR absorption rate, normalized as a fraction of a species' heat loss per unit of surface area, is independent of body mass over a range of 0.03-100 kg; however, a normalization of the RFR absorption rate to heat loss per unit of body mass is highly dependent on the species' mass. Normalizing the rate of RFR absorption to the surface area of the rat indicates that the current RFR exposure guideline of 0.4 W/kg may be too high.     

Waterlogging responses in dune,swale and marsh populations of Spartina patens under field conditions

Summary Soil waterlogging responses were examined in three Spartina patens populations along a steep flooding gradient in coastal Louisiana. Root anatomy and physiological indicators of anaerobic metabolism were examined to identify and compare flooding responses in dune, swale and marsh populations, while soil physicochemical factors were measured to characterize the three habitats. Soil waterlogging increased along the gradient from dune to marsh habitats and was accompanied by increases in root porosity (aerenchyma). Aerenchyma in marsh roots was apparently insufficient to provide enough oxygen for aerobic respiratory demand, as indicated by high root alcohol dehydrogenase activities and low energy charge ratios. Patterns of root metabolic indicators suggest that dune and swale roots generally respired aerobically, while anaerobic metabolism was important in marsh roots. However, in each population, relatively greater soil waterloging was accompanied by differences in enzyme activities leading to malate accumulation. In dune and swale roots under these circumstances, depressed adenylate energy charge ratios may have been the result of an absence of increased ethanol fermentation. These trends suggest that: 1) Aerenchyma formation was an important, albeit incomplete, long-term adaptation to the prevalent degree of soil waterlogging. 2) All populations adjusted root metabolism in response to a relative (short-term) increase in soil waterlogging.     

Endogenous indoles and the biosynthesis and metabolism of indole-3-acetic acid in cultures of Rhizobium phaseoli

Gas chromatography-mass spectrometric analyses of purified extracts from cultures of Rhizobium phaseoli wild-type strain 8002, grown in a non-tryptophan-supplemented liquid medium, demonstrated the presence of indole-3-acetic acid (IAA), indole-3-ethanol (IEt), indole-3-aldehyde and indole-3-methanol (IM). In metabolism studies with ³H-, ¹⁴C- and ²H-labelled substrates the bacterium was shown to convert tryptophan to IEt, IAA and IM; IEt to IAA and IM; and IAA to IM. Indole-3-acetamide (IAAm) could not be detected as either an endogenous constituent or a metabolite of [³H]tryptophan nor did cultures convert [¹⁴C]IAAm to IAA. Biosynthesis of IAA in R. phaseoli, thus, involves a different pathway from that operating in Pseudomonas savastanio and Agrobacterium tumefaciens-induced crown-gall tumours.Abbreviations IAA indole-3-acetic acid - IAld indole-3-aldehyde - IAAm indole-3-acetamide - IEt indole-3-ethanol - IM indole-3-methanol - HPLC-RC high-performance liquid chromatography-radio counting - GC-MS gas chromatography-mass spectrometry     

The relationship between turgor pressure and titratable acidity in mesophyll cells of intact leaves of a Crassulacean-acid-metabolism plant,Kalanchoe daigremontiana Hamet et Perr

Day/night changes in turgor pressure (P) and titratable acidity content were investigated in the (Crassulacean-acid-metabolism (CAM) plant Kalanchoe daigremontiana. Measurements of P were made on individual mesophyll cells of intact attached leaves using the pressure-probe technique. Under conditions of high relative humidity, when transpiration rates were minimal, changes in P correlated well with changes in the level of titratable acidity. During the standard 12 h light/12 h dark cycle, maximum turgor pressure (0.15 MPa) occurred at the end of the dark period when the level of titratable acidity was highest (about 300 eq H⁺·g^-1 fresh weight). A close relationship between P and titratable acidity was also seen in leaves exposed to perturbations of the standard light/dark cycle. (The dark period was either prolonged, or else only CO₂-free air was supplied in this period). In plants deprived of irrigation for five weeks, diurnal changes in titratable acidity of the leaves were reduced (H=160 eq H⁺·g^-1 fresh weight) and P increased from essentially zero at the end of the light period to 0.02 MPa at the end of the dark period. Following more severe water stress (experiments were made on leaves which had been detached for five weeks), P was zero throughout day and night, yet small diurnal changes in titratable acidity were still measured. These findings are discussed in relation to a hypothesis by Lüttge et al. 1975 (Plant Physiol. 56,613-616) for the role of P in the regulation of acidification/de-acidification cycles of plants exhibiting CAM.Abbreviations CAM crassulacean acid metabolism - FW fresh weight - P turgor pressure     

In vivo nitrate reductase activities in different organs of lucerne plants: Effects of combined nitrogen during first vegetative growth and after shoot harvest

Nitrate reductase (EC 1.6.6.1–3; NR) activity was evaluated in nodulated lucerne ( Medicago sativa L. cv. Europe) grown aeroponically in both the presence and absence of applied nitrogen. Determination of in vivo NR activity was done with organ pieces in 0.1 M K⁺-phosphate, pH 7.5, 0.1 M KNO₃ and 1% n -propanol. NR activity was detected in all plant parts. Leaves accounted for 40% of the whole plant activity. Root activity was as high as leaf activity. Stem NR activity accounted for 14 to 20% of the total plant activity. NR activity was also detected in symbolically dependent plants grown without combined nitrogen. Nodule NR in symbolically dependent plants accounted for 17% of the tolal plant aclivity. When nitrate was present in the nulrienl medium, NR increased 5-fold as compared lo N₂-dependenl plants. Varying levels of nitrale (1.65 to 4 m M ) had no influence on leaf or stem activities. However, root NR activity seemed to be related to the nitrale concentration in the nulrient medium. Throughoul inilial vegelative growth, in vivo NR and nitrogenase (acelylene reduction) increased simultaneously. After shoot harvest, nitrogenase (acetylene reduction) aclivity drastically decreased with reduction of photosynthate supply, whereas NR increased in all organs, especially in N₂-dependenl plants.     

Uptake and metabolism of taurine in the green alga Chlorella fusca

Taurine entered the alga Chlorella fusca Shihira et Krauss strain 21l-8b via a pH and energy-dependent system ("permease"). Transport followed triphasic kinetics from 10⁻⁶ to 10⁻² M with K_m values for taurine of 5.4 × 10⁻⁵, 4.1 × l0⁻⁴ and l.5 × 10⁻³ M. This uptake system was specific for sulfonic acids and showed no affinity for α- and β -amino acids or Na⁺; thus the permease of C. fusca is different from all known taurine transport systems with respect to structural specificity and lack of Na⁺ -dependence. Uptake was not observed in sulfate-grown algae but developed as a response to sulfate limitation within 2 h. Sulfate addition caused a rapid decline in taurine transport capacity. Labeled taurine was rapidly metabolized in C. fusca to sulfate and ethanolamine, suggesting oxidative hydrolysis as the mechanism of C-S bond cleavage. Further incorporation of these catabolic products in C - and S -metabolism was demonstrated. Taurine catabolism was also detected in other green algae and some cyanobacteria.     

Micronutrients and nitrogen metabolism

A sand-culture experiment was conducted to study the influence of a deficiency of and an excess of micronutrients on the uptake and assimilation of NH ₄ ⁺ and NO ₃ ⁻ ions by maize. By studying the fate of¹⁵N supplied as¹⁵NH₄NO₃ or NH₄ ¹⁵NO₃, it was demonstrated that in maize plants NH₄−N was absorbed in preference to NO ₃ ⁻ −N. The uptake and distribution of N originating from both NH ₄ ⁺ and NO ₃ ⁻ was considerably modified by deficiency of, or an excess of, micronutrients in the growth medium. The translocation of NH ₄ ⁺ −N from roots to shoots was relatively less than that of NO ₃ ⁻ −N. Deficiency as well as excessive amounts of micronutrients, in the growth medium, substantially reduced the translocation of absorbed N into protein. This effect was more pronounced in the case of N supplied as NO ₃ ⁻ . Amino-N was the predominant non-protein fraction in which N from both NH ₄ ⁺ and NO ₃ ⁻ tended to accumulate. The next important non-protein fractions were NO ₃ ⁻ −N when N was supplied as NO ₃ ⁻ and amide-N when NH ₄ ⁺ was the source. The relative accumulation of¹⁵N into different protein fractions was also a function of imposed micronutrient levels.