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No‐tillage systems utilizing winter cover crops can reduce erosion and leaching losses. Fall‐seeded legumes can also supply significant amounts of N to subsequent corn (Zea maysL.) crops. The suitability of 14 fall‐seeded legumes, three small grains and four legume/grass mixtures was evaluated for winter covers from 1982 through 1985 on Matapeake silt loam (fine‐loamy, mixed, mesic, Typic Hapludult) and Mattapex silt loam(fine‐silty, mixed mesic, Aqualfic Normuldult) Coastal Plain soils as well as Delanco silt loam and Chester silt loam (fine‐loamy, mixed, mesic, Aquic Hapludult) Piedmont soils. Hairy vetch (Vicia villosaRoth), crimson clover (Trifolium incarnatumL.) and Austrian winter peas [Pisum sativum(L.) Poir.] were the most promising cover crops. Fall growth and early soil coverage was highest with crimson and lowest with vetch which had higher winter survival and spring growth. Peas and, to a lesser extent, crimson clover stands were damaged in some years by Sclerotinia trifoliorumEriks. In some years top growth of vetch contained up to 350 kg N/ha. While N concentration varied among species, total N production was determined more by dry matter yield. Legume cover crops had a greater influence on corn grain yields on the heavier textured soils and longer growing season of the Coastal Plain. In 1985, N contribution to the subsequent corn crop was reduced when small grains were seeded with annual legumes. Results from these studies show that winter annual legumes can reduce N costs while providing better soil protection during winter months.

The decay kinetics of the redox states S2and S3of the water‐oxidizing enzyme have been analyzed in isolated spinach thylakoids in the absence and presence of the exogenous reductant hydrazine. In control samples without NH2NH2a biphasic decay is observed. The rapid decline of S2and S3with yDas reductant exhibits practically the same kinetics with t1/2= 6‐7 s at pH = 7.2 and 7°C. The slow reduction (order of 5‐10 min at 7°C) of S2and S3with endogenous electron donors other than yDis about twice as fast for S2as for S3under these conditions. In contrast, the hydrazine‐induced reductive shifts of the formal redox states Si(i = 0⋯3) are characterized by a totally different kinetic pattern: (a) at 1 mMNH2NH2and incubation on ice the decay of S2is estimated to be at least 25 times faster (t1/2⩽0.4 min) than the corresponding reaction of S3(t1/2≈13 min); (b) the NH2NH2‐induced decay of S2is even slower (about twice) than the transformation of S1into the formal redox state ‘S−1’ (t1/2≈6 min), which gives rise to the two‐digit phase shift of the oxygen‐yield pattern induced by a flash train in dark adapted thylakoids. (c) the NH2NH2‐induced transformation S0→‘S−2’ [Renger, Messinger and Hanssum (1990) in: Curr. Res. Photosynth. (Baltscheffsky, M., ed). Vol. 1, pp. 845‐848, Kluwer, Dordrecht] is about three times faster (t1/2≈ min) than the reaction. Based on these results, the following dependence on the redox state Siof the reactivity towards NH2NH2is obtained: S3< S1< S0⪡ S2. The implications of this surprising order of reactivity are discussed.

In the present study the effect of TBTQ on PS II and its mutual interaction with DCMU was analyzed by measurements of the oxygen yield oscillation pattern and of DCMU binding. It was found: 1)TBTQ in its reduced form is able to induce the reduction of Doxwhich gives rise to an accelerated decay of S2and S3of the wateroxidizing complex. 2) Triton X-100 treatment used for isolation of PS II membrane fragments does not significantly affect the lateral mobility of p lastoquinone within the membrane. TBTQ bound to the thylakoid membrane does not enhance the electron pool capacity in PS II membrane fragments. 3) Preincubation of thylakoids with TBTQ diminishes the blockage of O2-evolution by DCMU significantly. In correspondence with previous findings [18, 19] the effect strongly depends on the order of addition of TBTQ and DCMU . 4) Excitation with a single saturating flash causes enhanced DCMU binding in TBTQ pretreated samples leading to the inhibition of flash induced oxygen evolution. The rate of the latter process depends on the DCMU concentration. 5) In thylakoids pretreated in the d ark with TBTQ the oxygen yield of the 3rd flash slowly declines as a function o f dark incubation time at constant DCMU concentration. Based on the above mentioned findings it is inferred that a mutual interaction between TBTQ and DCMU takes place at the PS II acceptor side. Two alternative mechanisms are discussed: i) TBTQ tightly (covalently?) bound at the QB-site (or very close to it) is modified in its function by DCMU via structural effects (allosteric type), or ii) there occurs a TBTQ /DCMU exchange that is fast in the light and slow in the dark.

A CHO cell model is described for in vitro studies of the mechanisms underlying heat resistance in cells adapted to growth in acidic environments. Adaptation is defined as a loss of pH 6.7-induced sensitization to 42.0°C cytotoxicity and it is accompanied with an elevation of steady-state intracellular pH (pH). CHO cells cultured between 75 and 100 days at pH 6.7 became fully adapted (6.7G cells), and the adapted phenotype was maintained for at least 100 additional days of culture at pH 6.7. The surviving fraction (SF) of 6.7G cells heated (42.0°C) at pH 6.7 was comparable with that of cells cultured at pH 7.3 (7.3G cells) and heated at pH 7.3, while the SF of 7.3G cells acutely acidified to pH 6.7 and heated was an order of magnitude less. Although this resistance of 6.7G cells to killing was observed at 42.0°C, it was not observed at 43.0 and 45.0°C. Both 6.7G and 7.3G cells were able to develop comparable levels of thermotolerance during 42.0°C at their growth pHs. However, in agreement with the literature, development of thermotolerance was reduced in acutely acidified 7.3G cells. An acute acidification of only 0.2 pH unit from pH 6.7 to 6.5 also reduced the ability of 6.7G cells to develop thermotolerance during heating at 42.0°C. The acquired 6.7G phenotype reverted to the 7.3G phenotype following 17 days of culture at pH 7.3. Amiloride (0.5 mM), an inhibitor of the Na+/H+ exchanger (NHE), did not sensitize 7.3G and 6.7G cells to 42.0° at their growth pHs. However, sensitization was observed for acutely acidified 7.3G cells. This is consistent with the hypothesis that extracellular acute acidification causes a decrease in pHi, and that the recovery from that decrease is achieved in part by activation of the NHE. An elevation of steady-state pHi, measured by analysing intracellular BCECF excitation spectra, was documented in a suspension assay for cells grown at pH 6.7 for 180 days. The elevation was bicarbonate-dependent (negligible in the absence of HCO-3, +0.17 pH units in the presence of HCO-3). These results suggest that the altered regulation of pHi in CHO cells adapted to pHe 6.7 is maintained by bicarbonate-dependent processes.

A series of 3,7,9,9-tetraalkyl-3,7-diazabicyclo[3.3.1]nonane derivatives (bispidines) was synthesized and identified as potential antiischemic agents. Pharmacological experiments in vitro as well as in vivo are described, and the results are listed. For selection of those compounds fitting best to the desired profile of a specific bradycardic antianginal agent&sbd;decrease in heart rate without affecting contractility and blood pressure&sbd;these results were scored and ranked. Quantitative structure−activity relationship (QSAR) analyses were performed and discussed a posteriori by means of Hansch, nonelementary discriminant and factor analysis to get insight into the molecular features determining the biological profile. Highly significant equations were obtained, indicating hydrophobic and steric effects. Both pharmacological ranking and QSAR considerations showed compound 6 as the optimum within the structural class under investigation. Compound 6 (tedisamil, KC8857) has been selected as the most promising compound and was chosen for further pharmacological and clinical investigations as an antiischemic drug.

The exchangeability of the substrate water molecules at the catalytic site of water oxidation in photosystem II has been probed by isotope-exchange measurements using mass spectrometric detection of flash-induced oxygen evolution. A stirred sample chamber was constructed to reduce the lag time between injection of H2(18)O and the detecting flash by a factor of more than 1000 compared to the original experiments by R. Radmer and O. Ollinger [(1986) FEBS Lett. 195, 285-289]. Our data show that there is a slow (t1/2 approximately 500 ms, 10 degrees C) and a fast (t1/2 <25 ms, 10 degrees C) exchanging substrate water molecule in the S3 state of photosystem II. The slow exchange is coupled with an activation energy of about 75 kJ/mol and is discussed in terms of a terminal manganese oxo ligand, while the faster exchanging substrate molecule may represent a water molecule not directly bound to the manganese center.

Autumn residual fertilizer nitrogen (FN) can be easily leached into groundwater in humid climates. Winter cover crops were evaluated for their ability to assimilate residual corn FN and thereby reduce N losses. Labelled FN (15N depleted) was applied to corn in Maryland in 1986 and 1987 at rates of 0, 168, and 336 kg FN ha−on a Mattapex silt loam (fine‐loamy, mixed, typic Hapludult). Cover crop treatments following corn harvest were hairy vetch (Vicia villosaRoth), crimson clover (Trifolium incarnatumL.), cereal rye (Secale cerealeL.), or annual ryegrass (Lolium multiflorumLam.), and a weed/fallow control of chickweed (Stellaria mediaL.). The covers were harvested three times the following spring and dry matter yields (DM), %N, and atom % 15N were determined to assess FN uptake. Fall labelled N in the soil (to 80 cm) averaged 17 and 114 kg FN ha−1over both years for the 168 and 336 kg FN ha−1rates, respectively. However, the quantity of total residual mineral N (soil N plus FN) after the 168 kg ha−1rate was 87 kg N ha−1, which was comparable to the quantity of labelled N at the high fertilizer rate. The average cover crop FN uptake (kg FN ha−1) in mid‐April after the 336 kg N ha−1treatment was 48 for cereal rye, 29 for annual ryegrass, 9 for hairy vetch, 8 for crimson clover, and 6 kg FN ha−1for the native weed cover (LSD P= 0.05 of 7 kg FN ha−1). Corresponding percent recoveries of the fall N in the aboveground DM were 45% for cereal rye, 27% for annual ryegrass, 9 for hairy vetch, 8% for crimson clover, and 8% for native weed cover. These results show that grass cover crops conserved the most FN. Cereal rye recovered more FN through mid‐April because of its growth in cool weather, although annual ryegrass was equally effective if grown to mid‐May. Renewed efforts should be made to utilize grass cover crops to conserve N in humid climates.

Abstract: A totally self-contained instrument for the measurement of cardiac output is described. The microcomputer controlled instrument is based upon the principles of thermodilution and is capable of making cardiac output determinations on a minute by minute basis. A bolus of heat is delivered to the blood via a resistive heating element wound on the surface of a conventional thermodilution catheter, and the resulting transient pulmonary artery blood temperature increase is monitored with the thermistor located near the tip of the catheter. The performance of the instrument was tested in a mock circulatory loop and in dogs for periods of up to 13 hours. The accuracy and reproducibility of flow determinations made with the system compare favorably with those made with a conventional cardiac output monitor. This study demonstrates the feasibility of a stand-alone cardiac output computer that can provide virtually continuous measurements of blood flow without the intervention of a technician.

The decay kinetics of the redox states S 2and S 3of the water-oxidizing enzyme have been analyzed in isolated spinach thylakoids in the absence and presence of the exogenous reductant hydrazine. In control samples without NH 2NH 2a biphasic decay is observed. The rapid decline of S 2and S 3with y Das reductant exhibits practically the same kinetics with t1/2= 6-7 s at pH = 7.2 and 7°C. The slow reduction (order of 5-10 min at 7°C) of S 2and S 3with endogenous electron donors other than y Dis about twice as fast for S 2as for S 3under these conditions. In contrast, the hydrazine-induced reductive shifts of the formal redox states S i(i = 0⋯3) are characterized by a totally different kinetic pattern: (a) at 1 mMNH 2NH 2and incubation on ice the decay of S 2is estimated to be at least 25 times faster ( t1/2⩽0.4 min) than the corresponding reaction of S 3( t1/2≈13 min); (b) the NH 2NH 2-induced decay of S 2is even slower (about twice) than the transformation of S 1into the formal redox state ‘S −1’ ( t1/2≈6 min), which gives rise to the two-digit phase shift of the oxygen-yield pattern induced by a flash train in dark adapted thylakoids. (c) the NH 2NH 2-induced transformation S 0→‘S −2’ [Renger, Messinger and Hanssum (1990) in: Curr. Res. Photosynth. (Baltscheffsky, M., ed). Vol. 1, pp. 845-848, Kluwer, Dordrecht] is about three times faster ( t1/2≈ min) than the reaction ▪. Based on these results, the following dependence on the redox state S iof the reactivity towards NH 2NH 2is obtained: S 3< S 1< S 0⪡ S 2. The implications of this surprising order of reactivity are discussed.