Nitrate and N02-transport by roots of 8-day-old uninduced and induced intact barley (Hordeum vulgare L. var CM 72) seedlings were compared to kinetic patterns, reciprocal inhibition of the transport systems, and the effect of the inhibitor, p-hydroxymercuribenzoate. Net uptake of N03-and N02-was measured by following the depletion of the ions from the uptake solutions. The roots of uninduced seedlings possessed a low concentration, saturable, low Km. possibly a constitutive uptake system, and a linear system for both N03-and N02-. The low Km system followed Michaelis-Menten kinetics and approached saturation between 40 and 100 micromolar, whereas the linear system was detected between 100 and 500 micromolar. In roots of induced seedlings, rates for both N03-and N02-uptake followed Michaelis-Menten kinetics and approached saturation at about 200 micromolar. In induced roots, two kinetically identifiable transport systems were resolved for each anion. At the lower substrate concentrations, less than 10 micromolar, the apparent low Kms of N03-and N02-uptake were 7 and 9 micromolar, respectively, and were similar to those of the low Km system in uninduced roots. At substrate concentrations between 10 and 200 micromolar, the apparent high Km values of N03-uptake ranged from 34 to 36 micromolar and of N02-uptake ranged from 41 to 49 micromolar. A linear system was also found in induced seedlings at concentrations above 500 micromolar. Double reciprocal plots indicated that N03-and N02-inhibited the uptake of each other competitively in both uninduced and induced seedlings; however, Ki values showed that N03-was a more effective inhibitor than N02-. Nitrate and N02-transport by both the low and high Km systems were greatly inhibited by phydroxymercuribenzoate, whereas the linear system was only slightly inhibited.

A ground‐penetrating radar (GPR) survey was conducted in May 1999 on the 1 km2 Circumpolar Active Layer Monitoring (CALM) grid 5 km east of Barrow, Alaska. Spatially continuous measurements were collected along established transects while the active layer remained frozen. The primary objectives were to determine the ‘long‐term’ position of the permafrost table, to recognize ice wedges and ice lenses, and to locate the organic–mineral soil interface. GPR signal and core collection were performed in tandem to verify signal interpretation, to calibrate the instrument, and to determine optimal GPR data‐collection parameters. Two‐way travel times from the antenna to subsurface reflectors were compared with measured depths obtained from soil cores to estimate an average pulse propagation velocity of 0.13 m/ns through the frozen soil. The most conspicuous subsurface reflectors were ice wedges, which gave high‐amplitude hyperbolic reflections. Owing to its higher ice content, the approximate long‐term position of the permafrost table could be traced laterally across the profile. Radar interpretations were obscured by the effects of cryoturbation, and because some horizons lack sufficient contrast in electrical properties. Highly detailed information can be obtained by collecting radar data at relatively slow speeds of advance, by using faster scanning rates (>32 scans/s), and by employing high‐frequency antennas (>400 MHz). Copyright © 2001 John Wiley & Sons, Ltd.RÉSUMÉUn levé réalisé avec un radar dont les ondes pénètrent dans le sol a été réalisé en mai 1999 sur un km2 appartenant à la grille établie pour suivre l'évolution de la couche active circumpolaire (CALM), 5 km a l'est de Barrow, Alaska. Des mesures ont été réalisées le long de transects alors que la couche active était gelée. Les premiers objectifs étaient de déterminer la position à long terme de la table du pergélisol, de reconnaître les coins et les lentilles de glace, et de localiser le contact entre les sols organiques et minéraux. Les données radar et des carottes de sondages ont été recueillies au même moment pour vérifier l'interprétation des données radar, calibrer l'instrument et déterminer les meilleurs paramètres d'enregistrement. Deux facons de calculer les temps de parcours depuis l'antenne jusqu'aux réflecteurs souterrains ont été comparés avec des mesures obtenues par sondages, pour estimer une vitesse moyenne de propagation de 0.13 m/ns à travers le sol gelé. Les réflecteurs les plus apparents ont été les coins de glace qui donnent des réflexions hyperboliques de grande amplitude. En raison de leur haute teneur en glace, la position approximative à long terme de la table du pergélisol a pu être reconnue le long des profils. Les interprétations sont obscurcies par les effects des cryoturbations et aussi, parce que certains horizons n'ont pas un contraste suffisant dans leurs propriétés électriques. Une information hautement détaillée peut être obtenue par la méthode radar en utilisant des vitesses lentes d'avancée, de rapides vitesses de scannages (>32 scans/s) et en utilisant des antennes de hautes fréquence (>400 MHz). Copyright © 2001 John Wiley & Sons, Ltd.

Abstract. The disappearance of nitrate reductase activity in leaves of Hordeum vulgare L. during darkness was inhibited by cycloheximide, actinomycin D, and low temperature. Thus, protein synthesis was probably required for the disappearance of nitrate reductase in the dark.Since chloramphenicol did not affect the rate of loss of activity, the degradation or inactivation apparently required protein synthesis by the cytoplasmic ribosomal system. Consistent with this observation, nitrate reductase is also reportedly located in the cytoplasm. Thus, the amount of nitrate reductase activity present in leaves of barley may be controlled by a balanoe between activating and inactivating systems.It is well established that leaves from a variety of higher lplanlts lose activity of nitrate reductase iin darkness and regain it in light (4.8,9,21,23

Acala (Gossypium hirsutum L.) and Pima (G. barbadense L.) cotton growth, lint yield, and fiber quality responses to N in the San Joaquin Valley, CA were evaluated. Numerous reasons, including adaptation of N fertilization guidelines to modern production practices, recent increases in energy costs, and growing concerns about NO−3 contamination of ground water, led to the initiation of this study. Acala was grown for 3 yr on a Panoche clay loam [fine‐loamy, mixed (calcareous), thermic Typic Torriorthents] and a Wasco sandy loam (coarse‐loamy, mixed, nonacid, thermic Typic Torriorthents). Pima was grown for 2 yr on the Panoche clay loam. Four N treatments were established in a randomized complete block design: 56, 112, 168, and 224 kg N ha−1. Three‐year average aboveground dry matter production of Acala was 7800 and 12 600 kg ha−1 on the Panoche clay loam and 8500 and 11 900 kg ha−1 on the Wasco sandy loam for the 56 and 168 kg N ha−1 treatments, respectively. The equivalent 2‐yr averages for Pima were 7600 (56 kg N ha−1) and 10 800 kg ha−1 (168 kg N ha−1). Linear increases in lint yield with increased N fertility level occurred for Acala on Panoche clay loam in every year. Maximum lint yield averaged over 3 yr was 1842 kg ha−1 in the 224 kg N ha−1 treatment. The response of Acala lint yield to N management on the Wasco sandy loam was smaller than on Panoche clay loam, with a maximum lint yield of 1666 kg ha−1 (224 kg N ha−1, 3‐yr average). Pima lint yield responded to N management in a quadratic fashion with maximum yields in the 168 kg N ha−1 treatment in both years (1638 kg ha−1, 2‐yr average). Acala gin turnouts were greater at the Panoche than at the Wasco site. Decreases in gin turnout with increasing N were significant on the Panoche clay loam (Acala and Pima) but not on the Wasco sandy loam (Acala). There was a generally positive relationship between increasing N fertilization and yield; however, efficient N management should include an assessment of available soil residual N, soil type, and yearly climatic conditions.

Nitrate reductase activity was induced by nitrate in green corn (Zea mays) leaves in either light or darkness. The induction process required oxygen in darkness but not in light. A light treatment was required before the enzyme could be induced in etiolated leaves.The capacity for nitrate reductase induction by nitrate was positively correlated with the level of cytoplasmic polyribosomes under a variety of experimental conditions. (a) Light-grown leaves contained high levels of polyribosomes (84% of the total population, most of which were of the 80 S type); similarly high levels of nitrate reductase activity were induced. (b) The level of polyribosomes and the ability to form nitrate reductase activity rapidly decreased in lightgrown leaves following transfer to an anaerobic environment in the dark; both parameters were maintained at a high level when light-grown leaves were kept in the light under anaerobic conditions. (c) The The level of nitrate reductase activity in plants is regulated by the availability of nitrate (1). Light appears to be important in the induction process (1,2,3,7,28); the function of light, however, is a matter of controversy. The enzyme is induced by nitrate in darkness in leaves of light-grown seedlings (2, 3, 28). Increases in leaf nitrate content along with increased nitrate reductase activity in response to light led to the suggestion that light is unnecessary for induction but rather the increased activity results from increased uptake of nitrate (2). Subsequent experiments with darkgrown seedlings suggested a role of light more closely related to the induction process. Dark-grown oat and barley seedlings accumulate large amounts of nitrate in darkness, but nitrate reductase activity does not increase above the low endogenous level until light is supplied (3,27,28). However, when dark-grown oat leaves were induced in light for 12 hr and then returned to darkness, the activity continued to increase for another 24 hr (3). A single report of dark induction in dark-grown leaves (2) involved low levels of activity.The fact that green leaves can form nitrate reductase in darkness whereas dark-grown leaves require light for such induction, suggests that light is necessary for induction, and that the light ef-ects are carried over into a subsequent dark period. Induction in darkness probably utilizes respiratory energy. Mendel and Visser (22) reported that respiratory inhibitors prevented nitrate reduction per se in darkness. Their results indicate that photosynthesis also may provide energy for nitrate reduction since reduction was not prevented by respiratory inhibitors in light.Total leaf protein (5,20) and a number of other enzymatic activities (8,18,26)