Role of mycorrhizal fungi and phosphorus in the arsenic tolerance of basin wildrye.

Revegetation of arsenic (As)-rich mine spoils is often impeded by the lack of plant species tolerant of high As concentrations and low nutrient availability. Basin wildrye [Leymus cinereus (Scribner & Merr.) A. Löve] has been observed to establish naturally in soils with elevated As content and thus may be useful for the stabilization of As-contaminated soils. An experiment was conducted to evaluate how variable phosphorus (P) concentrations and inoculation with site-specific arbuscular mycorrhizal fungi influence As tolerance of basin wildrye. Basin wildrye was grown in sterile sand in the greenhouse for 16 weeks. Pots of sterile sand were amended to create one of four rates of As (0, 3, 15, or 50 mg As kg(-1)), two rates of P (3 or 15 mg P kg(-1)), and +/-mycorrhizal inoculation in a 2 x 4 x 2 factorial arrangement. After 16 weeks of growth, plants were harvested, shoots and roots thoroughly washed, and the tissue analyzed for total shoot biomass, total root and shoot As and P concentrations, and degree of mycorrhizal infection. Basin wildrye was found to be tolerant of high As concentrations allowing for vigorous plant growth at application levels of 3 or 15 mg As kg(-1). Arsenic was sequestered in the roots, with 30 to 50 times more As in the roots than shoots under low P conditions. Mycorrhizal infection did not confer As tolerance in basin wildrye nor did mycorrhizal fungi influence biomass production. Phosphorus concentrations of 15 mg kg(-1) effectively inhibited As accumulation in basin wildrye. Basin wildrye has the potential to be used for stabilization of As-rich soils while minimizing exposure to grazing animals following reclamation.

States must act to reform medical education.

U.S. medical education has remained largely unchanged for the past 40 years despite dissatisfaction with the training physicians receive. Efforts to reform medical education should focus on state medical boards, which control physician licensing, rather than on the faculties of medical schools and hospital residencies.

Distractibility of cats with lesions of the superior colliculus-pretectum during performance of a 4-choice visual discrimination.

(1) Intact cats and cats with bilateral lesions of the superior colliculus-pretectum were trained on 4-choice, luminous flux discriminations in an apparatus consisting of a 6-foot square open field with 4 stimulus panels along one wall. After cats attained a high performance criterion on a 4-choice dark-light discrimination they were tested for 'distractibility' by flashing a light behind one of the stimulus panels. (2) All intact cats and cats with lesions of the superior colliculus-pretectum learned the 4-choice luminous flux discriminations. Cats with lesions of the superior colliculus-pretectum, however, followed longer paths and had longer latencies to the correct door, even after attaining criterional performance. (3) All intact cats and cats with lesions of the superior colliculus-pretectum were distracted by the flashing light, as indicated by increased commission of errors, increased path lengths and increased response latencies on trials in which the distracting stimulus was presented. However, both intact cats and cats with lesions of the superior colliculus-pretectum habituated to the distracting stimulus. (4) These results are consistent with previous findings that cats with lesions of the superior colliculus-pretectum have difficulty in withholding incorrect responses or in shifting attention or response tendencies from the incorrect to the correct stimulus. (5) These results do not support the hypothesis that lesions of the superior colliculus produce deficits in attention as measured by distractibility to novel stimuli.

Helical, motile mycoplasmas associated with flowers and honey bees in California.

Spiroplasmas were cultured from nonsurface-sterilized flowers of magnolia tree (Magnolia grandiflora L.) and tulip tree (Liriodendron tulipfera L.) in Alameda, Solano, and Yolo counties in California. Spiroplasmas were also isolated from honey bees (Apis mellifera L.) collected in the vicinity of Davis and Berkeley, CA. Most of the isolates grew relatively slowly at 31 or 37 degrees C reaching maximum population at 31 degrees C in 8-10 days. The flower isolates were serologically indistinguishable by deformation and growth inhibition tests of spiroplasma strain AS-576 from honey bee from Maryland. Isolates from honey bees were serologically closely related to spiroplasma strain SE-3 from tulip tree flower from Connecticut.

The effect of the sequence of contralateral cortical and collicular lesions on the rate of relearning a visual discrimination by cats.

Visual field deficits which follow ablation of the posterior two-thirds of one cerebral hemisphere in the cat have been shown to be ameliorated by ablation of the contralateral superior colliculus. The present study was designed to determine whether the sequence in which contralateral cortical and collicular lesions are made is a significant factor affecting the rate of monocular relearning through the eye ipsilateral to the cortical lesion. Nine adult cats had the optic chiasm sectioned, were trained to criterion monocularly on a dark-light discrimination, and were divided into two groups. Four cats (Group S) had one superior colliculus ablated, followed one month later by ablation of the contralateral two-thirds of the neocortex. Five cats (Group C) had the same lesions in the reverse order. One month after the second brain lesion, each cat was retrained monocularly through each eye on the dark-light discrimination for food reward in a Y-maze. Through the eye ipsilateral to the cortical lesion, all cats in Group S relearned to criterion more rapidly than cats previously reported with only unilateral neocortical lesions. Four of the five cats in Group C were severely retarded in relearning and two of these cats failed to relearn. The results show that when chiasm-sectioned cats are trained monocularly in a Y-maze on a dark-light discrimination, ablation of the superior colliculus prior to ablation of the contralateral neocortex facilitates relearning through the eye ipsilateral to the cortical ablation. When ablation of the superior colliculus follows the neocortical lesion, learning occurs but is not facilitated by the additional lesion.

Visual discrimination of flux-equated figures by cats with brain lesions.

Cats with various brain lesions were compared in their abilities to learn or relearn for food reward to a strict performance criterion a simple dark--light discrimination and 3 sets of discriminations between pairs of triangle equated for overall luminous flux. The results revealed a spectrum of deficits in visual learning by cats with different lesions and indicate: (1) cats with bilateral lesions of the superior colliculus-pretectum can learn dark-light and geometric figure discriminations in approximately the same number of training trials as unoperated cats or as cats with bilateral lesions of the lateral-posterolateral and splenial gyri; (2) cats with bilateral lesions of the superior colliculus-pretectum can learn to discriminate from a distance between geometric figures equated for overall luminous flux; (3) cats with bilateral lesions of the suprasylvian and ectosylvian gyri in addition to the lateral-posterolateral and splenial gyri require more training to learn both types of visual discriminations than unoperated cats or cats with lesions either of the superior colliculus-pretectum or of the lateral-posterolateral and splenial gyri; (4) cats require either an intact superior colliculus-pretectum or intact lateral-posterolateral and splenial gyri in order to discriminate between geometric figures; (5) cats with bilateral lesions of the posterior two-thirds--three-fourths of the neocortex and most of the superior colliculus-pretectum can learn a simple dark-light discrimination after prolonged training.