Some Amino Acid-Folic Acid Interrelationships in Tetrahymena pyriformis

DL-serine, DL-methionine or DL-serine + DL-methionine in excess inhibited the growth of Tetrahymena pyriformis H. Excess serine was most inhibitory at high concentration of folic acid, whereas the effect of excess methionine or methionine + serine was most pronounced at low levels of folic acid. Inhibition due to excess serine was relieved by raising the level of methionine or by adding pyrimethamine to lower the effective folic acid level, and was intensified by adding Dl.-ethionine or by raising the level of folic acid. Similarly, inhibition due to excess methionine was relieved by supplying more serine or adding DL-ethionine (which reduced the amount of available methionine) and was intensified by adding pyrimethamine. Inhibition by excess methionine + serine was reversed by increasing threonine, provided there was ample guanine present. Low levels of guanine or the presence of 8-azaguanine prevented this reversal. Comparisons are made with the work of others.     

Phytoplankton production and growth rate in Lake Tanganyika: evidence of a decline in primary productivity in recent decades

1. This study focused on phytoplankton production in Lake Tanganyika. We provide new estimates of daily and annual primary production, as well as growth rates of phytoplankton, and we compare them with values published in former studies.
2. Chlorophyll- a (chl- a ) in the mixed layer ranged from 5 to 120 mg chl- a  m⁻² and varied significantly between rainy and dry seasons. Particulate organic carbon concentrations were significantly higher in the south basin (with 196 and 166 mg C m⁻³ in the dry and the rainy season, respectively) than in the north basin (112 and 109 mg C m⁻³, respectively).
3. Carbon : phosphorus (C : P) ratios varied according to season. Phosphorus limitation seemed to occur more frequently than nitrogen limitation, especially during the rainy season. Severe P deficiencies were rare.
4. Measured particulate daily primary production ranged from 110 to 1410 mg C m⁻² day⁻¹; seasonal contrasts were well marked in the north basin, but less in the south basin, where primary production peaks occurred also in the rainy season. Estimates of annual primary production, based on daily primary production calculated from chl- a and water transparency, gave values lower than those reported in previous studies. Picophytoplankton accounted on average for 56% of total particulate production in the south basin during the wet season of 2003.
5. Phytoplankton growth rates, calculated from primary production, ranged from 0.055 to 0.282 day⁻¹; these are lower than previously published values for Lake Tanganyika.     

Asymmetrical effects of mesophyll conductance on fundamental photosynthetic parameters and their relationships estimated from leaf gas exchange measurements

Worldwide measurements of nearly 130 C₃ species covering all major plant functional types are analysed in conjunction with model simulations to determine the effects of mesophyll conductance (g_m) on photosynthetic parameters and their relationships estimated from A/C_i curves. We find that an assumption of infinite g_m results in up to 75% underestimation for maximum carboxylation rate V_cmax, 60% for maximum electron transport rate J_max, and 40% for triose phosphate utilization rate T_u. V_cmax is most sensitive, J_max is less sensitive, and T_u has the least sensitivity to the variation of g_m. Because of this asymmetrical effect of g_m, the ratios of J_max to V_cmax, T_u to V_cmax and T_u to J_max are all overestimated. An infinite g_m assumption also limits the freedom of variation of estimated parameters and artificially constrains parameter relationships to stronger shapes. These findings suggest the importance of quantifying g_m for understanding in situ photosynthetic machinery functioning. We show that a nonzero resistance to CO₂ movement in chloroplasts has small effects on estimated parameters. A non‐linear function with g_m as input is developed to convert the parameters estimated under an assumption of infinite g_m to proper values. This function will facilitate g_m representation in global carbon cycle models.     

Differences in the success of sugar maple and red maple seedlings on acid soils are influenced by nutrient dynamics and light environment

Variation in tolerance to nutrient limitations may contribute to the differential success of sugar maple ( Acer saccharum Marsh.) and red maple ( Acer rubrum L.) on acid soils. The objectives of this study were to examine these relationships as influenced by light environment and test whether sensitivity to nutrient stress is mediated by oxidative stress. First-year sugar maple and red seedlings were grown on forest soil cores contrasting in nutrient availability under high or low light intensity. Foliar nutrition, photosynthesis, growth and antioxidant enzyme activity were assessed. Photosynthesis and growth of sugar maple were significantly lower on nutrient-poor soils and were correlated with leaf nutrient status with Ca and P having the strongest influence. For red maple, only chlorophyll content showed sensitivity to the nutrient-poor soils. High light exacerbated the negative effects of nutrient imbalances on photosynthesis and growth in sugar maple. Antioxidant enzyme activity in sugar maple was highest in seedlings growing on nutrient-poor soils and was inversely correlated with photosynthesis, Ca, P, and Mg concentrations. These results suggest that: (1) sugar maple is more sensitive to nutrient stresses associated with low pH soils than red maple; (2) high light increases sugar maple sensitivity to nutrient stress; (3) the negative effects of nutrient imbalances on sugar maple may be mediated by oxidative stress.     

Winter Fidelity and Apparent Survival of Lesser Snow Goose Populations in the Pacific Flyway

Abstract The Beringia region of the Arctic contains 2 colonies of lesser snow geese (Chen caerulescens caerulescens) breeding on Wrangel Island, Russia, and Banks Island, Canada, and wintering in North America. The Wrangel Island population is composed of 2 subpopulations from a sympatric breeding colony but separate wintering areas, whereas the Banks Island population shares a sympatric wintering area in California, USA, with one of the Wrangel Island subpopulations. The Wrangel Island colony represents the last major snow goose population in Russia and has fluctuated considerably since 1970, whereas the Banks Island population has more than doubled. The reasons for these changes are unclear, but hypotheses include independent population demographics (survival and recruitment) and immigration and emigration among breeding or wintering populations. These demographic and movement patterns have important ecological and management implications for understanding goose population structure, harvest of admixed populations, and gene flow among populations with separate breeding or wintering areas. From 1993 to 1996, we neckbanded molting birds at their breeding colonies and resighted birds on the wintering grounds. We used multistate mark-recapture models to evaluate apparent survival rates, resighting rates, winter fidelity, and potential exchange among these populations. We also compared the utility of face stain in Wrangel Island breeding geese as a predictor of their wintering area. Our results showed similar apparent survival rates between subpopulations of Wrangel Island snow geese and lower apparent survival, but higher emigration, for the Banks Island birds. Males had lower apparent survival than females, most likely due to differences in neckband loss. Transition between wintering areas was low (<3%), with equal movement between northern and southern wintering areas for Wrangel Island birds and little evidence of exchange between the Banks and northern Wrangel Island populations. Face staining was an unreliable indicator of wintering area. Our findings suggest that northern and southern Wrangel Island subpopulations should be considered a metapopulation in better understanding and managing Pacific Flyway lesser snow geese. Yet the absence of a strong population connection between Banks Island and Wrangel Island geese suggests that these breeding colonies can be managed as separate but overlapping populations. Additionally, winter population fidelity may be more important in lesser snow geese than in other species, and both breeding and wintering areas are important components of population management for sympatric wintering populations.     

Four New Species of Eimeria (Protozoa: Eimeriidae) from the Pika Ochotona princeps from Alberta and O. pallasi from Kazakhstan1

SYNOPSIS. Eimeria worleyi n. sp. and Eimeria barretti n. sp. from the pika Ochotona princeps from Alberta and Eimeria pallasi n. sp. and Eimeria shubini n. sp. from the pika Ochotona pallasi from Central Kazakhstan are described. Oocysts of E. worleyi were 12–16 by 10–15 μ (mean 13.5 by 12.5 μ) and spherical to subspherical. E. barretti oocysts were ellipsoidal to slightly ovoid and 27–36 by 21–27 μ (mean 32.9 by 23.8 μ). Oocysts of E. pallasi were ellipsoidal or ovoid and 19–34 by 17–26 μ (mean 26.3 by 21.3 μ). E. shubini oocysts were spherical and 22 μ in diameter. E. kriygsmanni Yakimoff and Gousseff, 1938 of Svanbaev (1958) in O. pallasi, [non] E. kriigsmanni Yakimoff and Gousseff, 1938 in Mus musculus, is a synonym of E. pallasi. E. musculi Yakimoff and Gousseff, 1938 of Svanbaev (1958) in O. pallasi, [non] E. musculi Yakimoff and Gousseff, 1938 in Mus musculus, is a synonym of E. shubini.     

Changes in Activity of Choline Acetylase in Central Nervous System of Rat after Intraventricular Administration of Noradrenaline

APPLICATION of strychnine or d-tubocurarine to the exposed cerebral cortex leads after a few minutes to abnormality in somatosensory evoked potentials^1,2. This consists of a surface negative wave (peak latency, 21–23 ms) which attains an amplitude five to twenty times greater than that of the normal evoked potentials and probably reflects excessive depolarization of the apical dendrites of pyramidal neurones. We wish to report the blocking of this effect by prior application of eserine to the cortex.